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Pubic Lice Infestation (Crabs)

What is Pubic lice infestation?

Pubic lice infestation, commonly known as “crabs,” is a parasitic infection caused by the tiny ectoparasite Pthirus pubis. These insects live on coarse hair—most often in the pubic region—but they can also colonize other body hair such as the chest, armpits, eyebrows, eyelashes, and even facial hair in men. The lice feed on small amounts of blood several times a day, which can lead to itching, inflammation, and secondary skin infections.

Unlike head lice (Pediculus humanus capitis) or body lice (Pediculus humanus corporis), pubic lice are shorter (about 1–2 mm) and have a crab‑like shape, giving the condition its popular nickname. Transmission occurs primarily through close, personal contact, most often sexual contact, but it can also be spread by sharing bedding, towels, or clothing that have recently been in contact with an infested person.

Common Causes

Pubic lice do not arise from a single “cause” in the same way a disease does; rather, they are the result of exposure to infested individuals or contaminated items. The following factors increase the risk of acquiring pubic lice:

• Sexual contact with an infected partner (the most common route).
• Sharing personal items such as towels, sheets, or clothing that have not been washed.
• Close skin‑to‑skin contact during activities like wrestling or communal bathing.
• Living in crowded conditions where personal hygiene is difficult (e.g., shelters, dormitories).
• Recent travel to regions with higher prevalence of pubic lice.
• Having other sexually transmitted infections (STIs), which can indicate higher-risk sexual behavior.
• Use of public laundry facilities without proper heat drying.
• Infestation in close family members, especially in children who may share bedding.
• Contact with infested animals – extremely rare, but possible if pets have acquired lice from humans.
• Immunocompromised state – can make secondary skin infections more likely after scratching.

Associated Symptoms

Many people with pubic lice notice symptoms within a few days to two weeks after exposure. Common manifestations include:

• Intense itching (pruritus) in the affected area, especially after heat or sweating.
• Visible lice or nits (eggs) attached to the base of hair shafts. Nits appear as tiny, white or yellowish specks.
• Small red or bluish papules where lice have bitten, sometimes forming a rash.
• Secondary bacterial infection due to scratching, presenting as crusted sores, pus, or cellulitis.
• Swollen lymph nodes in the groin (inguinal lymphadenopathy) if irritation is severe.
• Discomfort during sexual activity because of irritation.
• Rarely, eyelid involvement (phthiriasis palpebrarum) when lice spread to eyelashes, causing itching, redness, and crusting.

When to See a Doctor

While over‑the‑counter (OTC) treatments are often effective, professional evaluation is recommended when any of the following occur:

• Symptoms persist longer than two weeks despite attempted self‑treatment.
• You experience intense pain, swelling, or drainage that suggests a secondary infection.
• There is involvement of the eyes, ears, or nasal passages.
• You are pregnant, breastfeeding, or have a known allergy to common pediculicides.
• Multiple household members or sexual partners develop the infestation simultaneously.
• You have an existing skin condition (e.g., eczema, psoriasis) that could worsen with scratching.
• You are unsure whether you are dealing with pubic lice versus another rash or parasite.

Prompt medical attention can prevent complications and reduce the risk of spreading the infestation to others.

Diagnosis

Diagnosis of pubic lice is primarily clinical, performed by a healthcare professional during a physical exam.

1. Visual Inspection

The clinician uses a magnifying glass or dermatoscope to look for live lice and nits attached to hair shafts. Lice are brown‑gray, crab‑shaped, and move quickly when the skin is brushed.

2. Microscopic Confirmation (if needed)

If the diagnosis is uncertain, a small sample of hair and skin scrapings may be placed on a slide and examined under a microscope to differentiate pubic lice from other arthropods.

3. Assessment for Co‑existing STIs

Because pubic lice are sexually transmitted, clinicians often recommend screening for other STIs (e.g., chlamydia, gonorrhea, syphilis, HIV) through urine tests or swabs.

4. Evaluation for Secondary Infection

Signs of bacterial infection (erythema, warmth, purulent discharge) may prompt a swab for culture and the prescription of antibiotics.

Treatment Options

Effective treatment requires killing both the adult lice and their eggs while minimizing irritation.

Medical (Prescription) Treatments

• Permethrin 1% cream – applied to the affected area for 10 minutes, then washed off. Permethrin is the most widely used first‑line agent (CDC, 2022).
  Note: Repeat application after 7–10 days to eliminate newly hatched lice.
• Pyrethrins with piperonyl butoxide – a combination sold OTC and by prescription; works similarly to permethrin.
• Malathion 0.5% lotion – used when resistance to pyrethrins is suspected. Apply for 8–12 hours, then wash off.
• Ivermectin 1% cream – a newer option useful for patients with topical treatment intolerance.
• Oral ivermectin (200 µg/kg single dose) – reserved for refractory cases or extensive infestation; evidence from the WHO indicates high efficacy.

Home‑Based or Over‑the‑Counter (OTC) Remedies

• OTC lice shampoos containing 1% permethrin or 0.5% malathion.
• Wet‑combing with a fine-toothed lice comb after applying a conditioner to loosen nits; repeat every 2–3 days for two weeks.
• Heat treatment – washing infested clothing, bedding, and towels in hot water (≥ 130 °F / 54 °C) and drying on high heat for at least 20 minutes.
• Sealing non‑washable items (e.g., shoes, stuffed animals) in a plastic bag for 2 weeks, as lice cannot survive more than 48 hours off a host.

Managing Secondary Infection

If the skin is broken or infected, a short course of a topical antibiotic (e.g., mupirocin) or oral antibiotics (e.g., cephalexin) may be prescribed.

Partner and Household Treatment

All sexual partners and anyone who shared bedding or clothing should receive simultaneous treatment to prevent reinfestation.

Prevention Tips

While 100% prevention is impossible, the following strategies markedly lower risk:

• Practice safe sex – use condoms or dental dams, especially with new partners.
• Avoid sharing personal items such as towels, robes, or underwear.
• Wash clothes and bedding in hot water and dry on high heat after potential exposure.
• Regular self‑examination if you have multiple partners; early detection prevents spread.
• Prompt treatment of partners when an infestation is diagnosed.
• Maintain good personal hygiene – regular bathing does not prevent lice but can make detection easier.
• Educate peers about the signs and transmission routes, particularly in communal living settings.
• Use protective barrier methods during sexual activity when a partner's infestation status is unknown.

Emergency Warning Signs

If any of the following occur, seek immediate medical care (e.g., urgent care clinic, emergency department):

• Rapidly spreading redness, swelling, or warmth suggesting cellulitis.
• Fever (temperature ≥ 38 °C / 100.4 °F) with a rash.
• Pus or foul‑smelling discharge from scratched lesions.
• Severe pain or difficulty urinating due to swelling.
• Signs of an allergic reaction to a prescribed pediculicide (e.g., hives, difficulty breathing, facial swelling).
• Eye involvement with intense pain, vision changes, or discharge (possible phthiriasis palpebrarum).

Key Takeaways

Pubic lice infestation is a common, treatable condition that signals close personal contact. Accurate identification, prompt treatment of the patient and all close contacts, and attention to hygiene can eradicate the parasites and prevent complications. When symptoms are severe, atypical, or accompanied by signs of infection, professional medical evaluation is essential.

Sources: CDC. “Pediculosis Pubis.” 2022; Mayo Clinic. “Pubic lice (crabs).” 2023; WHO. “Guidelines for the Treatment of Lice Infestations.” 2021; Cleveland Clinic. “How to Get Rid of Pubic Lice.” 2022; NIH National Library of Medicine – PubMed articles on permethrin resistance (2020‑2023).

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