In the outbreak of abortions, premature births, stillbirths and congenital arthrogryposis-hydranencephaly (AH) syndrome in Japan during the summer through winter of 1972-73 and 1973-74, precolostral sera from calves with congenital AH syndrome and normal calves were tested for neutralizing antibodies against some arboviruses, i.e. Akabane, Aino, Getah and Japanese encephalitis (JE) viruses. The incidence of antibody for Akabane virus was very high in calves with AH syndrome (49/59 or 83 per cent) as compared with normal calves (3/11 or 27 per cent), indicating an intimate correlation between the AH syndrome and precolostral anti-Akabane antibody. Three stillborn fetuses also had anti-Akabane antibody. On the other hand, no precolostral serum antibody for the other viruses was detected in any of the calves tested. The mothers of these calves, normal and with AH syndrome, had anti-Akabane antibody in high percentages (44/52 or 85 per cent and 7/8 or 88 per cent), whereas a few of the mothers had antibodies for the other viruses. Serological surveys indicate a wide dissemination of Akabane virus in epizootic areas during the summer months of 1972 and 1973. Thus, 8 groups of cattle in epizootic areas showed high rates of seroconversion for Akabane virus during the 1972 or 1973 summer. Very high incidences of Akabane antibody were shown among cattle in epizootic areas but extremely low incidences in near-by non-epizootic areas. The geographic distribution of anti-Akabane antibody among cattle throughout the country in the 1973 spring generally agrees with the pattern of case distribution in the 1972--73 outbreak. All these findings strongly suggest that Akabane virus is the etiological agent of the outbreaks. Further studies are needed, particularly isolation of the virus, demonstration of infection with the virus in lesions by immunofluroescence and production of intrauterine infection by experimental infection of pregnant cows.

Outbreaks of an acute febrile disease of cattle occurred in Japan in 1959 and 1960. Its occurrence was limited in late summer and autumn, and in Kyushu, Shikoku and Honshu roughly south of 37 degrees north latitude, suggesting a close correlation of the incidence with the climatic conditions, hence a possibility of the presence of arthropod vector. The disease was characterized by fever and lesions affecting the mucous membrane and skin, musculature and vascular system. Degeneration of striated muscles was observed in the esophagus, larynx, pharynx, tongue and skeletal muscular system. Edema and hemorrhage were marked in the mouth, lips, abomasum, coronets etc., occasionally followed by degeneration of the epithelium leaving erosions or ulcerations. Severe lesions affecting the esophageal and laryngopharyngeal musculature caused deglutitive difficulty which in turn resulted in dehydration and emaciation, and occasionally in aspiration pneumonia, constituting the major causes of death of the affected animals. These findings indicate that the disease resembles bluetongue in sheep and cattle. The clinical materials obtained from natural cases induced a clinical illness when inoculated into calves, and the disease was transmitted serially in calves by intravenous inoculation of the blood obtained at the height of febrile reaction. The experimentally produced disease was clinically and pathologically indistinguishable from the natural disease.

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Previous serolgoical studies strongly suggested Akabane virus to be the etiologic agent of epizootic abortion and congenital arthrogryposis-hydranencephaly in cattle, and this view was further corroborated in this study by the isolation of the virus from an aborted fetus in an epizootic of the disease and from a fetus extracted froma cow which was suggested by serologic tests to have a recent infection with the virus. The latter fetus had histological changes of encephalomyelitis and polymyositis, and specific antigens of Akabane virus was shown by the immunofluorescent technique in brain tissues as well as skeletal muscular tissues. The virus was recovered from various fetal tissues and fluids, and in relatively large amounts from brain, spinal cord, cerebral fluid, skeletal muscles and fetal placenta. The intracranial inoculation of suckling mice, 1-2 days of age, was the most sensitive system for Akabane virus isolation and HmLu-1, a continuous cell line from hamster lung, seemed almost as sensitive as suckling mice.