Preparation and evaluation of Vero-cell infectious bursal disease vaccine in Pakistan.

The present work was carried out to develop an effective vaccine to control infectious bursal disease (IBD). The very virulent infectious bursal disease virus (vvIBDV) was adapted to grow in Vero-cell line after three serial passages. The virus was then attenuated by further serial passages and pathogenicity of different passages was determined in broiler chicks free from antibodies against IBDV. The ninth passage virus was completely attenuated, as it was non-pathogenic to chicks. The birds inoculated with ninth passage virus had bursa to body weight ratio comparable to un-inoculated control and zero mean lesion score. This ninth passage virus was evaluated as live attenuated Vero-cell adapted vaccine. A commercial live cell culture origin vaccine (IBD-VAC, Korea) was used for comparison. Experimental trials were conducted in 3-week-old broiler chicks. Clinical signs, gross and histopathological lesions and bursa to body weight ratio were all comparable to un-vaccinated control group in case of live attenuated Vero-cell vaccine (group A). High virus-neutralizing antibody titres were also found at 7, 14, and 21 days post-vaccination in group A. On challenge, 100% protection was achieved in group A and 65% in case of commercial vaccine (group B) in terms of bursal lesions. All the birds in control group showed sever bursal lesions post-challenge. The study indicated newly developed infectious bursal disease vaccine was found to be safe and immunogenic.