Epidemiological observations on bluetongue in sheep and cattle in Japan.

Bluetongue (BT) first occurred in Japan between late August and October 1994 in 23 cattle in three prefectures of the northern Kanto region, and between the end of October and mid-November in 23 Suffolk sheep in the same region. The affected cattle had fever, deglutitive difficulty, hyper-salivation, facial oedema, scabbing of the corner of the mouth and dysphagia. The BT virus (BTV) was isolated from blood cells of the affected sheep. Surveillance for BTV antibody conducted by prefectures in the affected region has detected seroconversion to BTV in some prefectures every year thereafter. In the autumn of 2001, again in the northern Kanto region, 45 sheep developed BT, and BTV was isolated. It is considered important that Japan has imported numerous cattle from Australia, the United States of America (USA), and New Zealand every year. In particular, BTV was isolated from cattle imported from the USA during quarantine although some of the serotypes isolated are not present in the USA. Furthermore, BTV is not present in New Zealand. The third RNA segment encoding the serogroup-specific VP3 protein of Japanese BTV isolates and reverse transcriptase-polymerase chain reaction (RT-PCR) positive blood cells was amplified by RT-PCR. Molecular phylogenetic analysis of the third RNA segment based on the sequence homology of the PCR products led to the classification of Japanese BTV isolates into two major groups.