Meteorological factors involved in Japanese encephalitis virus infection in cattle

From 1982 to 1987 a total of 4,371 dairy cattle in Saitama Prefecture, were examined for levels of hemagglutination inhibition (HI) antibody to Japanese encephalitis virus (JEV) and the correlation with meteorological factors and an antibody positive rate was studied. Positivity rates of HI antibody from July to October each year (Yi) ranged from 58.8 to 88.0% with a considerable annual variation. Simple regression analysis of Yi with the comparative meteorological value (Xi) was determined from mean temperatures (Ti, j-1), rainfalls (Ri, j-1) for 10-day-periods each, and the number of days showing 25 degrees C or above (ti, j-1) from June to September, which yielded a correlation coefficient of 0.8147 (p less than 0.05) and an equation for estimated HI antibody positivity rate: Yi = -0.04Xi+79.9 (p less than 0.05). Multiple regression analysis with the power values of three meteorological parameters as independent variables and Yi as the dependent variable, showed a multiple correlation coefficient of 0.987 (p less than 0.05) and a multiple regression equation: Yi = -3991T1/13-0.0035R-12+1978t1/9+4187 (p less than 0.05), giving estimated positivity rates almost equal to the values from the observations. Therefore, a predictive equation was formulated reflecting positive and negative correlations of sero-positivity with the temperature and the precipitation, respectively.