DDT for Health

By | August 16, 2007

The eight-year-old U.S. outbreak of West Nile virus shows no signs of abating. Last year, there were 4,300 serious cases and almost 200 deaths. And though it is still very early in the season, statistics released by the CDC on Tuesday are alarming: The insect-borne virus has been found in animal hosts (primarily birds) in 39 states, and in humans has caused about 450 serious infections and at least 15 deaths. The numbers have been increasing exponentially.

Many of these illnesses and deaths could have been avoided. Thanks to flawed, politically correct federal regulatory policy, however, the available tools are limited and largely ineffective.

West Nile virus is transmitted mainly between avian hosts and mosquitoes, and until the mid-1990s was associated with only mild infections of humans in Africa and the Middle East. Then more severe outbreaks of encephalitis and other serious manifestations were reported in Romania in 1996, and subsequently in Israel, Tunisia, Russia and North America.

In the current issue of Nature Genetics, researchers at several American universities and the National Institutes of Health reported the apparent reason for this worrisome transformation: A single mutation in a gene that encodes a viral enzyme can transform a low-virulence strain of the virus to one that is highly virulent. Ominously, the research also provides evidence that the mutated virus enjoys an evolutionary advantage that enables it to adapt rapidly to changing environments, to spread, and to cause disease outbreaks.

The CDC Web site suggests several measures to avoid West Nile virus infection: Wear clothes that expose little skin; use insect repellent; stay indoors during peak mosquito hours (dusk to dawn); and "get rid of mosquito breeding sites" by removing standing water and installing and maintaining screens. Conspicuously absent is any mention of insecticides or widespread spraying.

I guess the Atlanta-based CDC officials don’t get out much. Emptying birdbaths and the saucers under flower pots is not going to get rid of the zillion hungry mosquitoes in regions where there are woodlands or wetlands.

In the absence of a vaccine, eliminating the carrier — the mosquito — should be the key to preventing an epidemic. But in 1972, on the basis of data on toxicity to fish and migrating birds (but not to humans), the Environmental Protection Agency banned virtually all uses of DDT, an inexpensive and effective pesticide once widely deployed in the U.S. to kill disease-carrying insects. The effectiveness and relative safety of DDT were underplayed, as was the distinction between the large-scale use of the chemical in agriculture and more limited application for controlling carriers of human disease. There is a world of difference between applying large amounts of it in the environment — as American farmers did before it was banned — and using it carefully and sparingly to fight mosquitoes and other disease-carrying insects. A basic principle of toxicology is that the dose makes the poison.

The regulators who banned DDT also failed to consider the inadequacy of alternatives. Because of its persistence, DDT works far better than many pesticides now in use, some of which are toxic to fish and other aquatic organisms. With DDT unavailable, many local jurisdictions are depleting their mosquito-control budgets by repeated spraying with short-acting, marginally effective insecticides.

Of course, spraying any pesticide — let alone DDT — has been greeted by hysteria from environmental activists, who have attacked the killing of mosquitoes as "disrupting the food chain." New York’s Green Party literature declared several years ago, "These diseases only kill the old and people whose health is already poor."

Since countries around the world began to ban DDT in the 1970s, insect-borne diseases such as malaria and dengue, and now West Nile virus, have been on the rise. The World Health Organization estimates that malaria kills about a million people annually, and that there are between 300 million and 500 million new cases each year.

This huge toll has caused some bureaucrats to reconsider. In 2005, the United States Agency for International Development endorsed DDT for malaria control, following the lead of the WHO.

To control mosquitoes that carry West Nile virus, the pesticide would need to be used extensively — and it should be. DDT should be made available, immediately, for both indoor and outdoor mosquito control in the U.S.; and the government should oppose international strictures on the pesticide. Federal officials should also educate local authorities and citizens about its safety and potential importance. Right now, most of what people hear is the reflexively anti-pesticide drumbeat of the environmental movement.

Because DDT has such a bad rap, it will be politically difficult to resurrect. But we should begin the process now. In the meantime, we’ll just slather on the insect repellent, slap, scratch — and occasionally become infected with a life-threatening but preventable disease.

Dr. Miller, a physician and fellow at the Hoover Institution, was an official at the NIH and FDA from 1977-1994.