Map of life expectancy at birth from Global Education Project.

Tuesday, May 31, 2005

Mosquito control

CDC is now saying that it has received a few (they don't say exactly how many) reports of relatively young, healthy people who develop neurological complications from West Nile Virus -- partial paralysis of a limb, that sort of thing. It seems that people generally recover, but it can take months or as much as two years. And some people miss a week or ten days of work due to the acute illness. It is still true that the vast majority of people who are infected have no symptoms, or only mild symptoms, but it appears the strain prevalent in the U.S. is somewhat more virulent than the most common strains in Africa.

Now, this is still not really any big deal -- I promise that no matter where you are, you have bigger things to worry about. Nevertheless, this news is bound to ratchet up political pressure for intensified mosquito control efforts. (WNV is spread exclusively by mosquitoes.)

Now, that's where the real danger lies, in my view. Some years ago I did a literature review on the environmental fate of pesticides used in mosquito control, for the Massachusetts Audubon Society. We have an indigenous virus here called Eastern Equine Encephalitis. Every two or three years, two or three humans come down with EEE, which can be fairly serious. For decades, this problem, which I would label as rare, provided the impetus for a very substantial state-funded permanent infrastructure, administered at the county level, which geared up and sprayed our wetlands with a pesticide called malathion every time a case was reported. (The county level administration is one indication of how archaic this program was. The only other responsibility of county government in Massachusetts is the operation of jails.)

It turns out that the situation with pesticides is even worse than the situation with pharmaceuticals. Many approved pesticides have had inadequate testing for human and environmental safety. Most of the research that is done is funded by pesticide manufacturers, and the journals that publish the research are oriented toward people employed in the industry. The spin on some of these research reports is absolutely ludicrous. Malathion is a member of the class of chemicals called organophosphates, originally developed by German scientists during World War II as chemical weapons. Malathion is less potent, but works in exactly the same way, as Sarin, the nerve gas Saddam Hussein was falsely accused of possessing by the Bush administration. There is a substantial body of evidence, based on primate research, that chronic, low-level exposure to organophosphates, which causes no acute symptoms, causes permanent brain damage, and there are lots of case reports of individual humans who suffered acute poisoning from malathion in everday use. Yet the conclusions from these articles always were written so as to downplay the practical importance of these findings.

Well guess what? According to a Reuters report today:

Gardeners should wear protective clothing when using pesticides, say scientists who have concluded in a new study that the chemicals can increase the risk of Parkinson's disease. Researchers at the University of Aberdeen in Scotland have discovered that the more pesticides gardeners are exposed to, the more likely they are to develop the degenerative brain disease. Anthony Seaton and his team in Aberdeen interviewed 767 Parkinson's sufferers and 1,989 healthy people about risk factors for the disease, including their use of pesticides. They found that people with the chronic, irreversible illness were more likely to have used pesticides; amateur gardeners were 9 percent more likely to suffer from the disease than nonpesticide users.

Now this study can't distinguish which pesticides are responsible, but I'm willing to bet a case of Cutter's that organophosphates are the culprit. But wait, there's more. In the U.S. we moved away from use of another class of insecticides, the organochlorines (such as DDT and Methoxychlor) because they bio-accumulate in fish, mammals and fowl. Organophosphates, in contrast, are broken down by enzyme systems in the vertebrate liver. That may be good news for bald eagles, but it's no consolation to every insect, slug, snail, or earthworm exposed to organophosphates. They are completely non-selective and will kill your ladybird beetles and butterflies right along with your mosquitoes. They are also quite toxic to reptiles and amphibians, and oh yeah -- to human children, whose liver enzyme systems have not fully developed.

As Revere helpfully corrected me, the chemical used by the Boston Public Health Commission in response to mass hysteria over the West Nile Virus was resmethrin, which is a synthetic version of rotenone, a naturally occurring compound. Resmethrin is not highly toxic to humans or fowl, but it is extremely toxic to fish -- in fact, it is used by South American Indians as a fish poison. That does make it a rather odd choice for mosquito control. The spraying was done in my neighborhood precisely because I live near a chain of ponds and waterways. And of course, resmethrin is equally non-selective when it comes to insects and other invertebrates.

There are smart ways to control mosquitoes. Malaria is indigenous only to the tropics. Our mosquito born diseases are far less of a concern. Use of toxic chemicals to kill adult mosquitoes is a cure worse than the disease. People who are worried about West Nile Virus (and again, I would say you have bigger worries) can use mosquito repellent, according to directions. (Personally, and this is a controversy we don't have room for here, I would not use DEET on young children. Maybe I'll do that one another time.) Don't allow casual standing water on your property. Ponds can be stocked with fish that eat mosquito larvae, and dragonflies are also helpful. Mosquitoe larvae can be suffocated by spraying ponds with a micro-layer of vegetable oil, which will quickly degrade. There are other tricks available -- in general, it's much better to plan ahead and make the larvae's lives miserable, rather than attacking adults. (Draining swamps, however, is also a cure worse than the disease.) Spraying insecticides around to kill adult mosquitoes is evidence of imprudence, bad judgment, and usually, hysterical overreaction due to mass media hype, encouraged by people with a vested interest.

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