Lice are parasites of mammals and birds and have been a pest of humans for thousands of years. In the 1920s, lice were first found associated with excavated Egyptian mummies. Since lice have a close association with their hosts, they have been studied by scientists interested in human evolution. It is thought that body lice originated around the same time that humans started migrating into colder regions (72,000 ± 42,000 years ago), where humans started requiring body coverings to stay warm.
Lice go through several nymphal stages before reaching adulthood, and blood is required for both growth and development of eggs. Eggs (called nits) are cemented to hair follicles, and nymphs hatch up to nine days later. Lice cannot survive off of the host.
Lice Species of Public Health Importance
There are three species of lice that infest humans: Pediculus humanus (body louse), Pthiris pubis (pubic/crab louse) and Pediculus capitus (head louse). Of these species, only the body louse can cause disease.
Body lice inhabit the seams of clothing that are worn by infested people experiencing unclean or crowded living conditions (e.g., homeless, refugees, prisoners). Lice saliva injected during bites can cause itching, and, in long-term infestations, a systemic reaction called vagabond’s disease can occur. Vagabond’s disease may result in skin thickening and discoloration. Body lice can spread bacterial pathogens that cause epidemic typhus, trench fever and louse-borne relapsing fever.
Pubic lice are found in hair in the pubic region of the body and resemble crabs, as the adults have two large pincher-like front legs. Pubic lice are spread by sexual contact and are not associated with any diseases, although they can cause itching that can lead to secondary infections.
How do I help get rid of lice?
Items (e.g., hats, bedding, clothing) that may contain lice eggs, nymphs and/or adults should be washed and dried using hot temperatures. Vacuuming can remove strands of hair that may contain eggs.
Body lice are controlled by regularly cleaning the body, clothing and bedding of an infested individual. There are several different treatment options for head lice. There are some treatments that kill eggs and adults. For head and pubic lice, some treatments (e.g., shampoo containing insecticide) can be purchased over the counter, while others may require a prescription by a medical professional. The label instructions must be followed to ensure the safety and efficacy of the treatment. Dead and/or dying lice and eggs can be physically removed from the hair using a specialized fine-toothed comb for lice. For some shampoos, retreatment is recommended after about a week; follow the label instructions. In some cases, if active lice are still observed in the hair up to 12 hours post-treatment, the lice may be resistant to that insecticide.
If lice reappear, there may have been a re-infestation from another source. It is also possible that the treatment (e.g., shampoo) for the initial infestation was not properly applied and/or was washed out too quickly. In some cases, when lice are not eliminated post-treatment, insecticide resistance may be an issue. In these cases, a medical professional should be consulted to determine an alternative course of treatment.
Dr. Stephanie L. Richards is an Associate Professor of Health Education and Promotion in the Environmental Health Sciences program at East Carolina University. She received a B.S. in Biology and M.S. in Environmental Health from East Carolina University. She completed her Ph.D. in Entomology with a minor in geographic information science at North Carolina State University. She completed her post-doctoral work in Arbovirology at University of Florida, Florida Medical Entomology Laboratory. Learn more.