Virus of Hsw/N/type was isolated and identified in human beings in the United States in 1976 and in swine in Japan in 1977. It belonged to the same type as the etiological virus of“Spanish i nfluenza” prevalent previously. Attention has been paid to its rise and fall.
Then seroepidemiological studies were carried out on the rise and fall of hemagglutinationinhibiting (HI) antibody in the serum of swine to clarify the extent of invasion of virus of Hsw/N/type in Japan. The results obtained are summarized as follows.
1. The virus strain recently isolated and identified in human beings in the United States and in swine in Japan were confirmed to belong to the Hsw/N/type, which was the same as the type of the etiological virus strain of “Spanish influenza” prevalent previously.
2. No antibody was demonstrated in the serum of human beings examined in the rural district, except those who were more than 46 years old and who seemed to have been involved in the epidemic of “Spanish influenza”. Since it was confirmed that the Hsw/N/type was present in Japan, no antibody has been demonstrated either in the serum of junior-high school students examined. Any epidemic of this type among human beings was negated.
3. No antibody was detected from swine produced in Japan prior to 1975.
4. When surveyed in and after July, 1977, swine were found to possess antibody in various districts. There were large differences in the rate of antibody possession among these districts. There was no definite tendency in this rate in any district.
5. An antibody survey was conducted in various districts in Nagano prefecture which was adjacent to prefectures where virus had been isolated. As a result, the rate of antibody possession was high among swine in such districts as adjacent to Niigata prefecture. It was possible to presume that the epizootic might have been transmitted to that prefecture by this route.
6. The results of an antibody survey on imported swine lent support to the assumption that the infection with the Hsw/N/type might have been prevalent severely among swine in the United States in 1975 and 1976.
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