Evidence supporting the continued availability of DDT as an option for malaria control Chris Curtis London School of Hygiene & Tropical Medicine, London WC1E 7HT,

DDT is sprayed on inside surfaces of walls and ceilings of houses to kill resting adult mosquitoes, not for outdoor spraying of mosquito breeding sites If illegal selling of DDT to farmers can be prevented it does not enter outdoor food chains; On this basis use of DDT for disease vector control was accepted nem.con. in negotiations leading to the Stockholm Convention on Persistent Organic Pollutants

Evidence about DDT and human health Indian and Brazilian DDT spraymen showed no higher prevalence of diseases than other men of the same age; DDT derivatives found in breast milk where anti-malaria spraying is carried out in S.Africa; American serum samples and corresponding pregnancy histories from the 1950s show a correlation of DDT derivatives with probability of premature birth; However:- Compared with before the DDT anti-malaria campaign in Guyana, maternal and infant health improved greatly during the campaign and after successful malaria eradication; Conclusion:- if DDT causes any harm, this is greatly outweighed by its benefits when effectively used against malaria

Italy and Romania 1900s-1930sDrainage schemes and free provision of quinine reduced, but did not eradicate, malaria Second World War Wartime disruption ( plus deliberate re-flooding of the Pontine marshes with saline water ) massively increased malaria 1943Compulsory de-lousing with American supplied DDT ended a typhus epidemic in Naples sDDT campaigns on both sides of the “Iron Curtain” eradicated malaria in southern Europe 1960s – present No revival of malaria transmission because the many human cases imported from Africa and Turkey are effectively treated before becoming infectious to mosquitoes.

Indoor residual spraying in southern Africa 1940s-1994DDT successfully used to greatly reduce malaria in several countries; Anopheles funestus disappeared in South Africa 1995Switch to pyrethroid spraying in S.Africa by 1999In S.Africa 4x increase in malaria cases; detection of An.funestus resistant to pyrethroids but not DDT 2000Switch back to DDT spraying in S.Africa by % reduction in malaria cases in S.Africa

Zanzibar in the 1950s-60s DDT spraying ( combined with treatment of malaria cases with chloroquine to which there was then no resistance ) reduced very high endemicity to only 5% of children infected over a 10 year period; unfortunately the project was then terminated when eradication seemed imminent; nevertheless, the reduction achieved was far greater than any of the recent results with insecticide treated nets.

Madagascar highlands late 1950sDDT spraying ( plus compulsory chloroquine treatment ) eradicated malaria and its vector An.funestus 1960s-1980sall anti-malaria precautions withdrawn late 1980sreturn of An.funestus from lowlands led to a massive malaria epidemic in a human population which had lost immunity - c.40,000 deaths 1990srestoration of DDT spraying with Italian aid brought malaria and its vectors back under control.

In India in the 1930s there were about 75 million malaria cases/yr, but in the 1960s DDT spraying reduced this to about 100,000 (99.8% reduction) – a FAR greater reduction factor than has yet been achieved with treated nets Laboratory tests on Indian mosquitoes now show considerable DDT resistance However:- data of S.N.Sharma ( 2005 J Vec Borne Dis 42: 54 ) show that, provided a high % of the houses in a village are sprayed, DDT is still very effective in reducing mosquito vector populations and malaria; Indian made DDT is much cheaper, per house sprayed, than imported alternative insecticides; lower costs mean more communities can be covered from a limited budget for disease control.