A prospective study of the effects of ultralow volume (ULV) aerial application of malathion on epidemic Plasmodium falciparum malaria. IV. Epidemiologic aspects.

In the Miragoane Valley of Haiti a consistent pattern in the incidence of Plasmodium falciparum malaria over a 10-year period made it possible to predict an annual outbreak and perform a prospective study to test the effects of aerial ultralow volume (ULV) malathion on epidemic levels of this disease. At the end of October 1972, after epidemic levels (100 cases/month/10,000 population) had been reached, spray operations were begun. The first spray cycle produced a sharp and immediate drop in populations of the vector Anopheles albimanus, followed 4 weeks later by a decrease in the incidence of malaria throughout the valley. Although the incidence of malaria was similar in sprayed and unsprayed areas prior to the effect of ULV malathion (176.1 and 198.7 cases/month/10,000 population, respectively), it was significantly different during the subsequent 3 months (16.8 cases/month/10,000 population in sprayed areas and 65.4 in unsprayed; p less than 0.001). Travel histories indicated that only 4% of all cases had spent a night away from home during the 4 weeks prior to onset of symptoms; therefore, we concluded that these incidence data represent malaria transmission in the valley. Results of the study indicate that aerial spraying of ULV malathion can interrupt epidemic transmission of P. falciparum malaria by a susceptible vector.