Comparative immunohistopathology in pigs infected with highly virulent or less virulent strains of hog cholera virus

Eight pigs were inoculated subcutaneously with a highly virulent hog choler a virus (HCV) strain ALD. The infected pigs developed severe illness and be came moribund on postinoculation day (PID) 7 or PID 10. Histologic lesions were characterized by severe generalized vasculitis, necrosis of lymphocyte s, and encephalitis. HCV antigen was detected in crypt tonsilar epithelial cells, macrophages, and reticular endothelial cells of lymphoid tissues. An tigen localization corresponded well with histologic lesions. Five pigs wer e inoculated with less virulent HCV Kanagawa/74 strain and were euthanatize d on PID 30. All five infected pigs recovered from the illness but became s tunted. They also had a slight follicular depletion of lymphocytes, histioc ytic hyperplasia, and hematopoiesis in the spleen. Less virulent HCV antige n was observed in the tonsils, kidneys, pancreas, adrenal glands, and lungs . Although antigen localization was less associated with histologic lesions , immunoreactivity was stronger than that in the pigs infected with the ALD strain of HCV. An almost complete loss of B lymphocytes was recognized in pigs infected with the ALD strain and was correlated with follicular necros is in lymphoid tissues. Loss of B lymphocytes was not prominent in the pigs infected with Kanagawa/74 strain. The number of CD4+ and CD8+ T lymphocyte s was significantly higher than that in the noninfected control pigs.