DDT Makes a Comeback

The World Health Organization today announced it will officially encourage the use of the insecticide DDT, which has been banned in many parts of the world, to help combat mosquitoes that spread malaria. The move is part of WHO malaria chief Arata Kochi’s effort to reinvigorate the global movement to “roll back malaria,” which, when announced in 1998, was supposed to cut the incidence of the disease in half by 2012. More than half way there, there is, if anything, more malaria in the world today – an estimated 500 million cases a year. One to two million people die annually from the disease, most of them children in sub-Saharan Africa and South and Southeast Asia.

The WHO strategy for rolling back malaria has three parts: massive deployment of artemisinin-based combination therapy (ACT), which is effective against the most deadly form of the parasite, Plasmodium falciparum, which has grown resistant to most older drugs; deployment and use of insecticide-treated bednets in homes open to the elements, a common condition in much of the underdeveloped world; and indoor residual spraying, which can be effective in holding down nighttime mosquito feeding in homes that have standard walls, doors and windows.

The move to encourage the use of DDT for indoor spraying represents a major victory for conservative politicians and advocacy groups, who have been pushing the “use DDT” campaign for the past five years. Sen. Tom Coburn (R-OK), a physician, has been a major champion in the Senate, demanding that the U.S. Agency for International Development pour more of its anti-malaria effort into DDT purchases.

Beyond the politics of sticking a needle in the eye of anti-pesticide activists in the environmentalist community (for more on this aspect, see my post here), what’s behind this effort? I’ve spoken to numerous malaria experts in the past year. There is no doubt that DDT, which is extremely cheap to make, can play an important role in malaria control in some parts of the world. But how big a role? Are there any potential side effects from its use? And are there alternatives?

Last fall, I spoke with Prof. Janet Hemingway of the Liverpool School of Tropical Medicine shortly after the Bill and Melinda Gates Foundation awarded the school $50 million to develop new insecticides. Here’s her assessment:

Q. What role do you see DDT playing in the global anti-malaria campaign?

Hemingway: When you use DDT for indoor residual spraying, it has quite a lot going for it. It lasts longer. It still works in many countries, but not all. The idea that we should be using it everywhere, though, is blatant nonsense. There are countries where there are high levels of resistance.

Q. Since we know there are environmental issues, why not use alternatives?

Hemingway: Various environmental lobbies have other insecticides in their sites. Organo-phosphates like malathion are nerve poisons and there’s a big push to get rid of them altogether. The same is true for carbamates. Plus they’re relatively expensive to make, so if you take away agricultural uses, it doesn’t make sense to produce them for indoor residual spraying in the developing world. DDT is cheap to make.

Q. How about the chemical used on the bednets? That must be pretty safe.

Hemingway: Pyrethroids are the only ones used on bednets because of their rapid kill action. But we have a lot of pyrethroid resistance coming through now in Asia and Latin America and Africa. We’re going to lose them to resistance. So all we’ll have is DDT.

Q. But you said earlier that DDT resistance was emerging, too.

Hemingway: There is a lot of resistance to DDT in India, Zanzibar and parts of Tanzania. Down in South Africa (where many of the conservative groups pushing DDT use have outposts), there is no sign of resistance.

Q. So like the parasites that have become resistant to most drugs except artemisinin, the mosquitoes that spread malaria are growing resistant to most insecticides. What can you do about that?

Hemingway: It's clear we need new compounds. We just got a $50 million grant from the Gates Foundation to look for alternatives. The time frame is five years. We’re looking at better formulations of some of the insecticides we’ve already got. DDT lasts six months if you spray it on a wall, the others are 3-4 months, which is another advantage for DDT.

So we’re looking for something that lasts just as long, can be used on walls as well as bednets, and doesn’t have the potential health effects of DDT. We’re working closely with industrial partners (like Bayer Crop Science). Industry has some chemicals they’ve developed for the agricultural industry that may be modified to be used against public health pests.

Posted by gooznews at September 15, 2006 09:43 PM