0544. Do benefits of DDT for malaria prevention outweigh the risks?

DDT was introduced in the 1940s for control of vectors of malaria and other diseases. The chemical and metabolites are absorbed and are fairly fixed in human fat (½ life is 7-11 years), but the withdrawal of DDT from several countries in the 1970s and by WHO in 2001 was mainly because of emerging resistance and environmental impact (e.g. thinning of eggshells) and less out of concern for effects on human health. Furthermore, alternatives had become available and it seemed to make sense to make the change. Several African countries objected to the ban on DDT because at the time the agent was still effective and affordable, however South Africa was one that switched to pyrethroids. Surprisingly, case numbers increased and a recent article from KZN reports on the epidemic in 2001 that was attributed to pyrethroid resistance and was managed by reverting to DDT spraying. After DDT reintroduction the number of malaria cases decreased and the Anopheles funestus appears to have been eradicated from the province. Concerns are expressed about the likely emergence of resistance, but little comment is made about the possible risk of continued use of DDT. The latter was discussed in a comprehensive review in a recent Lancet, and it is clear that if nothing else we should be extremely vigilant. It would appear that after years of exposure there is a risk of neurological and psychiatric impairment and there is also some evidence that reproductive health and infant and child development might be affected by exposure to DDT. Fertility appears to be reduced, there is possibly a greater rate of abortion, birthweight might be reduced, some congenital abnormalities (e.g. cryptorchidism and hypospadias) might be more common, duration of breast feeding might be compromised and neurodevelopment could be suboptimal. There is evidence for all of the above, but in many cases confirmatory studies are lacking. Given the importance of malaria as a health risk in South Africa it is appropriate that we seek an effective and affordable intervention, but DDT is a potent chemical and is stored in the body, so we must maintain vigilance for possible adverse effects on those we are seeking to protect.

Read more:
S Afr Med J 2005; 95: 871-4
Lancet 2005; 366:763-73
Lancet Infect Dis 2005; 5 : 695-708
Envir res 2005; 29: 158-63