Resistance, in head lice, is the ability to survive against the chemical that is supposed to kill them. Death of the head lice is supposed to occur when the lice are exposed to a lethal dose of the chemicals. For example, Malathion (an organophosphate) causes paralysis and disruption of the nerve processes of the lice, causing them to fall from the head and starve. However, treatment does not guarantee that the eggs will be killed, and since the chemical residues cling to the hair after use, the newly hatched lice are exposed to a sub lethal dose. Some of them survive this and are then capable of surviving higher doses, as they will have gained mechanisms to cope with the chemicals in their bodies. Thus the chemical treatments become less effective as more and more lice build up resistance.
Synthetic products such as Malathion control head lice through a single mode of action. It only requires a single genetic change in the head lice population to lead to resistance. A natural extract from the Indian Neem Tree offers an exciting solution to the problem of resistance. Neem has many different modes of action and interferes with the feeding, growth and reproduction of head lice. These many modes of action make are extremely difficult for lice to overcome and we are unlikely to ever see resistance of head lice to Neem. |
