The pathology of Rift Valley fever. II. Lesions occurring in field cases in adult cattle, calves and aborted foetuses.

Since the original description of Rift Valley fever in sheep, cattle and man in the Rift Valley in Kenya in 1931, very little has been published on the disease in cattle. This report deals with the macroscopic and microscopic pathology of field cases of Rift Valley fever in 22 adult cattle, 8 calves and 8 aborted foetuses. The microscopic liver lesions in 13 adult cattle were characterized by marked centri- and midzonal eosinophilic necrosis, involving almost 2/3 of the lobules, and accompanied by sparsely distributed primary foci of necrosis. In 3 animals, however, the hepatic lesions were more focal in nature, while a massive hepatic necrosis was evident in 6 others. In calves, the lesions in the liver ranged from cases showing numerous haphazardly scattered primary foci of necrosis to cases where the latter were accompanied by eosinophilic necrosis of the remaining hepatocytes in the lobules. Vascular lesions, thrombosis and sinusoidal fibrin deposits were sometimes seen in the livers of both calves and adult cattle. Although the aborted foetuses were in a fairly advanced state of autolysis, it was still possible to make a diagnosis of Rift Valley fever from the characteristic lesions which were similar to those reported for new-born lambs. Other noteworthy lesions in adult cattle and calves included pyknosis and karyorrhexis of lymphocytes in the spleen and lymph nodes, widespread serosal and visceral haemorrhages which were sometimes accompanied by copious free blood in the gastrointestinal tract, and a nephrosis.