A few decades ago, world health specialists talked of eradicating malaria. Now they talk only of trying to regain control. Malaria is endemic in more than half the world's countries. In the time it takes to name the disease, 10 children will contract it and begin fighting for their lives. One child in four who dies in Africa has succumbed to malaria.
DDT has a bad name. It is a pesticide that damages the environment and has been widely used in agriculture. Since Rachel Carson exposed its depredations in her book Silent Spring in 1962, environmentalists have campaigned to curb its use. In the west they have been successful.
But in the developing world it has saved millions of lives. Sprayed inside houses, it kills or more often repels the mosquitoes whose bite transmits malaria, and it is cheap. Specialists argue that it does not migrate out of doors, and if we lose it through a global ban in 2007 millions who could have been protected will die.
It is a head-on clash between first world environmentalists, who insist that DDT must go for the health of the planet and that alternatives will and must be found, and the malaria specialists, who say that until alternatives are in place that are as cheap and effective it would be catastrophic to ban it.
What will happen is clear, say the doctors. Under pressure from the west, which has no malaria, and amid worries about damage to human health from DDT, some developing nations have stopped or cut down on its use. Their sickness and death toll from malaria has risen. Effective alternatives have not been put in place, being too complex or, usually, too expensive.
The World Wide Fund for Nature, at the forefront of the campaign to ban DDT, talks about environmental management and biological control instead of pesticides, citing examples in India, Tanzania, Mexico and the Philippines.
But even these small-scale projects have run into difficulties - apart from in Tanzania, where bed nets are sprayed with synthetic pyrethroids. This sort of alternative might be acceptable to all, but pyrethroids are up to three times more expensive than DDT, although on bed nets they are used in smaller quantities, and projects to provide sprayed nets for large numbers of people are inevitably more complex than spraying house walls.
Don Roberts, professor of tropical public health at the uniformed university of health sciences in Bethesda, Maryland, cites what happened in Belize under pressure from the US to abandon DDT. "They stopped in the late 1980s to early 1990s, and malaria rates spiralled out of control, peaking in 1994. In 1995 they started using DDT again and have brought disease rates down three years in a row."
Two years ago, in the journal Emerging Infectious Diseases, he showed that Ecuador, which increased its DDT spraying while others cut down, was the only one of 11 malaria-endemic South American countries to have reduced its detection rate. With organised DDT house spraying, malaria in urban areas of the Amazon basin largely disappeared, but it is again becoming a big health problem.
Sense of balance
Professor Roberts does not like the confrontation with the environmental lobby. "We're all concerned about the environment," he said. "This is not limited to a few who want to get rid of DDT. But environmental issues have to be treated with a sense of balance." If this were the battle to eliminate DDT from agriculture, he would be applauding. Is it feasible to get alternative malarial control measures in place before 2007? "Absolutely not," he said.
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.
"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."
Alternatives to DDT:
These pesticides are less toxic to wildlife and biodegrade far more efficiently than DDT. They are used to spray the inside of houses, like DDT, or more successfully to impregnate bed nets, which protect populations from malarial mosquito bites at night. They are three times as expensive as DDT, but less needs to be used in bed net spraying.
There are suggestions that malarial mosquitoes are becoming resistant to pyrethroids. WWF is not completely happy with them as an alternative to DDT and is calling for research on the "possible hazards" of pyrethroids to health.
Predators that eat mosquito larvae, such as fish like guppies or carp, are introduced to waters where mosquitoes breed. Other possibilities are parasitic wasps and natural bacteria. This method can pose a threat to biodiversity if the predator attacks indigenous wildlife, such as other fish or tadpoles.
The aim is to get rid of the stagnant waters where mosquitoes breed. Methods include drainage, filling in depressions and planting trees. A project cited by WWF in the Kheda district of Gujarat, India, covered water surfaces with polystyrene beads. But doubters point out that mosquitoes can breed in a muddy hoofprint.
There is work on several at the moment, but a vaccine is unlikely in the near future.