Byline: LUCY ELKINS
FAST becoming indestructible, they are responsible for millions of infestations each year - no wonder experts fear we have entered the era of the super head louse.
Whereas once they could be quickly destroyed with chemical lotions, now the lice are fighting back and have become resistant to even the most powerful formulas.
A recent report based on research carried out at the Communicable Disease Surveillance Centre in Cardiff found that almost 90 per cent of head lice are untroubled by permethrin and phenothrin, the most commonly used insecticide treatments.
The problem is so great that recently the Local Government Association claimed that each year in the UK there are 7.2 million head lice in circulation which are now resistant to chemical treatment, and warned that infestations were becoming a major source of disruption to schooling.
Worryingly, head lice have acquired resistance to these formulas with remarkable speed. Take permethrin, the chemical found in leading brands such as Lyclear. This chemical binds itself to the insect's nerve cells, causing a permanent nerve impulse.
The lice eventually die of exhaustion.
When it was introduced back in the Eighties, permethrin had almost a 100 per cent clear-up rate. These days, one study published in the British Medical Journal found, it clears only 13 cases out of 100.
There have been similar results noted with another chemical, malathion, which also attacks the nervous system of the insect. In certain areas of the country, the chemical is effective only in one in 17 cases.
As the insects have become resistant to treatment, the number of infections has rocketed.
In the Eighties, around one per cent of pupils were infected. These days around 720,000 schoolchildren a year are affected.
So how has this super louse come to be? 'It is a global problem, and rather than one reason there has been a chain of unfortunate events,' says Ian Burgess, a parasitologist and director of the Medical Technology Entomology Centre, a group that advises the NHS on parasitic behaviour.
HE HAS been studying the march of the lice since the 1970s and first noticed they were managing to resist chemical attack in 1993.
'What happened is that people did not use the chemical products properly,' he says. 'Either they did not use enough of the product or did not leave it on long enough.
'Consequently, the insects did not receive large enough doses of the chemicals to kill them. This had the effect of a vaccine on them - their bodies learn how to adapt so that the next time they encountered the chemical, they could break it down before it got to them.'
Now super lice have managed to evolve their nerve cells so that the chemical permethrin can no longer attach itself to them. With the chemical malathion, the resistant lice can produce an enzyme that blocks its action.
'What compounds the problem is that a lot of chemicals work in similar ways,' says Mr Burgess. 'So if the lice become resistant to one, it does not take much for it to become resistant to similar ones.' The problem of resistance is not a new one but the scale of it is. Until the 1970s, DDT was widely used to fight head lice, until scientists noticed that super lice were becoming resistant to it.
There have been health concerns about the use of chemicals, too.
DDT was banned from use on humans in the UK in 1973, amid fears that its use might be linked to cancer, despite patchy evidence.
Similarly, there have been questions raised about the use of malathion and its possible effects on the nervous system.
Even though malathion has been ruled to be safe, many parents have been looking for an alternative to chemical lotions. Yet it is not just synthetic chemicals that cause the resistance problem.
'Essential oils such as Tea Tree have very strong insecticide-like qualities, but we started noticing the head lice were forming a resistance to essential oils about five years ago,' says Mr Burgess. …