[Pathomorphological studies of infectious bursitis in chickens with a subclinical infection].

A total of 70 growing birds of three breed, aged 1 to 42 days in which the disease was serologically and morphologically demonstrated were studied. No apparent gross lesions were established with any of the birds. Histologically, there was in the bursa of Fabricius a drop of the lymphocytes within the lymphoreticular system of the follicles. There were in the center of the follicles histiocytes, and epithelial proliferation was seen with single follicles. The cover epithelium of the bursa presented vacuolar degeneration. The white pulp of the spleen was poorer in lymphocytes. There were in the thymus and the cecal tonsils of individual birds pseudoeosinophile leukocytes within the lymphoreticular system as well as lymphomalacia. Serologically, in birds aged 1-2 weeks high titers of antibodies were discovered (1:4 and 1:16), while in those aged 3-6 weeks the antibodies dropped--to 1:3 (with the 3-week-old ones) and to nil (in the 4-, 5-, and 6-week-old ones), which corresponded to the morphologic changes in the investigated organs. It was histologically demonstrated that the virus of infectious bursitis affects the lymphoreticular system of the birds as early as the first 20 days following hatching, which invariably has a bearing on their immune resistance.