HYDRANENCEPHALY, CEREBELLAR HYPOPLASIA, AND MYOPATHY IN CHICK-EMBRYOSINFECTED WITH AINO VIRUS

Pathogenesis of Aino virus (AIV), a suspected causative agent of conge nital abnormalities of calves, has not yet been established by experim ental infection of darns. To investigate the pathogenesis, 10(3) media n tissue culture infective doses per 0.2 ml of AIV strain JaNAr 28 was inoculated into the yolk sac of 8-day-old chick embryos. At 4, 7, 10, and 13 days post-inoculation (PI) 20 eggs were opened and macro- and microscopic studies combined with virus recovery and immunohistochemic al detection of the virus antigen were performed. At 7 to 13 days PI c hick embryos manifested marked hydranencephaly, cerebellar hypoplasia, arthrogryposis, and scoliosis, with the highest incidences of 86.7%, 73.3%, 80.0%, and 20.0%, respectively. At 4 days PI the viral antigen was found in nerve cells, gitter cells in mild necrotic foci of the ce ntral nervous system (CNS), degenerative myotubules, and macrophages i n the interstitium, which was associated with the early phase of AIV-i nduced encephalitis and polymyositis, with occasional accompanying hem orrhage and clumping of myotubular fragments. From 7 to 10 days PI, AI V antigen increased markedly in the liquefactive necrosis and in both degenerative and normal-looking myotubules in conjunction with develop ing hydranencephaly and arthrogryposis. The encephalitis and myositis had a tendency to mitigate by 10 days PI, coincident with a slight dec rease in amount of AIV antigen. At 13 days PI there was almost no dete ctable AIV antigen in CNS and skeletal muscles, probably due to deplet ion of cells having affinity to AIV.