Gumboro disease: evaluation of serological and anatomopathological responses in vaccinated broiler chickens challenged with very virulent virus strain

This paper describes the effects of a strong type of vaccine - Moulthrop G603 º and an intermediate-plus type of vaccine - 228E º in meat-type chickens challenged with a very virulent strain of infectious bursal disease virus (vvIBDV). Blood samples and bursa of Fabricius were taken weekly up to 42 days of age. It was concluded that bursa of Fabricius weight, bursa weight:body weight ratio, body weight and antibody titer evaluated before and after challenge with vvIBDV were not enough to consistently and conclusively differentiate or estimate the protection given by vaccination. Quantitative evaluation of injury intensity and the number of altered lymphoid follicles revealed that Moulthrop G603 caused moderate microscopic lesions in one out of seven birds vaccinated at 14 days of age, while 228E vaccine did not induce IBD-typical microscopic lesions in the bursa of Fabricius. Good protection against bursal microscopic lesions was obtained when a strong type of vaccine was used before challenging with vvIBDV. It was concluded that quantitative evaluation of microscopic lesions might be useful to measure the injury induced by vaccinal IBDV, as well as the level of protection and/or immunosuppression induced by IBDV challenge in vaccinated and non-vaccinated chickens