Infestations



Infestations


Robert Stavert

Alix J. Charles

Sarah J. Harvey

Abel D. Jarell



PEDICULOSIS


I. BACKGROUND

Infestation with lice is known as pediculosis. There are two species of lice specific to the human host: Pthirus pubis (Fig. 23-1) and Pediculus humanus (Fig. 23-2). These wingless, six-legged insects are obligate parasites and are host specific for humans. The lice that inhabit the head or body are both types of P. humanus (P. humanus humanus and P. humanus capitis); only the body louse is capable of transmission of disease-endemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and relapsing fever (Borrelia recurrentis and Borrelia duttoni). Pediculus capitis is not known to be a disease vector. The head louse is transmitted through shared clothing and brushes; the body louse, by bedding or clothing; and the pubic louse, from person-to-person contact and not infrequently through clothing, bedding, or towels.

The adult body louse (Pediculosis humanis) is 2 to 4 mm long, has three pairs of legs with delicate hooks, and is gray-white in appearance. Body lice prefer to live in clothing, particularly seams, and move to the body to feed. Heavy infestation is common in crowded, unhygienic surroundings such as military personnel and refugees during wartime, prisons, chronic health-care institutions, and homelessness. Head lice (P. capitis) most commonly affect children, between the ages of 3 and 11. The incubation period from exposure to pruritus is approximately 30 days. The ova (nits), which are oval, 1 mm long and gray, and firmly attached to the hair, hatch in approximately 7 to 9 days and become mature in another week (Fig. 23-3). Ova are laid very close to the scalp and hatch before the hair grows more than 1/4”. If no nits are found within 1/2” of the scalp and no lice are seen, treatment is not necessary because nits more than 1/2” from the scalp are eggshells from a past infection. Head lice do not jump or fly from one person to another.

The crab or pubic louse (P. pubis), which usually inhabits the genital region, is short (1 to 2 mm) and broad, and the first pair of legs is shorter than the claw-like second and third pairs. Infestation may occur in other areas, including the moustache, beard, axillae, chest, scalp, and eyelashes. Adult lice can live off the host for up to 36 hours and viable eggs, for 10 days. The chance of acquiring pediculosis pubis from one sexual exposure with an infected person is approximately 95%. Transmission of crab lice can occur without body contact, especially in warmer environments.


II. CLINICAL PRESENTATION

Extreme pruritus is the primary characteristic of pediculosis. It takes 4 to 6 weeks for the pruritus to develop in a nonsensitized individual and only 24 to 48 hours with repeat exposures. Chronic infection may lead to lichenification and hyperpigmentation from repeated scratching. In some cases, patients may be totally asymptomatic. Sleeplessness
may be reported, because lice are more active during nocturnal hours. Nits may be found most easily on the hairs on the occiput and above the ears. It is often difficult to differentiate a viable from a nonviable nit. Pseudonits are desquamated epithelium encircling the hair but are more readily removed than true nits. Secondary impetigo and furunculosis with associated cervical lymphadenopathy may occur. In severe cases, fever and anemia may be found. Feeling “lousy” was a term developed to describe the symptoms of pediculosis.






Figure 23-1. Pubic louse (crab). (Washington Winn Jr. Koneman’s Color Atlas and Textbook of Diagnostic Microbiology. 5th ed. Philadelphia, PA: Lippincott-Raven; 1997.)






Figure 23-2. Body louse. (Washington Winn, Jr. Koneman’s Color Atlas and Textbook of Diagnostic Microbiology. 5th ed. Philadelphia, PA: Lippincott-Raven; 1997.)

In cases of body lice, scratch marks, eczematous changes, lichenification, urticaria, and persistent erythematous papules may be seen. Lesions are often
most noticeable on the back. The lice will be found in the seams of clothing and only rarely on the skin.






Figure 23-3. Nits. (From Goodheart HP. Goodheart’s Photoguide of Common Skin Disorders. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.)

Unexplained pubic pruritus is very often a manifestation of pediculosis. Pubic lice may infest pubic, perianal, and thigh hair with only a few or with uncountable numbers of nits (Fig. 23-4). The infection load may be particularly severe at the base of the eyelashes. The yellow-gray adults may be difficult to find and are usually located at the base of the hairs, resembling small freckles, scabs, or moles. Blue-black macules (macula cerulea) present in infested areas are associated with chronic infestations.






Figure 23-4. Pubic louse (see arrow). (From Goodheart HP. Goodheart’s Photoguide of Common Skin Disorders. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.)







Figure 23-5. Pediculosis capitis (head louse).


III. WORKUP

For all forms of pediculosis, the presence of nits or adult lice is diagnostic (Fig. 23-5). Unexplained pruritus of the scalp should raise suspicion of head lice. Parents or school nurses can screen the posterior scalp with tongue blades or lice combs. It is necessary to be persistent in searching for nits. If suspicion is high, a therapeutic trial or reexamination in 2 to 3 days is indicated. In cases of body lice, close examination of clothing with attention to seams which come in contact with the neck, axillae, or waist may reveal lice or nits. In fastidious individuals, few adult lice and nits will be found, and a careful search—ideally employing a hand lens—should be made, with special attention to the genital area. In cases of public lice, the possibility of coexisting venereal diseases must be considered. Body and axillary hair as well as the eyelashes and beard should also be examined for nits; the scalp may rarely be involved.


Jun 10, 2016 | Posted by in Dermatology | Comments Off on Infestations

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