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Insect Repellents

Insect Repellents
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Insect Repellents
by Dr. Rajiv Narula

Maybe someday we will be using a commercially prepared version of crushed centipede on our skins to repel mosquitoes. A recent NYT article on this subject, described how certain African monkeys rub live centipedes (crunch-squish) over the bodies in order to keep mosquitoes from biting them. US studies on this underway, for now DEET and Permetherine are the repellents of choice for us humans .

Mosquito borne illnesses have been a source of human misery for a long time. Malaria, Dengue Fever, Japanese Encephalitis, Yellow Fever, Rift Valley Fever are some examples . Out of these four, only two are vaccine preventable – Japanese Encephalitis and Yellow Fever. Avoidance and repellent use are the only way to protect oneself from the other three.

Malaria is the biggest killer out of these, causing almost a million deaths yearly. Recent studies by British and American scientists have shown that a malaria outbreak was probably the cause that contributed to the decline of the Roman Empire in the fifth century A.D. Dengue Fever , is caused by daytime biting mosquitoes in urban areas. There have been several outbreaks over the last few years, especially in the summer months. Rift Valley Fever, took NY by storm last year, Staten Island became the epicenter, scientists tracked the disease by studying dead birds. It will be interesting to see if this summer will be another one for insecticide spraying. Excluding some anti-malarials the only protection that we have is the use of repellents i.e. DEET and Permetherine. Use of bath oils, ultrasound emitting devices have proven to be ineffective.

DEET (or for you chemistry buffs N,N –Diethyl-m-toluamide) repels mosquitoes, ticks, flies and fleas. It does this by disabling the heat seeking mechanism that is used by these insects. The higher the concentration of DEET the longer it is protective. Center for Diseases Control in Atlanta recommends use of 35% or less. Application is only to sun exposed skin surfaces, which in most cases would be the neck region, hands, and lower extremities. Studies have also shown DEET will repel the cerceriae ( the parasite, which enter your skin and cause Schistosomiasis AP June, 2000 issue). After applying DEET I would recommend that you wash your hands.

Permetherine, is usually in spray format, it is applied to clothing and mosquito netting. Hang the items to be sprayed outdoors, with sweeping arm movements apply the insecticide only on the outside surface of outer clothing. Each application will last for 6 washes, or if you want to de-permetherinize your clothing just dry-clean them. Repellent applied to mosquito lasts for 6 months. Permetherine kills the mosquitoes on contact. Since it does not bind to skin, it is ineffective when used this way.

So when traveling to tropical locations, no matter how short the trip plan ahead and remember those words that go something like ounce of prevention…..