Comparative Haemato-biochemical and Histopathological Studies in Birds Inoculated with Vaccine and Field Strain of Infectious Bursal Disease Virus

Background: Infectious bursal disease (IBD) is an economically important disease of birds which is controlled largerly by vaccination with live attenuated vaccine. The virus is more pathogenic in birds above three weeks of age. The problem of immuno-suppression in birds is one of the leading cause of increase in incidences and intensity of already existing diseases and also of new emerging diseases. Vaccination being one of the important preventive measure for IBD has been implicated as a cause of immunosuppression in many instances. This study was designed to compare the haemato-biochemical and gross-histopathological observations after infection with field and vaccine strain in birds below and above three weeks of age.Methods: In birds below and above three weeks of age, field and vaccine strain of IBD virus was inoculated with subsequent study of haemato-biochemical and gross-histopathological changes.Result: Results indicated that vaccine strain used in this study (IV-95 strain) caused a comparable damage with field strain. The bursal body weight index was not a good indicator for IBD pathogenicity. However, the clinical signs were dependent and could be correlated to aspects such as haemato-biochemical alterations, gross and histopathological lesions in organs other than bursa of Fabricius (BF). Bursal changes could not be correlated to clinical signs as the birds lacking frank clinical signs were equally suffering from bursal damage and depletion of lymphocytes. Hence attenuated intermediate invasive strain of vaccine was capable of damaging BF and may be responsible for immunosuppression.