Most head lice are resistant to a common treatment

Jun 18 2006

According to new research the British school nurse has her work cut out because it appears that most head lice are resistant to a common treatment used to eradicate them.

The most commonly used treatment for head lice in the UK are organophosphates (malathion) and pyrethroids (permethrin and phenothrin), which act directly on the insect’s nervous system.

But now researchers from the National Public Health Service for Wales Communicable Disease Surveillance Centre, have found, in a study of Welsh schoolchildren, that four out of five head lice are resistant to the treatments used to eliminate them.

Both treatments are available as over the counter preparations, and pyrethroids are the most popular because they require shorter application time and have a less strong smell than malathion.

For the study the authors used nit combs on a random sample of almost 300,000 primary schoolchildren at 31 schools spread across the five health authorities of Wales.

All the lice collected were tested for resistance to pyrethroids, including measuring increased amounts of enzymes, such as glutathione transferases, monooxygenases, or esterases.

The researchers say that as many as 80% of 316 lice tested were resistant to the treatment, which equates to four out of five head lice affecting primary schoolchildren in Wales.

It is unclear whether this pattern is reflected elsewhere in the UK and depends on how head lice treatments are used.

Dr. Daniel Thomas suggests that where resistance develops, a newer silicone based lotion might be a suitable alternative.

The research is published in the Archives of Disease in Childhood.