Human louse — General Information — AgriHunt
Human louse – General Information
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.
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.
The History of Pediculosis
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
- Evidence for the body louse was also recently discovered in the excavation of a fortress in Masada Israel, which was originally the storeroom for King Herod the Great. The store-room is believed to have housed soliders during the Jewish Revolt of 66 – 74 CE, which would have provided an ideal environment for a lice infestation.
- Combing or shaving hair (Ancient Egyptians)
- Aztec King Montezuma paid for his subjects to have their nits removed, and then he had them preserved.
- Drinking garlic concoctions (Greece)
- Military personnel in World War One helped control the spread of the disease typhus (commonly transmitted by body lice) by bathing soldiers and washing their clothes.
- Greek naturalist Pliny the Elder (23-79 CE) recommended destroying nits using dog’s fat or eating cooked serpents.
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
- Human to human transmission is the only way pediculosis is transmitted. Transmission and infection are usually the results of low levels of personal hygiene
- Tranmission of head and body lice is common where crowds of people are in close contact, such as in schools, prisons and trenches.
- Contact with infected hair (i.e. sharing combs and/or hair brushes) can transfer head lice between individuals
- Contact with clothing and bedding facilitates the transfer of head, body and pubic lice between human hosts
- Sexual contact facilitates the transmission of pubic lice between individuals
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
Diagnostic Test s
P. capitis :
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.
P. corporis :
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.
Management and Therapy
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:
- Inform the school of the infestation
- Treat all infected children for head lice – make sure to screen and track down the contacts of infected children
- Treat households by treating both infected people and cleaning clothing, bedding, towels and hair brushes and combs (wash in hot water and soap).
- Infected children may return to school 24 hours following hair treatment.
- Make sure school nurse or other officials inform parents of outbreak.
- When possible, avoid perpetrating stigma. Keep infected student’s names confidential.
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.
Lice Evolution Tracks the Invention of Clothes
The evolution of body lice shows that humans began wearing clothes between 50,000 to 200,000 years ago
Cooties come in three varieties: head lice, body lice and pubic lice. While head lice live and feed only on the scalp, body lice feed on the body’s skin but live in clothes. Humans have always had hair, but clothes are a more recent development. Figuring out just when body lice evolved, therefore, can give us hints as to when we became the trendy, clothes-wearing species we are today.
Early humans were covered with ape-like hair but started showing skin some 3.3 million years ago when they took to living in hot, savannah environments. (Bare skin promotes sweating and is a terrific way to keep cool, ergo much of the hair had to go, evolutionarily speaking.)
As humans started moving out of the savannah and into cooler climes, they had to start covering up. When they started wearing clothes, however, was always something of a gray area.
In 2003, a German researcher decided to put this theory to the test. He measured the difference between snippets of DNA in the two louse subspecies. Because DNA picks up small, random mutations at a more or less constant rate, the greater the difference between the DNA of divergent but related species, the longer the separation. As it turned out, the body louse branched off from the head louse about 70,000 years ago, give or take 42,000 years.
Clothing must have evolved at that time, too, the researchers figured. We also began drawing and carving, weaving, creating tools and burying our dead. In other words, we underwent a cultural revolution.
They are wearing clothes—lice-filled clothes, to be sure, but clothes nonetheless. Momentously, they are using language. And they are dramatically increasing their range. Homo sapiens is exploding across the planet.
The date is not set in stone, however. A 2010 study that performed a second DNA analysis claimed that the divergence between head and body lice actually occurred about 190,000 years ago. Though there is some discrepancy, we can estimate that humans began wearing clothes roughly 200,000 to 50,000 years ago.
Smithsonian clears up the remaining evolutionary mystery: the pubic louse.
And of course some of you out there may wonder where that intimate, third variety of louse came from. Oddly enough, the DNA record shows that its closest relative is the louse native to gorillas. Science has yet to provide an explanation as to how this happened. Bad case of “beer goggles” perhaps?