JOHANNESBURG — More than three decades after much of the developed world banned DDT use, South Africa maintains the maligned pesticide as a cornerstone of its malaria control strategy.
South Africa credits indoor DDT spraying in high-risk areas with dramatically decreasing the number of malaria cases and malaria-related deaths here in recent years. The negative effects of the chemical on humans, wildlife and the environment remain the topic of hot debates and scientific studies, but South Africa has determined that DDT’s efficacy in keeping disease-carrying mosquitoes at bay is too great to pass up.
“Overwhelmingly, the public health benefits are higher than any potential (pitfalls),” said Richard Tren, director of Africa Fighting Malaria, an advocacy group based both in South Africa and the United States.
South Africa introduced malaria control measures in the 1930s, and the risk of infection is now relatively low and seasonal — mostly during the wet summer months. Malaria transmission is limited to low-altitude areas in the northeastern part of the country near the border with Mozambique and Swaziland. Out of South Africa’s nine provinces, only three — Limpopo, Mpumalanga and Kwazulu-Natal — regularly report cases of malaria infection.
The number of malaria cases declined steadily until the mid-1990s, when it suddenly increased to peak at more than 64,000 cases and 458 deaths in 2000 — the highest number since the 1930s. The reason for the increase was three-fold. First, parasites had developed resistance to anti-malarial drugs; second, South Africa experienced unusually heavy rainfall after several years of drought; and third, mosquitoes weren’t deterred by synthetic pyrethroids, the insecticide that had replaced DDT for indoor spraying.
South Africa quickly reverted to DDT as its insecticide of choice, and the number of cases and deaths fell accordingly. For the 2006 to 2007 season, there were just 5,596 cases and 37 deaths, according to the South African Department of Health. Statistics for 2007 to 2008 — the most recent available — show a slight increase with 7,773 cases and 65 malaria-related deaths.
South Africa is the leader of regional efforts to fight malaria. Control of the disease is an integral part of the joint development program it started with Mozambique and Swaziland in 2000. South Africa also assists five other countries — including neighbors Botswana and Namibia — with DDT indoor spraying programs. South Africa’s malaria control efforts are self-funded, but some of these other countries receive support through the $1.2 billion U.S. President’s Malaria Initiative.
The regional strategy is particularly important as migrants carrying the disease flock to South Africa’s cities. For instance, Gauteng Province, home to the capital Pretoria and Johannesburg, is not located in a malaria area, but each year hundreds of malaria cases are diagnosed there among Mozambican immigrants.
After using DDT for decades, the United States and other Western countries banned the chemical in the 1970s following the publication of a book by an American biologist that detailed the negative impact of DDT on the environment. Under the Stockholm Convention, DDT is set to be phased out for all uses except for indoor residual spraying under the guidelines of the World Health Organization.
The United Nations just announced new projects in Africa and Asia to test non-chemical methods to eradicate malaria. The new $40 million effort is part of the U.N.’s effort to cut DDT use by 30 percent worldwide by 2014 and eliminate it completely by the early 2020s.
As powerful a tool as DDT is in fighting malaria, it has its detractors — even in South Africa. Christiaan de Jager, head of environmental and occupational health at the University of Pretoria, studied the effects of long-term exposure to DDT among young men in South Africa’s Limpopo province. Replicating an earlier study he conducted in Mexico, de Jager found that DDT exposure led to a decrease in semen quality and fertility in most men.
De Jager said new research is set to examine the link between DDT exposure and neurological abnormalities as well as spontaneous abortions. De Jager — who said his findings have been received coldly by health authorities intent on continuing DDT spraying — said he is not advocating an immediate ban on DDT use for malaria control. Rather, he said, he's pushing for more research on viable alternatives.
“We should work harder and do more research to develop safe methods,” de Jager said. “We cannot just say, ‘DDT is effective and cheap,’ and ignore the health effects associated with it.”
Gerhard Verdoorn, former chairman of the Poison Working Group of South Africa’s Endangered Wildlife Trust and an expert on the environmental impact of pesticides, said that DDT passes through the food chain of raptors and scavenger birds and that they are particularly vulnerable as DDT reduces the females’ ability to produce calcium for their eggs. He said spraying can only be conducted under strict conditions: It should only be used in areas where mosquitoes are resistant to other pesticides; the spraying should only take place indoors and should be done by qualified technicians; and all precautions should be taken to prevent water sources from being contaminated.
Verdoorn said that there have been mishaps but that overall DDT spraying has been done responsibly.
“In South Africa now we only use DDT in a very controlled manner,” he said.
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