Not enough to combat malaria
Kudos to the writer of "Protection against malaria" (letter, May 12) for successfully protecting his troops against malaria. There are probably some good reasons for impregnating uniforms with insecticide, but I’m not sure that protection against malaria is one of them.
Malaria is transmitted by the anopheles mosquito, which is normally — if not exclusively — a twilight and night-biter, mostly indoors. That would suggest that troops would have to sleep in their uniforms to obtain 24/7 protection from the impregnation. Assuming the mosquito can penetrate through uniform and skin, the insecticide would have to work almost instantly to kill the mosquito before it could "bite" and discharge its load of parasites.
The usual clothing recommendation applicable to night operations outdoors is to minimize exposed skin and to protect exposed skin with insect repellent. Common sense might suggest that insecticide-impregnated uniforms would offer better protection against malaria than unimpregnated, but a scientifically designed study to test this hypothesis might be justified, since common sense also suggests that unimpregnated uniforms would be just as effective.
More traditional — and, presumably, more effective — barrier protection against mosquitoes at night is screening on windows and insecticide-impregnated mosquito netting over bunks, as well as insect repellent on skin. Aerosol spraying of sleeping quarters with permethrin in the evening before entry has also been recommended.
Since the anopheles mosquito has a characteristic behavior of alighting on doorways, windowsills and other stationary parts of the sleeping quarters, it was common practice to paint those areas with concentrated DDT after that insecticide was created in the 1940s. Although initially quite effective, this was eventually discontinued largely because of adverse environmental effects, plus the emergence of resistant mosquitoes.
The difference in malaria incidence between the Korean and U.S. units on the same base is interesting and statistically significant, but there may well be other relevant differences besides those quoted. In fact, the writer only implied that the South Korean battalion did not also employ the same measures. One wonders if an epidemiological study was performed.
Dr. (Col.) Frank Leitnaker (retired)Bruchmühlbach-Miesau, Germany