Spraying tick-infested houses with lambda-cyhalothrin reduces the incidence of tick-borne relapsing fever in children under five years old

Abstract

Tick-borne relapsing fever (TBRF) is a major cause of morbidity and mortality of children in central Tanzania. This study assessed the effect of house interior residual spraying with lambda-cyhalothrin on domestic tick infestation and the incidence of TBRF in children under 5 years old. Two neighbouring villages were studied: one was sprayed with insecticide, the other left untreated. Samples of earth from the floors of 50 houses before and after spraying, and 50 houses in the control village, were sieved and ticks counted. The incidence of TBRF was estimated by microscopy of thick blood films taken from all children under 5 years old presenting with fever to the village dispensary or health workers. After 2 cycles of spraying, no tick was found in the treated houses; in the controls, tick numbers remained high. In the treated village there were 29 cases of TBRF among the 960 children under 5 years old in the 4 months before spraying, and one in the 4 months after spraying. In the control village there were 10 and 4 cases in the same periods among the 510 children. There was a significant reduction of 0·09 in the odds ratio of infection after spraying (95% confidence interval 0·01–0·87).