Researchers find ‘treatment-resistant’ super lice in 25 states

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Researchers find 'treatment-resistant' super lice in 25 states
Over 95 per cent (104 out of the 109) lice populations had gene mutations, which have been linked to resistance to pyrethroids - the commonly used over-the-counter treatment.

Evolution is constant and though it may be for the better in most cases, lice in the US have evolved to be treatment resistant and according to a new study as many as 25 states in the US have lice populations that are resistant to over-the-counter treatments.

In the study presented at the 250th National Meeting & Exposition of the American Chemical Society (ACS) researchers sampled lice from a large number of populations across the U.S. and found that over 95 per cent (104 out of the 109) lice populations had gene mutations, which have been linked to resistance to pyrethroids – the commonly used over-the-counter treatment.

Pyrethroids are a family of insecticides used widely indoors and outdoors to control mosquitoes and other insects. It includes permethrin, the active ingredient in some of the most common lice treatments sold at drug stores.

Kyong Yoon, Ph.D, from Southern Illinois University, Edwardsville who presented the paper explained that the mutations have occurred over years. According to Yoon, mutations were observed in late 1990s in Israel and he was the first tone to report the phenomenon in the U.S. in 2000.

Yoon tested pests for a trio of genetic mutations known collectively as kdr, which stands for “knock-down resistance.” kdr mutations had initially been found in house flies in the late ’70s after farmers and others had shifted to pyrethroids from DDT and other harsh insecticides. He found that many of the lice did indeed have kdr mutations, which affect an insect’s nervous system and desensitize them to pyrethroids. Since then, he has expanded his survey.

Lice populations in the states in pink have developed a high level of resistance to some of the most common treatments. CREDIT: Kyong Yoon, Ph.D.
Lice populations in the states in pink have developed a high level of resistance to some of the most common treatments. CREDIT: Kyong Yoon, Ph.D.

In the most recent study, he cast the widest net yet, gathering lice from 30 states with the help of a broad network of public health workers. Population samples with all three genetic mutations associated with kdr came from 25 states, including California, Texas, Florida and Maine. Having all the mutations means these populations are the most resistant to pyrethroids. Samples from four states — New York, New Jersey, New Mexico and Oregon — had one, two or three mutations. The only state with a population of lice still largely susceptible to the insecticide was Michigan. Why lice haven’t developed resistance there is still under investigation, Yoon says.

The solution? Yoon says that lice can still be controlled by using different chemicals, some of which are available only by prescription.

But the situation also offers a cautionary tale. “If you use a chemical over and over, these little creatures will eventually develop resistance,” Yoon says. “So we have to think before we use a treatment. The good news is head lice don’t carry disease. They’re more a nuisance than anything else.”