Possible persistent infection of Japanese encephalitis (JE) virus was investigated by detecting the virus genome using nested PCR from the blood or spleen of 6 to 7-month-old swine. In Kanazawa city, blood mononuclear cells were collected from 50 cases in September 1993 to February 1994, and 4 of 10 in September, 2 of 11 in October, 2 of 9 in November, 3 of 10 in December, were positive for the virus genome. In February 1994, the virus genome was amplified in splenic mononuclear cell samples of 3 of 10 cases, which were negative for virus genome in blood mononuclear cell samples. On the other hand, in Kagawa Precfecture where 160 cases were examined from July 1995 to March 1996, the virus genome was detectable from the blood samples in 5 of 20, 2 of 20 and one of 20 in September, October, and November, respectively. The virus genome was detected in January, February and March in spleen mononuclear cells from 4 cases, which were negative in the blood samples. These results suggested that JE virus persistently infected the mononuclear cells of blood and spleen of swine during the winter period.
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