An epidemiological study of the occurrence of habu snake bite on the Amami Islands, Japan.

ABSTRACT

This study was carried out in order to estimate the risk of habu snake bite on the Amami Islands in relation to meteorological and human behavioural factors. A time-series analysis of the seasonal variation of habu snake bite was also carried out in order to clarify the possible mechanism of the epidemiological features of habu bite. It was found that the risk of habu bite has been decreasing over a long period of time on both the islands of Amamioshima and Tokunoshima. In general, the risk is higher on Tokunoshima for males and on Amamioshima it is higher for females. There was a significant positive correlation between risk and time spent in the sugar cane fields. Analysis of annual cumulative risk revealed that the inhabitants of Tokunoshima were more likely to be bitten by the habu than those of Amamioshima. The probable explanation for this was the difference between the two islands in the size of cultivated area or the proportion of the labour force engaged in primary industry. Seasonal variation of habu bite showed a maximum occurrence in June. This seasonality was probably caused by the effects of climate on the activities of both humans and habu snakes. Meteorological conditions were investigated by multiple regression analysis for causal effects on the seasonal variation in the occurrence of habu bite; as a result, temperature and humidity were presumed to have an important influence. These facts supplied the most probable explanation for the highest incidence of habu bite being in June rather than in August--the hottest season--on the Amami Islands.