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INFECTIOUS BURSAL DISEASE
1. Introduction
IBD is known since 1962 and is also called Gumboro disease (after the town of Gumboro in
Delaware (U.S.A.) where first descriptions took place). Synonym is Infectious Avian Nephrosis.
It is a highly contagious disease, caused by a Birna virus.
The virus is widespread and is present in almost all areas of intensive poultry farming. Two
serotypes (I and II) are known, type I is the most common one and is spread world-wide, so far
there has been no isolation of virulent type II viruses.
To distinguish between these two types only VN tests can be done.
The disease can be transmitted both directly (bird to bird) and indirectly (contaminated water,
feed, faeces).
Infection can take place via the mouth, the respiration tract, and the eyes and by experiment
via infection in the blood and via the cloaca.
Economical impact on production can be enormous, varying from direct losses due to mortality
to secondary infections and the financial losses due to reduced production parameters as a
result of sub-clinical infections.
2. The disease
The IBD-virus destroys lymphocytes, primarily in the bursa of Fabricius, but also in other
organs of the immune system, like the thymus, the spleen and the caecal tonsils. The result is
a marked immune-suppressive effect, causing:
a. increased susceptibility to other diseases
b. impaired response to many vaccinations.
Clinical and sub-clinical types of the disease may occur:
2.1.Clinical disease
The clinical symptoms of IBD are seen in chickens between 2 and 9 weeks, but mainly
between 3 and 6 weeks. In some exceptional cases even outbreaks up to 16 weeks have been
reported.
The incubation period is very short (1-2 days) and the disease spreads very quickly in a flock.
Symptoms are: - severe depression, tremor
- severe diarrhoea
- rough feathering.
- decreased appetite
dehydration
The disease usually runs its course in 4-7 days, but outbreaks of 2-3 days are also possible.
Mortality can go up to 30%, survivors recover in a few days. The birds have a, temporary
immune-suppression, which makes them susceptible to other diseases.
2.2 Sub-clinical disease
The greatest economic losses are due to sub-clinical disease, particularly in broilers of less
than 4 weeks of age.
Symptoms are retarded growth and poor feed conversion.
Immune-suppression may also occur.
2.3 Influencing factors
Some factors which can influence the severity of a field infection:
a) infection pressure
b) virus characteristics
c) level of immunity
d) genetic constitution
e) other immune-suppressive agents
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2.3.a
infection pressure
The IBD virus is a very stable virus and can survive for months on a farm even without birds. It
is very resistant to several disinfectants.
Consequently, once a farm is infected only very thorough cleaning and disinfection can reduce
virus pressure, elimination of the virus will be extremely difficult. But with sound sanitary
measurements and good vaccinations, the disease can be controlled.
2.3.b
virus characteristics
Most of the Gumboro isolates belong to the same serotype (serotype I) but there is a wide
variety within this serotype.
Both the pathogenic type and most of the weak types used for vaccination belong to this
group. The serotype II isolates were first found in turkeys. This type can also infect chickens.
2.3.c
level of immunity
There are 2 forms of immunity; active and passive.
Passive immunity consists of the maternal antibodies derived from the mother.
Active immunity is a result of developed antibodies after challenge with field virus or after
challenge with vaccine virus.
The level of maternal immunity depends on the immune status of the parents; the vaccinations
and the disease history influence this. These two together will greatly influence the optimal
moment for vaccination.
A vaccination for Gumboro can only be effective if the vaccine virus can break through the
level of immunity of the chicken.
Vaccine virus can be neutralised by maternal antibodies if they are at a high level, in this
situation vaccination is done too early.
When field virus will break through the maternal immunity it will lead to an immunesuppression.
Birds, which have suffered from IBD, have a definitely lower response to vaccinations for
example ND.
2.3.d
genetic constitution
The genetic constitution of the bird influences the ability to respond to vaccines and to
pathogenic field exposure.
There appears to be a relation between the bursa size and the susceptibility to IBD.
In general susceptibility occurs in the following order from greatest too lowest: white layers,
brown layers and meat type birds.
2.3.e
other immune-suppressive agents
Various agents, besides IBD viruses are known to give an immune-suppressive effect. The
best known examples are Chicken Anaemia Virus (CAV), Reticulo Endotheliosis Virus (REV)
and Mycotoxines, which can effect the response to Gumboro challenge or vaccination.
3. Post Mortem
Pathological changes can vary a lot depending on the severity of the disease (and depending
on secondary infections or other diseases), but in general we find:
- most important : enlarged Bursa of Fabricius with yellowish oedema, possible haemorrhages
(varying from small haemorrhages to completely “cherry red” bursa’s)
- dehydration
- haemorrhages in muscles and gizzard
- swollen kidneys
- enteritis
Recovered birds can have atrophic bursae.
Histological changes of the bursa are typical to the disease.
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4. Diagnosis
The diagnosis may be based on;
- clinical symptoms
- post mortem examination
- histology of bursa
- Immune Fluorescence Test of bursa
- Polymerase Chain Reaction
- serology :
most common is ELISA test
serum Virus Neutralisation test can be done to detect the virus
Serotyping only after Virology
Sporadically AGP tests are being used (not very sensitive)
5. Therapy
There is no specific therapy for the disease.
Facilitate the access to water to prevent dehydration.
As with every disease optimise climate and reduce stress to a minimum.
Use of antibiotics can sometimes be advisable to limit the impact of secondary infections.
6. Prevention
6.1. Hygiene
The IBD virus is very resistant and can survive for more than 100 days in a contaminated area.
Disinfection with formalin or phenol is advisable but not completely effective. Other
disinfectants are not or less effective.
6.2. Vaccination
The stability of the virus, reflected in its resistance to disinfection, makes
eradication difficult.
A vaccination will be the best solution in all areas of intensive poultry farming and in all larger
poultry farms.
6.2.1. Live vaccines
The objective of a live vaccination of broilers is to induce a protective level of immunity before
a field virus can infect the bird.
This is a difficult thing to accomplish because one needs to find the optimum date for
vaccination. The average level and the variation (spreading) of the maternal immunity influence
this.
Another important factor is the strength of the vaccine used. There are mild, intermediar and
hot vaccine strains, see manufacturers information. Vaccination is possible at the moment
when the ELISA titres are 1:128 for intermediate vaccines and 1:512 for “hot” vaccines. The
half-life time of maternal antibodies in broilers is 3-3,5 days and for meat type breeders 4 days.
The half-life time of maternal antibodies in layers is 4-5,5 days.
Blood sampling must be done as soon as possible, but you must take into account that the half
life time counting starts after 3 days. The first 3 days the yolk is used. Sometimes a double
vaccination is needed when there is a relative big variation in the titres.
Hot strains are used when very virulent IBDV is present.
Advises for vaccinating chickens against IBD.
-Try to prevent mixing chickens derived from different Parent stock flocks, with different levels
of immunity against IBD.
-When given in the drinking water.
A good quality cool drinking water and properly cleaned drinkers (no traces of desinfectants!) is
essential to avoid neutralisation of the virus.
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Add 2% skimmed milkpowder to the water to protect the virus (before opening the vaccine
vials).
Let the birds become thirsty for a while, then provide enough drinking water with vaccine for
1.5 –2 hours.
Other vaccination techniques can be coarse spray or eye drop.
Another approach is IN-OVO application, were the vaccine needs to be injected in the hatching
eggs, at transfer time. Maternal antibody levels have no influence on this technique.
To check the drinking water vaccination technique one can use water-soluble dyes.
6.2.2 Inactivated vaccines
Inactivated vaccines can be given to breeders in order to increase the level of maternal
immunity in the offspring. Priming with a live vaccine should always precede it. World-wide
there are 2 systems practised for IBD priming.
The cheapest method is only the priming used as first vaccination at +/- 21-24 days of age.
Some producers use a second priming (live vaccine) at 6-14 weeks of age in order to try to get
a higher and a more uniform titre at (Grand) Parent stock level.
The killed vaccine can be given as a combination with other vaccinations.
Some producers do not use inactivated IBD vaccines; this will lead to a higher variation in
titres, especially when Parent stock is challenged with field virus.
For integrated companies who practice mixing broilers of different origin, it is advisable to have
a uniform titre between all producing flocks, this needs killed vaccines.
Declination of titres during the time in Parent stock can be monitored by serology but is in
general very low.
If mixing of broilers is practised it is advisable to mix from flocks from more or less the same
age.
In general, offspring of parents, which have been vaccinated with killed vaccines, are provided
with a longer lasting maternal immunity and therefore must be vaccinated at a later moment.
Combatting the IBD virus is a dynamic procedure, which needs continuous monitoring and
dedicated people who carry out exactly the vaccination procedures and sanitary standards.
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