VOA常速英語(yǔ)：頭虱困擾美國(guó)在校學(xué)生

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17-year-old Ben Kupferman from California just returned from a summer camp, bringing some unwanted guests home.

"I was just scratching my head and one of the lice just came out. It was just on my finger, crawling around," he recalled.

The Centers for Disease Control and Prevention estimate some six to 12 million lice infestations occur each year in the U.S. in children 3 to 11 years old. Until recently, all a parent had to do was buy some over-the-counter product that gets rid of lice within days. But increasingly these remedies do not work. Scientists say that's because lice have developed tolerance and even resistance to chemicals.

"Certain ones have the potential to mutate and protect themselves against whatever we are using to try to kill them," said Angela Baker, a pediatrician at the Children’s Hospital of Wisconsin.

David Gaines, a public health entomologist in Virginia said lice have been developing resistance for some time.

"This has probably been coming for many, many years. There have been reports of insecticide-resistant lice going back decades,” said Gaines.

When standard treatments don't work, parents are referred to a doctor for prescription drugs. But some parents don't like using strong chemicals on their kids, preferring more natural methods. Beverly Mann, a California mom, banded together with other parents to start Nit Fairies, a natural lice-treatment business.

"We use an all-natural treatment oil and we do give guarantees with our services. It is pesticide-free. We do the combing, we do the picking, so the parent at home doesn't have to," said Mann.

In the state of Virginia, Gerry Wolburg started his lice-removal business three years ago when his daughter Rachel got lice. He uses heat to kill lice eggs, known as nits.

"It desiccates the lice with hot air, and if you leave eggs in the hair they're desiccated. That means they shrivel up. They are dried up and we like to point out that it's like leaving a boiled egg in a hen-house. It's not going to hatch," explained Wolburg.

The good news is that lice don't carry diseases. They are only annoying parasites that are sometimes hard to get rid of.