DDT can stymie malaria-carrying mosquitoes in Haiti

http://wiki.dickinson.edu/images/b/bc/DDT2.jpgBY HENRY I. MILLER

henry.miller@stanford.edu

On top of the almost unimaginable devastation caused by January’s earthquake in Haiti, the nation is bracing for the ravages of the rainy season. Torrential downpours have already flooded homes and turned tent cities into muddy misery. Ominously, the number of cases of malaria, which is spread by the bite of mosquitoes and which was endemic in Haiti even before the earthquake, is increasing.

To reduce the incidence of malaria, various aid groups are planning to distribute more than 3 million bed nets, an ultra-low-tech, only modestly effective intervention. What is really needed is the chemical DDT, an old, cheap and safe tool to control the vector — the Anopheles mosquito — that spreads the disease.

Malaria is a scourge of humanity, particularly for the inhabitants of poor tropical countries. Forty-one percent of the world’s population live in areas where malaria is transmitted, and each year 350 to 500 million cases of malaria occur worldwide. The disease imposes huge costs on individuals, families and governments, which are a crushing economic burden on malaria-endemic countries and impede their economic growth. It has been estimated that economic growth per year of countries with a high incidence of malaria was 1.3 percentage points lower than that of similar countries without malaria.

A drug called chloroquine is a useful preventive but many strains of the malaria parasite in Haiti have developed resistance to it. Other drugs called artemisinins are safe and exhibit potent, rapid antimalarial activity, and in combination with other anti-malarials they have been used effectively for several years to treat multiple-drug-resistant malaria. But resistance has arisen and is increasing, so that in the absence of a vaccine elimination of the mosquitoes that spread the disease is the key to preventing epidemics.

Unfortunately, flawed public policy limits the available options.

In 1972, on the basis of data on toxicity to fish and migrating birds (but not to humans), the U.S. Environmental Protection Agency banned virtually all uses of the pesticide DDT, an inexpensive and effective pesticide once widely deployed to kill disease-carrying insects. DDT was subsequently banned for agricultural use worldwide under the 2001 Stockholm Convention on Persistent Organic Pollutants, which stigmatized the chemical and effectively constituted a prohibition.

Although DDT is a (modestly) toxic substance, there is a vast difference between applying large amounts of it in the environment — as farmers did before it was banned — and using it carefully and sparingly to fight mosquitoes and other disease-carrying insects. DDT remains largely near where it is sprayed, and no study has ever linked environmental exposure to DDT to harm to human health.

When DDT is used at all now, it is sprayed indoors in small amounts to prevent mosquitoes from nesting, so exposures would be low. A basic principle of toxicology is that the dose makes the poison, and with modern regimens, both environmental and human exposures would be very low.

The regulators who banned DDT failed to take into consideration the inadequacy of alternatives. Because it persists after spraying, 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 mosquito-control authorities are depleting their budgets by repeated spraying with short-acting, marginally effective insecticides.

Moreover, even if mosquitoes become resistant to the killing effects of DDT, they are still repelled by it. An occasional dusting of window- and door-frames (and, in Haiti, tent openings) is extremely effective.

Since the banning of DDT, insect-borne diseases such as malaria and dengue have been on the rise. In fact, the huge toll of diseases spread by mosquitoes caused some public health officials to rethink DDT’s use.

In 2006, after some 50 million preventable deaths, the U.N.’s World Health Organization reversed course and endorsed the use of DDT to kill and repel malaria-causing mosquitoes. At the time, Arata Kochi, the World Health Organization official in charge of malaria said, “We must take a position based on the science and the data. One of the best tools we have against malaria is indoor residual spraying. Of the dozen or so insecticides WHO has approved as safe for house spraying, the most effective is DDT.”

But policies based on science and data enjoy a short half-life at the United Nations, and last year, with a notable absence of fanfare, WHO reverted to endorsing less effective methods for preventing malaria. In May 2009 the WHO and the UN Environment Program announced that their goal is “to achieve a 30 percent cut in the application of DDT worldwide by 2014 and its total phase-out by the early 2020s, if not sooner.”

In the absence of effective vaccines or new anti-malarial drugs — and the funding and infrastructure to deliver them — this decision is tantamount to mass murder, a triumph of radical, cynical enviro-politics over public health.

How radical? How cynical? In his book The Population Bomb, Stanford University biologist Paul Ehrlich disparaged DDT for being too effective at reducing death rates and thereby contributing to “overpopulation.” Ecologist Garrett Hardin condemned spraying pesticides in the Third World because “every life saved this year in a poor country diminishes the quality of life for subsequent generations.” Malaria was nature’s way of limiting population growth, and anything that prevented the disease interfered with nature’s plan.

Poor tropical countries like Haiti where malaria is endemic desperately need cheap, effective control of mosquitoes. Instead of continuing the politically correct stigmatization of DDT, United Nations agencies and NGOs such as the Red Cross should be rushing supplies of it to Haiti.

Henry I. Miller, a physician and molecular biologist, is a fellow at Stanford University’s Hoover Institution. He was an official at the NIH and FDA.

Read more: http://www.miamiherald.com/2010/05/03/v-fullstory/1610610/ddt-can-stymie-malaria-carrying.html#ixzz0muOTKOut

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