A new study found that head lice have developed immunity to treatments that are still currently prescribed by doctors and schools. The researchers specifically discovered that at least 25 states in the US have head lice populations that are resistant to common drugs being sold at pharmacies. As the school year starts once again, children and parents look as if they are in for another round of battle against this rampant childhood health issue.

Permethrin is an active component found in the most common lice treatments available at over-the-counter drug stores. This is classified under a family of insecticides called pyrethroids, which are often utilized to control indoor and outdoor insects.

The researchers found that many of the lice in the study samples contain "knock-down resistance" (kdr) mutations, which is a set of triple genetic mutations that disturbs the nervous system of the insects and renders them insensible to the effects of pyrethroids.

Together with a vast network of public health workers, the researchers, led by Kyong Yoon, Ph.D from Southern Illinois University, Edwardsville, conducted the study by obtaining head lice samples across 30 US states. After their investigations, it was found that the samples of head lice obtained from 25 states exhibited kdr mutations. The samples from Texas, California, Maine and Florida had the three genetic mutations and thus made them the most resistant states to pyrethroids. Other states such as New Mexico, New York, Oregon and New Jersey had samples that contain varying number of mutations. Michigan, however, may be pleased with the results of the study as it was found to have the greatest susceptibility to the insecticide. The reason for such feat for Michigan remains unknown and will require further investigations, says Yoon.

"We are the first group to collect lice samples from a large number of populations across the U.S.," says Yoon. Out of the 109 populations of lice obtained from the samples, 104 were found to have high amounts of gene mutations, which are associated with immunity to pyrethroids.

The resistance of lice to pyrethroids has long been existent, says Yoon. In the 1990s, the first report on this matter was recorded in Israel. In 2000, Yoon became one of the first researchers to report the development in the US, when he was still a graduate student at the University of Massachusetts.

Yoon recalls that he was then working on a potato beetle project, investigating the metabolic processes of insecticides. John Clark, his mentor at that time, suggested that he study the rejuvenation of head lice. When Yoon asked Clark about the specific country for such project, he was surprised that Clark answered the US.

Many other chemicals are available to treat head lice but some may require medical prescriptions upon purchase. Yoon also warns the public that applying the same chemical for a long time may subject the lice to resistance. Nonetheless, he explained that head lice do not cause diseases and are nothing but a cause for irritation of some sort.

The study will be presented at the 250th National Meeting & Exposition of the American Chemical Society (ACS).

Photo: Gilles San Martin | Flickr

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