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Pediculosis pubis and pediculosis ciliaris

Pediculosis pubis and pediculosis ciliaris
Literature review current through: Jan 2024.
This topic last updated: Jan 25, 2023.

INTRODUCTION — Pediculosis pubis (also known as phthiriasis pubis), pediculosis corporis, and pediculosis capitis are disorders caused by infestation by one of three varieties of lice that specifically infest humans (figure 1). Pediculosis pubis is usually sexually transmitted and can extend beyond the pubic area to involve other areas of the body, including the eyelashes (also known as pediculosis ciliaris and phthiriasis palpebrarum). Phthirus pubis, the crab louse, is the responsible organism.

The clinical findings, diagnosis, and management of pediculosis pubis and pediculosis ciliaris will be reviewed here. Pediculosis capitis and pediculosis corporis are discussed separately. (See "Pediculosis capitis" and "Pediculosis corporis".)

PHTHIRUS PUBIS — P. pubis is a 0.8 to 1.2 mm long, translucent parasite (figure 1 and picture 1D). Four of its six legs terminate in prominent crab-like claws, which are suited to grasp pubic and other body hairs.

Life cycle — The life span of the female crab louse is three to four weeks, during which time she lays a maximum of three eggs (nits) per day. The eggs are cemented firmly to the base of a hair and hatch after six to eight days [1].

Transmission — P. pubis is usually transmitted during sexual contact. Transmission via contact with fomites, such as clothing, towels, or linen, may also occur but is thought to be less common [1,2]. Acquisition of P. pubis from a toilet seat is unlikely because the organism gravitates toward warm environments and is not adapted to crawling on smooth surfaces [1].

Close contact with nongenital sites of infestation on an adult or shared fomites are the sources of pediculosis ciliaris in most infested children. However, childhood pediculosis ciliaris may also be a sign of sexual abuse. (See 'Additional evaluation' below.)

EPIDEMIOLOGY — Pediculosis pubis and pediculosis ciliaris occur worldwide. Given that sexual transmission is most common, pediculosis pubis most often affects teenagers and young adults. Pediculosis ciliaris can occur in adolescents or adults with pediculosis pubis or as isolated involvement in children.

Although epidemiologic data on pubic louse infestation are limited, the incidence appears to be decreasing [3-5]. In one study, the incidence of confirmed pubic lice infestations among patients presenting to a medical unit in the United Kingdom fell from 1.82 to 0.07 percent between 2003 and 2013 [3]. The rising popularity of pubic hair removal has been suggested as a potential contributor [3-5].  

CLINICAL MANIFESTATIONS — Pruritus in the affected area is the chief complaint. Pediculosis ciliaris can also present with symptoms of eye irritation. Close inspection reveals translucent, 0.5 mm nits at the base of hair shafts and crawling lice (picture 1A-C).

Pediculosis pubis typically involves the pubic and perianal areas but may also involve the axilla or other body areas with significant terminal hair (eg, chest, extremities). The scalp is typically spared but is occasionally involved in individuals with thick, curly hair [1,6].

Pale, bluish, 0.5 to 1 cm macules (maculae ceruleae) may develop in individuals with prolonged infestation and are the result of injection of louse anticoagulant saliva during feeding. These lesions are usually found on the lower abdomen, proximal thighs, or buttocks [1]. The affected area can also contain crusts and rust-colored flecks of fecal material [7]. Small blood stains can be observed on the underwear [7,8]. Inguinal lymphadenopathy is present in some patients.

In pediculosis ciliaris, there is reddish crusting and matting of the lashes, and associated conjunctivitis is common. Involvement is usually bilateral. Children may continually rub their eyes. Eyebrow involvement may also occur in children, and, in very young children, a few lice are occasionally found clinging to hairs at the periphery of the scalp. Preauricular and submental nodes may be enlarged.

DIAGNOSIS — The diagnosis of pediculosis pubis and pediculosis ciliaris is made through demonstration of lice or nits (louse eggs) (picture 1A-B). Examination with the naked eye may be sufficient, but lice can be difficult to see unless filled with blood from a recent meal. When the diagnosis is uncertain, the presence of nits can be confirmed with microscopic examination of hair shafts (picture 2). Alternatively, dermoscopic examination can confirm the presence of lice and nits in vivo [9,10].

DIFFERENTIAL DIAGNOSIS — Other disorders that affect pubic and axillary hair can be confused with pediculosis pubis. Examples include:

Trichomycosis axillaris – Trichomycosis axillaris is a superficial bacterial infection in which tan concretions composed of corynebacteria occur on hair shafts (picture 3). Corynebacteria are evident on Gram stain. (See "Trichomycosis (trichobacteriosis)".)

White piedra White piedra, a fungal infection of the hair shaft characterized by white or tan, adherent nodules, can be mistaken for nits (picture 4). Fungal hyphae can be seen on a potassium hydroxide (KOH) preparation. (See "Infections due to Trichosporon species and Blastoschizomyces capitatus (Saprochaete capitata)" and "Office-based dermatologic diagnostic procedures", section on 'Potassium hydroxide preparation'.)

Scabies – Scabies can present with pruritus and excoriations in the pubic area. However, scabies mites are not visible with the naked eye, and nits are absent (picture 5). (See "Scabies: Epidemiology, clinical features, and diagnosis".)

Conjunctival redness and/or crusting similar to pediculosis ciliaris can occur in other disorders. If careful examination for nits is not performed, pediculosis ciliaris may be mistaken for bacterial conjunctivitis, allergic contact dermatitis, or blepharitis associated with seborrheic dermatitis or rosacea [11].

ADDITIONAL EVALUATION — A thorough sexual history and screening for other sexually transmitted diseases is warranted in patients with pediculosis pubis [12,13]. In a series of 121 individuals with pediculosis pubis, for example, 31 percent had another sexually transmitted disease [12]. (See "Screening for sexually transmitted infections".)

Pediculosis pubis or pediculosis ciliaris in children may be a sign of sexual abuse, and the possibility of abuse should be investigated [1]. (See "Evaluation of sexual abuse in children and adolescents".)

MANAGEMENT

Pediculosis pubis — Topical pediculicides are the primary treatments for pediculosis pubis. In addition, nits should be removed with fingernails, a nit comb, or tweezers, if feasible. Shaving of hair in the affected area is not necessary.

Permethrin and pyrethrins — Topical permethrin or topical pyrethrins with piperonyl butoxide have neurotoxic effects on lice and are the preferred pediculicides for initial treatment [14,15]. Although other pediculicides can be effective, these agents are preferred based upon wide availability, safety, and relatively low cost compared with other therapies.

Administration — Patient-administered use of permethrin 1% cream rinse or pyrethrins 0.33% with piperonyl butoxide 4% involves the following steps:

Ensure the skin is cool and dry before application to minimize percutaneous absorption

Apply the pediculicide to all areas of suspected involvement (typically pubic and perianal areas, thighs, trunk, and axillae)

Wash off the pediculicide after 10 minutes

Remove nits with fingernails, a nit comb, or tweezers

Put on clean underwear and clothing following treatment

More than one application may be necessary to eradicate infestation. (See 'Retreatment' below.)

Retreatment — A second application is often needed. Although high cure rates following topical treatment with pyrethrins 0.3% with piperonyl butoxide 3% plus nit combing were reported in a small trial published in 1979 [16], a single application may not eradicate all infestations [17,18]. One small, unblinded, randomized trial that compared treatment with a single application of permethrin 1% with a single application of lindane 1% (both in combination with nit combing) found that 10 days following treatment, there was persistent infestation in 43 and 40 percent of subjects, respectively [17]. (See "Pediculosis capitis", section on 'Lindane toxicity'.)

Recommendations for follow-up after an initial treatment vary. The United States Centers for Disease Control and Prevention (CDC) recommends treating with a pediculicide plus nit combing, re-evaluating patients after 9 to 10 days, and retreating at that time if lice are seen [19]. In contrast, European guidelines recommend routinely retreating after 7 to 10 days [15].

We re-evaluate patients after 9 to 10 days prior to retreatment but instruct patients who will not be able to receive a follow-up clinical examination to proceed with a second treatment. Since the typical incubation period for louse eggs is six to eight days [1], at least one week should elapse prior to retreatment. We advise patients to reapply the drug after 9 to 10 days to kill any lice that have hatched from eggs that survived the initial treatment [17].

Alternative therapies — We typically restrict alternative therapies to infestations that persist despite adequate use of permethrin and/or pyrethrins and piperonyl butoxide. Alternatives for the eradication of pediculosis pubis include [14]:

Malathion lotionMalathion 0.5% lotion is applied to the affected areas and washed off after 8 to 12 hours. A single treatment is generally performed unless persistent lice are detected after treatment. The long application time, poor odor, and potential flammability of malathion make this therapy less preferable as an initial treatment. (See "Pediculosis capitis", section on 'Malathion'.)

Oral ivermectin Ivermectin is usually given as 200 mcg/kg, repeated after seven days [15]. Clinical studies examining the efficacy of oral ivermectin for the treatment of pediculosis pubis are not available. However, clinicians have reported success with this therapy in clinical practice [20]. Ivermectin should not be used in pregnant or lactating women; in addition, there are not adequate safety data for ivermectin in children weighing less than 15 kg [14,21].

Benzyl alcohol, spinosad, and topical ivermectin, effective and generally well-tolerated therapies for pediculosis capitis, have not been evaluated for the treatment of pediculosis pubis. Lindane is not recommended as a first-line treatment for pediculosis pubis because of the drug's adverse effect profile. (See "Pediculosis capitis", section on 'Lindane toxicity'.)

Pediculosis ciliaris — Treatment for pediculosis ciliaris must be modified to protect the eyes. Manual removal or application of topical ophthalmic-grade petrolatum, rather than topical pediculicide application, is the preferred first-line treatment.

Manual removal or petrolatum ointment — Manual removal involves removal of lice and nits with a nit comb or fingernails. If additional treatment is necessary, ophthalmic-grade petrolatum ointment can be applied to the eyelid margins two to four times per day for 10 days [19]. Petrolatum ointment therapy is favored for the treatment of children [22].

Alternative therapies — Medications are primarily reserved for patients for whom manual removal cannot be performed effectively. Data are limited to case series, and there are no studies comparing the efficacy of different treatments for pediculosis ciliaris:

Oral therapy – Oral ivermectin (two doses of 200 mcg/kg by mouth given one week apart) has appeared effective in case reports [21,23]. Ivermectin should not be used in pregnant or lactating women; in addition, there are not adequate safety data for ivermectin in children weighing less than 15 kg [14,21].

Topical therapy – Topical treatments have been reported as successful in small numbers of patients. These include pilocarpine gel [11,24], fluorescein 20% drops [25], yellow mercuric oxide ointment [26], permethrin 1% cream rinse [27], lindane 1% lotion [28,29], and malathion 1% shampoo [30]. The potential for irritation or ocular damage should be considered before employing any of these therapies [11,28,31,32]. Eyes are kept closed during application of pediculicides.

Eyelash removal – Removal of the eyelashes is an infrequently employed alternative therapy [33,34].

Close contacts — Sexual partners (current and dating back to three months prior to the onset of symptoms) should be examined for infestation [15,35]. Patients should be encouraged to notify partners of this recommendation. Infested sexual partners should be treated. Individuals who are infested should abstain from sexual contact until they are re-examined to rule out persistent infestation [36]. Nonsexual household contacts do not need to be treated if they have no signs of infestation.

Environment — Bedding and clothing used by the infested person within the preceding two to three days should be machine washed in hot water and dried in a hot dryer [14,37]. Temperatures should reach at least 130°F. Dry cleaning is also effective.

If clothing or bedding cannot be washed or dry cleaned, placing it in a sealed plastic bag is an option. Crawling lice die within 48 hours after removal from the host; items that cannot be cleaned should be bagged or removed from body contact for at least 72 hours [14]. Bagging items for two weeks may eliminate the possibility of reinfestation from newly hatched lice [11]. Fumigation of living areas is not indicated [14].

Follow-up — Patients should be examined after treatment to confirm eradication of live lice. Persistent live lice after a second treatment with permethrin or pyrethrins and piperonyl butoxide may result from a failure to eradicate all viable lice and eggs or from re-exposure to P. pubis.

In the event of treatment failure, proper adherence to the treatment instructions should be confirmed and the possibility of re-exposure examined. Drug resistance does not appear to be a major factor in treatment failure. In contrast to pediculosis capitis, reports of resistance of P. pubis to pediculicides are almost nonexistent [38].

If treatment of pediculosis pubis with permethrin and/or pyrethrins with piperonyl butoxide was performed appropriately and re-exposure has not occurred, it is appropriate to proceed with an alternative therapy. (See 'Alternative therapies' above.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Pediculosis".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

Basics topics (see "Patient education: Lice (The Basics)")

Beyond the Basics topics (see "Patient education: Head lice (Beyond the Basics)" and "Patient education: Pubic lice (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

Overview – Pediculosis pubis (phthiriasis pubis) is a primarily sexually transmitted infestation. Phthirus pubis, the crab louse, is the causative organism (picture 1A, 1D). (See 'Phthirus pubis' above.)

Infestation of the eyelashes (pediculosis ciliaris, phthiriasis palpebrarum) may occur in individuals with pediculosis pubis or in children who are in close contact with individuals who are infested. (See 'Transmission' above.)

Clinical manifestations:

Pediculosis pubis – Pediculosis pubis typically involves the pubic and perianal areas but may also involve the axilla or other hair-bearing body areas (picture 1A-B). Pruritus in the affected areas is the primary symptom. (See 'Clinical manifestations' above.)

Pediculosis ciliaris – In pediculosis ciliaris, reddish crusting and matting of the lashes, associated conjunctivitis, and symptoms of eye irritation and pruritus are common clinical findings (picture 1C). (See 'Clinical manifestations' above.)

Diagnosis – The diagnosis of pediculosis pubis or pediculosis ciliaris is made through the visual identification of lice and nits (picture 1A-C). Individuals with pediculosis pubis should be screened for other sexually transmitted diseases. Although the majority of children with pediculosis ciliaris acquire the infestation via nonsexual contact, the possibility of sexual abuse should be considered. (See 'Diagnosis' above and 'Additional evaluation' above and "Evaluation of sexual abuse in children and adolescents".)

Management:

Pediculosis pubis – Pediculosis pubis is treated with topical pediculicides. Based upon safety and ease of use, we suggest treatment with topical permethrin 1% or a product containing pyrethrins with piperonyl butoxide (Grade 2C). Treatment should be repeated after 9 to 10 days if lice remain. (See 'Pediculosis pubis' above.)

Sexual partners of individuals with pediculosis pubis should be treated simultaneously. Bedding and clothing should be laundered in hot water. (See 'Close contacts' above and 'Environment' above.)

Pediculosis ciliaris – Manual removal or application of ophthalmic-grade petrolatum ointment is the preferred initial treatment for pediculosis ciliaris. We suggest treatment with manual removal or ophthalmic-grade petrolatum ointment due to the relative safety of these therapies (Grade 2C). (See 'Pediculosis ciliaris' above.)

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References

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