Chris Curtis, a medical entomologist at the London School of Hygiene and Tropical Medicine, cited Madagascar. "The highlands eradicated malaria in the late 1950s and complacency set in. They stopped spraying. In the 1980s there was a huge epidemic which killed many thousands. They have now gone back to DDT and brought things back under control.
"In Venezuela there were 1m cases a year in the 1930s and lots of deaths. After the second world war they got into DDT immediately. In the north-central states malaria was eradicated in the 1940s and 1950s. Since the 1980s things have gone back quite a bit. There are about 24,000 cases a year in developed parts, in spite of pyrethroid spraying - much better than the 1930s and much worse than in the 1960s."
Roger Bate, director of the European Science and Environment Forum and a fellow of the Institute of Economic Affairs, pointed to areas of South Africa where malaria is once more on the rise since other pesticides were substituted for DDT. "It has gone from a couple of hundred cases a year to 15,000 in South Africa as a whole." Restricting DDT use was not the only factor, but it was part of the equation.
These numbers are tiny compared with the malaria toll in other parts of Africa. But South Africa once had it firmly under control. A paper by a consultant to the government there, Roger Tren, to be released by the IEA at the UN pesticides meeting next week, traces the virtual eradication of the disease in most parts after DDT's arrival. Measures to stop mosquitoes from breeding and then weekly spraying with pyrethroids reduced cases, but malaria was still a serious problem.
Transvaal experience
"After the introduction of DDT in the vector (mosquito) control programme in 1946, the number of cases in the then Transvaal declined to about one tenth of those reported in 1942-43," Tren writes. "In some areas DDT spraying was reduced and sometimes stopped because of the success it had in vector control."
Only two major South African provinces are now affected: Northern Province and Mpumalanga. Yet Tren's report (on http://www.iea.org.uk/env/malaria.htm) calculates that the cost of malaria to the economy in terms of people unable to work and needing hospital and home care is 4% of gross domestic product.
Bate said: "If the cost is so great to South Africa, where malaria is not endemic in 50-60% of the country, what is it like for the rest of Africa? Yet people I have spoken to involved in mosquito control in Botswana and Zimbabwe, where there are much higher levels of malaria, have no knowledge that this convention (on banning DDT) is taking place ... The first they will know is when there is suddenly a ban by 2007. That is a major scandal when DDT will reduce the number of deaths significantly and save countries hundreds of millions of dollars."
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