Body louse

Pediculus humanus humanus (the body louse) is indistinguishable in appearance from Pediculus humanus capitis (the head louse) but will interbreed only under laboratory conditions. In their natural state, they occupy different habitats and do not usually meet. Unlike their close relations, head and pubic lice, body lice do not live directly on the host. They lay their eggs in articles of clothing or bedding and only come into contact with the host when they need to feed.[2] They can feed up to five times a day and can live for about thirty days, but if they are separated from their host, they will die within a week. If the conditions are favourable, the body louse can reproduce rapidly. After the final molt, female and male lice can mate immediately. They typically live for some 20 days before dying.[3] A female louse can lay up to 200-300 eggs in clothing, bed sheet fibers or seams of clothes during her life.

The life cycle of the body louse consists of three stages: egg (also called a nit), nymph, and adult.

1. Nits are louse eggs that are laid in the folds of clothing and nowhere else. The mother louse secretes an adhesive that is produced by her accessory gland and holds the egg in place until hatched. They are oval and usually yellow to white in color and when in the correct temperature and humidity, they will develop 6 to 9 days after being laid.[3]
2. A nymph is an immature louse that hatches from the nit (egg). Once the nymph is hatched, it immediately starts feeding on the host's blood and then returns to the clothing until it needs to feed again. The nymph will molt three times after hatching and after the third molt, it emerges as an adult louse. The nymph developing into an adult louse usually takes 9-12 days after hatching.[3]
3. The adult body louse is about the size of a sesame seed (2.5–3.5 mm), has six legs, wingless and is tan to grayish-white.

Life cycle of Pediculus humanus capitis, which is similar to the body louse. The location of the body louse eggs are different from the head louse eggs. The head louse will lay eggs on hair roots, whereas a body louse will lay eggs in articles of clothing. This picture represents the louse from egg to adult and the process of going through three molts to achieve adulthood.

The two P. humanus subspecies are anatomically almost identical. Their heads are short with two antennae that are split into five segments each, compacted thorax, seven segmented abdomen with lateral paratergal plates.[3] Specialists can distinguish between body and head lice based on differences in pigment coloration in the abdomen, and differences of the lengths of the tibia have been observed between the two subspecies.[3]

The body louse diverged from the head louse at around 100,000 years ago, hinting at the time of the origin of clothing.[4][5][6] Body lice were first described by Carl Linnaeus in the 10th edition of Systema Naturae. The human body louse had its genome sequenced in 2010, and at that time it had the smallest known insect genome.[7] Other lice that infest humans are the head louse and the crab louse. The claws of these three species are adapted to attachment to specific hair diameters.[8]

The body louse belongs to the phylum Arthropoda, class Insecta, order Phthiraptera and family Pediculidae. There has been roughly 5,000 species of lice described, 4,000 specialized to birds, 800 specialized to mammals and are seen all over the world in various habitats.[9]

Body lice infestations can involve thousands of mites, each biting an average of 5 times per day.[10] When an individual is infested with body lice, this condition is called pediculosis. The number and severity of the bites can vary depending on how many lice that individual is infested with. Since an infestation can include thousands of lice and with each of them biting 5 times a day, the bites can cause uncontrollable itching that can result in infections. If an individual or a population of people are exposed to a long-term infestation, they may start to experience apathy, lethargy and fatigue.

When feeding, the body lice resemble a mosquito feeding process. The body louse pierces the skin of the host and injects a salivary anticoagulant that helps the louse consume the hosts blood. Bites of the body louse can produce skin lesions that looks like a rash and in some cases, pruritus. Intense scratching of pruritic bites can result in skin excoriation, potentially leading to significant secondary bacterial infections.[10]

Treatment is usually done by manually removing the lice or by the use of chemicals known as pediculicides. In many cases, a change in the individual's personal hygiene can treat a body lice infestation without the use of pediculicides. The infected individuals should shower as well as wash all of their clothes, towels, and bed sheets in hot water that is at least 50 °C (122 °F) and dried using a hot cycle. The itching can be treated with topical antibiotics; corticosteroids and systemic antihistamines. If the itching has caused secondary infections, then antibiotics will be prescribed based on the type of infection.

Pediculicides aren't necessarily needed when appropriate hygiene requirements are met, but they can be used in cases where other lice species are present. Since the chemicals that are used can be toxic to humans, directions need to be followed when applying them. However, many of the most widely used pediculicides have become ineffective as a result of the spread of resistant strains.[11]

Body lice can cause the cutaneous condition Pediculosis corporis, characterised by intense itching.

Unlike other species of lice they can also act as vectors to transmit disease. Some types of bacterial infections that are transmitted by body lice are Rickettsia prowazekii (causes typhus), Borrelia recurrentis (causes relapsing fever), and Bartonella quintana (causes trench fever). Body lice are dependent on a variety of conditions that can lead to an increase in population. Some conditions that are needed is the weather, humidity and lack of hygiene.[12] Diseases like typhus are reported mainly in the winter/spring months, during these months, individuals have to wear multiple articles of clothing, which serves as a great place for the body louse to live and breed.

All of these diseases negatively impact human health, but can now be treated. If they go without treatment, two of the diseases have a high fatality rate. Typhus can be treated with one dose of doxycycline, but if left untreated, the fatality rate is 30%.[12] Relapsing fever can be treated with tetracycline and depending on the severity of the disease, if left untreated it has a fatality rate between 10–40%.[12] Trench fever can be treated with either doxycycline or gentamicin, if left untreated the fatality rate is less than 1%.[12]

• List of parasites of humans

• Body and head lice on the UF / IFAS Featured Creatures Web site