Study: 98% Of Head Lice In 42 States Now Resistant To Common Treatments

Kerry Picket | Reporter

Lice are becoming more difficult to eradicate in young children’s hair, according to a study released last week in the Journal of Medical Entomology (JME).

New evidence shows that head lice have developed resistance to two types of common over the counter insecticide treatments for lice infestation. JME studied 48 states and found that, on average, 98 percent of head lice in at least 42 states managed to grow gene mutations that enable them to become resistant to different insecticides other wise known as pyrethrins, pyrethroids, and permathrins.

According to the study, “Lice were collected from 7 July 2013 to 11 May 2015 by 71 volunteers (school nurses and professional lice combers) from 138 collection sites in 48 states. Four of these states (AZ, CA, FL, and TX) had collection sites that had been sampled twice before (1999–2006 and 2006–2008) and an additional eight states (OH, MA, MI, MN, NY, SC, TN, and WI) had been sampled only once before (2007– 2009), allowing the determination of kdr-type mutation frequency changes in those locations over time.”

Parapro.com notes in its timeline that the first natural pyrethrins to treat lice happened in 1945. By the 1980s, the over-the-counter insecticide solution to treat lice known as Nix, a permathrin, was the most commonly used treatment and was “nearly 100 percent effective.”

However, 20 years later, lice in Florida and Massachusetts begin to show evidence of mutation and resistance to permathrin. By 2001, three permathrin gene mutations are witnessed in 37 percent of the lice sampled from numerous states.

In 2009, Nix is now only 25 percent effective and by 2015, Parapro writes, “The three pyrethrin- and pyrethroid-resistant gene mutations are observed in an average of 98% of lice gathered from 48 states.”

“This newly published data supports what we’ve been seeing in our offices and clinics: an increase in treatment-resistant super lice,” said Chris Belcher, M.D., Peyton Manning Children’s Hospital at St. Vincent, Indianapolis, IN. “It’s important that parents contact a clinician if they suspect their child has head lice. There are effective, non-pyrethrin, non-pyrethroid-based prescription agents that can be used if treatment with over-the-counter products such as Nix® has been unsuccessful.”

The study stresses that patient self-diagnosis and misuse of over-the-counter (OTC) treatments contributed remarkably to the spike in treatment-resistant head lice. Other research shows, parapro says, that when self-treating with OTC products, up to 69 percent of people admit to using more than the suggested dose in an attempt to increase the effectiveness of the treatment.

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