The National Pediculosis Society designates September as National Head Lice Prevention Month.
Head lice and body lice are separate species. Evolutionary biologists have pinpointed the emergence of body lice species as an offshoot of its more ancient head lice progenitors, about 170,000 years ago. The development of primitive forms of clothing in past ice ages may have facilitated this evolutionary divergence.
Head lice can survive on the human scalp, as well as in hats, clothing and other objects. September, a back-to-school month, is an opportune time to contemplate head lice, in particular.
An obligate human parasite, the lowly louse dies after 24 hours without a blood meal. The eggs of the louse, however, can survive for ten days as “nits,” protectively encrusted and attached to individual hair shafts. The term “nit-picker,” not surprisingly, connotes an individual who is patient enough to remove these eggs.
Treatments for lice, including lindane and other insecticides, may be appropriate in some cases. Aggressive vacuuming of rugs and furniture will often suffice to rid a home of lice. Pets are not typically intermediate vectors. No method of eradicating lice from persons or homes is foolproof, however.
Lice can transmit disease on occasion. For example, epidemic typhus is transmitted by lice. The causative organism, Rickettsia prowazekii, is excreted in the feces of the louse and typically enters the bloodstream due to skin abrasions induced by scratching. In fact, DDT, which gets little in the way of good press, undoubtedly saved millions of lives in the World War II era by eradicating both lice and malaria-causing mosquitos.
Sprayed directly into dwellings, or applied topically as a powder, this compound was remarkably effective as an insecticide. DDT fell into disfavor in recent decades, however, and is now rarely used for vector control.
Rachel Carson’s ”Silent Spring,” a book linking DDT use to toxic effects on the eggs of eagles and other birds, was a major nail in the coffin of DDT use worldwide.
Epidemic typhus still crops up, generally in third world war zones. There is also recognition that America’s squirrel populations harbor species of lice that may be infected with the typhus-causing bacterium.
Lice cannot jump or fly. Sharing of brushes, combs and hats, however, can furnish the louse with a bus ticket to a friend’s scalp. Military organizations, by and large, take a narrow view of what constitutes appropriate hair length. Having served in the Air Force as a physician, I think that this mentality reflects concerns regarding parasitic infestations in congregate living environments. As recently as the World War I era, 25 million Russians developed lice-borne epidemic typhus, with three million deaths resulting. The take-home message in modern American societies is that our kids should probably avoid sharing combs or hats with friends.
While working as an emergency room physician in New York City years ago, I encountered a patient who had been living on the streets in poor health. As he leaned forward to facilitate my examination of his lungs, I noted a couple of lice crawling up the sheets of the gurney behind him. Although I showered at the end of my shift, I still kind of worried that lice might crop up on my body. That is kind of the way lice impact our thinking. Although the public health implications of lice, particularly in children, are quite small, we tend to magnify our fears through endless rumination and concern.
Public education and awareness can serve to not only minimize lice infestations, but also to mitigate public fear that might be mediated through lack of understanding. The National Pediculosis Association maintains a website called HeadLice.org, which addresses many questions about lice.
Scott T. Anderson, M.D., Ph.D. (firstname.lastname@example.org) is clinical professor of medicine, UC Davis. This column is informational and does not constitute medical advice.