A congenital abnormality of calves, suggestive of a new type of arthropod-borne virus infection.

About 1000 calves with a congenital disease were born in Kagoshima prefecture, Japan, between October 1990 and October 1991, the peaks of the epidemic being in March and July 1991. Of 85 abnormal calves examined pathologically and serologically, 70 appeared to have been suffering from a viral disease. Of these 70 animals, 17 had lesions bearing some resemblance to those of the diseases produced by Akabane, Chuzan, Aino, bluetongue and bovine viral diarrhoea-mucosal disease viruses-diseases known to occur in Kagoshima-but serum samples contained no antibodies to these viruses or to infectious bovine rhinotracheitis virus. This suggested the occurrence of a new type of viral infection in southern Japan. Six of the 17 calves were born dead and the others manifested clinical signs such as weakness, difficulty in sucking, inability to stand, vertigo, opisthotonus, staggering and weak eyesight or blindness. They were of small size and showed domed head, scoliosis, arthrogryposis, maxillary retraction, sunken eye, cataracts, and irregularities and defects of the teeth. At necropsy, almost all cases showed hydranencephaly, and many had cerebral defects and cerebellar hypoplasia or agenesis. Both cerebral and cerebellar lesions were seen in six cases, two of which showed a hypoplastic defect of the brain stem. Histopathological examination of the affected organs revealed gliosis, loss of cerebral parenchyma resulting from dilation of the ventricles, perivascular cuffing with round cells such as lymphocytes and plasma cells, proliferation of blood vessels, thick-walled blood vessels in the brain stem, dilation of mesencephalic aqueducts, cerebellar cortical dysplasia, decreased nerve cells in the ventral horn of the spinal cord, and myodysplasia of skeletal muscle.