Sunday, April 25, 2010

World Malaria Day: Fighting back against the tiny parasite that kills 1 million each year

Today is World Malaria Day. It's a disease that's spread by the simplest of pests, the mosquito, responds well to treatment, and yet it kills 1 million people every year, 90% of them in sub-Saharan Africa. We've wiped out polio and controlled the measles (diseases that are more virulent and infectious than malaria), but a deadly mosquito bite still claims the lives of 3,000 children every day. Those children are far away from most of us, they play with different toys than our own children, but their lives are just as real; their smiles just as bright.

One thing you can do to help fight malaria in the developing world is donate to purchase bed nets for sleeping under, preventing the mosquito bites that spread malaria infection. Unfortunately, recent evidence shows nets are not enough in the fight against malaria mortality. For an individual, a net is the best way to protect against malaria infection. But, from an epidemiological standpoint, it takes a very high net coverage (and those nets must be insecticide treated, raising the cost) within a given village for the parasitic load to fall, and the malaria threat to lessen. Getting to that threshold of protection is an extremely tricky proposition, especially since even the longest lasting nets must be retreated every 3 years.

Therefore, to really conquer malaria, we need an integrated strategy of vector control, infection prevention, and treatment.

Vector control: A "vector" is an organism that carries an infectious agent, whether parasite, bacteria, or virus. Historically, rats have been one large vector of disease--controlling the rodents helped control illness. Mosquitoes are the vector of malaria infection, and to fight malaria, we have to control mosquitoes. Vector control is carried out by doing some fairly benign things, such as clearing brush and eliminating standing pools of water, but the major avenue involved dumping large amounts of insecticide into mosquito breeding grounds. There is an inherent conflict between controlling disease (at least this particular disease) and protecting the environment, and I think it's one we need to learn to be comfortable with. Massive insecticide spraying pushed malaria to the brink of eradication in the 60s and 70s, but Rachel Carson's book Silent Spring and a burgeoning environmental movement, (also the end of colonialism, which meant more technologically advanced countries stopped investing in disease control in developing countries) brought it roaring back in the 80s. Concern for the environment might be a positive thing, and people might have different views on how much environmental degradation they're willing to live with to save human lives. But, to me, the fundamental unfairness of environmentalism is that, in most cases, the things we're trying to stamp out have already benefited rich countries, and arguing against them mainly keeps this benefit from extending to poor countries. We used DDT to wipe out malaria in the United States, and it worked. Perhaps we will find better alternatives to DDT, but regardless, malaria control will not be achieved without widespread use of insecticides to bring mosquito populations down. It's a truth I'm willing to live with, and I hope you will be, too.

Infection prevention: Versus vector control, which stops mosquitoes before they get near people, infection prevention focuses on blocking them or killing them in the vicinity of humans, to prevent bites. I use infection prevention to refer to two main avenues of individual-level protection, Indoor Residual Spraying (IRS), and sleeping under insecticide treated nets (ITNs). Once again, the insecticide is key to controlling mosquitoes. An insecticide treated net not only prevents mosquito bites during sleeping hours, but also kills mosquitoes in the environment around the net, and prevents them from hanging around the home. Insecticide treated nets can have their own environmental consequences, especially if misused, but are another great tool of prevention. The problem is distributing them and ensuring they're used correctly and consistently, and retreated on schedule. Like any mass distribution scheme, this is extremely difficult to achieve at the centralized level. But, forays into market distribution have found that willingness to pay might not be high enough to achieve high levels of coverage. Residual spraying, on the other hand, is something that can be easily (and in fact naturally) handled at the central level. It does not require intimate knowledge of each individual within the community, available sleeping spaces, and time since re-treatment, nor does it rely on individuals to whom the private cost of malaria (or at least the cost they perceive) may be lower than the public one to carry it out. To complete residual spraying, a government or NGO need only have a list of villages in an area, go to each one, and spray the interior surface of each dwelling after getting the consent of the owner. I'm oversimplifying things--there are insecticide drums, equipment, hazardous waste disposal, etc. to think about, but I think IRS is an important, manageable complement to ITN distribution in areas where net coverage or use is incomplete.

Diagnosis and treatment: Treatment is important for two reasons. First, with prompt treatment, malaria is not deadly. When anti-malarials are taken within 24 hours of the onset of symptoms, mortality rates from malaria are vanishingly low. That means, even if we did nothing else, making treatment available to anyone infected with malaria could virtually eliminate the human cost of malaria. Unfortunately, if we did nothing else, the cost and distribution structure required to get that treatment out would spiral out of control, and the parasites would quickly become drug resistant (more on this below). Luckily, treatment also serves a prevention purpose: The more quickly someone gets treated, the less time they spend with parasites in their bloodstream, meaning the less chance a mosquito has to bite them and infect someone else. And, in Coartem, we have a new, highly effective treatment regimen that malarial parasites are not yet resistant to. Potential drug resistance, cost, and the simple fact that anti-malarials are strong medications with their own side effects are the reason we also need proper diagnosis. Malaria is actually frequently over-reported, and treating people who don't have malaria with malaria drugs makes it harder to reach those who do need treatment. Until the last few years, proper diagnosis of malaria has actually been very difficult--requiring a microscope and a trained technician, two things many rural health clinics did not have. The recent development of Rapid Diagnostic Tests (RDTs), which use a pin-prick of blood to instantly identify malaria infection, provide new hope for getting accurate treatment to those who need it.

Last summer, I worked in Zambia on several research projects, one involving malaria. I came down with malaria myself, just a few weeks into my stay, leading my family to conclude our research team wasn't doing a very good job. I was given Coartem within 24 hours of the onset of my symptoms, quickly recovered, and lived to tell the tale. For about a day and a half, I was probably the sickest I'd ever been, but I was back on my feet in a week, malaria but a minor nuisance. One day, it will be like that for everyone (if malaria isn't wiped out completely): a nuisance illness, preventable and easily treatable. We can all see that day, if we act now to aid in malaria eradication.

See the president's 6-year plan to fight malaria. Watch Bill Gates discuss the issue at TED. Donate here or here.

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