Crab Lice
Order: Phthiraptera
Species:
Pthirus pubis - Crab Lice
Size
Young crab lice are very small approximately the size of a grain of sand. Adults are approximately 2 mm long.
Colour
Crab lice are virtually colourless, except for their claws which are darker.
Description
The crab louse is a very small square insect with six legs, the middle and hind legs have very well developed claws for grasping onto the hair.
Habitat
P. pubis is found in coarse body hair, not just pubic hair as the scientific name suggests. They can be found in underarm hair, leg hair, beards, moustaches, chest hair, eyelashes and even eyebrows.
Crab lice are host specific living ONLY on humans; they cannot live on pets, or any other animal.
Transmission
These insects are spread by skin to skin contact often, but not necessarily, sexual. By the time the infection is discovered it is usually several weeks old and may already have been passed on to other friends and family members.
Crab lice are incapable of living away from the host as they are parasites and will never willingly leave their host except for another of the same species. They are blood feeders and rely on the host for their blood meal in order to survive.
They are young crab lice are relatively inactive and will settle down and remain in one place until disturbed. They grasp onto the hair with their claws which have been specially adapted for such a purpose. They bite and feed intermittently in the same spot, often causing Maculae cerulae : blue spots.
Diagnosis
A positive diagnosis for the presence of crab lice is made by finding a living louse. They are difficult to find and often the first indication that crab lice are present is an intense itching. Often the best way to check for crab lice is to ask someone else to look for signs of the lice. A sexual partner, family member or friend can do the checking.
Treatment
The most effective treatments for crab lice available over the pharmacy counter include:
Derbac M and Quellada M both containing Malathion as the active ingredient, and Lyclear Dermal Cream which contains Permethrin 5%. Other products are licensed for use against crab lice, but they are alcoholic and should be used with extreme caution.
The aqueous liquid Carylderm can be used against Crab lice, but is not licensed for this application and only available on prescription. Full Marks Liquid can also be used, but it is not licensed for this purpose either. However, it is available over the counter in the pharmacy and does not require a prescription.
These products should be applied with care and should not be used on skin which is broken, sore and excoriated.
Treatment should be applied over the whole body, not just to the pubic area and should include the head hair. It is recommended that there should be a second treatment 7 days later, this is important to kill any newly emerged crab lice from any eggs which may not have been killed with the first treatment.
All treatments should be left on for the recommended treatment time as per the manufacturer's instructions.
Treatment should not be made on a 'just in case' basis as this can lead to resistance, and to skin problems through the over use of a product.
The potential to infect other people whether they are sexual partners or a close family member is high.
