Pediculosis (Lice) Clinical Presentation

Patients may come to the attention of a health care provider after discovering lice or nits. Parents and teachers typically make the initial diagnosis of head louse infestation. In the case of head lice, a school nurse usually discovers infestation (routine nit inspections by school nurses are standard in many parts of the United States), or a generic letter is sent home to parents indicating that they should inspect their children for lice, and concerned parents bring their children to their health care provider or the local emergency department.

Pruritus is the most common symptom of infestation. Children often have trouble sleeping because of intense pruritus at night when lice are feeding. Areas affected in head louse infestation include the scalp, the back of the neck, and postauricular areas. However, lice infestation may be asymptomatic. The duration of the problem is often valuable information because most children are infested with head lice for as long as 2 months before their discovery.

Patients infested with P corporis experience nocturnal pruritus, particularly in the axillary, truncal, and groin regions, when the lice move from the clothing to the body to feed. The investigating physician should inquire about the patient's socioeconomic status and living conditions, as body louse infestation generally affects people of low socioeconomic status.

Adults infested with P pubis are usually sexually active and have groin and body hair involvement. Involvement with pruritus of the groin, axillae, and eyelashes or eyebrows can help differentiate P pubis infestation from head or body louse infestation.

Children have eyelash and eyebrow involvement. Parents of children infested with P pubis should be questioned about being infested because the parents are usually the source of infestation.

Patients may describe associated features such as papules or wheals, indicating bite reactions. Patients may have a history of secondary infection after excoriation, which may help to confirm the presence of an infestation.

A diagnosis of any type of pediculosis rests on the observation of eggs (nits), nymphs, or mature lice. Detecting live lice is difficult. Nymphs and mature lice, although unable to hop or jump, can move rapidly through dry hair. Wetting the hair and using a fine-tooth "bug-busting" comb is useful to dislodge eggs and to remove live lice/nymphs. The use of a magnifying glass and knowing where to look for lice (based on the biology of each species) assists diagnosis.

Lice move rapidly. A helpful technique is to fasten a piece of transparent adhesive tape to the infested areas. Lice stick to the tape, which then becomes a convenient coverslip for a microscopic slide.

Mature lice are 3-4 mm long (approximately the size of a sesame seed), with an elongated body, 3 pairs of legs, and narrow anterior mouthparts. Wide crablike bodies and claws distinguish pubic lice. Nits are approximately 1 mm in length, transparent, and flasklike in appearance. (See images of lice below.)

P humanus capitis

Manifestations of head louse infestation include scalp pruritus, occipital lymphadenopathy, and impetigo. Examination of the scalp reveals excoriations, dark specks of louse feces, nits, and adult lice. The heaviest infestation typically is in the retroauricular scalp. For the diagnosis of P capitis, the use of a louse comb is more efficient than direct visual examination of the scalp.^[21]

Pruritus commonly leads to excoriation, secondary bacterial infection, and enlargement of the posterior auricular and cervical nodes. A generalized exanthem rarely accompanies louse infestation (pityriasis rosea–like pediculid).

If excoriations are present, secondary infection (ie, impetigo) should be excluded and treated, if present. Bite reactions manifested as pruritic papules and/or wheals may be present, depending on the length of time since the blood meal.

Uncommonly, the hair of patients who are heavily infested and untreated is tangled with exudates, predisposing the area to fungal infection. This results in a malodorous mass known as a plica polonica. Numerous lice and nits are found under the matted hair mass.

Nits

Nits can be differentiated from dried hairspray and hair casts by attempting to separate the nit from the hair; hair casts and dried hairspray separate easily, while nits remain securely attached. If the physician remains unsure, a Wood lamp examination can be performed. Live nits are fluorescent white when illuminated with a Wood lamp; empty nits are fluorescent gray.

Eggs depend on body warmth to incubate, so nits are attached to the hair shafts just above the level of the scalp. Since human scalp hair grows at a rate of approximately 10 mm/mo (0.37 mm/day), the distance of nits from the scalp can be used to estimate the duration of infestation. Nits found several millimeters from the scalp are nonviable empty egg cases. They indicate chronic infestation.

P humanus corporis

Physical examination findings in body louse infestation include multiple lesions from bites. Uninfected bites present as erythematous papules, 2-4 mm in diameter, with an erythematous base. The development of secondary infections due to excoriations is also possible.

Bites may be located anywhere on the body, but they are concentrated in the axillae, groin, and trunk (ie, areas most often covered by clothing). Thus, the face, feet, and arms are not commonly affected. Body lice tend to avoid the scalp, except at the margins. Eyelash nits are a manifestation of pubic louse infestation, not head louse infestation.

The finding of maculae cerulea is believed to be pathognomonic for infestation with lice. Maculae cerulea are blue-gray macules, which are actually a discoloration of the skin due to the insect's bite. Enzymes in the louse saliva are believed to cause the breakdown of human bilirubin to biliverdin, causing the change in skin color associated with maculae cerulea.

The diagnosis of body lice depends on the close examination of the patient's clothing for lice, nits, and insect feces. The inner seams of clothing worn on the axillae and groin regions are common sites of residence. The number of body lice per host is usually approximately 10, although as many as 1000 lice can be present.

Body louse infestation is also known as vagabond disease, and patients who have an infestation for many years can develop a condition termed vagabond skin. The skin becomes thickened and darkened after years of bites and subsequent rubbing and excoriations.

Individuals with P corporis infestation should also be examined for the presence of pubic and head lice. It is also important to examine for systemic illness that may be related to one of the vector-borne diseases associated with P corporis (see Complications, below).

P pubis

The primary symptom in patients with pubic lice is pruritus in the affected areas. Another clinical feature of pubic louse infestation is the presence of pathognomonic maculae cerulea secondary to bites.

Pubic hair is the most common site. Pubic lice and nits generally are plainly visible throughout the pubic hair. Because of the less-mobile nature of pubic lice, they are more likely to be found on affected areas clasping onto the hairs near the skin's surface.

Involvement may spread to hair around the anus, abdomen, axillae, chest, and eyebrows and eyelashes. Rarely, facial hair is a site of infestation. Scalp involvement is rare and is usually confined to the marginal areas. In adults, eyelash involvement in the absence of genital involvement is rare. In prepubertal children, however, eyebrows and eyelashes are common sites of infestation.

In children, P pubis infestation is usually acquired from an infested parent and is rarely the consequence of sexual abuse; however, P pubis infestation may be acquired secondary to sexual abuse, and the child should be examined for signs of abuse.

Excoriations are common. Inguinal lymphadenopathy and axillary lymphadenopathy have also been reported with pubic louse infestation.

There is no evidence indicating that any species of louse has the ability to transmit HIV. However, lice may carry Staphylococcus aureus and group A Streptococcus pyogenes on their surface and transmit these coagulase-positive pathogens to humans.

The body louse, P humanus corporis, is a known vector of 3 major bacterial diseases, all of which have caused epidemics: typhus, trench fever, and relapsing fever.

Typhus

The intracellular pathogen Rickettsia prowazekii causes typhus. Typhus fever epidemics have consistently been related to times when overcrowded conditions and body louse infestations were prevalent. For example, mass migration, refugee camps, and times of war have been linked to body louse infestations and secondary epidemics of typhus.

The illness begins with a high fever and progresses over hours to days with malaise, backache, headache, and myalgia. A petechial rash appears approximately on day 4, beginning in the flank and axillary regions and quickly spreading to the trunk and extremities. By the second week, the fever begins to wane, profuse sweating occurs, and convalescence ensues. CNS involvement during this period places the patient at high risk of mortality.

Trench fever

The extracellular pathogen Bartonella quintana causes trench fever. Although rarely fatal, this disease has been the cause of many epidemics and is believed to be related to bacterial infective endocarditis. Infection in humans results from autoinoculation of louse feces into abraded or scratched skin. The infection has a 10- to 30-day latency period and results in a fever similar to that of typhus, with headache, myalgia, and pain in the back and the legs.

Relapsing fever

The spirochete Borrelia recurrentis causes relapsing fever. This disease is highly fatal in malnourished persons. Although not common in North America, epidemics have been described during the last few decades in Asia, South America, Africa, and Europe.

Human infection with this spirochete occurs only when a crushed louse comes into contact with an abrasion. The bacteria replicate in the louse hemolymph, not in the gut; therefore, no transmission occurs through the salivary glands or via the feces. The bacterial infection causes a high fever, headache, dizziness, and myalgia. Rash and sweating also appear and wane approximately on day 5. As the name indicates, this fever often returns several times.