Can DDT eradicate malaria?
In some places.
The insecticidal properties of DDT were first discovered in 1939. The chemical’s most remarkable property is its staying power: it works to repel and kill insects for months with a single application. This makes it especially cheap and efficient.
Many malarial mosquitoes fly indoors to bite their hosts. But the weight of the blood they ingest makes them too heavy to fly properly, so they tend to land on the nearest vertical surface. There, they rest and excrete out all the water from the blood they’ve consumed, leaving them lightweight enough to fly again. These habits, and DDT’s long-lasting power, made malariologists especially hopeful about DDT. A thin film of DDT applied on the insides of walls, just once or twice a year for a few years, could potentially kill enough blood-fed mosquitoes resting on walls to disrupt malaria transmission for good. Unlike other methods of malaria control—drainage, window screening, prompt health care and medical treatment—DDT spraying could be cheap, fast, and required little infrastructure.
“This is the DDT era of malariology,” wrote the Rockefeller Foundation’s Paul Russell. “For the first time it is economically feasible for nations, however underdeveloped and whatever the climate, to banish malaria completely from their borders.” The WHO launched its global malaria eradication campaign, based on indoor spraying of DDT, in 1955.
But despite years of effort, the WHO’s DDT campaign succeeded in eradicating malaria only from a few marginal areas in southern Europe and a couple islands. Malarial mosquitoes resistant to DDT-cousin dieldrin emerged in Nigeria as early as 1955. Malarial mosquitoes in Venezuela learned to avoid DDT-sprayed walls and bite people outside instead by 1957. By 1972, when the US finally banned DDT, 19 species of malarial mosquitoes had become impervious to the toxin. By the early 1970s, the WHO abandoned its collapsed malaria eradication campaign.
Many populations of malarial mosquitoes are still resistant to DDT. Other species bite outdoors, or if they bite indoors, fly outdoors to rest, avoiding DDT-sprayed walls. Many people who carry malaria don’t live in domiciles that allow for proper DDT spraying. Many don’t live in domiciles at all.
The consensus among malariologists today is that DDT, while still useful in fighting malaria in some places, is no cure-all for malaria. Nevertheless, some DDT advocates have exaggerated DDT’s limited role against malaria to tar environmentalists who have agitated for bans on DDT.
These DDT advocates often imply that DDT wiped out malaria in the United States. In fact, The CDC’s door-to-door DDT spray campaign of 1947-1951 was not about eradicating malaria in the United States, because by then, malaria had already receded. The campaign’s goal, rather, was to prevent the re-introduction of malaria from troops returning home from World War II.
The U.S. Public Health Service had noted the “diminishing menace” of malaria in the United States by 1928—17 years before DDT was launched. Malariologists generally agree that the pockets of malaria that persisted in the South up until the late 1930s were finally vanquished by the swamp-draining, electricity-giving activities of the Tennessee Valley Authority and other rural development schemes, which cut down on mosquito breeding sites and enabled locals to start living in well-screened houses.
Another myth promulgated by anti-environmentalist DDT advocates is that Rachel Carson and those that followed her were the sole critics of DDT. In fact, by the time Carson wrote Silent Spring in 1962, concerns about DDT had been circulating among government experts for years. One month after DDT’s launch in the consumer market in September 1947, experts noted that DDT was dangerous for birds and possibly fatal to fish in the New York Time. USDA scientists urged Congress to ban DDT use on dairy animals in May 1947. (Rachel Carson herself never called for a ban on DDT—which was enacted a decade after her book was published—but rather increased regulation.)
Finally, as anti-environmentalist DDT advocates note, it is true that environmental groups initially supported a UN-led worldwide ban on DDT in 2000. But they quickly about-faced when informed about its use in malaria control. “You can only accuse them of naiveté,” says malaria expert Amir Attaran.
The truth is that DDT and its environmental impact remain controversial. But its role in malaria control is not: DDT spraying will alleviate malaria in some places, sometimes. It won’t work everywhere.
For more:
WHO Global Malaria Programme: Indoor Residual Spraying—DDT and malaria vector control
http://www.who.int/malaria/ddtandmalariavectorcontrol.html
Socrates Litsios, The Tomorrow of Malaria (Wellington, NZ: 1996)
Margaret Humphreys, “Kicking a dying dog: DDT and the demise of malaria in the American South, 1942-1950,” Isis, March 1996
Priscilla Coit Murphy, What a Book Can Do: the publication and reception of Silent Spring (Amherst: University of Massachusetts Press, 2005)
“Any attempt to banish disease is by definition an attempt to alter evolved relationships among living things, in this case between disease organisms and their victims.” – historian Gordon Harrison
