Sleeping sickness and the factors affecting it in Botswana.

From the first appearance of sleeping sickness in Botswana in 1934 outbreaks increased in severity up to 1971. All populated areas around the fly belt were affected. Rates of infection are highest in the hot wet season and males aged between 30 and 50 years most affected. Rates vary considerably between tribes and have greatly increased in one tribe since 1966. Between 5 and 20% of cases die each year. Increase both in area of tsetse fly infestation and in human population size can account for the increase in severity of outbreaks. Timing of outbreaks correlates with years of low rainfall when people move closer to the fly belt. Seasonal variation in infection rates can be related to temperature and human movements in relation to agricultural activities. Adult males tend to travel and enter the fly belt more than other sections of the population and tribal differences in disease prevalence relate to cultural differences. Early tsetse control measures had little effect on sleeping sickness but aerial spraying with endosulfan coincided with a decline in the disease since 1973. In 1979 aerial spraying was shown to be effective in eliminating a threatened epidemic of sleeping sickness.