Thursday, November 22, 2007
DDT - busting some myths
aei.org reports: [edited]
DDT is probably the single most valuable chemical ever synthesized to prevent disease. It has been used continually in public health programs over the past sixty years and has saved millions from diseases like malaria, typhus, and yellow fever. Despite a public backlash in the 1960s, mainstream scientific and public health communities continue to recognize its utility and safety.
DDT's delisting for various uses in the United States in 1972 was a political, not a scientific, judgment. After decades of extensive study and use, DDT has not been proven to be harmful to humans. But by 1997, its future looked bleak. Environmentalists were pushing for it to be banned worldwide, and its most articulate champion, the South African Department of Health, stopped using it.
Surprisingly, DDT recovered its reputation, and in 2006 the World Health Organization (WHO) championed it again. But celebrations have been short-lived. The momentum to increase DDT use has stalled for lack of increased political and financial support.
DDT, the scientific name of which is dichlorodiphenyltrichloroethane, was first synthesized by Othmar Zeidler in 1874, but it was not until the 1930s that a scientist working for a Swiss chemical company discovered its insecticidal properties. Paul Mueller happened upon it when looking for an insecticide to control clothes moths. He sprayed a small amount of DDT into a container and noted the slow but sure way it killed flies. He wiped the container clean, but when he added new flies, they died, too. Mueller soon realized he had come across a persistent, powerful residual insecticide.
DDT was first used by the Allies during World War II to control lice-borne typhus. In October 1943, Allied forces liberated Naples as they advanced northward through Italy. A typhus epidemic broke out shortly after the liberation, posing a significant threat to both troops and civilians.
Dusting stations were set up around the city, and in January 1944, two delousing stations dusted 1,300,000 civilians. Within three weeks of the dusting (along with other less important treatment and vaccination programs), the epidemic was under control.
MALARIA & DDT
Malaria is a parasitic disease that has plagued mankind for centuries. Today the disease is mostly confined to tropical and subtropical areas of Africa, Asia, and Latin America, but this was not always so. Until the 1950s, malaria was widespread in Europe and North America, and epidemics were even recorded above the Arctic Circle.
In 1898, Ronald Ross, a medical doctor stationed with the British army in India, discovered that mosquitoes transmit malaria. Shortly thereafter, a leading Italian zoologist, Giovanni Battista Grassi, identified the specific genus of mosquito (Anopheles) responsible for transmitting the malaria-causing parasite.
When used in malaria control, DDT has three separate mechanisms: repellency, irritancy, and toxicity, which together are remarkably successful at halting the spread of the disease. Repellency is the most important mechanism, and along with DDT's long residual time, it makes DDT superior to other insecticides. Its repellency qualities have long been known, but they have largely been forgotten by the malaria-fighting community.
Mosquito control officers in the United States used DDT in two ways: as a residual insecticide on the walls of houses and as a larvicide. The results were dramatic. By 1952, there were virtually no cases of malaria transmitted domestically, in contrast to the 1-6 million cases just a few years earlier. Of the 437 confirmed malaria cases in the United States in the first half of 1952, only two were domestically caught. Just as DDT was being used within the United States, it was also saving lives in overseas, within a few years of its widespread use malaria was almost unheard of in Europe.
WHY DDT BECAME A 'BANNED' SUBSTANCE
Rachel Carson's 1962 book Silent Spring questioned the effect that synthetic chemicals were having on the environment. Her argument was that DDT and its metabolites make bird eggshells thinner, leading to egg breakage and embryo death. She also implied that DDT was a human carcinogen based on stories of individuals dying of cancer after using it.
In 1971, after considerable pressure from environmentalist groups, the newly formed Environmental Protection Agency (EPA) held scientific hearings investigating DDT. The hearings lasted for more than eight months, involving 125 witnesses with 365 exhibits. After many months of hearings, DDT was not found to represent a cancer threat to humans, to cause mutations in humans, or to threaten the development of fetuses. DDT was relatively benign, and the allegations against it did not stand up to scrutiny.
Although Sweeney ruled that any existing uses of DDT should not be cancelled, he was overruled in 1972 by the administrator of the EPA, William Ruckelshaus, who did not attend one hour of the hearings. According to a report in the Santa Ana Register quoting Ruckelshaus's chief of staff, Marshall Miller, Ruckelshaus did not even read the entire hearing report. The decision to cancel certain uses of DDT was essentially a political one without any grounding in good science.
THE COST OF DITCHING DDT
DDT leaves stains on mud walls, which was the primary reason South Africa's malaria control program replaced the use of DDT in 1996 with another chemical class - synthetic pyrethroids - although pressure from environmentalists certainly contributed. What followed was one of the country's worst malaria epidemics. Over four years, malaria cases increased by around 800 percent and malaria deaths increased tenfold.
In 2000, the South African Department of Health reintroduced DDT. In just one year, malaria cases fell nearly 80 percent in KwaZulu-Natal province, which had been hit worst by the epidemic. In 2006, malaria cases in the province were approximately 97 percent below the previous high of 41,786 in 2000. DDT remains an essential part of South Africa's malaria control program, and the success of its use in that country has encouraged other countries in the region to follow suit.
For over fifty years, DDT has been on WHO's list of approved insecticides for use in vector control. It experienced a resurgence with reforms to WHO's malaria control policy in late 2005 when the then-director-general, the late J. W. Lee, appointed Arata Kochi to lead the malaria unit. On September 15, 2006, Kochi launched WHO's revised policy position on IRS. In his candid remarks, he explained how and why WHO had arrived at a position that strongly supports IRS and DDT:
I asked my staff; I asked malaria experts around the world: "Are we using every possible weapon to fight this disease?" It became apparent that we were not. One powerful weapon against malaria was not being deployed. In a battle to save the lives of nearly one million children every year - most of them in Africa - the world was reluctant to spray the inside of houses and huts with insecticides; especially with a highly effective insecticide known as DDT".
DDT is no panacea, but it has a better track record on malaria control than any other intervention. Lives are lost every day because of continued opposition to its use. With development and modernization and, perhaps, a vaccine, DDT will one day no longer be necessary, but that day is still a long way off.
at 8:00 am