Bad Blood

(Page 2 of 5)

The burden is profound. Globally, more than 500 million individuals are infected with malaria every year, of whom more than a million die, mostly babies and pregnant women. More than 90 percent of the deaths occur in sub-Saharan Africa, where the most virulent form of the disease resides. Malaria is caused by a single-celled parasite -- Plasmodium -- which is transmitted by Anopheles mosquitoes. Of the four Plasmodium species that infect humans, P. falciparum, carried by the Anopheles gambiae mosquito, is by far the most lethal. This deadly duo has brought Mbita, and regions like it throughout vast swaths of Africa, to their knees.

On the medical front today, gene sequencing and molecular manipulation raise the real possibility that a vaccine, elusive for so long, may be on the horizon, but even optimistic researchers say practical results are many years away. In any case, even as science fuels hope, it also more fully illuminates the pathogenic intransigence of the parasite -- crucial yet sobering knowledge. A drug cocktail known as ACT (artemisinin-based combination therapy) works well provided patients are treated promptly. Artemisinin is derived from the leaf of China's sweet wormwood tree; the drug is formulated along with synthetic antimalaria agents in a single pill. The cocktail approach is designed as a hedge against resistance, though Sawa says he is already beginning to see signs that the drug is losing its edge.

Efforts to control malaria essentially have run along one of two lines: drugs, such as ACT, to kill the parasite or insecticides to kill the mosquito. But both targets are ruthlessly mutable, evolving quickly and in ways that leave them impervious to our most calculated chemical assaults. Chloroquine was hailed as a miracle drug 50 years ago for its ability to trounce the parasite, but is now all but useless. Post-World War II faith in DDT was once so strong that Paul Müller, the scientist who discovered its insecticidal properties, was awarded the 1948 Nobel Prize for medicine. In 1955, armed with these two marvels, the World Health Organization (WHO) mounted a global malaria eradication campaign. Despite some successes, mostly in contained island environments such as in the West Indies, or in more prosperous regions such as parts of Australia and southern Europe, the effort failed. In Africa it never got off the ground. The campaign was finally abandoned in 1969, its collapse traceable to three main causes: the onset of mosquito resistance to DDT, the insuperable logistics of indoor spraying in endemic areas, and a dawning awareness that DDT was toxic to more than just mosquitoes and other pesky arthropods. In the void left by the discarded WHO operation, malaria slipped from the world's attention. Cloaked for 20 years in obscurity (to all but the suffering millions), the disease dug in and proliferated.

What brought malaria back to public consciousness was an unprecedented wave of epidemics, especially in Africa, in areas that had not previously been affected. This brought fresh infusions of cash and led to a campaign called Roll Back Malaria, which was cobbled together from an international cross-section of expertise involving major aid agencies, governments, the private sector, and NGOs. Promoting drugs, insecticides, and bed nets, the campaign was launched in 1998 with the goal of halving the incidence of the disease by 2010. A decade into that effort, however, there's little to show for it: malaria is far more pervasive today than it was when the campaign started.

In 2005 the Bush administration pledged $1.2 billion to fight the disease. And setting a new standard of engagement for private philanthropy, the Bill and Melinda Gates Foundation has been spending nearly $400 million a year, mostly on vaccine development; but it also directs funds to bed nets, drug research, and mosquito control. Meanwhile, malaria rages on--as does the debate over whether to bring back DDT to fight it.

International protocols governing the use of DDT are set by the 2001 United Nations-sponsored Stockholm Convention on persistent organic pollutants, or POPs. A POP is generally defined as a toxin that remains in the environment for years and often decades, is prone to bioaccumulate (collect in fatty tissue and become more concentrated as it moves up the food chain), and is readily conveyed around the globe by either air or water currents. DDT appears on the Stockholm Convention's original register of 12 banned toxins, but it is the only such item listed with an asterisk: nations meeting strict criteria of demonstrable need for fighting malaria are exempt from the DDT ban. This paradox, in which DDT is at once revered (for its real or perceived ability to save lives) and reviled (for its toxicity) has generated an often loud and unruly dispute.

In September 2006 the World Health Organization issued a press release headlined, "WHO Gives Indoor Use of DDT a Clean Bill of Health for Controlling Malaria." It was a startling announcement, apparently contradicting the position the agency had held on DDT since the 1970s, and numerous WHO malaria researchers resigned in protest.

Five years earlier the Stockholm Convention had sanctioned the use of DDT in prescribed circumstances. DDT tends to be most desperately needed, and most reliable, in epidemic conditions, where the break in the transmission cycle that it provides can be dramatically effective. In such instances, the immediate need to save lives trumps concerns about subsequent health or environmental complications (including the potential for mosquitoes to develop resistance to the toxin). It was recognition of this stark calculus that forged the 2001 compromise on DDT, which was agreed to by groups with histories of firm opposition to the insecticide, such as the World Wildlife Fund, the Natural Resources Defense Council (NRDC), and the Pesticide Action Network (PAN).

"We fully support the Stockholm approach to DDT because we understand that DDT can be effective under certain circumstances," said Kristin Schafer, campaigns director for PAN, "but also because the convention stipulates that use of DDT must be accompanied by efforts to develop alternative approaches. That's the point that is so often lost in these discussions: the Stockholm Convention is meant specifically to mobilize funds and attention to develop capacities such that DDT will no longer be needed." Asterisk notwithstanding, DDT remains on the convention's so-called dirty dozen list of banned chemicals. All signatories to the treaty agree to a goal of ultimate phaseout. Thus, the 2006 WHO announcement ran counter to both the spirit and the letter of the Stockholm Convention. However, at the most recent Stockholm conference, in Dakar, Senegal, in April 2007, WHO officials backed away from their earlier statement and reconfirmed their commitment to finding alternatives to DDT.

Today's most ardent proponents of DDT suggest that the sole obstacle to routing malaria half a century ago was the onset of the environmental movement. Mosquito resistance to DDT and the crippling logistics of effective spraying campaigns are overlooked in favor of the much juicier target of Rachel Carson and her green descendants. Carson's 1962 book, Silent Spring, was indeed a watershed. Invoking DDT as Exhibit A and sounding her alarms in graceful, elegiac prose, Carson awakened readers to the idea that pesticides might have a downside.

The use of DDT was banned in the United States in 1972. But while the chemical is no longer manufactured here, other organochlorine compounds are, and many are or are likely to be subject to scrutiny by regulators. This may be what really concerns DDT's more aggressive advocates in the private sector. In a chapter of a book on "message crafting," economist Roger Bate, a fellow at the Competitive Enterprise Institute, warns, "DDT may be today's target, but it's not going to be long before chemicals that the industry cares about are added to the POPs Convention and other chemicals regulations." 

DDT proponents are generally reluctant to acknowledge the complicating and protean factor of mosquito resistance. Entomologist May Berenbaum finds this galling. An expert on insecticide metabolism, Berenbaum is director of the entomology department at the University of Illinois at Urbana-Champaign. "Read the entomological literature of the 1950s," she said in a telephone interview. "Way before Silent Spring, scientists were already trying to understand resistance. That's what insecticide toxicology was all about back then. Resistance to DDT was first detected in Italy, in houseflies, in 1947!"

Environmentalists' objections to DDT, Berenbaum said, were just one piece of an intricate puzzle. In a 2005 Washington Post article that discussed mosquito resistance to DDT, she warned: "Overselling a chemical's capacity to solve a problem can do irretrievable harm not only by raising false hopes but by delaying the use of more effective long-term methods."

After Berenbaum published the article, she said, she was barraged by e-mails demanding that she support her claims. "To get them off my back, I finally culled a list of peer-reviewed articles documenting resistance to DDT and other pesticides in pockets all over Africa. This is not my life's work. I spent 10 minutes--10 minutes--and I found 15 articles. What would I have found if I'd spent an hour?"

DDT kills by attacking a mosquito's nervous system. But in any given population, a random smattering of individuals will have a genetic mutation that renders them resistant to certain toxins. At first the number is insignificant, but over time it will grow until the only mosquitoes that continue to breed will be resistant ones.

ICIPE physician Patrick Sawa acknowledged that "DDT is a cheap and effective method of controlling malaria, with the capacity to drastically reduce infection rates." Initially.

People who live in malarial areas and survive bouts of the disease acquire a level of immunity that mitigates its severity in subsequent infections. When spraying campaigns temporarily suppress mosquitoes and malaria, human populations lose the immunity they once had. But where mosquito populations grow resistant to DDT, "the severity of the rebound will be inversely proportional to the span of time DDT has been effective," Sawa said.

"If DDT remains effective, say, for five years," he continued, "we'll have a generation of children who, without the DDT intervention, would at least have developed some immunity had they been exposed to malaria; instead they'll be susceptible to the most severe manifestations of the disease." It is cruelly ironic that a temporary respite from malaria is, ultimately, more pernicious than no respite at all.

Theoretically, five years should be long enough to interrupt the cycle of malaria transmission. Plasmodium falciparum does not survive for more than a few months in the human bloodstream (the other three, less lethal, malaria parasites last longer). Using DDT to suppress Anopheles gambiae mosquitoes for half a year would seem enough to clear the blood of everyone in a community. One might suppose that even as mosquitoes start breeding again, no parasites would remain for them to distribute. But towns like Mbita that are "holo-endemic"-- meaning that just about anyone you meet carries the parasite--are neighbor to countless other such towns and villages where migration is the norm because of farming cycles, civil unrest, or any number of other factors. In order to succeed, a DDT eradication campaign would require a synchronized, fail-safe effort that is nearly impossible to pull off anywhere, let alone across contiguous, cross-border endemic zones that cover thousands of square miles deep in destitute Africa.

Continued...