Survival of the Resistance

"You will kill some lice, leaving the more resistant lice to breed and create more resistant lice."
J. Marshall Clarke, author, super-lice study, Journal of Medical Entomology

"The marked reduction in effectiveness reflects the development of resistance in [head lice. Insecticide resistance is] now the most common cause of treatment failure."
2012 paper, Canadian Family Physician

They are primitive and hugely unsavoury, the dread of all mothers, hoping their children will not be infected through their primary and elementary school years when young children easily pass that dread infestation innocently along, from one to another, heads in close proximity, poring over colouring books, focused on manipulating crayons and remaining nicely within the borders. Head lice are impolite enough not to remain within borders.

To arrive at their conclusion, a new study conducted out of the University of Massachusetts of Canadian head-lice cases warns that the issue of infestation and the traditional methods of destroying the parasites are failing spectacularly. New methods are "critically needed" to kill new mutated parasites resistant to formerly-useful methods. A "T1 mutation" represented by a gene resistant to pyrethrins and pyrethroids has proven the death-knell for those once-reliable solutions.

Most inexpensive and safe insecticides for use in removing head lice use one of those ingredients in anti-lice shampoos, creams and sprays. Over 3,500 consumer products use either pyrethrins or pyrethroids for effectiveness. In Canada, the market is dominated with over-the-counter delousing products using those ingredients. Once they were viewed as a miracle lice-killing cure for the plague of head-lice.

Dave Sidaway/Postmedia News Service    As recently as the mid-1990s, pyrethrin and pyrethroid-based treatments were killing lice with almost 100% effectiveness. But as traditional lice were progressively wiped out, super lice moved in to take their place.

 

At the present time, a mere 2.9% of Canadian head-lice cases can claim success with the use of those products. Used in sufficiently high concentrations, these anti-lice products will succeed in killing some of the mutated lice "but usually not all", according to Dr. Clark, Professor of Environmental Toxicology and Chemistry. Director, Massachusetts Pesticide Analysis Laboratory. 

Lice samples were collected from 16 sites in Quebec, Ontario and British Columbia from test subjects aged four to 64. Mutated lice had completely supplanted the unmutated types in 13 of those areas. Ontario communities of Sudbury, Oakville and Central Toronto presented lingering pockets of easily destroyed "susceptible" lice. The researchers feel convinced that these holdout lice populations may continue to exist "in more rural areas". Canada, it appears, doesn't yet represent the worst of the cases.

The University of Massachusetts study found U.S. super lice rates presenting at 99.6%. That's fairly impressive at the same time as it is daunting and wretchedly nasty in its implications. Benign head lice varieties are almost extinct in other countries. A survey of T1-mutated head lice found rates of 100% in Britain, Australia and Uruguay, and making headway elsewhere, from Denmark to Israel to Argentina.

Mutated lice developed with the common use of anti-lice shampoos. Analogous to widespread antibiotic use producing deadly strains of drug-resistant "superbugs". And the desperate need now to create more effective antibiotics to restrain them. These organisms are, after all, answering to nature's biological instructions to her creatures, large and small: the survival imperative. Survival of the fittest relates to those biological organisms most successful in adapting to changing environments.

In case further proof be required, those countries that had never used pyrethrin and pyrethroid treatments have experienced no rise of super-lice in reaction to the use of a human-safe-and-inexpensive prophylactic. In South Korea and Thailand, lice infestations have been treated with the use of a harsher chemical known as lindane. Recent surveys in those countries did not turn up even one T1-mutated head louse.

On the other hand, lindane is a harsh and dangerous synthetic organochlorine insecticide. It is restricted in use as a result of its toxicity and persistence in the environment. And there's the rub; in the need to find a safe and effective and inexpensive response to head lice infections, kinder chemicals were used to which, over time, resistance was built until the susceptible strain was overtaken by the resistant strain of lice.

In countries where concern over product danger to human health and the environment might have been less stringent than in most other countries, the head-lice situation remains unchanged. The insecticide lindane is utterly lethal to those disgusting creatures preying on the human scalp. And its use may also be inimical to the health of those using it. And it may come back to haunt the society using it, due to its deleterious environmental presence.


But they're also not anxiously looking for another solution to destroy the ultra super-lice which now bedevil medical science in North America and Europe. An example of "picking the poison that suits you best".