The crab louse (Latin Phthirus pubis) is a parasite that prefers to settle in the pubic hair area of humans. The infestation by crabs is medically also called pediculosis pubis. The parasite is about 1.0-1.5 mm long and has a broad, grey body.
Therefore it is visible to the naked eye. At the end of its legs, the crab louse has hook-like claws with which it anchors itself in the human hair. Overall, in contrast to head lice, crab lice move very little.
Crab lice occur worldwide. They are usually transmitted from one person to another through close physical contact, such as during sexual intercourse. For this reason, felt lice infestation belongs to the sexually transmitted diseases.
Transmission through shared towels or bed linen is also possible. The crab louse is strongly imprinted on humans and needs them to survive. Preferably it settles in the pubic hair, more rarely also on the inside of the thighs, if there is enough hair.
More rarely, the crabs are found in the armpit or beard hairs, even more rarely on the eye hairs (eyelashes, eyebrows). In contrast to the head louse, the crab louse does not nest in the head hair. After settling in the human pubic hair, the crab louse feeds on human blood.
It also secretes a sticky secretion with which it anchors its eggs to the roots of the pubic hair. When the crab louse is removed from the human body, it can survive for a maximum of 24 hours. The adult female crab louse lays about two to three eggs per day.
These are also called nits. The female uses a special secretion to attach them to the hair roots of the human body. After one week, the larvae hatch, which are already fully grown after another two to three weeks.
In the course of its entire life, a female felt louse can lay up to 200 eggs. Crabs can sting. The stinging site often reacts with severe itching and a blue discoloration (so-called “Taches bleues”; French for “bruises”), which the affected person notices.
In addition, the crabs are usually already visible with the naked eye or a magnifying glass. The excrements of the parasites can be seen as small rust-colored spots in underwear. Other symptoms do not usually occur.
The symptoms usually set in three to six days after infection. Crabs play no role as disease carriers. Infestation with crabs in itself does not pose a direct health risk.
However, over time the itching leads to scratched skin areas, which in turn can be entry points for other pathogens. Thus, in the case of an attack by aphids, the risk of infection with infectious diseases, especially sexually transmitted diseases, is indirectly increased. The diagnosis of an athlete’s foot can usually be made very easily by a doctor based on the typical symptoms.
At the latest when examining the pubic area with a magnifying glass, the small parasites become noticeable. The crabs can usually be easily eliminated by various measures. On the one hand, a complete shave of the affected body part including removal of eggs, nits and adult crabs is recommended, as well as treatment with chemical preparations.
Active substances used against crabs are for example lindane and malathion, as well as pyrethrum preparations, fluorescein, physostigmine, petroleum jelly, yellow mercury oxide ointment and pilogel. After the treatment, nits can be combed out of the hair with a special nits comb. A complete shave is not absolutely necessary, but it works prophylactically against a renewed infestation.
The entire therapy should be repeated after eight to ten days to remove mature crabs as well. Accompanying the therapy it is important to follow certain rules to prevent a new infection with crabs. Underwear and other clothing that comes into contact with the affected body area must be changed daily and washed hot (at least at 60 degrees).
The same applies to bed linen and towels. These should also not be shared with other people, so that the crabs do not spread further. Clothes that cannot be washed at 60 degrees should be kept tightly closed in plastic bags for about two weeks, so that the crabs and their offspring die.In addition, sexual contact with other people should be avoided during the treatment phase, as otherwise they may become infected.
Persons who live in the direct vicinity of the affected person should also be treated. Crabs can be eliminated very easily. With the mentioned therapy options the infestation can be removed within a short time. Overall, the infestation with crabs has become much rarer in western countries. Scientists attribute this to the increasingly frequent intimate shaving, which makes it impossible for the parasites to settle on the human body.
