Abstract
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.
Highlights
Gumboro Disease (GD), called infectious bursal disease (IBD), is a chicken disease caused by a Birnavirus from serotype 1
The outbreak was an infection caused by a virus from the molecular group 11 (Gm 11), similar to the very virulent samples found in Europe and classified as very virulent virus (Ikuta et al, 2001)
- T1 = non-vaccinated, not challenged; T2 = non-vaccinated, challenged; T3 = vaccinated with Moulthrop G603 and challenged; T4 = vaccinated with 228E and challenged; 2 - a = significantly different from T1 at the same age (p
Summary
Gumboro Disease (GD), called infectious bursal disease (IBD), is a chicken disease caused by a Birnavirus from serotype 1. According to the virus virulence and pathogenicity, IBD cause more severe or less severe lesions on the bursa of Fabricius and other organs such as: spleen, thymus and kidneys, and may induce immunosuppression and mortality in birds (Lukert & Saif, 1997; McFerran, 1993). According to Lasher & Shane (1994), the occurence of a very virulent virus strain capable of inducing 100% mortality in chickens without specific antibodies was notified in Europe in 1989. The most virulent viruses reported caused at most 10 to 15% mortality in experimentally infected birds without specific antibodies, for instance, the reference sample 52/70 or Faragher. The first cases of high mortality due to Gumboro disease in Brazil were observed approximately in mid-1997 (Di Fabio et al, 1999 a,b). The outbreak was an infection caused by a virus from the molecular group 11 (Gm 11), similar to the very virulent samples found in Europe and classified as very virulent virus (Ikuta et al, 2001)
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