The aim of this work was to describe outbreaks of IBD including different breeds of birds in a rural area and in an urban area of Bangladesh and isolation of the field virus. Furthermore to evaluate the virulence of a local isolate of vvIBDV in vaccinated and unvaccinated local Sonali chickens against IBDV.
Outbreaks of infectious bursal disease (IBD) in one chick shed at Mirpur Central Poultry Farm, Dhaka (urban area) and six chick rearing units at Madarganj, Jamalpur (rural area) were investigated during the period from July to October 2001. The number of birds in the shed was approximately 1000-2000 (urban area) and 400-500 in the rural units. The age groups of the birds ranged from day old to two months. Detailed particulars of the outbreaks of IBD including history, age, breed of affected chicks, flock size, mortality and clinical signs were recorded. A local isolate of vvIBDV from a recorded outbreak with the titre of 103.15 EID50 per 100µl was used for challenge experimental infection.
Within the study period seven outbreaks were recorded. The highest and lowest mortality recorded was 85% and 13% respectively. The birds were affected at the age between 20 and 54 days. Mixed infection and dehydration was found in the urban farm while helminth infection in the rural units. Highest and lowest morbidity and mortality recorded was 27% and 18% and 11% and 3% respectively after experimental infection in different groups of birds. It was found that 14 and 24 days after 2nd vaccination against IBD at day 35 and at day 45 there was a significant difference in antibody titre in unvaccinated and vaccinated groups of birds against IBD.
In this study it was found that mortality was much higher in small flocks than in big flocks. Moreover, it was found that the outbreaks in the small flocks almost affects all birds simultaneously. This might be due to only two persons giving the technical assistance and visiting all chick units and very poor bio-security management practice. Grouping of diseases on the basis of pathology revealed that dehydration was a common cause of death and it was only found in Govt. farm. However there was no helminth infection found in the urban unit but it was found in the rural unit. This might be due to managemental problem. In Govt. farm helminth infection was not found because of regular deworming. In the rural units helminths poses a problem because deworming does not take place. In addition the infection builds up in the village environment. Airway infection was found also in the Govt. farm but not in the rural unit. This could be due to improper ventilation in the farm.
It is clear from the present findings that IBD is prevalent in different production systems of poultry in Bangladesh. It is one of the major poultry viral diseases causing very high mortality in chickens. In experimental infections the virus cause lower mortality than natural outbreaks suggesting that good biosecurity coupled with vaccination can prevent mortality in a great extent. However, the vaccine against IBDV produced from the Intervet company did not give full protection to the challenged isolate. There was no significant difference in antibody titre until 7 days after 1st vaccination in unvaccinated birds compared to vaccinated birds but significant difference in antibody titre was found 14 days and 24 days after 2nd vaccination of IBDV. |
