Scratching the rash may lead to impetigo, a bacterial skin infection with oozing sores.

Scabies is most common in poor countries but can be found anywhere. It has been diagnosed in American high-school wrestling teams. In January, infestations were detected in firefighters at two New York City firehouses, one of which had to be closed for decontamination.

In the study, published in the New England Journal of Medicine, Australian and Fijian researchers tested three treatment regimens in three groups of isolated island villages in Fiji.

A third got the standard treatment prescribed in Fiji: skin lotion containing permethrin was given to people with scabies and their family members. (Permethrin is an insecticide used in insect-repellent clothing and in some mosquito nets.)

In the second group, everyone in the village got the lotion.

In the third group, everyone in the village who agreed to participate got one ivermectin pill; those with confirmed scabies got a second pill a week later.

Ivermectin, which was discovered in Streptomyces avermitilis bacteria in 1975, is a powerful drug that kills many types of parasitic worms. Because ivermectin lingers in the blood, it also kills insects that bite humans, including mosquitoes, lice and mites.