Infestation

Infestation means the presence of a living parasite either on the body (such as head lice), or within the body (such as scabies in the skin or tapeworms in the gut). Skin infestations most commonly occur with scabies, caused by the mite sarcoptes scabei. The pregnant female burrows into the skin, laying eggs as she goes, usually between the fingers, on the feet, or on the genitals. The body mounts an allergic reaction and the response is the formation of red papules which are itchy, particularly at night. Cross-infection between close contacts is common. There may be an associated allergic rash affecting the inside of the thighs, the abdomen and the armpits. Unless there is a very severe infestation (called Norwegian scabies) the rash does not extend above the neck. There are a number of treatments which need to be applied to the whole body (except the head and neck). Antihistamines may help to reduce the itch. In order to prevent re-infestations all members of a household should be treated, and all bedding laundered.

Lice are parasites that live on blood, which they suck through piercing mouthparts. There are three different lice which infest humans: the head louse which affect the scalp, causing itching. The female lays eggs attached to hairs, and the empty egg has a white shell, commonly known as a nit, which can be seen attached to the base of the hair. Spread is by head to head contact, which is why this is common in children. Head lice are no respecters of social class, and seem to prefer clean hair, so that to regard this as a disease of the poor and dirty is wide of the mark. There are treatments available using shampoos, but resistance is growing to the commonly used agents - assiduous use of a fine-tooth comb through wet hair may be as effective. The body louse actually lives in the clothes and only visits the body to feed, where its bites produce intense itching; the resulting scratches often become infected - this is a disease of the socially deprived. The lice themselves may be infected by germs called rickettsia which cause typhus and relapsing fever.

Pubic lice, also known as crab lice, prefer living in the coarser hair of the pubic region, where they spend their time clinging to the shaft of the hair and taking the occasional feed, which causes itching at night. This is a disease of the sexually active.

Fleas and ticks, normally resident on animals, are happy to feed on humans where their bites cause itchy raised papules which may become secondary infected. A number may transmit other diseases such as a Lyme disease or Rocky Mountain spotted fever. While those carried by domestic animals are usually responsible only for the bites that they inflict, these can be a source of considerable distress. Domestic animals should be de-flead.
 
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