Status of natural infection with Japanese encephalitis virus in Japan: prevalence of antibodies to the nonstructural 1 protein among humans and horses.

The literature on natural infections with Japanese encephalitis virus in Japan and subclinical:clinical infection rates was summarized. To detect natural infections, conventional serologic methods were used in the past, while nonstructural 1 protein-based methods have been used recently. Annual infection rates in humans and horses indicated the status of natural virus activity in Japan.