Humans serve as the host for Phthirus pubis, which is mainly transmitted by sexual contact.  Phthirus pubis is found in coarse hairs, most commonly in pubic hair, but infestation frequently extends to hair around the anus as well as hair on the abdomen and thighs.  It may also be found occasionally on the eyelashes of children.  Phthirus pubis dispersal is linked to hair density.  Crab louse is most commonly found it the pubic hair because the spacing between the hairs matches the hind leg span of the crab louse.  The four hind legs are used for locomotion by attaching to two hairs.  Crab lice are dioecious, meaning there are two separate male and female lice, and reproduce sexually.  One to two days after mating the female begins laying three eggs a day.  On average, the female will lay 26 eggs total.  Once the eggs are laid, they attach to the base of a single hair.  Phthirus pubis eggs appear dark opaque brown with a hard chitin covering.  There is a seven to eight day incubation period after which the larva emerges.  Over the next thirteen to seventeen days, the larva sheds its skin three times before becoming an adult.  The adult crab louse has a lifespan of about a month.  The adult crab louse also appears dark grey to brown in color and moves a relatively small amount (Fisher and Morton 1970).

©Michael Patrick Corriss


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