With Labor Day looming and the beginning of school, many of the academically minded among us turn their thoughts and eyes to topics like classroom supplies, textbooks and the likelihood little Johnny is going to come home with head lice.
It’s hard to know how many people get head lice (Pediculus humanus capitis) each year. The Centers for Disease Control estimates 6 to 12 million infestations annually in the United States among children three to 11 years of age – the most common targets.
Getting head lice is not a matter of cleanliness. The wingless parasitic insect is spread primarily by direct contact with the hair of an infested person. The most common way is head-to-head contact. Some studies suggest girls get head lice more often than boys.
Less common modes of transmission are wearing infested clothing, such as hats or scarves, using infested combs, brushes or towels or lying on a bed, couch, pillow or carpet recently in contact with an infested person.
Head lice are not known to transmit disease, but secondary bacterial skin infections may occur from scratching the infestation site. Some folks argue that beyond their basic harmlessness, head lice might actually promote health by boosting a natural immune response to body lice (Pediculus humanus humanus), which pose a more serious health threat.
Head lice spend their entire lives on human scalps, clamped onto a strand of hair, feeding exclusively on human blood. There are other species of lice that infest other mammals and birds.
Treatment involves the use of pediculicides – medicines that kill lice and their eggs. Supplemental measures include thorough cleaning of all clothes and exposed materials and grooming with a special, fine-toothed comb to extract adults and eggs, called nits.
Above: A colorized scanning electron micrograph of a nit (green) affixed to a strand of human hair, courtesy of Kevin Mackenzie, one of the winners of this year’s Wellcome Image Awards.