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Crab Lice Symptoms And Diagnosis

April 4th, 2016

Crab Lice Symptoms And Diagnosis

Crab Lice Symptoms And Diagnosis

As the name indicates, pubic lice are parasites living in the genital area of males and females, particularly under the pubic hairs. These tiny insects are more commonly reported in individuals with sexually transmitted infections. As compared to head and body lice, pubic lice are smaller in size. Rarely crab lice may infest eyelashes, armpit hairs, leg hair and facial hairs (such as mustache, beard) as well to cause a variety of infections.

Pubic lice infestation is also referred to as crabs due to crab like appearance of lice. When viewed under a strong magnifying glass, the parasite has six legs; with two rather larger claw-shaped front legs (hence the nick name, crabs). The adult female lice lay eggs and is comparatively larger than a male lice. It is imperative to mention that crab lice is not transmitted or carried by animals.

According to a new study reported in the peer reviewed journal Sexually Transmitted Diseases (2), the incidence of pubic lice in general population is 1.3% to 4.6%.

Crab Lice Infestation And Mode Of Spread

Crab lice infestation is usually a result of sexual contact with a person who is already infested with public lice. Other than getting intimate with the affected person, the pubic lice may also spread via sharing personal articles such as blanket, towels or clothes; though evidence is rather sparse. Children can also get crab lice infestation by sleeping on the bed of an affected person. In order to live, the adult lice must feed onto human blood. If the louse falls off the human skin, it usually dies within a period of 1-2 days. In addition, pubic lice infestation in children can also be an indication of a child being sexually abused. In children pubic lice are usually found in eyebrows and eyelashes.

Crab lice lays eggs under the hair, nearer to the skin. These eggs are known as nits. After seven to ten days, eggs hatch into nymphs which starts feeding on the human blood immediately and grows to adult form within 2-3 weeks to continue the reproductive cycle. Since louse are unable to fly or crawl over non-bodily surfaces, close physical contact is generally the most frequent mode of transmission (3).

Signs And Symptoms Of Crab LiceMaintaining Genital Hygiene Image

The most prominent symptom of crab lice infestation is itching all over the pubic region and/or anus which may get intense at night. The itching usually starts after five days of infestation. Excessive itching can lead to wounds and infections as a result of scratching. You may also see visible lice crawling on your skin or eggs (also known as nit) attached to the hair. Other symptoms include:

  • Low grade fever
  • Appearance of pale blue spots near the area where lice has bitten
  • Irritability
  • Sluggishness

If you suspect pubic lice infestation but not sure about it, refer to your primary care provider.

According to a case study reported in the New England Journal of Medicine (1), the clinical presentation in a 6-year old child is specific for erythema (or redness of eyelids) as well as itching that was initially mistaken for allergic conjunctivitis or atopic dermatitis. With proper treatment, absolute resolution of infection is possible.

How To Differentiate Crab Lice From Other Varieties Of Lice?

Crab lice can be differentiated from body lice or head lice on following grounds:

  • The movement of crab lice is generally slow as compared to the other two varieties.
  • Generally, people with crab lice have other sexually transmitted infections as well and usually have a risky lifestyle.

How To Diagnose Pubic Lice

The diagnosis of pubic lice is usually clinical. Affected individuals usually suspect crabs by carefully examining the pubic hair through magnifying glass under bright light. Lice are pale gray in color but they darken after sucking human blood. The eggs are quite tiny and white in color and are usually located around the roots of pubic hair.

So if you see tiny crab shaped insects moving through pubic hair, immediately seek medical help.


1. Micali, G., & Lacarrubba, F. (2015). Phthiriasis Palpebrarum in a Child. New England Journal of Medicine, 373(27), e35.

2. Dholakia, S., Buckler, J., Jeans, J. P., Pillai, A., Eagles, N., & Dholakia, S. (2014). Pubic lice: an endangered species?. Sexually transmitted diseases, 41(6), 388-391.

3. Bonilla, D. L., Durden, L. A., Eremeeva, M. E., & Dasch, G. A. (2013). Pediculus Infestations and Louse-borne Diseases: Challenges in Diagnosis, Treatment, Prevention, and Control. PLOS Pathogens, 9(11).

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