Epidemiological survey for visna-maedi among sheep in northern prefectures of Japan.

Ovine sera collected from the northern Prefectures of Hokkaido, Iwate and Aomori in Japan, were examined for the presence of antibodies against visna-maedi virus using the agar gel immunodiffusion test and enzyme-linked immunosorbent assays. Three animals (1.12%), out of 267 samples tested, were found to be seropositive to the visna-maedi antigens in both tests. Levels of infection were found in flocks from Hokkaido and Iwate Prefectures, but not in the Aomori Prefecture. Nucleic acid detection by polymerase chain reaction on serum samples did not give positive results. Although no diagnostic measures were in place, the infection could not be related to losses in sheep production or to reduced survival rates. The very limited visna-maedi distribution indicates a highly favourable condition for the application of eradication strategies in this area.