Caracterización clínico-patológica de tres aislamientos del virus de la infección de la bolsa de Fabricio, obtenidos en granjas comerciales de pollo de engorda en México

Three field isolates of infectious bursal disease virus (IBDV) were obtained from commercial broiler flocks in Mexico. Their antigenic properties were determined by antigen -capture-ELISA using monoclonal antibodies: B-29, R-63, BK-9, B-69 and 57. Virulence of the three isolates was evaluated in inoculated birds based on clinical signs, production of neutralizing antibodies against IBDV, mortality, bursa/body weight ratio, histological lesions, IBDV antigen permanence in lymphoid tissues and humoral response against Brucella abortus and red blood cells of sheep. Isolates P and G held the epitopes recognized by the monoclonal antibodies B-29, R-63 and B-69. These epitopes usually appear in classical IBDV strains, whereas isolate H was not recognized. The three isolates caused the subclinical form of IBD. Marked bursal atrophy with severe lymphocyte depletion was observed in inoculated birds. IBDV was detected by immunofluorescence up 14 days postinoculation, and antibody production between the first to the second week postinoculation. Although immunosuppression wa s not detected by the measurement of immune response towards antigens used, the eventual immunosuppressive effect by isolate H cannot be excluded. Finally, no difference of virulence among the three isolates was observed.