About head lice infestations

Which of the following statements is true regarding head lice infestations?

• A) Females are more likely affected.
• B) Retreatment with pyrethrin is rarely needed.
• C) Head lice can live off the body up to 1 week.
• D) Low socioeconomic children are more likely affected.
• E) Dogs are a common vector for head lice.

The answer is:  ( A ).

Head lice are thought to be the most common type and are developing resistance to commonly used pediculicides. Every year, between 6 million and 12 million people in the United States, primarily children 3 to 10 years of age, are infested with head lice. Girls are at greater risk because they have more frequent head-to-head contact.
Head lice affect people of all socioeconomic status. Head lice are obligate parasites that live on human skin and survive on human blood. No other animal is affected. Head lice die if they are away from the host head for more than 2 days.

Lice are wingless and cannot jump, but they climb quickly from hair to hair when the hair is dry. Lice move slowly on wet hair and can be removed more easily with a gloved hand or a fine-toothed comb. The adult female louse lays 7 to 10 eggs daily that attach to human hair with a gluelike, water-soluble substance. By 7 to 10 days, a nymph emerges from the egg and is close enough to the scalp to obtain its first meal of blood. Adult lice, after the 7- to 10-day period of molting stages, live about 30 days. Infested people usually have no more than 10 to 12 live head lice at a time, but can harbor hundreds of eggs and nits. Those affected describe itching and a sensation of “something crawling on my head"? Scratching may cause excoriations and secondary infection. Most infestations are asymptomatic.

Prior to treatment, live lice can be identified under a magnifying glass, which is best done when the hair is wet. After infestation is confirmed, treatment consists of application of a pediculicidal agent to the hair, followed by mechanical removal. 

The hair should not be washed for 2 to 3 days after the pediculicide is applied. Thorough physical removal of lice and nits with a sturdy, fine-tooth comb is recommended for several days after application because no pediculicide guarantees total eradication of lice. First-line topical agents containing pyrethrins or permethrin are available over the counter and are relatively nontoxic. Retreatment is advised 7 to 10 days after the first application of pyrethrins. Because permethrin remains active for a longer period, retreatment generally is not necessary. Permethrin 5% cream is available by prescription for use in resistant cases. Alternative agents include lindane or malathion. Lindane has been shown to have limited success and is systemically absorbed, so its use is now considered second-line. Malathion was recently labeled by the U.S. Food and Drug Administration (FDA) for the treatment of head lice and is available in a lotion that is left on the head for 8 to 12 hours. Oral agents include ivermectin and trimethoprim–sulfamethoxizole. Resistance is possible with any treatment because of reduced susceptibility or incorrect use of the medication.

All household members with active infestation should be treated simultaneously. For children younger than 2 years, there is no recommended pediculicide; therefore, treatment consists of manual removal only. Lice that remain active 8 to 12 hours after treatment may require an alternative agent. Itching may persist for up to 10 days after successful treatment and should not be mistaken for treatment failure. The Centers for Disease Control and Prevention recommend that all clothing and bedding in contact with the infested person during the 2 days before application of the pediculicide be laundered in hot water and machine dried using a hot dry cycle. All nonwashable items should be quarantined in a plastic bag for 2 weeks. Combs and brushes should be disinfected with hot water or alcohol.