More than one thousand swine were imported from the Ryukyus and foreign countries, such as America, Australia, Holland, Poland, and Sweden in 1961 and 1962. They were quarantined at Yokohama. Serum antibodies of both hernagglutinationinhibition and complement-fixation against Japanese encephalitis virus were negative in all the swine, except those from the Ryukyus, at the time of arrival. The antibodies turned positive at a high rate by the end of the quarantine period in summer. About thirty percent of the swine imported in summer became feverish 4 to 10 day after arrival. Some of them expressed clinical symptoms, such as depression, anorexia, and abnormal delivery associated with fever.
There was a close relationship between the rise in antibody titer and the appearance of such symptoms as eliminated by means of mosquito control. It was supposed that there would be infection of Japanese encephalitis virus. However, the abnormal delivery or abortion observed within the quarantine, period in summer must be studied further before it is asserted virologically that such disorders may be induced by infection with Japanese encephalitis virus.
In short, it became clear that the swine imported from America and Europe had been free from Japanese encephalitis, but that they had been infected with the disease soon after their arrival in Japan in summer to manifest such symptoms as fever, anorexia, and abortion at high percentage.
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