4 February, 2013 3:39PM ACDT

Head lice common in the classroom

Some kids weren't itching to return to school this year, but they could be itching now they're back. Head lice are part of many school ecosystems.

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Head lice are the most common parasitic disease in the country, says Dr Stephen Cameron, research fellow at Queensland University of Technology.

"It's pretty much the case that virtually every child will get infested with them at some point."

With the start of school term some parents will be called in for 'head lice patrol', searching kids' locks for these 2-3mm long insects.

"They're generally pale although once they've fed they will have a red abdomen from the blood, because they're blood feeding," Dr Cameron explains.

Detecting and destroying active head lice can be problematic due to the insects' eggs, called nits.

"You can kill off the active lice, but the eggs stay because they're glued to the hairs and some of them can hatch out and cause more lice."

Conversely empty eggs also stay attached to the hair, so a child can still appear to have nits, even if the lice have all hatched and gone.

Dr Cameron says determining how head lice spread is surprisingly difficult, and experiments have often proved inconclusive.

"The lice themselves dehydrate and die very quickly when they're removed from a head, the eggs similarly are glued to the hair so they can't really get around.

"The nits have basically got to walk from one head to the next."

He says there is no evidence behind rumours that nits can swim and transfer in pools, or be harboured in hats.

"The truth is we don't have a great notion of it, things like getting around in hats are probably not true because they don't really leave your hair."

He also debunks the myth head lice can jump up to 30cm betweens heads, saying this was confusing lice for fleas.

"Fleas have specific legs for jumping and fleas spend most of their life off their host, lice spend their entire life on their host so they're not adapted to jumping."

Lice live for four to five weeks, with females laying one egg a day once they're mature.

"They have cement glands that are around the ovipositor, which is the technical term for insect vagina, so as she passes the egg out she covers it in a cement, a biological glue, and glues it by one end to the hair shaft."

This egg binding glue is not water soluble and has even been considered for use as surgical glue due to its strength and resilience.

Treatment tips

The tight fusing of eggs to hair has long proved bothersome for parents wanting to rid their kids of head lice.

"The best and simplest way is still the pesticide shampoos that you can get from chemists," advises Dr Cameron.

But some lice have developed pesticide resistance, plus these shampoos don't eliminate the eggs, so infected heads need to be treated multiple times.

"The eggs will last 5-10 days before hatching, so treat, treat again in a week's time, then again, and keep treating."

He says fine toothed lice combs can be used to tear eggs off the shaft, but they're difficult to use and often rip out a lot of hair.

"So on really small kids that can't be explained why mummy or daddy is tearing a lot of their hair out this is probably not recommended, for older kids, yes.

"Alternatively you can shave their heads, that works very effectively too!"

And if your head's getting itchy simply reading this article, you're not alone.

"It's a well-known psychological thing called delusional parasitosis that simply discussing parasites makes people itch," Dr Cameron assures.