Gene mutation in lice

21.10.2009 11:20

Resistance does not equal treatment failure

Are head lice resistant to lice medications? There has been speculation about this question since the Kiel University Hospital presented the results of a laboratory study in September: All lice examined had a gene mutation that could possibly make them less sensitive to insecticidal active ingredients (pyrethrum, permethrin, allethrin). Data from a current French study with resistant Anopheles mosquitoes prove that the pyrethrum extract obtained from chrysanthemum flowers is also effective against existing resistance caused by gene mutations. Although the kill effect occurred with a delay, it reached a clinically relevant level of 90 percent.

Due to the gene mutation, the parasites remain able to move longer than usual. This so-called knock-down resistance does not necessarily have to impair the clinical effectiveness of lice medications. Lice treatments are clinically effective if they kill lice, i.e. have a kill effect. Knock-down and kill effects are two different approaches within the spectrum of effectiveness of insecticidal head lice treatments. Resistance to synthetic active ingredients such as permethrin and malathion has been demonstrated several times worldwide.

Losses of effectiveness due to specific pyrethrum resistance, on the other hand, are hardly common. One of the reasons is its active ingredient profile and drug formulation, which differ from synthetic insecticides. Pyrethrum consists of six active components with different chemical structures that independently damage the louse. If the mutation only affects the paralyzing drug components (knock-down effect), this does not necessarily affect the activity of other components that are primarily responsible for the kill effect.

Pyrethrum is also combined with the synergist piperonyl butoxide. The excipient enhances the knock-down and killing effect by, above all, preventing the enzymatic breakdown of the insecticides in the louse organism. In this way, the clinical effectiveness of pyrethrum is increased many times over. Piperonyl butoxide is considered a reliable resistance breaker, even if resistance already exists.