Thursday, November 22, 2007

DDT - busting some myths 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 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.

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.

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.


Ed Darrell said...

You're right that DDT is no panacea. So why you advocate its use as a panacea mystifies me.

Malaria has no better track record against malaria than integrated pest management (by any title) -- in fact, DDT has a much worse track record. Gains against mosquitoes made with the almost exclusive use of DDT were completely obliterated when the mosquito populations roared back, but the predators of the mosquitoes had been wiped out by DDT.

DDT is a very dangerous substance. While it is not acutely toxic to humans, due to humans' size, it is a suspected carcinogen (recent research strengthened the case that DDT causes breast cancer), it IS toxic to humans, and it mimic estrogen in the environment. These are serious concerns, but they are not the reasons DDT was banned.

In the wild DDT is uncontrollable. The estrogen mimicking causes fetal animals to die, fetal animals that may survive to become very sickly, which causes them to die, and eggshells to become dysfunctional -- all of which adds up to severe damage to bird populations, lizard and reptile populations, and to populations of anything that eats anything from an area where DDT is used.

Contrary to your claim, DDT has been in constant use against malaria, since 1946. Mexico never backed off its use until recently, when it became so ineffective against mosquitoes that the bugs could be heard laughing, practically.

If one follows health care, one knows that beating malaria requires a good health care system, especially to deliver curative pharmaceuticals to malaria victims (if we could wipe out malaria in humans, there would be no need to worry about mosquito transmission of the disease, by the way; malaria cannot survive without human hosts in the chain). We also need a lot of work to prevent mosquitoes from biting, such as draining breeding pools near homes, and creating housing with screened windows (one of the keys to the almost complete eradication of malaria from the U.S.). Bednets are a poor second to such housing, but no malaria control program has been able to provide effectiveness without bednets in the past two decades. Increasing use of bednets has dramatically cut malaria rates everywhere the tactic has been tried. Barriers to bednets have been political, chiefly -- some U.S. policy makers thought it would be more effective if a token charge were made for the bednets instead of giving them away for free. The token charge of $1.00 was more than a day's income for many families in the target populations, which meant simply they did not get nets. DDT is more expensive than bednets, and effective for a tenth as long.

A vaccine may help. In the meantime, there are many things we can do, most of them much less destructive than poisoning the tarnation out of Africa.

Poisoning won't increase the use of bednets. Poisoning with DDT won't improve the delivery of health services. Poisoning won't decrease the breeding rate of mosquitoes if local breeding pools are not drained. Poisoning won't speed development of a vaccine.

DDT is no panacea, you're right. So don't claim it as one, please.

brett jordan said...

hi ed

good to get your feedback on this... i really wish i had time to look into these things more... i published the (edited) white paper because i found some of the facts fascinating, and because it seemed to me that a lot of the things that i took for granted were perhaps based on old or distorted facts.

thank you very much for your 'two penn'orth'


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Ed Darrell said...

The author of has written an article based in incorrect history and bad science. No matter how excellent the writing, it misleads readers to bad conclusions.

There shouldn't be much to argue about if we just stick to the facts.

Banning DDT us in the U.S. in 1972 could not possibly be blamed for WHO's cessation of its eradication of malaria campaign in Africa, in 1966.

Banning DDT use in Texas has not contributed to the continuation of malaria in Africa. Mosquitoes do not migrate across the Atlantic.

DDT was never banned in Africa. But malaria rates, and malaria deaths, are lower now than they were at the height of DDT use.

DDT is not a panacea. Fighting malaria requires more than just spraying poison on Africa and Africans.

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