Epizootic Aspects of Japanese B Encephalitis Virus among Swine in the Southern Kyushu District
1969 Volume 22 Issue 9 Pages 423-429
Details
1969 Volume 22 Issue 9 Pages 423-429
In the city and neighboring areas, of Kagoshima, swine sera were collected mainly over a seven-month period beginning in April every year from 1966 to 1968. They were examined for virus-neutralizing (VN) and hemagglutination-inhibiting (HI) antibodies against Japanese B encephalitis (JBE) virus. In addition, similar antibody survys were conducted on sera of small numbers of horses, cattle, and rabbits in 1966 and 1967. Furthermore, viral isolation was carried out from the blood of experimental breeding swine, rabbits, and mosquitoes collected during the epizootic season. The results obtained are as follows.
1) In all the years, VN and HI antibodies turned positive in all the animals. JBE virus was recovered from swine blood and mosquitoes when the epizootic season came. These results suggested that inapparent infection of JBE virus might have broken out among animals in the southern Kyushu district over a period from early June to middle July, though variable with year. Furthermore, there was a close relationship between atmospheric temperature and the beginning of prevalence.
2) In 1967, antibody turned positive irregularly in the pigs of the same group and a JBE virus epizootic spread very slowly. In addition, VN and HI antibody titers were generaly lower in the sera collected in 1967 than those in any other year, and turned quickly to negativity. This result indicates that there is a fairly remarkable difference in epizootiological aspect between the occurrence in 1967 and that in 1966 and 1968.
3) Viral isolation was carried out from swine, rabbits, and mosquitoes in ESK-1 cell culture. As a result, three strains of JBE virus were recovered from swine blood, and two strains from mosquitoes over a period from 1966 to 1968. Cytopathogenesis was observed in an ESK-1 cell culture infected with all the isolates. Exceptionally, the Taniyama S-2 strain isolated from swine blood in 1967 had no hemagglutinating activity in the liquid phase of infected ESK-1 cell culture. It was suggested that there might be a difference in property between the Taniyama S-2 strain and any other strain.
