Ectoparasitic infections are those that are caused by parasites that live on the skin’s sur­face. The two ectoparasitic infections that are sexually transmitted are pubic lice and scabies.

Pubic Lice

Pubic lice (or “crabs”) are a parasitic STI; the lice are very small, wingless insects that can attach themselves to pubic hair with their claws. They feed off the tiny blood ves­sels just beneath the skin and are often difficult to detect on light-skinned people. Under closer observation, it is possible to see the movement of their legs. They may also attach themselves to other hairy parts of the body, although they tend to prefer pubic hair. When not attached to the human body, pubic lice cannot survive more than 24 hours. However, they reproduce rapidly, and the female cements her eggs to the sides of pubic hair. The eggs hatch in 7 to 9 days, and the newly hatched nits (baby pubic lice) repro­duce within 17 days.

Ectoparasitic Infections: Pubic Lice and ScabiesIncidence Pubic lice are common and regularly seen by health clinics and various healthcare providers. Although there are no mandated reporting laws, pubic lice affect millions of people worldwide.

Symptoms The most common symptom is a mild to unbearable itching, which of­ten increases during the evening hours. This itching is thought to be a result of an al­lergic reaction to the saliva that the lice secrete during their feeding. People who are not allergic to this saliva may not experience any itching.

Diagnosis The itching usually forces a person to seek treatment, though some peo­ple detect the lice visually first. Diagnosis is usually made fairly quickly because the pu­bic lice and eggs can be seen with the naked eye.

Treatment To treat pubic lice, it is necessary to kill both the insects and their eggs. In addition, the eggs must be destroyed on sheets and clothing. Healthcare providers can prescribe Kwell ointment, which comes in a shampoo or cream. The cream must be applied directly to the pubic hair and left on for approximately 12 hours, whereas the shampoo can be applied and directly rinsed off. There are also some fairly effective over-the-counter products that can be purchased in drugstores; however, these products are usually not as effective as Kwell. Sheets and all articles of clothing should be either dry cleaned, boiled, or machine washed in very hot water. As with the other STIs, it is important to tell all sexual partners to be checked for lice because they are highly contagious.

Question: Can crabs be spread through casual contact, such as sleeping on the same sheets or sharing clothes? What if someone with crabs sat on my couch and I sat down right after them?

If you slept in the bed of a person who was infected with pubic lice, or wore the same clothes without washing them, there is a chance that you could become infected. Although crabs are usually spread through sexual contact, it is possible to acquire them if you share towels, linens, articles of clothing, combs and brushes, or toilet seats with a person who is infected. They can also be transferred while sharing a bed, even if there is no sexual contact.