Head Lice Basics

The Natural History of Pediculus humanus capitis

Dec 14, 2007

Head Louse: Pediculus humanus capitis, Amy Moon

Head lice are parasites. They cling to hairs, feed on blood and crawl from head to head. They are not dangerous; however, treatment is usually difficult.

Head lice, Pediculus humanus capitis, are parasitic insects that live on the hair and feed on blood. They spread from person to person and reproduce by laying eggs (nits), which they cement to the sides of hairs. Larval lice hatch from the nits, mature, mate, and produce their own nits. The whole life cycle takes two to three weeks

How do Head Lice Feed?

Head lice have specially adapted mouthparts designed for cutting through the skin and penetrating a blood vessel. Once the mouth parts are in a blood vessel, the louse sucks blood. It produces saliva that prevents blood from clotting while it is taking its meal, and blood cells break down quickly so that the blood does not clot before the louse digests it.

How do You Catch Head Lice?

Head lice crawl from one head to another. They can hitch a ride on a hair brush, hat, scarf or anything else they’ve had a chance to crawl onto. They tend to spread more readily among small children who are more likely to share these items or have their heads close together during play. Lice don’t survive long away from the body, however. In northern climates, the opening of schools and a return of cold weather in the fall often brings on an outbreak of head lice.

Do Head Lice Spread Diseases?

Theoretically, head lice can spread infectious bacteria and fungi to their hosts; however, this is rather unusual, especially in peaceful Western cultures. They are not really considered a health hazard. Outbreaks of disease related to lice typically occur during war, and when people are living in crowded conditions but even then, the culprit is more commonly the body louse.

How are Head Lice Treated?

Getting rid of lead lice requires a many-pronged approach:

Wash hair with an insecticidal shampoo available from pharmacies. A physician or public health professional can offer advice about product options.
Use a louse comb—a specially designed comb with teeth that are very close together—to remove louse nits from hair.
Carefully check all family members and close friends to be sure the infestation has not spread.
Wash hats and other head wear, dirty clothes, and bedding in hot water; soak hair brushes in hot water. Items that cannot be effectively washed can be put in the freezer for a few days to kill lice.

Head lice are becoming more and more resistant to the shampoos used to treat them, so treatment often fails. In the case of persistent louse infestation after treatment, consult a professional about other methods of eradicating them.

Interesting fact: in antiquity, and even to the present day, native peoples have used lice for medicinal and cosmetic purposes, and have also commonly eaten them.

Sources:

Clinical Parasitology 9th ed. Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. Philadelphia: Lea and Febiger, 1984.

Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.

Parasites and Parasitic Infections in Early Medicine and Science. Hoeppli, R. Singapore: University of Malaya Press, 1959.

Foundations of Parasitology 6th ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.

The copyright of the article Head Lice Basics in Human Infections is owned by Rosemary Drisdelle. Permission to republish Head Lice Basics in print or online must be granted by the author in writing.