The Effect of Precipitation on the Transmission of Japanese Encephalitis (JE) Virus in Nature: A Complex Effect on Antibody-Positive Rate to JE Virus in Sentinel Pigs

Japanese encephalitis (JE) is one of the most important mosquito-borne viral diseases in Asia. Pigs are a natural host and the amplifier of JE virus. The sero-conversion rate to JE virus in sentinel pigs reflects the activity of JE virus in the region. We analyzed whether precipitation has any effect on the sero-conversion rate to JE virus in sentinel pigs. Linear regression analysis was performed to determine the correlations between the levels of precipitation and sero-conversion rates to JE virus, in the entire year and during summertime over the period of 32 years from 1969 to 2000. The levels of the annual and summertime precipitation demonstrated statistically significant positive correlations with sero-conversion rates for the whole of the country and for some regions in Japan. The levels of the summertime precipitation, on the other hand, demonstrated statistically significant inverse correlations with the sero-conversion rates in other regions. Further, the levels of precipitation during preceding 10-day periods from days 1–40 before blood collection showed inverse correlation with antibody-positive rates in some regions. The results indicate that the relationship between the annual and summertime precipitation, and the sero-conversion rate to JE virus is complex; both positive and inverse effects are demonstrated depending on the regions.