Revenge of the Super Lice.
Karen Sokoloff finds a certain satisfaction in picking lice off a person's scalp, smoothing olive oil into the hair strands and carefully pulling a metal comb through them to catch the stragglers. It's a good thing she enjoys it: Sokoloff co-founded LiceDoctors, one of a handful of national chains of lice pickers, and business is booming, in part because conventional treatments have become largely ineffective.
For decades people have turned to special over-the-counter shampoos containing plant-derived insecticides known as pyrethrins or their synthetic counterparts, called pyrethroids, to treat cases of head lice. When they first came to market, these products worked well. But sustained use of these same few chemicals has allowed the blood-sucking parasites to evolve widespread resistance to them. Indeed, a recent study of lice in the U.S. carried out by pesticide toxicologist John Marshall Clark of the University of Massachusetts Amherst and his colleagues found that two thirds to three quarters of them are immune to the effects of these insecticides. They have become “super lice.”
This high prevalence of resistance means that most people are wasting their money when they turn to over-the-counter lice shampoos, which range in price from about $6 to more than $30 a bottle and remain the weapon of choice for those doing battle with lice. Use of these shampoos may also prolong the misery of the patients, given that it can take a week or more to determine that the treatment has failed. The problem is particularly disruptive for children, the most common victims of lice, because some schools require students to stay home until their scalps are totally clear of both lice and their eggs, called nits.
This resistance problem has spurred scientists to look for new methods of controlling lice. In Europe, nonpesticide treatments have met with success. In the U.S., doctors have recently added new prescription medications to their arsenal. But scientists warn that those drugs need to be used wisely to keep lice from developing resistance to them, too.
https://www.scientificamerican.com/article/revenge-of-the-super-lice/?WT.mc_id=SA_TW_HLTH_NEWS&sf88705850=1
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