Download Acute infectious bursal disease in poultry: a review

Avian Pathology ( 2000) 29, 175–194
REVIEW ARTICLE
Acute infectious bursal disease in poultry: a review
Thierry P. van den Berg*
Veterinary and Agrochemical Research Centre, Section of Avian Virology and Biotechnology,
Groeselenberg 99, 1180 Brussels, Belgium
This review is focused on the acute form of infectious bursal disease ( IBD) caused by very virulent IBD
virus ( vvIBDV). First described in Europe about 10 years ago, this new form of the disease has rapidly
spread all over the world, causing dramatic losses; after a decade, it still represents a considerable
threat to the poultry industry.
Emergence of the acute forms of the disease has drastically changed the epidemiology of IBD.
Although their origin is still under investigation, vvIBDVs have spread all over the world in a very
explosive but conserved manner. This raises the question of the origin of vvIBDVs, of the possible
existence of reservoirs and of the possible emergence of new, distinct lineages in the future.
While it has become clear that amino acids within the variable region of virus protein VP2 account
for the molecular basis of antigenic variation, no definite hot spot that determines pathogenicity has
been identified. Fingerprints of VP2 on vvIBDVs have to be considered more as common evolutionary
markers than as virulence markers. The search for such markers is in progress.
Pathogenesis of the disease is still poorly understood, and cytokines might play a crucial role in the
onset of the disease and in the development of immunosuppression. Mechanisms such as apoptosis and
necrosis have been described in lymphoid organs and are involved in the severity of the disease.
Macrophages, especially, could play a specific role in the acute phase.
Classical serotype 1 vaccines still induce good protection, but the actual problem for control of the
disease has became the interference of maternally derived antibody in the establishment of the
vaccination schedule. The development of safe vaccines that could either transmit a high passive
immunity which could protect broilers during the whole growing period or prime an immune response
before or at hatching in the presence of passive immunity might be established in the near future. In
this context, recombinant vaccines and virus-neutralizing factor technology might have an advantage
over other approaches.
Introduction
Infectious bursal disease ( IBD) has been a great
concern for the poultry industry for a long time, but
particularly for the past decade. Indeed, its “reemergence” in variant or highly virulent forms has
been the cause of significant economic losses. Until
1987, the strains of virus were of low virulence,
causing less than 2% specific mortality, and satisfactorily controlled by vaccination. But in 1986 and
1987, vaccination failures were described in different parts of the world. In the US, it was demonstrated that the new isolates had been affected by
antigenic drift against which classical IBD virus
( IBDV) vaccines were not satisfactorily protective
( Jackwood & Sa¨õ f, 1987; Snyder et al., 1992),
whereas in Europe, the first cases of acute IBDV
were described ( Chettle et al., 1989; van den Berg
et al., 1991). Surprisingly, some of these first acute
outbreaks occurred in broilers, at the end of the
fattening period, at farms where all the hygienic and
prophylactic measures had been taken. These
findings indicated a dramatic change in the field
situation. Although no antigenic drift was detected,
strains of increased virulence were identified. This
sudden onset of hypervirulent IBD created the need
for a better characterization of the circulating
strains so that, in the future, the vaccination
* Tel: +32 2 3754455; Fax: +32 2 3750979; E-mail: [email protected]
Accepted 20 January 2000.
ISSN 0307-9457 (print)/ISSN 1465-3338 (online)/00/030175-20 © 2000 Houghton Trust Ltd
176 T.P. van den Berg
Figure 1. Structure of IBDV. Electron microscopy of ( a) IBDV particles; ( b) tubule-like structures obtained when VP2a is expressed
via the baculovirus system: (c) virus-like particle (VLP ) obtained when the polyprotein is expressed via the baculovirus system; ( d)
VLPs obtained when the polyprotein is expressed via the vaccinia virus system ( kind gift of Paco Rodriguez, CSIC, Madrid,
Spain).
schedule could be adapted faster to a new epidemiological situation. Further improvement in the control of the disease will only be realized through a
better understanding of the viral structure and the
mechanisms of pathogenesis.
During the 63rd General Session of the Office
International des Epizooties ( OIE, Paris, 15 to 19
May 1995), it was estimated that IBD has considerable socio-economic importance at the international
level, as the disease is present in more than 95% of
the Member Countries ( Eterradossi, 1995). In this
survey, 80% of the countries reported the occurrence of acute clinical cases. Although isolates from
different countries have been examined, the current
typing confuses antigenic and pathogenic criteria.
The situation is sufficiently unclear as to require
more extensive comparative studies. Particularly,
the absence of known markers to easily characterize
very pathogenic viral strains is a serious hindrance,
preventing early detection and application of specific prophylactic measures as soon as they appear.
Moreover, there is a wide variation in disease
control procedures that seldom conform to a
specific or standard plan. These features justified
the elaboration of a specific resolution ( Resolution
XVIII in 1995).
The European picture has been dominated for a
decade by the emergence of very virulent ( vv)
IBDV strains of infectious bursal disease. These
strains have now spread all over the world.
Therefore, this review will focus on the acute form
of the disease, referring to outbreaks due to
vvIBDV, as proposed by Stuart ( 1989) in his
letter.
Properties of the Virus
Several structures and sequences are essential for
the viability of IBDV, while others are specific for
strains and types, including serotypes and pathotypes. Each modification in the genetic make-up of
these structural and regulatory proteins and/or
sequences could influence the viral cycle, the host
specificity and the virulence of the strain. In order
to understand the molecular basis of virulence, a
better knowledge of the natural life cycle of IBDV
is necessary. Three years ago, Nagarajan & Kibenge
( 1997) reviewed the viral genome structure, organization and replication. Interesting recent progress
has been made in the structure of the virus and,
therefore, this section will focus on viral
morphogenesis.
Structure of the virus
IBDV is a small, non-enveloped virus, belonging to
the family Birnaviridae, which is characterized by a
bisegmented dsRNA genome ( Kibenge et al.,
1988). The prototype of the family is infectious
pancreatic necrosis virus ( IPNV) of fish. Other
members of the family can be found in insects
( Drosophila X virus, DXV) and bivalve molluscs
( tellina and oyster virus). The virion has a single
capsid shell of icosahedral symmetry composed of
32 capsomers and a diameter of 60 to 70 nm ( Figure
1a). The viral genome structure and organization
are presented in Figure 2. The larger segment A
( approximately 3400 base pairs ( bp)) contains two
open reading frames ( ORF). The larger ORF of
segment A is monocistronic and encodes a polyprotein that is auto-processed after several steps
into mature VP2, VP3 and VP4 ( Müller & Becht,
1982; Azad et al., 1985, 1987; Hudson et al., 1986;
Kibenge et al., 1997). Segment A can also encode
VP5, a short 17 kDa protein, from a short, partially
overlapping ORF ( Mundt et al., 1995). The smaller
genome segment B ( approximately 2800 bp)
encodes VP1, the viral RNA polymerase of 90 kDa
( Müller & Nitschke, 1987; Spies et al., 1987).
Review of infectious bursal disease 177
Figure 2. ( a) Genomic organization of IBDV; ( b) post-translational modifications in the open reading frame of segment A;
j , Regulatory region; NC, non-coding sequence.
Morphogenesis
The external surface of the virion is composed of
trimeric sub-units formed by VP2 and the inner
capsid is built of trimeric subunits formed by VP3
( Böttcher et al., 1997; Lombardo et al., 1999). The
positively charged C terminus of VP3 might interact
with the dsRNA genome ( Hudson et al., 1986;
Böttcher et al., 1997). Infection of mammalian or
insect cells with recombinant viral vectors like
vaccinia virus ( Fernandez-Arias et al., 1998; Lombardo et al., 1999) and baculovirus ( Hu et al., 1999;
Kibenge et al., 1999; Martinez-Torrecuadrada et al.,
1999), which express different parts of the IBDV
genome, have given more insight into the structure
and components of the virus. Single expression of
VP3 results in massive expression of the protein but
no structure could be detected. The expression of
VP2a alone, not VP2b, leads to the formation of
tubule-like structures ( Figure 1b). Only expression
of the polyprotein gives the formation of virus-like
particles ( VLPs) with size and shape very similar to
those of authentic IBDV particles ( Figure 1c,d).
Moreover, the final processing of VP2a into VP2b
does not occur in VLPs that remain in the cell
cytoplasm, but only in IBDV particles. This reinforces the assumption that the final processing of
VP2 might be associated with the last steps of the
viral cycle ( maturation or release process; Müller &
Becht, 1982; Kibenge et al., 1999).
Viral proteins
VP1, the RNA-dependent RNA polymerase of the
virus, is present in small amounts in the virion, both
as a free polypeptide and as a genome-linked
178 T.P. van den Berg
Figure 3. Worldwide geographical distribution of the acute forms of IBDV ( updated from Eterradossi, 1995). In gray, countries where
acute forms have been reported. In black, countries where no acute forms have been reported. In white, countries with no report.
protein ( Müller & Nitschke, 1987; Kibenge &
Dhama, 1997). It plays a key-role in the encapsidation of the viral particles ( Lombardo et al., 1999).
VP2 has long been identified as the hostprotective antigen as it contains the antigenic region
responsible for the induction of neutralizing antibodies and for serotype specificity ( Fahey et al.,
1989). This protein is highly hydrophobic and
conformation dependent, as demonstrated by the
observation that all neutralizing monoclonal antibodies ( Mabs) react in immunoprecipitation but not
in Western blot ( Öppling et al., 1991; Schnitzler et
al., 1993; van den Berg et al., 1996).
VP3 is a group-specific antigen that is recognized
by non-neutralizing antibodies, some of which
cross-react with both serotypes 1 and 2 ( Becht et
al., 1988; Öppling et al., 1991). Inoculation of
baculovirus-derived VP3 alone failed to induce
neutralizing antibodies ( Pitcovski et al., 1999). As
suggested by Böttcher et al. ( 1997), VP3 would act
as an intermediary, interacting with both VP2 and
VP1, and the formation of VP1–VP3 complexes is
likely to be an important step in the morphogenesis
of IBDV particles ( Lombardo et al., 1999; Tacken
et al., 2000).
VP4 is a fourth, minor and non-structural polypeptide. It is involved in the auto-processing of the
polyprotein as a virus-encoded protease producing
VP2a, VP3 and VP4 itself ( Azad et al., 1987).
Although VP4 has little homology with any other
known protease, a specific proteolytic activity
could be demonstrated ( Hudson et al., 1986;
Kibenge et al., 1997). The amino acids responsible
for this proteolytic activity have been recently
characterized as a serine-lysine catalytic dyade
( Birghan et al., 2000). In addition, Sanchez &
Rodriguez ( 1999) have carried out a systematic
analysis, using a series of plasmids encoding
polyproteins containing either deletions or single
amino acid substitutions, to identify the processing
sites. Electron microscopy of density gradient
purified viral preparations using a specific anti-VP4
Mab has shown that VP4 is associated with the
formation of specific microtubules present in infected cells and that it is not a constituent of the mature
virion ( Granzow et al., 1997). This was in contrast
with previous studies describing this protein as a
minor structural component present in mature
virion purified by various methods ( reviewed in
Kibenge et al., 1988).
VP5 was first described in IPNV particles
( Havarstein et al., 1990) and has been identified
recently in IBDV infected cells ( Mundt et al.,
1995). Its participation in the viral structure could
not be demonstrated. This viral protein more likely
has a regulatory function and could play a key role
in virus release and dissemination ( Mundt et al.,
1997).
Short History and Epidemiology of Acute IBD
First described in Europe at the end of the 1980s
( Chettle et al., 1989; van den Berg et al., 1991;
Eterradossi et al., 1992), the acute forms of the
disease were then described in Japan in the early
1990s ( Nunoya et al., 1992; Lin et al., 1993), and
they have rapidly spread all over Asia and to other
major parts of the world ( reviewed in Eterradossi,
1995). Since then, they have been isolated in many
countries ( Figure 3) including Central Europe
( Savic et al., 1997) and Russia ( Scherbakova et al.,
1998), the Middle East, South America ( Di Fabio et
al., 1999) and Asia ( Cao et al., 1998; Chen et al.,
1998; To et al., 1999). On the other hand, Australia,
New Zealand, Canada and the US are so far
unaffected ( Snyder, 1990; Proffitt et al., 1999;
Sapats & Ignjatovic, 2000). Moreover, only a
sporadic severe outbreak has been described in
Finland ( Nevalainen et al., 1999), whereas the other
northern European countries are still free ( Czifra &
Janson, 1999).
Figure 4. Generalized phylogenetic tree of IBDVs (non-exhaustive) based on the comparison of vVP2 nucleotide sequences and simplified from Yamaguchi et
al. ( 1997), Cao et al. (1998), Chen et al. ( 1998), Eterradossi et al. ( 1999), Sapats & Ignjatovic (2000) and Zierenberg et al. ( 2000). Branch lengths have no
particular meaning.
Review of infectious bursal disease 179
180 T.P. van den Berg
Figure 5. Molecular basis of the antigenicity of IBDV. Neutralizing antibodies have been shown to bind to VP2, within a minimal
region, called the variable domain or vVP2, which is highly hydrophobic with a small hydrophilic region at each terminus. These two
hydrophilic peaks are located at the surface of the virus and constitute the neutralizing epitopes. Important changes in the sequences
of these peaks might determine an antigenic shift as described for serotype 2 viruses. Point mutations inside or outside these peaks
might produce an antigenic drift, giving raise to sub-types such as the serotype 1 variant strains described in the US.
Molecular epidemiology
Origin and phylogeny
Due to the high mutation rate in the VP2 variable
domain ( vVP2) sequence, comparison of this
region among strains offers the best evolutionary
clue for IBDVs ( Figure 4). These studies, together
with epidemiological observations and mortality
studies, clearly suggest that vvIBDV strains
belong to the same genetic lineage ( Brown et al.,
1994, van den Berg et al., 1996; Yamaguchi et al.,
1997; Eterradossi et al., 1997b). The first published sequence, strain UK661, is now considered
as the reference strain for European vvIBDVs
( Brown & Skinner, 1996). The Asiatic very virulent strains were probably derived from Europe
and then spread throughout Asia in an extremely
explosive and conserved manner ( Lin et al., 1993;
Yamaguchi et al., 1997; Cao et al., 1998; Chen et
al., 1998; To et al., 1999). Moreover, some recent
phylogenetic analyses performed on the vVP2
sequences of vvIBDV strains isolated in Africa in
the late 1980s ( Eterradossi et al., 1999; Zierenberg
et al., 2000) demonstrated that they belong to the
common very virulent lineage. There are, however, significant distances between these strains
and the European and Asiatic ones, indicating
independent evolution. Taken together, all these
data might indicate the possible emergence of all
vvIBDV from an unique event and, hence, a
common ancestor. However, comparison of total
viral genome sequences should be performed for a
more detailed analysis of the spatio-temporal relationships among strains. Changes in vVP2 have to
be considered as a common evolution, not as a
virulence marker, and the occurrence of new and
diverging lineages of vvIBDVs should not be
excluded in the future.
The question of the origin of vvIBDV is still open.
Phylogenetic analyses performed on segment A of
vvIBDVs ( Brown & Skinner, 1996; Yamaguchi et
al., 1997; Pitcovski et al., 1998) confirm that they
constitute a specific cluster and that they are more
closely related to classical virulent strains, e.g.
52/70, than to other lineages. On the other hand, the
topology tree performed on segment B is quite
different, indicating that a genetic re-assortment
from an unidentified reservoir ( wild birds, fish or
insects ) might have played an important role in the
emergence of hypervirulent strains ( Howie &
Thorsen, 1981; Lasher & Shane, 1994; Yamaguchi
et al., 1997). Moreover, although no data on viral
shedding have been reported, serological surveys in
wild birds ( Wilcox et al., 1983; Gardner et al.,
1997; Ogawa et al., 1998b) suggest their possible
role as a reservoir. Finally, the possible existence of
asymptomatic carriers or latently infected birds
should also be considered.
Antigenic and Pathotypic Variation
The high mutation rate of the RNA polymerase of
RNA viruses generates a genetic diversification that
could lead to emergence in the field of viruses, with
new properties allowing them to persist in immune
populations. In the case of IBDV, these mutations
lead to antigenic variation and modification in
virulence in vivo and attenuation in vitro.
Antigenic variation
Two serotypes of IBDV are described and distinguished by cross-neutralization and cross-protec-
Review of infectious bursal disease 181
Figure 6. Classification of IBDV strains as pathotypes. IBDV strains can be defined as apathogenic (serotype 2); mild, intermediate
or ‘‘hot’’ ( serotype 1 vaccines); classical virulent (IBDV), variant, or very virulent (serotype 1). Serotype 2 strains cause neither
mortality nor bursal lesions in specified pathogen free birds. Serotype 1 vaccines cause no mortality but possess residual
pathogenicity with bursal lesions varying from mild to moderate or even severe. Virulent serotype 1 strains induce both mortality and
bursal lesions.
tion tests. Antigenic variation among serotype 1
isolates of IBDV has been shown in the US since
1985. These antigenic variants were of different
subtypes compared with classical strains, as determined by serum neutralization tests, and could be
antigenically differentiated by the use of a selected
panel of neutralizing monoclonal antibodies
( Snyder et al., 1992). Even though only one of these
subtypes could be considered as truly variant based
on cross-protection experiments ( Jackwood & Saif,
1987), important economic losses have been sustained due to the emergence of these antigenic
mutants. Neutralizing Mabs have been shown to
bind to VP2, within a minimal region– called the
variable domain– between amino acids 206 and
350, which is highly hydrophobic with a small
hydrophilic region present at each terminus ( Bayliss
et al., 1990). Sequencing of the VP2 gene of
numerous different IBDV strains and selection of
escape mutants have proven that this variable
domain represents the molecular basis of antigenic
variation ( Figure 5) ( Öppling et al., 1991; Schnitzler et al., 1993; van den Berg et al., 1994a;
Vakharia et al., 1994b).
Vaccination failures due to vvIBDVs have caused
great concern for possible antigenic variation
among the recent isolates. There is no evidence of
antigenic variation in the very virulent strains as
described in the US: they belong to classical
serotype 1 ( van der Marel et al., 1990; van den Berg
et al, 1991; Eterradossi et al., 1992). Nevertheless,
a modified epitope could be identified on all the
vvIBDVs tested by Eterradossi et al. ( 1997b) by the
use of a panel of neutralizing Mabs. This corresponded to a mutation of amino acid at position 222
( numbering following Bayliss et al., 1990) that is
located in the first hydrophilic peak, as demonstrated by the selection of an escape mutant.
Anyway, no drift could be demonstrated by crossneutralization tests ( Eterradossi et al., 1998). Other
amino acid changes have been shown in the
hydrophilic peaks of the variable domain in
vvIBDVs but their antigenic relevance and epidemiological significance is questionable. For
instance, in China, where poultry is one of the
fundamental industries of animal production, there
have been recent molecular indications for the
emergence of variant very virulent strains ( Cao et
al., 1998) but their biological and epidemiological
relevance still needs to be established. In France,
during their monitoring of the field, Eterradossi et
al. ( 1998) have also shown atypical antigenicity in
some vvIBDVs due to critical amino acid changes
in the second hydrophilic peak, but these strains
were not shown to replace the more typical
prevalent vvIBDVs.
All these observations indicate that vvIBDVs are
evolving but, in contrast to the US, where a change
in the field situation was demonstrated, the biological significance of several antigenic differences has
to be demonstrated by cross-neutralization tests.
Moreover, molecular investigations must be related
to the field situation, with a good characterization
of the circulating strains in terms of prevalence and
virulence.
Pathotypic variation
In addition to antigenic differences in serotypes and
subtypes, the viral strains can also be classified
according to their virulence ( Figure 6). But there
has been a great deal of confusion in these
definitions. In particular, the term “very virulent”
has been used to describe both European hypervirulent strains and variant American strains that
cause less than 5% mortality but are able to
multiply to a higher degree in the bursa of Fabricius
of vaccinated animals. In the absence of the
identification of specific virulence determinants,
the only valuable criteria for the classification of
182 T.P. van den Berg
Figure 7. The reverse genetics system is based on the full-length cDNA cloning of the IBDV segments in a vector producing fulllength RNAs and their subsequent transfection into eukaryotic cells, allowing the generation of completely new synthetic viruses
(Mundt & Vakharia, 1996). The synthesis of a re-assortant between segment A of a serotype 1 strain and segment B of a serotype
2 strain is illustrated. This allows the directed mutagenesis of cDNAs prior to reverse genetics in order to study the effect of any
mutation.
IBDV strains as “pathotypes” should refer to their
virulence ( mortality or lesions) in 3- to 6-week-old
specific pathogen free birds and not to any antigenic
specificity.
Virulence markers
The search for virulence markers, now considered
to be the “holy grail” by most IBDV researchers, is
still in progress, and no biological or molecular
structure has been identified as responsible for the
virulence of IBDV strains. The finding of a
molecular marker like, for instance, the presence of
basic residues in the cleavage site of the fusion
protein of Newcastle disease virus ( Collins et al.,
1993; Kant et al., 1997; Oberdörfer & Werner,
1998) can only progress through a better knowledge
of the viral structure and infectious cycle. While it
has become obvious that amino acids within the
variable region of VP2 represent the molecular
basis for antigenic variation, no definite hot spot
that determines pathogenicity has been identified.
As demonstrated by the selection of re-assortant
IBDV strains that possessed segment A of the
pathogenic serotype 1 strain Cu-1 and segment B
from serotype 2 strain 23/82, pathogenicity is not
driven by one of the two genomic segments. Both
segments contribute to the replication in the bursa
of Fabricius and virulence ( Müller et al., 1992;
Mundt, 1999). Sequence comparisons between
pathogenic and non-pathogenic serotype 1 strains
showed nucleotide changes throughout the genome
on segments A and B ( Brown & Skinner, 1996;
Yamaguchi et al., 1997; Pitcovski et al., 1998;
Yehuda et al., 1999), indicating that nucleotide
changes in different areas of the genome probably
contribute to a multigenic nature of virulence. Since
the two genomic segments of IBDV are relatively
short, one may expect that additional sequences will
be available in the near future that will allow the
mapping of the principal pathogenicity determinants. Moreover, the development of the reverse
genetics system ( Figure 7), based on the full-length
cDNA cloning of the IBDV segments in vector
producing full-length RNAs, and subsequent transfection in eukaryotic cells, allows the generation of
completely new synthetic viruses ( Mundt &
Vakharia, 1996; Mundt et al., 1997; Yao et al.,
1998; Boot et al., 1999). More recently, simplifications of the method have been proposed for the
Review of infectious bursal disease 183
generation of synthetic particles by direct transfection of cDNA vector into chick embryo fibroblast
cells ( Lim et al., 1999) and by improved methods of
reverse transcription, polymerase chain reaction
( PCR) and cloning of full-length segments of both
strands of IBDV ( Akin et al., 1999, Boot et al.,
2000). The genetic engineering of re-assortants,
recombinants or mutants will be of considerable
help to elucidate the role of segments, genes,
regions or even single amino acids in the disease.
Attenuation and adaptation to cell culture
In the same context, a characteristic of serotype 1
field strains, especially vvIBDVs, is their inability
to grow in cell culture. Adaptation requires several
blind passages in cell culture or embryonated eggs
and leads to attenuation for chickens ( Spies et al.,
1987; Yamaguchi et al., 1996a). This property is
used for the production of live vaccine strains. In
order to identify the sequences involved in attenuation and tissue culture adaptation, comparison of
the nucleotide sequences of wild type and its
attenuated counterpart has been performed by
different groups with classical ( Müller et al., 1992;
Hassan et al., 1996) or hypervirulent ( Yamaguchi et
al., 1996b) IBDV strains. Sequence comparisons
confirmed a multigenic nature of attenuation, as
mutations are located in different parts of the
genome. Taking into account that the complete 5
and 3 termini of the adapted strains have not been
fully determined, the significance of each change
for attenuation remains to be established.
Study of infection at the level of virus binding is
also important for understanding the virus– host cell
interactions and subsequent pathogenesis of the
disease ( Nieper & Müller, 1996; Ogawa et al.,
1998a). As previously mentioned, two types of
serotype 1 viruses can be classified on the basis of
their ability to infect and replicate in cultured cells
and/or in the B lymphocytes of the bursa of
Fabricius. Several amino-acid exchanges in vVP2
have been identified, using the reverse genetics
system, as being responsible for cell culture adaptation ( Lim et al., 1999; Mundt, 1999). Although
these findings might be an indication of a possible
role of VP2 in virulence, this is probably limited to
cell tropism, as each modification in the fitness of
VP2 for its target cell might increase infectivity.
Diagnosis of Acute IBD and Characteristics of
vvIBDVs
Symptomatology and lesions
Hypervirulent IBDV infections are characterized
by severe clinical signs and high mortality. Indeed,
the vvIBDVs produce disease signs similar to
conventional type 1 infection, with the same
incubation period ( 4 days), but the acute phase is
exacerbated and more generalized in the affected
flock. Severe outbreaks are characterized by sudden onset of depression in susceptible flocks.
Animals in the acute phase of the disease are
prostrate and reluctant to move, with ruffled
feathers and frequently watery or white diarrhoea.
The age susceptibility is extended, covering the
entire growing period in broilers, and the peaks of
mortality show a sharp death curve followed by
rapid recovery ( Chettle et al., 1989; van den Berg
et al., 1991; Nunoya et al., 1992; Tsukamoto et
al., 1992).
On post mortem examination of birds that died
during the acute phase of vvIBD, the bursa of
Fabricius is the principal diagnostic organ: it is
turgid, oedematous, sometimes haemorrhagic and
turns atrophic within 7 to 10 days. This atrophy
might be more rapid, even 3 to 4 days after
inoculation ( Tsukamoto et al., 1992). In addition,
dehydration and nephrosis with swollen kidneys are
common, and ecchymotic haemorrhages in the
muscle and the mucosa of the proventriculus are
observed in the majority of the affected birds.
Severe depletion of lymphoid cells is observed
not only in the bursa of Fabricius, but also in the
non-bursal lymphoid tissues. Pathogenicity of
IBDV has been associated with virus distribution in
non-bursal lymphopoietic and haematopoietic
organs. Indeed, using various immunostaining
methods, a higher frequency of antigen-positive
cells could be demonstrated after infection of birds
with vvIBDV compared with other strains, in the
thymus ( Nunoya et al., 1992; Sharma et al., 1993;
Inoue et al., 1994), the spleen and the bone marrow
( Tanimura et al., 1995; Tsukamoto et al., 1995;
Inoue et al, 1999). In particular, atrophy of the
thymus has been associated with the acute phase of
the disease and might be indicative of the virulence
of the isolate, although it is not associated with
extensive viral replication in thymic cells ( Sharma
et al., 1993). An increased number of macrophages
are found in various organs ( Tanimura et al., 1995).
Thrombocytes also represent a target for IBDV, and
acute disease is characterized by disseminated
haemorrhages probably related to an impairment of
the clotting mechanism ( Skeeles et al., 1980).
Molecular tools for diagnosis
Antigenic and molecular similarity among the new
vvIBDV isolates from different parts of the world is
an indication of a common origin and a similar
antigenic evolution. Nevertheless, although the
marked increase in acute IBD in different parts of
the world dominates the field picture, strains of
different virulence still co-exist, warranting the
need for a rapid discrimination between circulating
strains. So far, no Mab specific for the very virulent
strains have been obtained but, as previously
mentioned, a modified neutralizing epitope has
been identified by Eterradossi et al. ( 1997a). This
modification is present on all tested vvIBDVs, and
184 T.P. van den Berg
the usefulness of such a marker for epidemiological
investigations is considerable. On the other hand,
vVP2 sequence can also be used as a molecular
marker, and generalization of the molecular testing
like reverse transcription ( RT)-PCR followed by
restriction enzyme digestion or restriction fragment
length polymorphism ( RFLP) analysis of the amplified fragment might also prove very helpful in the
near future ( Jackwood & Sommer, 1999). These
approaches, however, are less related to the biological properties of the virus, as mutations at nucleotide level are not subjected to the same selection
pressure as amino acids. Only time and the
accumulation of sequences will prove the usefulness of such approaches. So far, RT-PCR techniques
on selected fragments of the genome ( essentially
the variable domain of VP2) have to be followed by
sequencing and phylogenetic comparison. This
represents actually the only valuable molecular
alternative for the classification of IBDV strains.
Such alignments have shown that vvIBDVs share
unique amino acid residues at positions 242A, 256I
and 294I ( numbering following Bayliss et al., 1990)
that might represent the genetic fingerprints of
vvIBDV ( Yamaguchi et al., 1997; Cao et al., 1998;
Eterradossi et al., 1999).
Recently, Cardoso et al. ( 2000) have shown that
the Lukert strain of IBDV can be grown in the
chicken embryo rough ( CER) cell line ( Smith et al.,
1997). This may be an advantage in a diagnostic
laboratory if it were to be shown that field isolates
could grow readily in this cell line, as CER cells
may also be used for the propagation of avian
pneumovirus ( Arns & Hafez, 1995; Dani et al.,
1999). Vero and other mammalian cell lines, e.g.
baby grivet monkey kidney cells, have also been
used to grow IBDV ( Jackwood et al., 1987;
Cardoso et al., 1998).
Pathogenesis and Immunosuppression
Pathogenesis can be defined as the method used by
the virus to cause injury to the host with mortality,
disease or immunosuppression as a consequence.
These injuries can be evaluated at different levels:
the host, the organ and the cell, and are exacerbated
in the acute forms of the disease.
The selected host of the virus is young chickens
where a clinical disease occurs, while in older birds
the infection is essentially subclinical. Susceptibility of different breeds has been described with
higher mortality rates in light than in heavier breeds
( Bumstead et al., 1993; Nielsen et al., 1998).
Inoculation of IBDV in other avian species fails to
induce disease ( McFerran, 1993).
The target organ of IBDV is the bursa of
Fabricius at its maximum development, which is a
specific source for B lymphocytes in avian species.
Bursectomy can prevent illness in chicks infected
with virulent virus ( Hiraga et al., 1994). The
severity of the disease is directly related to the
number of susceptible cells present in the bursa of
Fabricius; therefore, the highest age susceptibility is
between 3 and 6 weeks, when the bursa of Fabricius
is at its maximum development. This age susceptibility is broader in the case of vvIBDV strains ( van
den Berg et al., 1991; Nunoya et al., 1992).
After oral infection or inhalation, the virus
replicates primarily in the lymphocytes and macrophages of the gut-associated tissues. Then virus
travels to the bursa via the blood stream, where
replication will occur. By 13 h post-inoculation
( p.i.), most follicles are positive for virus and by
16 h p.i., a second and pronounced viraemia occurs
with secondary replication in other organs leading
to disease and death ( Müller et al., 1979). Similar
kinetics is observed for vvIBDVs but replication at
each step is amplified.
Actively dividing, surface immunoglobulin
M-bearing B cells are lysed by infection ( Hirai &
Calnek, 1979; Hirai et al., 1981; Rodenberg et al.,
1994), but cells of the monocyte–macrophage
lineage can be infected in a persistent and productive
manner, and play a crucial role in dissemination of
the virus ( Burkhardt & Müller, 1987; Inoue et al.,
1992; van den Berg et al., 1994b) and in the onset of
the disease ( Sharma & Lee, 1983; Kim et al., 1998;
Lam, 1998). Indeed, the exact cause of clinical
disease and death is still unclear but does not seem to
be related only to the severity of the lesions and the
bursal damage. Indeed, after infection, some birds
with few bursal lesions can be found dead, while
others can survive despite extensive bursal damage.
Moreover, mortality rates are often variable and the
establishment of median lethal dose for standardization has always been hazardous. In addition, the
narrow age range for susceptibility to clinical disease
has not yet been clearly explained. Prostration ( with
ruffled feathers, diarrhoea and inappetence) preceding death is very similar to what is observed in acute
coccidiosis, and is reminiscent of a septic shock
syndrome ( Figure 8). The macrophage could play a
specific role in this pathology by an exacerbated
release of cytokines such as tumor necrosis factor or
interleukin 6 ( Kim et al., 1998). However, an
intermediate role of TH cells in this pathophysiological mechanism should also be considered ( Tanimura & Sharma, 1997; Vervelde & Davison, 1997).
As chicken macrophages are known to be activated
by interferon ( Dijkmans et al., 1990), this role could
occur through an increased secretion of interferon as
has been described in vitro after infection of chicken
embryo cultures or in vivo in chicken ( Gelb et al.,
1979a,b).
Depletion of lymphoid cells in the bursa of
Fabricius after IBDV infection is due to both
necrosis and apoptosis. Apoptosis, or programmed
cell death, is a process where, in response to
specific stimuli, cells die in a controlled, programmed manner. Many different cell species can
undergo apoptosis but immature B and T cells are
particularly susceptible to apoptotic cell death.
Review of infectious bursal disease 185
Figure 8. The septic shock syndrome or ‘‘cytokine storm’’. ( a) Sepsis is a systemic clinical situation caused by toxic substances
released by microorganisms during severe infection and coincides with a rapid increase in circulating levels of inflammatory
cytokines such as tumour necrosis factor alpha (TNF a ), gamma interferon (IFNg ), and interleukins IL8 and IL6. ( b) Macrophages
can be activated either directly (persistent infection by IBDV) or indirectly (stimulation of T cells to secrete high levels of IFN ( that
activates macrophages) and produce apoptotic mediators, e.g. NO or TNF a . ( c) Inflammatory mediators identified in the chicken with
tests and references.
186 T.P. van den Berg
Figure 9. Measurement of immunosuppression. Although the immunosuppression caused by IBDV is principally directed towards B
lymphocytes, an effect on cell-mediated immunity has also been demonstrated. Therefore, immunosuppression can be measured in
vitro by using proliferation tests or by measuring cytokine (ChIFNg ) release after mitogen activation of T cells using either the HD11
biological assay or a specific capture enzyme-linked immunosorbent assay ( ELISA) for chicken IFNg .
Apoptosis is usually initiated by a variety of
physiological stimuli, although pathological stimuli, such as viral infections, can also trigger the
phenomenon. Recent studies have shown that
immunosuppression induced by IBDV is caused, at
least in part, by apoptosis ( Vasconcelos & Lam,
1994; Ojeda et al., 1997; Tanimura & Sharma,
1998, Nieper et al., 1999). A direct effect of viral
proteins like VP2 and VP5 has been implicated in
the induction of the mechanism ( Fernandez-Arias et
al., 1997; Yao et al., 1998) but further investigations are needed to establish their exact role in
pathogenesis and immunosuppression, notably by
comparing them in strains with different virulence.
On the other hand, apoptotic cells have also been
observed in viral antigen-negative bursal cells
( Tanimura & Sharma, 1998; Nieper et al., 1999),
reinforcing the possible role of immunological
mediators in the process.
Recovery from disease or subclinical infection
will be followed by immunosuppression with more
serious consequences if infection occurs early in
life. Although the immunosuppression caused by
IBDV is principally directed towards B lymphocytes, an effect on cell-mediated immunity ( CMI)
has also been demonstrated ( Sharma & Fredricksen,
1987; Sharma et al., 1989; Cloud et al., 1992a,b).
Mechanisms such as the development of suppressor
cells and the impairment of helper T cells have been
suggested ( Sharma & Fredricksen, 1987; Vervelde
& Davison, 1997). This can be demonstrated in
vitro by using proliferation tests ( Confer et al.,
1981, Confer & MacWilliams, 1982; Sharma &
Lee, 1983; Karaca et al., 1996; McNeilly et al.,
1999) or by measuring cytokine release after
mitogen activation of T cells ( Lambrecht et al.,
2000) ( Figure 9).
Prevention and Control
Due to the high resistance of IBDV to environmental exposure and its wide distribution, hygienic
measures alone, while essential, are often insufficient. Vaccination is thus essential ( reviewed in
Lütticken, 1997). The economic impact of both
clinical and sub-clinical diseases warrants the
search for and the use of efficient vaccines. While
the protective role of cellular immunity cannot be
ruled out, good protection is achieved by the
induction of neutralizing antibodies, as proven by
the excellent passive protection of young chicks
against infection. This satisfactory protection can be
achieved by immunization with live or inactivated
vaccines. Classical live vaccines achieve lifelong
and broad protection, but possess residual pathogenicity and a proportional risk of reversion to
virulence. Inactivated vaccines, although costly,
were used successfully until the emergence of the
hypervirulent strains. Indeed, it was a normal
practice in broiler production to vaccinate hens with
an oil-emulsion vaccine just before laying in order
to induce a high level of passive immunity in the
offspring, which could protect them until an age
where infection is less detrimental with regards to
immunosuppression ( Box, 1989). This procedure
was satisfactory until the emergence of vvIBDVs
when all classical prophylactic measures were
called into question. The first cases occurred in
flocks where all hygienic measures and vaccinations had been properly applied. It was no longer
possible to protect broilers passively during the
whole growing period and a live vaccination
became necessary. But the interference of maternally derived antibody ( MDA) ( see Figure 10)
became the crucial problem in establishment of the
vaccination schedule. Serological monitoring is
usually necessary to determine the optimal timing
for vaccination ( van den Berg & Meulemans, 1991;
Kouwenhoven & van den Bos, 1994). In this
context, the development of tests allowing the
differentiation between passive ( antibody-positive,
CMI-negative) and active immunity ( antibodypositive, CMI-positive ) could be of considerable
help ( Lambrecht et al., 2000).
Inactivated vaccines might prove helpful if they
can induce higher antibody levels in breeders,
which will then be passively transmitted to the
offspring and protect them during their entire
growing period. Subunit IBDV proteins expressed
in yeast ( Macreadie et al., 1990) or via the
baculovirus system ( Vakharia et al., 1994a; van den
Berg et al., 1994a; Pitcovski et al., 1996; Dybing &
Jackwood, 1998; Yehuda et al., 2000) might help to
reach this goal. Another advantage of these technologies is that a vaccine based on VP2 alone should
allow monitoring of the field situation by the
Review of infectious bursal disease 187
Figure 10. Interference of MDA in the establishment of the vaccination schedule. ( a) A good vaccine will be in balance regarding
safety and potency. Attenuated live vaccines achieve lifelong and broad protection, but possess a residual pathogenicity and a risk
of reversion to virulence. Inactivated vaccines are safe but more expensive as more antigen will be necessary to induce a satisfactory
response. This situation is complicated by the passive transmission of MDA from dams to the offspring via the egg. This passive
immunity, although protective, will interfere with vaccination. (b) There is a strong competition between field and vaccine strains to
break through MDA, and the optimal timing has became the crucial problem in establishment of the vaccination schedule. At the flock
level, this situation is particularly hazardous as immune and susceptible birds coexist. In this context, recombinant vaccine virus like
the herpes virus of turkey ( HVT) and virus neutralizing factor ( VNF) technology might have an advantage over other
approaches.
discrimination between vaccinial ( anti-VP2 only)
and infectious antibody ( anti-VP2 and VP3).
There is no evidence of antigenic variation in the
very virulent strains as described in the US: they
belong to classical serotype 1 ( van der Marel et al.,
1990; van den Berg et al., 1991; Eterradossi et al.,
1992) and, therefore, they can be controlled adequately under experimental conditions by vaccina-
tion with commercial vaccines prepared from
classical attenuated strains ( Öppling et al., 1991;
van den Berg & Meulemans, 1991; Eterradossi et
al., 1992). Live vaccines have another advantage in
that they are excreted in the environment, where
they can compete with field viruses. Unfortunately,
most intermediate vaccines are inadequate for
interfering with vvIBDVs that could break through
188 T.P. van den Berg
Table 1. Two European Union concerted actions in the field of IBDV
(a) COSTa Action 839 on Immunosuppressive Viral Diseases of Poultry
Definition
Framework for scientific and technical co-operation allowing the coordination of national
research at an European level
Objective
To contribute to reduce the economic impact of both clinical and subclinical forms of the
Immunosuppressive Viral Diseases of Poultry (IBDV and CAV)
Participating countries
Austria, Belgium, Croatia, Denmark, Finland, France, Germany, Hungary, Ireland, Italy,
Netherlands, Norway, Poland, Spain, Sweden, UK
Tasks (five working groups)
WG1:
WG2:
WG3:
WG4:
WG5:
Duration
5 years ( 1998 to 2003)
Useful addresses
<http://www.netmaniacs.com/cost/>
<http://home.pages.at/cost839/>
<http://www.iah.bbsrc.ac.uk/costwg5/>
Epidemiology
Diagnosis and Economic Impact
Vaccination
Pathogenesis
Molecular Virology
(b) INCO-DCb Action 97 on Acute Infectious Bursal Disease of Poultry
Definition
Concerted action in the frame of the ‘‘Cooperation with Third Countries and International
Organizations research and technological development programme’’
Objective
To increase knowledge of the epidemiology of IBD by establishing common systems of
diagnosis and epidemiosurveillance in order to reveal the incidence and prevalence of the
different forms of IBD
Participating countries
Asia: China (four partners); Europe: Belgium, France, Germany; and three associated partners:
Bangladesh, India, Indonesia
Tasks
1.
2.
3.
4.
5.
Duration
3 years ( 1998 to 2001)
Useful addresses
<http://www.cordis.lu/inco2/home.html> <http://www.hku.hk/ibdv/>
a
b
Selection and characterization of reference material
Genomic data bank
Studies on pathogenesis
Construction of clones by the reverse genetics system
Vaccination trials
COST, Cooperation in the field of Scientific and Technological research.
INCO-DC, International Cooperation with Developing Countries.
higher MDA levels. However, the use of less
attenuated ( ’hot’) vaccines, even with an acceptable
reduction of mortality, is dangerous as these
vaccines induce immunosuppression and carry the
risk of reversion to virulence ( Guittet et al., 1992).
Although the reverse genetics system ( Mundt &
Vakharia, 1996) will represent a basis for the
genetic attenuation of strains and for the generation
of new vaccines, interference of passive immunity
will still exist. Therefore, as they are less sensitive
to neutralization by anti-IBDV MDA, recombinant
viral vaccines expressing the VP2 protein of IBDV,
such as fowl pox virus ( Bayliss et al., 1991; Heine
& Boyle, 1993), herpes virus of turkey ( HVT)
( Darteil et al., 1995; Tsukamoto et al., 1999) or
fowl adenovirus ( Sheppard et al., 1998) might
prove to be powerful in the near future to prime an
active immune response. In this context, DNA
vaccines could also be considered but some limitations, especially cost, individual variability in the
response and general low humoral response might
limit these vaccines to laboratory investigations
( Fodor et al., 1999; van den Berg et al., 1999). The
efficacy and safety of HVT vaccines in ovo have
now been demonstrated ( Johnston et al., 1997) and
might give this recombinant technology an advantage over the other approaches. Recently, a new
concept, which consists of the in ovo inoculation of
a virus– antibody complex vaccine, has emerged
( Haddad et al., 1997). This novel technology
utilizes specific hyperimmune neutralizing antiserum ( or “virus neutralizing factor” ( VNF)) with a
vaccine virus under conditions that are not sufficient to neutralize the vaccine virus but which are
sufficient for delaying the pathological effects of
the vaccine alone. This allows young chicks to be
Review of infectious bursal disease 189
vaccinated more effectively in the presence of
passive immunity even with a strain that would be
too virulent for use in ovo or at hatching. Although
some questions still remain concerning the batch
variations and risks of contamination of VNF, the
residual pathogenicity of the vaccine strain and the
mechanisms involved in the delay of the immune
response ( Jeurissen et al., 1998), this technology is
very promising for the future control of IBDV.
Conclusions
Due to their complexity and to the multifaceted
nature of the infections, immunosuppressive viral
diseases require a multidisciplinary approach that
can probably only be achieved by combining
scientific expertise and resources ( strains,
reagents) from different countries. As stated by the
OIE Resolution XVIII in 1995, the first requirement for the progress in the diagnosis and the
control of IBD is a coordinated effort among
States. For instance, in Europe, several initiatives
following the principle of concerted actions, have
been built under the auspices of the European
Union ( COST Action 839 and INCO-DC Action
97; see Table 1). As continuation of the OIE
recommendations, expected outcomes from these
working groups are a harmonization between
states, a co-ordination of the efforts, the standardization of tools and nomenclature, and the elaboration of guidelines and recommendations for future
research and current practices.
In recent years, as illustrated by the numerous
references presented in this review, considerable
effort has been made all over the world to
understand the disease. Molecular virology and
avian immunology have made considerable progress and should generate new tools in the near
future. However, additional research will be needed to overcome some of the current obstacles.
First of all, the definition of virulence markers
should allow the development of specific and
more sensitive diagnostic methods warranting a
better definition of the epidemiological situation.
In this regards, the reverse genetic system, providing the tool to construct chimeric viruses, might
be decisive in the identification of virulence
markers and the genetic attenuation of strains. A
better knowledge of the immunological mechanisms involved in the disease might give tools for
the measurement of immunosuppression in the
field situation. Together with a better epidemiological definition of the field situation ( circulating
strains ), this should allow a more accurate estimate of the economic impact of immunosuppressive viral disease and a cost/benefits analysis.
Moreover, better identification of the protective
criteria and differentiation between active and
passive immunity might be of considerable help in
the establishment of vaccination schedules.
Finally, the development of safe vaccines that
could prime an immune response before or at
hatching in the presence of passive immunity
might be established in the near future.
Acknowledgements
The author is very grateful to Peter Flanagan and
William ( Bill ) Ragland for proof-reading the manuscript, and to Nicolas Eterradossi, Guy Meulemans
and Bénédicte Lambrecht for helpful discussions.
Gérard Charlier is also acknowledged for the
electron microscopy work.
References
Akin A., Wu, C.C. & Lin, T.L. (1999). Amplification and cloning of
infectious bursal disease virus genomic RNA segments by long and
accurate PCR. Journal of Virological Methods, 82, 55–61.
Arns, C.W. & Hafez, H.M. (1995). Isolation and identification of avian
pneumovirus from broiler breeder flocks in Brazil. In Proceedings of
the 44th Western Poultry Disease Conference (pp. 124–125).
USA.
Azad, A.A., Barrett, S.A. & Fahey, K.J. (1985). The characterization
and molecular cloning of the double-stranded dsRNA genome of an
Australian strain of infectious bursal disease virus. Virology, 143,
35–44.
Azad, A.A, Jagadish, M.N., Brown, M.A. & Hudson, P.J. (1987).
Deletion mapping and expression in E. Coli of the large genomic
segment of a birnavirus. Virology, 161, 145–152.
Bayliss, C.D., Spies, U., Shaw, K., Peters, R.W., Papageorgiou, A.,
Muller, H. & Boursnell, M.E.G. (1990). A comparison of the
sequences of segment A of four infectious bursal disease virus strains
and identification of a variable region in VP2. Journal of General
Virology, 71, 1303–1312.
Bayliss, C.D., Peters, R.W., Cook, J.K.A., Reece, R.L., Howes, K.,
Binns, M.M. & Boursnell, M.E.G. (1991). A recombinant fowlpox
virus that expresses the VP2 antigen of infectious bursal disease
virus induces protection against mortality caused by the virus.
Archives of Virology, 120, 193–205.
Becht H., Müller, H. & Müller, H.K. (1988). Comparative studies on
structural and antigenic properties of two serotypes of infectious
bursal disease virus. Journal of General Virology, 69, 631–640.
Birghan, C., Mundt, E., & Gorbalenya, A.E. (2000). A non-canonical
Lon proteinase lacking the ATPase domain employs the Ser-Lys
catalytic dyad to exercise broad control over the life cycle of a
double-stranded RNA virus. EMBO Journal, 4, 114–123.
Boot H.J., ter Huurne, A.H.M., Peeters, B.P.H. & Gielkens, A.L.J.
(1999). Efficient rescue of Infectious Bursal Disease Virus from
cloned cDNA: evidence for involvement of the 3-terminal sequence
in genome replication. Virology, 265, 330–341.
Boot H.J., ter Huurne, A.H.M. & Peeters, B.P.H. (2000). Generation of
full-length cDNA of the two genomic dsRNA segments of Infectious
Bursal Disease virus. Journal of Virological Methods, 84, 49–58.
Böttcher B., Kiselev, N.A., Stel’Mashchuk, V.Y., Perevozchikova,
N.A., Borisov, A.V. & Crowther, R.A. (1997). Three-dimensional
structure of infectious bursal disease virus determined by electron
cryomicroscopy. Journal of Virology, 71, 325–330.
Box, P. (1989). High maternal antibodies help chickens beat virulent
virus. World Poultry, 53, 17–19.
Brown, M.D. & Skinner, M.A. (1996). Coding sequences of both
genome segments of a European “very virulent” infectious bursal
disease virus. Virus Research, 40, 1–15.
Brown, M.D., Green, P. & Skinner, M.A. (1994). VP2 sequences of
recent European “very virulent” isolates of infectious bursal disease
virus are closely related to each other but are distinct from those of
“classical” strains. Journal of General Virology, 75, 675–680.
Bumstead, N., Reece, R.L. & Cook, J.K.A. (1993). Genetic differences
in susceptibility of chicken lines to infection with infectious bursal
disease virus. Poultry Science, 72, 403–410.
190 T.P. van den Berg
Burkhardt, E. & Müller, H. (1987). Susceptibility of chicken blood
lymphoblasts and monocytes to IBDV. Archives of Virology, 94,
297–303.
Cao, Y.C., Yeung, W.S., Law, M., Bi, Y.Z., Leung, F.C. & Lim, B.L.
(1998). Molecular characterization of seven Chinese isolates of
infectious bursal disease virus: classical, very virulent, and variant
strains. Avian Diseases, 42, 340–351.
Cardoso, T.C., Sousa, R.L., Alessi, A.C., Montassier, H.J. & Pinto, A.A.
(1998). A double antibody sandwich ELISA for rapid diagnosis of
virus infection and to measure the humoral response against
infectious bursal disease on clinical material. Avian Pathology, 27,
450–454.
Cardoso, T.C., Rahal, P., Pilz, D., Teixeira, M.C.B. & Arns, C.W.
(2000). Replication of classical infectious bursal disease virus in the
chicken embryo related (CER) cell line. Avian Pathology, 29,
213–217.
Chettle, N.J., Stuart, J.C. & Wyeth, P.J. (1989). Outbreaks of virulent
infectious bursal disease in East Anglia. Veterinary Record, 125,
271–272.
Chen, H.Y., Zhou, Q., Zhang, M.F. & Giambrone, J.J. (1998) Sequence
analysis of the VP2 hypervariable region of nine infectious bursal
disease virus isolates from mainland China. Avian Diseases, 42,
762–769.
Cloud, S.S., Lillehoj, H.S. & Rosenberger, J.K. (1992a). Immune
dysfunction following infection with chicken anaemia virus and
infectious bursal disease virus. I. Kinetic alterations of avian
lymphocytes subpopulations. Veterinary Immunology and Immunopathology, 34, 337–352.
Cloud, S.S., Rosenberger, J.K. & Lillehoj, H.S. (1992b). Immune
dysfunction following infection with chicken anaemia virus and
infectious bursal disease virus. II. Alteration of in vitro immune
response. Veterinary Immunology and Immunopathology, 34,
353–366.
Collins, M.S., Bashiruddin, J.B. & Alexander, D.J. (1993) Deduced
amino acid sequences at the fusion protein cleavage site of
Newcastle disease viruses showing variation in antigenicity and
pathogenicity. Archives of Virology, 128, 363–370.
Confer, A.W. & MacWilliams, P.S. (1982). Correlation of hematological changes and serum and monocyte inhibition with the early
suppression of phytohemagglutinin stimulation of lymphocytes in
experimental infectious bursal disease. Canadian Journal of Comparative Medecine, 46, 169–175.
Confer A.W., Springer, W.T., Shane, S.M. & Donovan, J.F. (1981).
Sequential mitogen stimulation of peripheral blood lymphocytes
from chickens inoculated with infectious bursal disease virus.
American Journal of Veterinary Research, 42, 2109–2113.
Czifra, G. & Janson, D.S. (1999). Infectious Bursal Disease in Sweden.
Proceedings of the First Working Group 1 meeting on Epidemiology,
COST Action 839, 06–08/06/99. Ploufragan, France.
Dani, M.A.C., Arns, C.W. & Durigon, E.L. (1999). Molecular
characterization of Brazilian avian pneumovirus isolates using
reverse transcription-polymerase chain reaction, restriction endonuclease analysis and sequencing of a G gene fragment. Avian
Pathology, 28, 473–476.
Darteil, R., Bublot, M., Laplace, E., Bouquet, J.F., Audonnet, J.C. &
Riviere, M. (1995). Herpesvirus of turkey recombinant viruses
expressing infectious bursal disease virus (IBDV) VP2 immunogen
induce protection against an IBDV virulent challenge in chickens.
Virology, 211, 481–490.
Di Fabio, J., Rossini, L.I., Eterradossi, N., Toquin D. & Gardin, Y.
(1999). European-like pathogenic infectious bursal disease viruses in
Brazil. Veterinary Record, 145, 203–204.
Dijkmans, R., Creemers, J. & Billiau, A. (1990). Chicken macrophage
activation by interferon: do birds lack the molecular homologue of
mammalian interferon-gamma? Veterinary Immunology & Immunopathology, 26, 319–332.
Dybing, J.K. & Jackwood, D.J. (1998). Antigenic and immunogenic
properties of baculovirus-expressed infectious bursal disease viral
proteins. Avian Diseases, 42, 80–91.
Eterradossi, N. (1995) Progress in the Diagnosis and Prophylaxis of
Infectious Bursal Disease in Poultry. Comprehensive reports on
technical items presented to the International Committee or to
regional Commissions (pp. 75–82). Paris: OIE.
Eterradossi, N., Picault, J.P., Drouin, P., Guittet, M., L’Hospitalier, R. &
Bennejean, G. (1992). Pathogenicity and preliminary antigenic
characterization of six infectious bursal disease virus strains isolated
in France from acute outbreaks. Journal of Veterinary Medicine,
B39, 683–691.
Eterradossi, N., Toquin, D., Rivallan, G. & Guittet, M. (1997a).
Modified activity of a VP2-located neutralizing epitope on various
vaccine, pathogenic and hypervirulent strains of infectious bursal
disease virus. Archives of Virology, 142, 255–270.
Eterradossi, N., Rivallan, G., Toquin, D. & Guittet, M. (1997b).
Limited antigenic variation among recent infectious bursal disease
virus isolates from France. Archives of Virology, 142, 2079–2087.
Eterradossi, N., Arnauld, C., Toquin, D., Rivallan, G. (1998). Critical
amino acid changes in VP2 variable domain are associated with
typical and atypical antigenicity in very virulent infectious bursal
disease viruses. Archives of Virology, 143, 1627–1636.
Eterradossi, N., Arnaud, C., Tekaia, F., Toquin, D., Le Coq, H.,
Rivallan, G., Guittet, M., Domenech, J., van den Berg, T.P. &
Skinner, M.A. (1999). Antigenic and genetic relationship between
European very virulent Infectious Bursal Disease Viruses and an
early West-African isolate. Avian Pathology, 28, 36–46.
Fahey, K.J., Erny, K. & Crooks, J. (1989). A conformational
immunogen on VP2 of infectious bursal disease virus that induces
virus-neutralizing antibodies that passively protect chickens. Journal
of General Virology, 70, 1473–1481.
Fernandez-Arias, A., Martinez, S. & Rodriguez, J.F. (1997). The major
antigenic protein of infectious bursal disease virus, VP2, is an
apoptotic inducer. Journal of Virology, 71, 8014–8018.
Fernandez-Arias, A., Risco, C., Martinez, S., Albar, J.P. & Rodriguez,
J.F. (1998). Expression of ORF A1 of infectious bursal disease virus
results in the formation of virus-like particles. Journl of General
Virology, 79, 1047–1054.
Fodor, I., Horvath, E., Fodor, N., Nagy, E., Rencendorsh, A., Vakharia,
V.N. and Dube, S.K. (1999). Induction of protective immunity in
chickens immunised with plasmid DNA encoding infectious bursal
disease virus antigens. Acta Veterinaria Hungarica, 47, 481–492.
Gardner, H., Kerry, K., Riddle, M., Brouwer, S. & Gleeson, L. (1997).
Poultry virus infection in Antarctic penguins. Nature, 387, 245.
Gelb, J., Eidson, C.S., Fletcher, O.J. & Kleven, S.H. (1979a). Studies
on interferon induction by infectious bursal disease virus (IBDV). I.
Interferon production in chicken embryo cell cultures infected with
IBDV. Avian Diseases, 23, 485–492.
Gelb, J., Eidson, C.S., Fletcher, O.J. & Kleven, S.H. (1979b). Studies
on interferon induction by infectious bursal disease virus (IBDV). II.
Interferon production in White Leghorn chickens infected with an
attenuated or pathogenic isolant of IBDV. Avian Diseases, 23,
634–645.
Granzow, H., Birghan, C., Mettenleiter, T.C., Beyer, J., Kollner, B. &
Mundt, E. (1997). A second form of infectious bursal disease virusassociated tubule contains VP4. Journal of Virology, 71,
8879–8885.
Green, L.C., Wagner, D.A., Glogowski, J., Skipper, P.L., Wishnok, J.S.
& Tannenbaum, S.R. (1982) Analysis of nitrate, nitrite, and
[15N]nitrate in biological fluids. Analytical Biochemistry, 126,
131–138.
Guittet, M., Le Coq, H., Picault, J.P., Eterradossi, N. & Bennejean, G
(1992). Safety of infectious bursal disease vaccines: assessment of
an acceptability threshold. Developments of Biological Standards,
79, 147–152.
Haddad, E.E., Whitfill, C.E., Avakian, A.P., Ricks, C.A., Andrews,
P.D., Thoma, J.A. & Wakenell, P.S. (1997). Efficacy of a novel
infectious bursal disease virus immune complex vaccine in broiler
chickens. Avian Diseases, 41, 882–889.
Hassan, M.K., Nielsen, C.K., Ward, L.A., Jackwood, D.J. & Saif, Y.M.
(1996). Antigenicity, pathogenicity and immunogenicity of small &
large plaque infectious bursal disease virus clones. Avian Diseases,
40, 832–836.
Havarstein, L.S., Kalland, K.H., Christie, K.E. & Endresen, C. (1990).
Sequence of the large double-stranded RNA segment of the N1 strain
of infectious pancreatic necrosis virus: a comparison with other
Birnaviridae. Journal of General Virology, 71, 299–308.
Heine, H.G. & Boyle, D.B. (1993). Infectious bursal disease virus
structural protein VP2 expressed by a fowlpox virus recombinant
Review of infectious bursal disease 191
confers protection against disease in chickens. Archives of Virology,
131, 277–292.
Hiraga, M., Nunoya, T., Otaki, Y., Tajima, M., Saito, T. & Nakamura,
T. (1994). Pathogenesis of highly virulent infectious bursal disease
virus infection in intact and bursectomized chickens. Journal of
Veterinary Medical Science, 56, 1057–1063.
Hirai, K. & Calnek, B.W. (1979). In vitro replication of infectious
bursal disease virus in established lymphoid cell lines and chicken B
lymphocytes. Infection and Immunity, 25, 964–970.
Hirai, K., Funakoshi, T., Nakai, T. & Shimakura, S. (1981) Sequential
changes in the number of surface immunoglobulin-bearing B
lymphocytes in infectious bursal disease virus-infected chickens.
Avian Diseases, 25, 484–496.
Howie, R.I. & Thorsen, J. (1981). Identification of a strain of infectious
bursal disease virus isolated from mosquitoes. Canadian Journal of
Comparative Medicine, 45, 315–320.
Hu, Y.C., Bentley, W.E., Edwards, G.H. & Vakharia, V.N. (1999)
Chimeric infectious bursal disease virus-like particles expressed in
insect cells and purified by immobilized metal affinity chromatography. Biotechnology and Bioengineering, 63, 721–729.
Hudson, P.J., McKern, N.M., Power, B.E. & Azad, A.A. (1986).
Genomic structure of the large RNA segment of infectious bursal
disease virus. Nucleic Acid Research, 14, 5001–5012.
Inoue, M., Yamamoto, H., Matuo, K. & Hihara, H. (1992). Susceptibility of chicken monocytic cell lines to infectious bursal disease virus.
Journal of Veterinary and Medical Science, 54, 575–577.
Inoue, M., Fukuda, M. & Miyano, K. (1994). Thymic lesions in
chicken infected with infectious bursal disease virus. Avian Diseases,
38, 839–846.
Inoue, M., Fujita, A. & Maeda, K (1999). Lysis of myelocytes in
chickens infected with infectious bursal disease virus. Veterinary
Pathology, 36, 146–151.
Jackwood, D.J. & Saif, Y.M. (1987). Antigenic diversity of infectious
bursal disease viruses. Avian Diseases, 31, 766–770.
Jackwood, D.J. & Sommer, S.E. (1999). Restriction fragment length
polymorphisms in the VP2 gene of infectious bursal disease viruses
from outside the United States. Avian Diseases, 43, 310–314.
Jackwood, D.J., Saif, Y.M. & Hughes, H.J. (1987). Replication of
infectious bursal disease virus in continuous cell lines. Avian
Diseases, 31, 370–375.
Jeurissen, S.H., Janse, E.M., Lehrbach, P.R., Haddad, E.E., Avakian, A.
& Whitfill, C.E. (1998). The working mechanism of an immune
complex vaccine that protects chickens against infectious bursal
disease. Immunology, 95, 494–500.
Johnston, P.A., Liu, H., O’Connell, T., Phelps, P., Bland, M.,
Tyczkowski, J., Kemper, A., Harding, T., Avakian, A., Haddad, E.,
Whitfill, C., Gildersleeve, R. & Ricks, C.A. (1997). Applications in
in ovo technology. Poultry Science, 76, 165–178.
Kaiser, P., Hughes, S. & Bumstead, N. (1999). The chicken 9E3/CEF4
CXC chemokine is the avian orthologue of IL8 and maps to chicken
chromosome 4 syntenic with genes flanking the mammalian
chemokine cluster. Immunogenetics, 49, 673–684.
Kant, A., Koch, G., Van Roozelaar, D. J., Balk, F. & Ter Huurne, A.
(1997). Differentiation of virulent and non-virulent strains of
Newcastle disease virus within 24 hours by polymerase chain
reaction. Avian Pathology, 26, 837–850.
Karaca, K., Kim, I.J., Reddy, S.K. & Sharma, J.M. (1996). Nitric oxide
inducing factor as a measure of antigen and mitogen-specific T cell
responses in chickens. Journal of Immunological Methods, 10,
97–103.
Kibenge, F.S.B. & Dhama, V. (1997). Evidence that virion-associated
VP1 of avibirnaviruses contains viral RNA sequences. Archives of
Virology, 142, 1227–1236.
Kibenge, F.S.B., Dhillon, A.S. & Russel, R.G. (1988). Biochemistry
and immunology of infectious bursal disease virus. Journal of
General Virology, 69, 1757–1775.
Kibenge, F.S.B., Qian, B., Cleghorn, J.R. & Martin, C.K. (1997).
Infectious bursal disease virus polyprotein processing does not
involve cellular proteases. Archives of Virology, 142, 2401–2419.
Kibenge, F.S., Qian, B., Nagy, E., Cleghorn, J.R. & Wadowska, D.
(1999). Formation of virus-like particles when the polyprotein gene
(segment A) of infectious bursal disease virus is expressed in insect
cells. Canadian Journal of Veterinary Research, 63, 49–55.
Kim, I.J., Karaca, K., Pertile, T.L., Erickson, S.A. & Sharma, J.M.
(1998). Enhanced expression of cytokine genes in spleen macrophages during acute infection with infectious bursal disease virus in
chickens. Veterinary Immunology and Immunopathology, 61,
331–341.
Klasing, K.C. & Peng, R.K. (1990). Monokine-like activities released
from a chicken macrophage line. Animal Biotechnology, 1,
107–120.
Kouwenhoven, B. & van den Bos, J. (1994). Control of very virulent
Infectious Bursal Disease (Gumboro Disease) in the Netherlands
with more virulent vaccines. Proceedings of the International
symposium on infectious bursal disease and chicken infectious
anaemia (pp. 262–271). Rauischholzhausen, Germany.
Lam, K.M. (1998). Alteration of chicken heterophil and macrophage
functions by the infectious bursal disease virus. Microbiological
Pathogenesis, 25, 147–155.
Lambrecht, B., Gonze, M., Meulemans, G., & van den Berg, T.P.
(2000). Production of antibodies against chicken interferon-g :
demonstration of neutralizing activity and development of a
quantitative ELISA. Veterinary Immunology and Immunopathology,
74, 137–144.
Lasher, H.N. & Shane, S.M. (1994). Infectious bursal disease. World’s
Poultry Science Journal, 50, 133–166.
Leutz, A., Damm, K., Sterneck, E., Kowenz, E., Ness, S., Frank, R.,
Gausepohl, H., Pan, Y.C., Smart, J., Hayman, M. & Graf, T. (1989).
Molecular cloning of the chicken myelomonocytic growth factor
(cMGF) reveals relationship to interleukin 6 and granulocyte colony
stimulating factor. EMBO Journal, 8, 175–181.
Lim, B.L., Cao, Y., Yu, T. & Mo, C.W. (1999). Adaptation of very
virulent infectious bursal disease virus to chicken embryonic
fibroblasts by site-directed mutagenesis of residues 279 and 284 of
viral coat protein VP2. Journal of Virology, 73, 2854–2862.
Lin, Z., Kato, A, Otaki, Y., Nakamura, T., Sasmaz, E. & Ueda, S.
(1993). Sequence comparison of a highly virulent infectious bursal
disease virus prevalent in Japan. Avian Diseases, 37, 315–323.
Lombardo, E., Maraver, A., Casten J.R., Rivera, J., Fernandez-Arias,
A., Serrano, A., Carrascosa, J.L. & Rodriguez, J.F. (1999). VP1, the
putative RNA-dependent RNA polymerase of infectious bursal
disease virus, forms complexes with the capsid protein VP3, leading
to efficient encapsidation into virus-like particles. Journal of
Virology, 73, 6973–6983.
Lowenthal, J.W., Digby, M.R. & York, J.J. (1995). Production of
interferon-gamma by chicken T cells. Journal of Interferon and
Cytokine Research, 15, 933–938.
Lütticken, D. (1997). Viral diseases of the immune system and
strategies to control infectious bursal disease by vaccination. Acta
Veterinaria Hungarica, 45, 239–249.
Macreadie, I.G., Vaughan, P.R., Chapman, A.J., McKern, N.M.,
Jagadish, M.N., Heine, H.G., Ward, C.W., Fahey, K.J. & Azad, A.A.
(1990). Passive protection against infectious bursal disease virus by
viral VP2 expressed in yeast. Vaccine, 8, 549–552.
Martinez-Torrecuadrada, J.L., Caston, J.R., Rodriguez, F. & Casal, J.I.
(1999). New alternatives in the use of structural proteins of IBDV as
subunit vaccines. Proceedings of the First Working Group 3 meeting
on Vaccination, COST Action 839, 18–19/06/99 (p. 13). Belfast, UK.
McFerran, J.B. (1993). Infectious Bursal Disease. In J.B. McFerran &
M.S. McNulty (Eds.), Virus Infections of Birds (pp. 213–228).
Amsterdam: Elsevier Science Publishers B.V.
McNeilly, F., Walker, I., Allan, G.M. & Adair, B. (1999). Bursal
lymphocyte proliferation in the presence of phorbol myristate
acetate: effect of IBDV strains on the proliferation response. Avian
Pathology, 28, 301–303.
Müller, H. & Becht, H. (1982). Biosynthesis of virus-specific proteins
in cells infected with infectious bursal disease virus and signification
as structural elements for infectious virus and incomplete particles.
Journal of Virology, 44, 384–392.
Müller, H. & Nitschke, R. (1987). The two segments of the infectious
bursal disease virus genome are circularized by a 90,000-Da protein.
Virology, 159, 174–177.
Müller, R., Kaufer, I., Reinacher, M. & Weiss, E. (1979). Immunofluorescent studies of early virus propagation after oral infection
with infectious bursal disease virus (IBDV). Zentralblad Veterinarmedicine [B], 26, 345–352.
192 T.P. van den Berg
Müller, H., Schnitzler, D., Bernstein, F., Becht, H., Cornelissen, D. &
Lutticken, D.H. (1992). Infectious bursal disease of poultry:
antigenic structure of the virus and control. Veterinary Microbiology,
33, 175–183.
Mundt, E. (1999). Tissue culture infectivity of different strains of
infectious bursal disease virus is determined by distinct amino acids
in VP2. Journal of General Virology, 80, 2067–2076.
Mundt, E. & Vakharia, V.N. (1996). Synthetic transcripts of doublestranded birnavirus genome are infectious. Proceedings of the
National Academy of Sciences of the United States of America, 93,
11131–11136.
Mundt, E., Beyer, J. & Müller, H. (1995). Identification of a novel viral
protein in infectious bursal disease virus-infected cells. Journal of
General Virology, 76, 437–443.
Mundt, E., Kollner, B. & Kretzschmar, D. (1997). VP5 of infectious
bursal disease virus is not essential for viral replication in cell
culture. Journal of Virology, 71, 5647–5651.
Nagarajan, M.M. & Kibenge, F.S.B. (1997). Infectious Bursal Disease
Virus: a review of molecular basis for variations in antigenicity and
virulence. Canadian Journal of Veterinary Research, 61, 81–88.
Nevalainen, M., Ek-Kommonen, C. & Sihvonen, L. (1999). Infectious
bursal disease. Epidemiosurveillance in Finland. Proceedings of the
First Working Group 1 meeting on Epidemiology, COST Action 839,
06–08/06/99, Ploufragan, France.
Nielsen, O.L., Sorensen, P., Hedemand, J.E., Laursen, S.B. &
Jorgensen, P.H. (1998). Inflammatory response of different chicken
lines and B haplotypes to infection with infectious bursal disease
virus. Avian Pathology, 27, 181–189.
Nieper, H. & Müller, H. (1996). Susceptibility of chicken lymphoid
cells to infectious bursal disease virus does not correlate with the
presence of specific binding sites. Journal of General Virology, 77,
1229–1237.
Nieper, H., Teifke, J.P., Jungmann, A., Löhr, C. V. & Müller, H. (1999).
Infected and apoptotic cells in the IBDV-infected bursa of Fabricus,
studied by double-labelling techniques. Avian Pathology, 28,
279–285.
Nunoya, T., Otaki, Y, Tajima, M, Hiraga, M. & Saito, T. (1992).
Occurrence of acute infectious bursal disease with high mortality in
Japan and pathogenicity of field isolates in SPF chickens. Avian
Diseases, 36, 597–609.
Oberdörfer, A & Werner, O. (1998). Newcastle disease virus: detection
and characterization by PCR of recent German isolates differing in
pathogenicity. Avian Pathology, 27, 237–243.
Ogawa, M., Yamaguchi, T., Setiyono, A., Ho, T., Matsuda, H.,
Furusawa, S., Fukushi, H. & Hirai, K. (1998a). Some characteristics
of a cellular receptor for virulent infectious bursal disease virus by
using flow cytometry. Archives of Virology, 143, 2327–2341.
Ogawa, M., Wakuda, T., Yamaguchi, T., Murata, K., Setiyono, A.,
Fukushi, H. & Hirai, K. (1998b). Seroprevalence of infectious bursal
disease virus in free-living wild birds in Japan. Journal of Veterinary
and Medical Science, 60, 1277–1279.
Ojeda, F., Skardova, I., Guarda, M.I., Ulloa, J. & Folch, H. (1997).
Proliferation and apoptosis in Infection with Infectious Bursal
Disease Virus: a flow cytometric study. Avian Diseases, 41,
312–316.
Öppling, V., Müller, H. & Becht, H. (1991). Heterogeneity of the
antigenic site responsible for the induction of neutralizing antibodies
in infectious bursal disease virus. Archives of Virology, 119,
211–223.
Pitcovski, J., Di-Castro, D., Shaaltiel, Y., Azriel, A., Gutter, B., Yarkoni,
E., Michael, A., Krispel, S. & Levi, B.Z. (1996). Insect cell-derived
VP2 of infectious bursal disease virus confers protection against the
disease in chickens. Avian Diseases, 40, 753–761.
Pitcovski, J., Goldberg, D., Levi, B.Z., Di-Castro, D., Azriel, A.,
Krispel, S., Maray, T. & Shaaltiel, Y. (1998). Coding region of
segment A sequence of a very virulent isolate of IBDV-comparison
with isolates from different countries and virulence. Avian Diseases,
42, 497–506.
Pitcovski, J., Levi, B.Z., Maray, T., Di-Castro, D., Safadi, A., Krispel,
S., Azriel, A., Gutter, B. & Michael, A. (1999). Failure of viral
protein 3 of infectious bursal disease virus produced in prokaryotic
and eukaryotic expression systems to protect chickens against the
disease. Avian Diseases, 43, 8–15.
Proffitt, J.M., Bastin, D.A. & Lehrbach, P.R. (1999). Sequence analysis
of Australian infectious bursal disease viruses. Australian Veterinary
Journal, 77, 186–188.
Rodenberg, J., Sharma, J., Belzer, S.W., Nordgren, R.M. & Nagi, S.
(1994). Flow cytometric analysis of B cell and T cell subpopulations
in virus. Avian Diseases, 38, 16–21.
Samad, F., Bergtrom, G., Eissa, H. & Amrani, D.L. (1993). Stimulation
of chick hepatocyte fibronectin production by fibroblast-conditioned
medium is due to interleukin 6. Biochim Biophys Acta, 19,
207–213.
Sanchez, A.B. & Rodriguez, J.F. (1999). Proteolytic processing in
infectious bursal disease virus: identification of the polyprotein
cleavage sites by site-directed mutagenesis. Virology, 262,
190–199.
Sapats, S. & Ignjatovic, J. (2000). Antigenic and sequence heterogeneity of infectious bursal disease virus strains isolated in Australia.
Archives of Virology, 145, 773–785.
Savic, V., Bidin, Z., Cajavec, S., Stancic, M., Gjurcevic, D. & Saviv, G.
(1997). Epidemic of infectious bursal disease in Croatia during the
period 1995–1996: field and experimental observations. Veterinarski
Arhiv, 67, 243–251.
Scherbakova, L.O., Lomakin, A.I., Borisov, A.V., Drygin, V.V. &
Gusev, A.A. (1998). Comparative analysis of the VP2 variable
region of the gene from infectious bursal disease virus isolates. Mol
Gen Mikrobiol Virusol, 1, 35–40.
Schnitzler, D., Bernstein, F., Müller H. & Becht, H. (1993). The genetic
basis for the antigenicity of the VP2 protein of the infectious bursal
disease virus. Journal of General Virology, 74, 1563–1571.
Sekellick, M.J., Ferrandino, A.F., Hopkins, D.A. & Marcus, P.I. (1994).
Chicken interferon gene: cloning, expression, and analysis. Journal
of Interferon Research, 14, 71–79.
Sharma, J.M. & Fredricksen, T.L. (1987). Mechanisms of T cell
immunosuppression by infectious bursal disease virus of chickens.
Proceedings of Avian Immunology, 238, 283–294.
Sharma, J.M. & Lee, L. (1983). Effects of infectious bursal disease
virus on natural killer cell activity and mitogenic response of chicken
lymphoid cells. Infection and Immunity, 42, 747–754.
Sharma, J.M., Dohms, J.E. & Metz, A.L. (1989). Comparative
pathogenesis of serotype 1 and variant serotype 1 isolates of
infectious bursal disease and their effect on humoral and cellular
immune competence of SPF chickens. Avian Diseases, 33,
112–124.
Sharma, J.M., Dohms, J., Walser, M. & Snyder, D.B. (1993). Presence
of lesions without virus replication in the thymus of chickens
exposed to infectious bursal disease virus. Avian Diseases, 37,
741–748.
Sheppard, M., Werner, W., Tsatas, E., McCoy, R., Prowse, S. &
Johnson, M. (1998). Fowl adenovirus recombinant expressing VP2
of infectious bursal disease virus induces protective immunity
against bursal disease. Archives of Virology, 143, 915–930.
Skeeles, J.K., Slavik, M., Beasley, J.N., Brown, A.H., Meinecke, C.F.,
Maruca, S. & Welch, S. (1980). An age-related coagulation disorder
associated with experimental infection with infectious bursal disease
virus. American Journal of Veterinary Research, 41, 1458–1461.
Smith, L.A., Tignor, G.H., Mifune, K., Narita, M. & Maeda, M. (1997).
Isolation and assay of rabies serogroup viruses in CER cells.
Intervirology, 8, 92–99.
Snyder, D.B. (1990). Changes in the field status of Infectious Bursal
Disease Virus–Guest Editorial. Avian Pathology 19, 419–423.
Snyder, D.B., Vakharia, V.N. & Savage, P.K. (1992). Naturally
occuring-neutralizing monoclonal antibody escape variants define
the epidemiology of infectious bursal disease viruses in the United
States. Archives of Virology, 127, 89–101.
Spies, U., Müller, H. & Becht, H. (1987). Properties of RNA
polymerase activity associated with infectious bursal disease virus
and characterization of its reaction products. Virus Research, 8,
127–140.
Stuart, J.C. (1989). Acute Infectious Bursal Disease in Poultry.
Veterinary Record, 125, 281.
Tacken, M.G., Rottier, P.J., Gielkens, A.L. & Peeters, B.P. (2000).
Interactions in vivo between the proteins of infectious bursal disease
virus: capsid protein VP3 interacts with the RNA-dependent RNA
polymerase, VP1. Journal of General Virology, 81, 209–218.
Review of infectious bursal disease 193
Tanimura, N. & Sharma, J.M. (1997). Appearance of T cells in the
bursa of Fabricius and cecal tonsils during the acute phase of
infectious bursal disease virus infection in chickens. Avian Diseases,
41, 638–645.
Tanimura, N. & Sharma, J.M. (1998). In-situ apoptosis in chickens
infected with infectious bursal disease virus. Journal of Comparative
Pathology, 118, 15–27.
Tanimura, N., Tsukamoto, K, Nakamura, K., Narita, M. & Maeda M.
(1995). Association between pathogenicity of Infectious Bursal
Disease Virus and viral antigen distribution detected by immunochemistry. Avian Diseases, 39, 9–20.
To, H., Yamaguchi, T., Nguyen, N.T., Nguyen, O.T., Nguyen, S.V.,
Agus, S., Kim, H.J., Fukushi, H. & Hirai, K. (1999). Sequence
comparison of the VP2 variable region of infectious bursal disease
virus isolates from Vietnam. Journal of Veterinary and Medical
Science, 61, 429–432.
Tsukamoto, K., Tanimura, N., Hihara, H., Shirai, J., Imai, K.,
Nakamura, K. & Maeda, M. (1992). Isolation of virulent infectious
bursal disease virus from field outbreaks with high mortality in
Japan. Journal of Veterinary and Medical Science, 54, 153–155.
Tsukamoto, K., Tanimura, N., Mase, M. & Imai, K. (1995). Comparison of virus replication efficiency in lymphoid tissues among three
infectious bursal disease virus strains. Avian Diseases, 39,
844–852.
Tsukamoto, K., Kojima, C., Komori, Y., Tanimura, N., Mase, M. &
Yamaguchi, S. (1999). Protection of chickens against very virulent
infectious bursal disease virus (IBDV) and Marek’s disease virus
(MDV) with a recombinant MDV expressing IBDV VP2. Virology,
10, 257, 352–362.
Vakharia, V.N., Snyder, D.B., Lutticken, D., Mengel-Whereat, S.A.,
Savage, P.K., Edwards, G.H. & Goodwin, M.A. (1994a). Active and
passive protection against variant and classic infectious bursal
disease virus strains induced by baculovirus-expressed structural
proteins. Vaccine, 12, 452–456.
Vakharia, V.N., He, J., Ahamed, B. & Snyder D.B. (1994b). Molecular
basis of antigenic variation in IBDV. Virus Research, 31,
265–273.
van den Berg, T.P. & Meulemans, G. (1991). Acute infectious bursal
disease in poultry; protection afforded by maternally derived
antibodies and interference with live vaccination. Avian Pathology,
20, 409–421.
van den Berg, T.P., Gonze, M. & Meulemans, G. (1991). Acute
infectious bursal disease in poultry: isolation and characterisation of
a highly virulent strain. Avian Pathology, 20, 133–143.
van den Berg, T.P., Gonze, M., Morales, D. & Meulemans, G. (1994a).
Relevance of antigenic variation for protection in infectious bursal
disease. Proceedings of the International symposium on infectious
bursal disease and chicken infectious anaemia (pp. 22–36).
Rauischholzhausen, Germany.
van den Berg, T.P., Godfroid, J., Morales, D., & Meulemans, G.
(1994b). The use of HD11 macrophage cell line in the study of
IBDV. Proceedings of the International Symposium on Infectious
Bursal Disease and Chicken Infectious Anaemia (pp. 133–142).
Rauischholzhausen, Germany.
van den Berg, T.P., Gonze, M., Morales, D. & Meulemans, G. (1996).
Acute infectious bursal disease in poultry: immunological and
molecular basis of antigenicity of a highly virulent strain. Avian
Pathology, 25, 751–768.
van den Berg, T.P., Lambrecht, B., Morales, D., Gonze, M. &
Meulemans, G. (1999). Partial protection of chickens against IBDV
by DNA vaccination. Proceedings of the Keystone Symposium: DNA
Vaccines: Immune responses, mechanisms and manipulating antigen
processing. Snowbird, UT, 12–17 April.
Van der Marel, P., Snyder, D. & Lutticken, D. (1990). Antigenic
characterization of IBDV field isolates by their reactivity with a
panel of monoclonal antibodies. Deutsch Tierarztl Wochenschrift,
97, 81–83.
Vasconcelos, A.C. & Lam, K.M. (1994). Apoptosis induced by
infectious bursal disease virus. Journal of General Virology, 75,
1803–1806.
Vervelde, L. & Davison, T.F. (1997). Comparison of the in situ changes
in lymphoid cells during infection with infectious bursal disease
virus in chickens of different ages. Avian Pathology, 26, 803–821
Weining, K.C., Sick, C., Kaspers, B. & Staeheli, P. (1998). A chicken
homolog of mammalian interleukin-1 beta: cDNA cloning and
purification of active recombinant protein. European Journal of
Biochemistry, 15, 994–1000.
Wilcox, G.E., Flower, R.L., Baxendale, W. & Smith, V.W. (1983).
Infectious bursal disease in Western Australia. Australian Veterinary
Journal, 60, 86–87.
Yamaguchi, T., Kondo, T., Inoshima, Y., Ogawa, M., Miyoshi, M.,
Yanai, T., Masegi, T., Fukushi, H. & Hirai, K. (1996a). In vitro
attenuation of highly virulent infectious bursal disease virus: some
characteristics of attenuated strains. Avian Diseases, 40,
501–509.
Yamaguchi, T., Ogawa, M., Inoshima, Y., Miyoshi, M., Fukushi, H. &
Hirai K. (1996b). Identification of sequence changes responsible for
the attenuation of highly virulent infectious bursal disease virus.
Virology, 223, 219–223.
Yamaguchi, T., Ogawa, M., Miyoshi, M., Inoshima, Y., Fukushi, H. &
Hirai, K. (1997). Sequence and phylogenetic analyses of highly
virulent infectious bursal disease virus. Archives of Virology, 142,
1441–1458.
Yao, K., Goodwin, M.A. & Vakharia, V.N. (1998). Generation of a
mutant infectious bursal disease virus that does not cause bursal
lesions. Journal of Virology, 72, 2647–2654.
Yehuda, H., Pitcovski, J., Michael, A., Gutter, B. & Goldway, M.
(1999) Viral protein 1 sequence analysis of three infectious bursal
disease virus strains: a very virulent virus, its attenuated form, and an
attenuated vaccine. Avian Diseases, 43, 55–64.
Yehuda, H., Goldway, M., Gutter, B., Michael, A., Godfried, Y.,
Shaaltiel, Y., Levi, B.Z. & Pitcovski, J. (2000). Transfer of antibodies
elicited by baculovirus-derived VP2 of very virulent infectious
bursal disease virus strains to progeny of commercial breeder
chickens. Avian Pathology, 29, 13–19.
Zierenberg, K., Nieper H., van den Berg, T.P., Ezeokoli, C.D., Voss, M.
& Müller, H. (2000). The VP2 variable region of two German and 11
African isolates of Infectious Bursal Disease Viruses (IBDV):
comparison of the amino acid sequences with very virulent,
“classical” virulent, and attenuated tissue culture-adapted strains.
Archives of Virology, 145, 113–125.
RÉSUMÉ
Maladie de Gumboro aigu‘ chez les volailles
Cette synth‘ese est centrée sur la forme aigu‘ de la maladie de
Gumboro (IBD) due au virus hyper-virulent (IBDV). La premi‘ere
description en Europe remonte ‘a environ 10 ans, cette nouvelle forme
de la maladie a rapidement disséminé par le monde, entraˆõ nant des
pertes importantes et représente toujours, apr‘es une décade, une
menace pour l’aviculture industrielle.
L’émergence des formes aigu‘s a radicalement changé l’épidémiologie de l’IBD. Bien que leur origine soit toujours ‘a l’étude, les virus
hypervirulents (vv) d’IBD ont disséminé partout dans le monde d’une
façon explosive. Ceci pose la question de l’origine de ces vvIBDVs, de
l’existence possible de réservoirs, et l’éventualité de l’émergence dans
le futur de nouveaux lignages.
Tandis qu’il est apparu clair que les acides aminés au niveau de la
région variable de la protéine virale VP2 explique la variation
antigénique au plan moléculaire, aucune zone précise n’a été identifiée
comme déterminant la pathogénicité. Les fingerprints de VP2 des
vvIBDVs ont été considérés plus comme des marqueurs de l’évolution
que des marqueurs de la virulence. La recherche de tels marqueurs est
en cours.
La pathogénicité de la maladie est encore peu connue et les cytokines
doivent jouer un rôle important au début de la maladie et dans le
développement de l’immunodépression. Les mécanismes tels que
l’apoptose et la nécrose ont été observés dans les organes lympho¨õ des
et sont impliqués dans la gravité de la maladie. Les macrophages
peuvent jouer un rôle spécifique dans la phase aigu‘.
Les vaccins classiques appartenant au sérotype 1, induisent une
bonne protection, mais le probl‘eme actuel concernant le contrôle de la
maladie réside dans l’interférence des anticorps d’origine maternelle et
l’établissement d’un programme de vaccination. Des vaccins présentant une parfaite innocuité pourraient être développés dans un futur
194 T.P. van den Berg
proche, ils pourraient, soit transmettre une immunité passive élevée et
ainsi protéger les poulets de chair durant toute la période de croissance,
soit induire une réponse immunitaire avant ou au moment de l’éclosion
en présence d’anticorps maternels. Dans ce contexte, les vaccins
recombinants et la technique utilisant le facteur neutralisant pourraient
avoir un avantage parmi d’autres approches.
geschafft werden. In diesem Kontext könnten rekombinante Vakzinen
und Technologien mit virusneutralisierenden Faktoren einen Vorteil
gegenüber anderen Verfahren haben.
RESUMEN
Bursitis infecciosa aguda a en avicultura
ZUSAMMENFASSUNG
Die akute infektiöse Bursitis beim Geflügel
Diese Übersicht konzentriert sich auf die akute Form der infektiösen
Bursitis (IBD), die durch sehr virulentes IBD-Virus (IBDV) verursacht
wird. Zuerst vor etwa zehn Jahren in Europa beschrieben, hat sich diese
neue Form der Krankheit unter Verursachung dramatischer Verluste
schnell in der ganzen Welt verbreitet und stellt nach einem Jahrzehnt
immer noch eine erhebliche Bedrohung der Geflügelwirtschaft dar.
Das Auftauchen der akuten Formen der Krankheit hat die Epidemiologie der infektiösen Bursitis drastisch verändert. Obwohl noch immer
an der Erforschung ihres Ursprungs gearbeitet wird, haben sich sehr
virulente (vv) Bursitisviren in einer sehr explosiven, aber konservierten
Art und Weise in der ganzen Welt ausgebreitet. Das wirft die Frage
nach dem Ursprung der vvIBDVs, der möglichen Existenz von
Reservoiren und dem möglichen zukünftigen Auftauchen neuer,
besonderer Stämme auf.
Obwohl es klar geworden ist, dass Aminosäuren in der variablen
Region des Virusproteins VP2 für die molekulare Basis der antigenen
Variation verantwortlich sind, ist bisher keine definitive vielversprechende Stelle identifiziert worden, die die Pathogenität bestimmt.
Die Kennzeichen von VP2 auf vvIBDVs müssen eher als allgemeine
Evolutionsmarker als als Virulenzmarker angesehen werden. Die Suche
nach solchen Markern ist im Gange.
Die Pathogenese der Krankheit wird noch immer schlecht verstanden. Zytokine könnten beim Ausbruch der Krankheit und bei der
Entwicklung der Immunsuppression eine entscheidende Rolle spielen.
Mechanismen wie Apoptose und Nekrose sind in lymphoiden Organen
beschrieben worden und haben mit der Schwere der Krankheit zu tun.
Besonders Makrophagen könnten in der akuten Phase eine spezielle
Rolle spielen.
Klassische Serotyp 1-Vakzinen bewirken nach wie vor einen guten
Schutz, aber die Interferenz von maternalen Antikörpern ist ein
aktuelles Problem bei der Festlegung des Impfplans geworden. Die
Entwicklung von sicheren Vakzinen, die entweder eine starke passive
Immunität vermitteln, die die Broiler während der gesamten Mastzeit
schützen kann, oder eine Immunantwort vor oder beim Schlüpfen in
Gegenwart einer passiven Immunität anregen, könnte in naher Zukunft
Esta revisión se centra en la forma aguda de la bursitis infecciosa
(IBD) causada por una cepa muy virulenta (vv) del virus de la IBD
(IBDV). Descrita por primera vez en Europa hace aproximadamente
diez años, esta nueva forma de la enfermedad se ha extendido
rápidamente por todo el mundo, dando lugar a graves pérdidas, y
después de una década, todav’a supone un riesgo considerable para
la avicultura.
La aparición de formas agudas de la enfermedad ha cambiado
drásticamente la epidemiolog’a de la IBD. Aunque su origen todav’a
no está muy claro, los (vv) IBDVs se han diseminado por todo el
mundo de forma muy explosiva aunque constante. Esto plantea la
cuestión del origen de los vvIBDVs, de la posible existencia de
reservorios y de la posible aparición de nuevas y distintas cepas en
el futuro.
Aunque de cada vez está más claro que la secuencia de aminoácidos de la región variable de la prote’na v’rica VP2 es la responsable
de la variación antigénica, no se ha podido identificar que parte
exacta de ésta determina la patogenicidad. Las técnicas de fingerprint
de VP2 de vvIBDVs deben ser consideradas más como marcadores
de la evolución que como marcadores de la virulencia. Actualmente
se está trabajando en la búsqueda de estos marcadores.
La patogenia de la enfermedad todav’a no está clara y las
citoquinas podr’an jugar un papel esencial en la aparición de la
enfermedad y en el desarrollo de la inmunosupresión. Se han descrito
fenómenos de apoptosis y necrosis en órganos linfoides que están
implicados en la gravedad de la enfermedad. Los macr ófagos podr’an
jugar un papel espec’fico en la fase aguda.
Las vacunas contra el serotipo 1 clásico todav’a son capaces de
producir una buena protección, pero el problema real para controlar
la enfermedad es la interferencia de anticuerpos maternales en el
calendario de vacunación. En el futuro próximo se deber’a trabajar en
el desarrollo de vacunas seguras que transmitieran una elevada
inmunidad pasiva protectora para los broilers, durante le periodo de
crecimiento completo; o bien, que dieran lugar a una respuesta
inmune antes o después de la eclosión en presencia de inmunidad
pasiva. En este contexto, las vacunas recombinantes y la tecnolog’a
del factor de virus-neutralización podr’an tener ventajas sobre otros
planteamientos posibles.