DDT makes a comeback in effort to halt malaria

August 27, 2006|By Scott Calvert | Scott Calvert,Sun foreign reporter

MAPHUNGWANE, Swaziland -- Men in blue coveralls and white surgical masks began their annual trek into the countryside here last week. Methodically, they sprayed one home after another with a chemical most Americans probably thought disappeared from use long ago: DDT.

As villagers looked on, the workers doused inside and outside walls with a fine mist. It is a yearly effort to repel and kill mosquitoes that carry malaria - a disease that kills more than a million people a year, mostly children in sub-Saharan Africa.

This small kingdom near South Africa is one of a handful of countries still using the pesticide, banned in the United States in 1972 because of its toxic effect on eagles and other wildlife.

But now DDT is poised for expansion in the developing world.

The influential World Health Organization plans to promote DDT as a cheap and effective tool against malaria. And the U.S. government has boosted its budget for malarial insecticide spraying in Africa twenty-fold, to $20 million next year.

The new push for household spraying reflects a growing belief in some quarters that significant progress on malaria will require a third major front, alongside insecticide-treated bed nets and novel anti-malarial drugs.

No one proposes a return to the widespread agricultural use that severely harmed ecosystems in the United States and Europe decades ago. The results of such spraying were famously depicted in Rachel Carson's landmark 1962 book Silent Spring, which launched the modern environmental movement.

Advocates of household spraying say the comparatively minute amounts used in homes pose no known dangers. Any potential risk, they say, is far outweighed by DDT's potency against malaria, as was seen in the late 1940s and '50s when it helped eradicate the disease in the United States and other industrialized nations.

But environmental groups, while recognizing DDT's public health benefits, argue that it should be only a temporary measure. Greenpeace worries that some will inevitably be diverted to farming uses and asserts that long-term health effects on humans are still not conclusively known.

Some public health experts, meanwhile, say that DDT has a role but is no "magic bullet." Mosquitoes can grow resistant to it; it might not work as well where malaria is found year-round; and effective house spraying requires organizational capacity severely lacking in places such as the Democratic Republic of Congo.

"You could have a container-load of DDT in every district town in Congo and not save a single life," said Matthew Lynch, who directs the Global Program on Malaria at the Center on Communication Partnerships, a branch of the Johns Hopkins Bloomberg School of Public Health in Baltimore.

"We have to be looking at other tools we have," he said. "What they didn't have in the '50s was insecticide-treated nets, and we have those now. We know they work, and we have long-lasting nets that will last three to five years." Such nets are not treated with DDT.

WHO officials maintain that they are not minimizing the role of nets or treatment, just restoring proper emphasis to spraying - a move that some critics see as long overdue.

"We don't want to keep on treating people," said Dr. Shiva Murugasampillay of the WHO. "We want to prevent people from getting malaria, so the issue is prevention. And one of the best tools is residual house spraying." Of 12 WHO-approved pesticides, "the best chemical we have is DDT."

Aside from Swaziland, he said, countries that use DDT include China, Ecuador, Ethiopia, India, Mozambique, Namibia, South Africa and Zimbabwe. Tanzania and Uganda are considering it, he said, and he expects others to do the same.

A half-century ago, public health officials hoped that DDT would banish malaria from the planet after centuries of suffering and death. The disease was long thought to be transmitted by air, hence the name malaria, or "bad air."

Malaria's fevers and shivers are caused by a parasite transmitted through bites of certain mosquitoes. Through the 1800s malaria occurred in parts of the United States, including port cities such as Baltimore. In the American South, it was still present in the late 1930s when a key discovery was made in a Swiss laboratory.

In 1939, a chemist found that dichloro-diphenyl-trichloroethane killed insects and that a little bit lasted a long time. Toward the end of World War II, the U.S. military sprayed DDT in Europe, Africa and Asia to kill typhus-causing lice and malarial mosquitoes. DDT was dubbed the "atomic bomb" of the insect world.

After the war, the U.S. government began spraying houses across the South. By 1952 malaria was officially gone, although some historians say modernization had nearly wiped out malaria by the mid-1940s anyway.

In 1958 the World Health Organization embarked on a global campaign against malaria based on DDT. Successes were notched in southern Europe, North Africa, Asia, Australia and the Caribbean.

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