Pediculus or lice, come in three varieties. The first is Pediculus humanis capitis, also known as the head louse and the second is Pediculus humanis corporis, more commonly known as the body louse. The third type of louse is Phthirus pubis, also known as “crabs.” Head, body and pubic lice have a tendency to emerge in crowded areas with low levels of personal hygiene.
humanus (corporis, capitis, pubis)
Pediculi are ectoparasites, meaning they live on top of their hosts instead of inside of them. They are small, six-legged insects with claws adapted to clinging onto their host’s hairs or clothes. Pediculi mouth-parts are adapted to sucking the host’s blood, and in the case of capitis, they are also adapted to eating dermal parts of the host’s scalp, neck and eyelids. See the picture in general information, above.
gray and white
tan to greyish white
3 to 4 mm in length
4 to 5 mm in length
2 to 3 mm in length
Mouth adapted to suck blood and legs adapted to grip hairs
six-legged, mouth adapted for blood sucking and claws for grasping
six-legged, with four legs resembling crab claws. Legs are adapted to grasp pubic hairs.
Pediculosis as a human problem dates back to the earliest Homo sapiens. Researchers at the Max Plank Institute for Evolutionary Anthropology used Molecular Clock Analysis (MtDNA) to date the origins of human lice to approximately 72, 000 years ago in Africa. Expansion of lice into other parts of the world follow the expansion of modern man out of Africa approximately 50, 000 years ago.
“Out of Africa” – The orange arrows outline the likely route of modern human beings out of Africa ~50,000 years ago.The spread of Pediculosis humanus is believed to have followed this same route.
Fun Historical Facts About Pediculosis
Ancient Remedies for Pediculosis
Typically asymptomatic. Symptoms that may appear are itchiness of the neck, scalp and ears, pruritis, as well as puss in affected areas (bites). In more severe cases secondary bacterial infections can develop which may lead to febrile episodes as well as enlargement of the cervical and nucal lymph nodes.
Itchiness and visible bite marks on the body and pruritis, especially around the waist and armpits. There may also be crusting and redness due to secondary bacterial infections.
Itchiness in public areas and armpits is the most common complaint although not always a complaint. Pale blue spots at the follicular orifices may appear in the case of a prolonged infestation.
Clinical presentation of head, body and pubic lice. P. capitis presentation includes brown fecal matter around the ear. The P. corporis image is the clinical presentation of pruritis due to a prolonged lice infection. P. pubis were found attached to pubic hairs in the third image.
Transmission, Reservoir and Vector Information
Humans are the only reservoir for all human lice species. Lice do not typically survive more than 30 days without a human host.
There is no vector for pediculosis, but body lice have been known to act as vectors in the spread of other diseases such as typhus, trench fever and relapsing fever.
Life Cycle and Incubation
Life cycle of P. capitis
The adult female will lay her eggs (7-10 per day) near the hair shaft. The egg (nit) will take approximately 8 days to develop and emerge as a nymph. The nymph will mature into an adult louse in approximately 8 days and will then begin to feed and reproduce on the scalp, neck and eyes of the infected person.
P. corporis life cycle
P. pubis life cycle
The body louse follows a similar developmental and maturation pattern as the head louse. The adult body louse will then feed on the skin of the body of the infected individual but dwells and lays its eggs in the seams of the individuals clothing and/or bedding.
Pubic lice have a life cycle similar to both the head and body lice, although parallel the head lice more because the eggs are deposited near the base of the pubic hairs. The development and aturation of the nymph into an adult louse is similar to the development described in the diagram above.
The incubation period is the length of time the laying of the egg and the hatching of the Pediculus nymph.
P. capitis: 8 days
P. corporis: 6-10days
P. pubis: 6 – 8 days
Identification of louse and nits. This can be aided with the use of a fluorescent Underwood light. Careful and thorough combing can also be done to search for nits and lice. Official measure of diagnosis is the presence of nits within 6.5 mm of scalp.
Identification of louse or nits on clothing. The adult louse may hard to identify because they move quickly across the body and clothes.
Identification of louse or nits in the pubic and armpit areas. Identification of the adult may be difficult because of its translucence.
The best preventative measure against all types of lice is to practice consistent and adequate measures of personal hygiene. This includes washing head and body hair in warm water (temperatures of greater than 130 degrees Fahrenheit may kill adult lice), as well as laundering clothing on a regular basis.
Other means of preventing the spread of pediculosis include not sharing personal hygiene items such as hair brushes and combs, as well as towels and unwashed clothing. One recommendation as a preventative measures for elementary-school aged children is to provide them with individual hooks for caps and coats to prevent the spread of head lice.
What to do when you do have lice
Have infected individual bathe thoroughly. Be sure to wash clothes and bedding in warm water and dry in heat. Body lice can survive off of the body for 30 days so it is important to prevent re-infection by washing items that may have come in contact with infected person and his/her clothing.
Lindane lotion may be recommended (washed off after 8 hours) . Corticosteroid creams can be used for pruritic and irritated areas, applied twice daily
Remove nits with finger nails, a comb and/or tweezers. Be sure to check for recurrent infection, treat contacts such as sex partners and wash bedding and clothing in warm water.
Permethrin, Lindane and Pyrethrin lotions may be used for treatment (see directions above). Be sure to dry and cool skin before applying lotions.
Iveremectin may be used as a second-line medication if resistance occurs. Typically use in conjunction with 5% permethrin cream. Leave cream on for 8 – 12 hours or give two doses of ivermectin (200 mcg/kg) one week apart.
Do not use ivermectin in children less than 15 kg or in pregnant or breast-feeding women.
About 1/3 of people with pubic lice will have a second venereal disease and they should be screened.
Epidemiology and Public Health Strategies
Lice are found in countries all over the world, not excluding the most developed societies of Western Europe and the North America. Individuals from all socio-economic backgrounds can be affected by lice, although this is more true for head lice than body lice, which typically affect homeless individuals to a greater extent than individuals who have access to washing machines and hot baths. Head lice have infected elementary-aged school children in North America at epidemic proportions, and head lice infect more children than all other communicable diseases combined (6-12 million children infected each year).
Public Health Strategies
CDC recommendations for head lice outbreaks in schools:
Other public health strategies for all types of lice include encouraging proper hygiene practices. Regular laundering of clothing and bedding in hot water for at least 20 minutes can kill lice. Additionally, increasing peoples accessibility to hot water can help slow the spread of Pediculosis.