Download evaluation of safety of malaysian isolate infectious bursal disease

International Conference on One Health and 24th Veterinary Association Malaysia Congress. Marriott
Hotel, Putrajaya, Malaysia (21-23 September 2012)
EVALUATION OF SAFETY OF MALAYSIAN ISOLATE INFECTIOUS BURSAL
DISEASE VIRUS STRAIN 9050/93 AS LIVE ATTENUATED VACCINE
IN SPF CHICKENS
ISWADI M.I., SURIANI M.N., NORMAH M., NOR HALIZA S., GOON S.C.,
JAMALIAH H., KHAIRUL ANUAR M., ONG G.H., AZIZAH D.
& NOOR SUHAILA S.
Veterinary Research Institute, 59, Jalan Sultan Azlan Shah, 31400 Ipoh, Perak, Malaysia
Corresponding author: [email protected]
Abstract
Infectious bursal disease (IBD) is a common disease of worldwide importance and considered
as a threat to the poultry industry. IBD virus (IBDV) destroys B-lymphocytes in the bursa of
Fabricius in young chickens, causing both immunosuppression and mortality. Strategies to
control IBD were largely based on vaccination programs. In Malaysia, many live attenuated
IBD vaccine available commercially but none are from the local strain. The aim of this study
is to determine the safety of live attenuated infectious bursal disease vaccine Malaysian strain
9050/93 in SPF chickens. Fourty five one-day old SPF chickens were divided into 2 groups;
25 birds in Group 1 (vaccinated) and 20 birds in Group 2 (control-unvaccinated) and
monitored weekly for body weight and some were culled to monitor bursal weight. The
results from this study revealed that both vaccinated and control-unvaccinated groups showed
no significant changes in the growth performance indicating that IBDV of Malaysian strain
9050/93 is safe to be used as vaccine strain.
Keywords: safety, infectious bursal disease, vaccine, SPF chicken
INTRODUCTION
Gumboro disease or infectious bursal disease (IBD) is a chicken disease targeting the bursa of
Fabricius, an important organ in the young chicken's developing immune system (OIE, 2004).
The causative agent, a birnavirus, destroys immature B-lymphocytes in the bursa of Fabricius
resulting in immunosuppression. Very virulent strains of IBD virus (IBDV) can result in
mortality of up to 40% of chicken’s population in herd. It commonly affects poultry industry
in worldwide including Malaysia. This disease caused serious economic losses especially in
commercial poultry industry (Thangavelu et al., 1998).
The prevalence of IBD in Malaysia is quite endemic and vaccination is one of the best
measures taken to control the infections in commercial poultry farms. IBD was controlled by
a number of alternative vaccination strategies, including administration of live vaccines of
low attenuation or simultaneous doses of live intermediate strain attenuated vaccine. An
effort has been made by Veterinary Research Institute, Malaysia to investigate the potential
and safety to use Malaysian IBDV strain 9050/93 as vaccine strain to develop live attenuated
IBD vaccine to be used in commercial poultry in Malaysia. Previous study by Lim et al.,
(1994) has shown that Malaysian isolate strain 9050/93 is antigenically similar to the field
isolates 3529/91 that is endemic/actively circulating in the environment. Therefore, this
vaccine is expected to provide broad spectrum of protection against IBD infection in chicken.
International Conference on One Health and 24th Veterinary Association Malaysia Congress. Marriott
Hotel, Putrajaya, Malaysia (21-23 September 2012)
Hence, this study will provide a more protective vaccine against IBD infection in Malaysia
since the vaccine strain used is of similar antigenicity to the field virus in the country.
MATERIALS AND METHODS
Specific Pathogen Free (SPF) Chickens
Total of 45 one-day old SPF (White Leghorn) chickens were obtained from SPF Unit,
Veterinary Research Institute, Malaysia. The chickens were divided into 2 groups; 25 birds in
Group 1 (vaccinated) and 20 birds in Group 2 (control-unvaccinated). Three birds in Group 2
died in the first week of the experiment and were discarded. All birds were reared and raised
in cages in the experimental house and kept for observation for 28 days and the body weight
were measured from first week until fourth week, and all birds were culled at the fourth week
after body weight were measured. The bursa was collected from all the culled birds.
IBD vaccine
A Malaysian isolate of IBD vaccine strain 9050/93 was obtained from Viral Vaccine Unit,
Veterinary Research Institute, Malaysia. The IBD vaccine was isolated in 1993 from an
apparently healthy poultry broiler farm as reported by Lim et al. (1994).
Vaccination procedure
For vaccine safety test, at least 25 two-week-old SPF chickens were used. They were
weighed and vaccinated via oral with 0.3 ml/bird (105.7 EID50/0.1 ml) of the local isolate
vaccine strain 9050/93. The vaccine was administered via oral route at 10 times doses of 105.7
EID50/0.1 ml following Code of Federal Regulations 9 (2002) requirement. Seventeen (17)
SPF chickens of the same source were kept and maintained isolate as negative controls. After
28 days of observation, all surviving birds were culled and necropsied. Evaluation criteria
were mortality, body weight, bursal size and weight, relative bursal weight:body weight ratio
and gross bursal lesion.
Relative bursa weight:body weight ratio
Birds were weighed weekly and the bursal was immediately weighed after being removed.
The relative bursa to body weight was calculated according to previously described by
Moraes et al. (2004).
Statistical analysis
All data were statistically analyzed by student’s t-test in Statistical Package for Social
Science (SPSS version 14.0, SPSS Inc., USA) software for the analysis of variance. All data
were show as mean±SEM. Means were considered significant at p<0.01.
RESULTS
Three birds in Group 2 (control-unvaccinated) died in the first week of the experiment and
were discarded. No mortality related IBD was observed throughout the study period in both
groups of chicken. Total of 42 chickens were observed for 28 days.
Statistically, the mean body weight showed significant changes (p<0.01) of the chickens in
Group 1 (vaccinated) as compared to Group 2 (control-unvaccinated) after 21 days
observation. Body weight in Group 1 for 1st week (100.23±0.95 g), 2nd week (162.80±1.57 g),
3rd week (271.53±4.01 g) and 4th week (355.38±5.92 g) were higher as compared to body
International Conference on One Health and 24th Veterinary Association Malaysia Congress. Marriott
Hotel, Putrajaya, Malaysia (21-23 September 2012)
weight in Group 2 for 1st week (93.65±5.54 g), 2nd week (138.71±8.33 g), 3rd week
(255.38±12.74 g) and 4th week (298.85±14.44 g) respectively.
The mean bursal size and weight in Group 1 (vaccinated) and Group 2 (control-unvaccinated)
were measured in this study. Statistically, bursa size and weight in Group 1 (1.33±0.04 cm)
and (0.95±0.06 g) were significantly decrease (p<0.01) as compared to Group 2 (1.63±0.08
cm) and (1.76±0.18 g).
Mean relative bursa weight:body weight ratio was calculated. A decrease of relative bursa
weight:body weight ratio was found in Group 1 (vaccinated). The relative bursa weight:body
weight ratio in Group 1 (0.27±0.02%) was significantly decrease (p<0.01) than that of Group
2 (control-unvaccinated) (0.59±0.05%).
DISCUSSION AND CONCLUSION
Despite the advancement of vaccination technology, the safety of vaccine used against
various infectious agents in chickens is not always satisfactory. Some chickens immunized
with live attenuated IBD vaccines was found show certain degree of bursal atrophy and are
not fully protected against IBDV infection (Giambrone and Closser, 1990). Furthermore,
according to Muskett et al. (1985), live attenuated IBD vaccine after passage in chickens has
been noted to increase in virulence which was characterized with bursal lesions,
immunosuppression, loss of body weight and high mortality. Therefore the need of
antigenically live attenuated IBD vaccine similar to the local field IBDV is crucial, thus will
potentially give optimum protection against IBD in chickens. The evaluation of safety of
local IBD vaccine strain will be beneficial because of its antigenically similar to local field
IBDV.
Results of this study show vaccination in 14 day-old chick cause reduction of body weight at
day 21 of age, however the chickens were recovered at day 28 of age. The results were
similar to Hair-Bejo et al. (2004a) in vaccination against IBD using broiler chickens.
Although the weight of the bursa in the chickens in Group 1 (vaccinated) was measured about
0.27% of body weight, the results were comparable to the McMullin (2004) which stated, the
normal weight of the bursa in the chickens is about 0.3% of body weight, and weights below
0.1% are highly suggestive of infection. Briefly, after oral infection or inhalation, the IBDV
replicates primarily in the lymphocytes and macrophages of the gut-associated lymphoid
tissues (GALT). Then virus travels to the bursa of Fabricius via the blood stream, where
further replication will occur (Hair-Bejo et al., 2004b). Bursa of Fabricius, a specific organ
source for B-lymphocytes in avian species is the main target of IBDV infection. The degree
of IBDV infection was found correlated with the bursa size and weight (Armstrong et al.,
1981). One of the effects of IBDV infection was characterized by the atrophy of the bursa
and reduced bursa weight:body weight ratio which could be responsible for
immunodeficiency.
As for safety evaluation of live attenuated IBD vaccine Malaysian isolate strain 9050/93
which shows no significant changes in body weight, bursal size and weight with the
unvaccinated group, the strain could be considered has a high potential and safe to be used in
vaccination program for controlling IBD infection in Malaysia.
ACKNOWLEDGEMENTS
International Conference on One Health and 24th Veterinary Association Malaysia Congress. Marriott
Hotel, Putrajaya, Malaysia (21-23 September 2012)
Authors are highly thankful to Dr. Ramlan Mohamed, Director of Veterinary Research
Institute, Malaysia for his support, Dr. Rozanah Asmah Abd Samad for her advice in the
paper writing, Mr. Peter Mangalam Dus, SPF Unit for providing SPF chickens, and all staff
members of Viral Vaccine Unit, Avian Virology Unit, Pathology Unit, Epidemiology Unit
and Animal House Unit, Veterinary Research Institute, Malaysia in their assistance for the
successful completion of this study.
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