Coping with Head Lice Resistance
Many parents face the misery of head lice. For most this means a variety of failed lotions, sprays and mousses. Worst of all are the endless weeks of combing in a desperate attempt to rid your children of that last head louse. But why is this problem getting worse? Can natural products succeed where the most potent synthetic products have failed?
There is a general consensus that the incidence of head lice is on the increase and the success of current treatments is declining. Recent clinical tests of head lice treatments have found that the most used, the pyrethroids and organophosphates, have success rates of only 13% and 36% respectively (Downs et al 1999).
In addition, a recent study of 2800 children carried out by the Liverpool School of Hygiene and Tropical Medicine and the National Public Health Service for Wales found that two thirds of head lice were resistant to pyrethroid-based head lice products. Pyrethroids are the active ingredient in many popular mousse and lotion products.
The increase in resistance is partly as a result of misuse of head lice treatments. If a product is not used according to the directions on the packaging, head lice are exposed to lower levels of insecticide. These ‘sub-lethal’ levels are not enough to kill all the lice on the scalp and thus allow the ‘fittest’ lice to survive and breed. Resistance has also arisen because the most popular products have a single mechanism of action, targeting a single part of the nervous system of the louse. This makes it much easier for head lice to overcome these products and to become resistant.
Naturally derived insecticides are one of the most exciting new tools in managing head lice resistance. Of these, the Neem tree (Azadirachta indica) is one of the best understood. The active ingredient in Neem, Azadiractin, has multiple modes of action against insects, interfering with their feeding, growth and reproduction. This means that lice cannot overcome these products with only a single genetic change as they can with synthetic products. Even with the use of Neem worldwide against more than 350 species of insect pests, there have been no known cases of resistance.
The success of head lice treatments can be improved by combing with a fine tooth comb to physically remove head lice from the scalp. As a result of the dramatic decline in the effectiveness of many products, there is now an over-reliance on combing as part of the treatment programme. For many parents this daily combing is the worst part of treating head lice, being very distressing for children and adults alike. It will come as a great relief to many parents to know that, as Neem based products are very effective, daily combing is not necessary as part of the treatment. Combing is required only to detect lice prior to treatment and to confirm that the lice are clear when the course is complete.