The standard method of malaria control in south and west Asia has been to spray insecticide on surfaces of houses to kill mosquitoes. This is quite expensive and newer approaches are needed. Since the mosquitoes of this region mainly feed on domestic animals and only secondarily on human beings, applying insecticide on the skin of cattle instead might prove quite cost-effective.
A study was carried out in Pakistan to investigate whether cattle treated with an insecticide deltamethrin would prove toxic to mosquitoes and therefore aid in malaria control. Deltamethrin was applied by a sponge to the cattle. Deltamethrin is commonly used in cattle for controlling ticks and tsetse flies and the small amounts penetrating the skin are not hazardous. Six Afghan refugee settlements were selected and randomly assigned to one of two groups. In one group, the cattle were treated with deltamethrin during the malaria transmission seasons of 1995 and 1997, whereas the other group was treated during the 1996 season. The number of cases at the village clinics aided in the monitoring of malaria.
According to the clinic records the incidence of malaria for Plasmodium falciparum decreased by 56% and for Plasmodium vivax by 31% in the villages where the cattle were treated. The density and the life expectancy of the mosquito populations were also reduced in the treated villages. The study showed that cattle treated with the deltamethrin were toxic to the host-seeking mosquitoes for more than a month. Cattle treatment had an effect similar to indoor spraying of the insecticides. The cattle treatment method costs were 80% less and also the incidence of malaria decreased drastically.
The improvement in the cattle health and productivity was more evident to the villagers. There was no report of toxic reaction in any of the treated animals. The incidence of malaria showed a significant reduction in the cases during the trail. As 90% of the mosquitoes feed on cattle and treating the cattle is less time consuming in comparison to spraying the houses, this new way to control malaria, could prove very useful and effective.
The Lancet ; June 2001, vol 357 : (9271)