The researchers have found that lice populations in 25 American states have undergone genetic mutations that make them resistant to common treatments. The scientists are presenting their research at the 250th National Meeting & Exposition of the American Chemical Society (ACS).
According to Kyong Yoon, Ph.D., his research team is the first group to collect samples from lice populations across the United States. He explained that his team has found that 104 out of the 109 lice populations that have been tested had high levels of gene mutations linked to resistance to pyrethroids.
Pyrethroids are a type of insecticides used to control mosquitoes and other insects. The insecticide family of pyrethroids includes permethrin, which is the active ingredient in some of the most common lice treatments that are sold over-the-counter at drug stores.
Yoon is a professor and researcher at the Southern Illinois University, Edwardsville. He explains that the widespread pyrethroid-resistant lice issue has been building for years. In the late 1990s the first report on this development came from Israel and later in 2000 Yoon became one of the first to report the phenomenon in the U.S. when he was a graduate student at the University of Massachusetts, Amherst.
The researcher said that while he was working on insecticide metabolism in a potato beetle at that time, his mentor John Clark suggested him to research the resurgence of head lice. When Yoon asked his mentor in what country he was surprised when Clark said the U.S.
Yoon followed up on the lead and started to contact schools near the university in order to collect samples. He developed a theory explaining that the resurgence of lice is due to the fact that the insect had developed resistance to the most common insecticides people were using to combat them. Yoon started to test it for genetic mutations known collectively as "knock-down resistance" or kdr. This type of mutations had initially been found in the late '70s in a house flies after farmers and others had shifted from DTT to pyrethroids.
Yoon discovered that many of the lice have indeed the kdr mutations, which desensitize the insect to pyrethroids. The researcher has expanded his survey since then. With the help from a broad network of public health workers, in his most recent study Yoon has gathered lice from 30 states.
The results have shown that all three genetic mutations associated with kdr are present in lice populations from 25 states, including Maine, Florida, Texas, and California. These populations are the most resistant to pyrethroids, having all kdr mutations. Samples from other four states -- New Mexico, New Jersey, New York and Oregon -- had from one to all three mutations. Yoon's findings show that Michigan is the only state with a population of lice still susceptible to the insecticide.
