Scientists have discovered that lice populations in at least 42 states have mutated to develop a resistance to over-the-counter treatments still widely recommended by doctors and schools.
Researchers found that 137 out of the 138 lice populations tested in 48 states had high levels of gene mutations, which have been linked to resistance to pyrethroids. 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.
A separate study published last year found that only 25 states had mutant super lice. This latest study indicates that the mutant gene is spreading across the United States.
According to the U.S. Center for Disease Control, infestation with head lice is most common among pre-schoolchildren attending child care, elementary schoolchildren, and the household members of infested children.
Although reliable data on how many people in the United States get head lice each year are not available, the CDC estimates 6 million to 12 million infestations occur each year in the United States among children 3 to 11 years of age.
Areas in the above map marked with red dots indicate a 100% presence of the mutant super lice gene.
Head lice move by crawling; they cannot hop or fly. Head lice are spread by direct contact with the hair of an infested person. Anyone who comes in head-to-head contact with someone who already has head lice is at greatest risk. Spread by contact with clothing (such as hats, scarves, coats) or other personal items (such as combs, brushes, or towels) used by an infested person is uncommon. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.
In February, an outbreak of super lice was discovered infesting Brevard County Public School children in Titusville, Florida.
Photo credit: Head louse. Credit: Flickr / Gilles SM