Understanding Lice and Scabies - the Basics

What Are Lice?

Lice are tiny parasites that live on human beings and feed on blood.  They seldom cause serious medical problems, but they are both annoying and contagious.  Every 4 hours or so, a louse bites into a tiny blood vessel for a meal.  You don't feel the initial bites, because lice inject an anesthetic in your skin.  However, the bites later begin to itch, and your scratching can lead to infection.

Head lice (Pediculus humanus capitis) are about the size of a sesame seed and can be easily seen, although they hide quickly in response to light.  Their eggs, called nits, are barely visible, whitish ovals, which attach to human hair shafts.  Head lice are extremely contagious, especially among schoolchildren.  They afflict an estimated 6 million to 12 million children in the United States. Twice as many girls as boys get head lice -- not because of longer hair, but because girls have more physical contact with one another and share more personal articles (hats, clothing, combs, headphones) that can transmit head lice.  Head lice are rare among African-Americans, possibly because the shafts of their hair have a shape that lice cannot grasp easily.

Pubic lice (Phthirius pubis) are yellow-gray insects found in the pubic region and transmitted by sexual contact.  The size of a pinhead, they are slightly translucent and barely visible against light-colored skin.  They are also called crab lice, or crabs, because of their shape and the crab-like claws with which they cling to hair.  Eggs can barely be seen; these tiny white particles attach so firmly to hair shafts that they are not removed by normal washing.

Body lice (Pediculus humanus corporis) are nearly identical in appearance to head lice but are more difficult to find.  When not feeding, they tend to hide in the seams of clothing and folds of bedding.  Signs of their presence are scratch marks, hives, or small red pimples, usually on the shoulders, torso, or buttocks.  If the lice are not treated, the person can develop complications such as bacterial infection of the affected area.  Body lice can also spread blood infections.

Contrary to common belief, lice are not related to poor hygiene.  In fact, head lice are thought to prefer clean hair to dirty hair.  Lice live successfully all over the world, wherever people gather in close proximity, such as in schools.

What Are Scabies?

Scabies is another contagious skin disease caused by the mite Sarcoptes scabiei.  The primary symptom -- incredibly itchy, red lesions -- results when the female mite burrows into the skin and deposits eggs and feces.  Closed environments such as nursing homes and child-care centers provide ideal breeding grounds for this parasite, which needs a human host to survive. An estimated 300 million new cases spring up each year worldwide.  The number of cases in the United States is currently on the rise, probably because more children under the age of 5 are being cared for in day-care centers.