Despite generally improved standards of cleanliness, the problem of head lice is becoming commoner in England once again. Head lice are small wingless insects, 1mm to 3mm long, whose eggs, called nits, are glued on the hairs. Lice live on the scalp, from which they suck blood. They are easily passed from child to child, especially in school where children work and play together. They cause itching and scratching and so may lead to secondary infection. You can remove them by applying a proprietary insecticide and by combing out the nits with a fine metal comb.

The same louse, Pediculus humanus, can also infect hair elsewhere on the body. Another insect, the crab louse Phthrisus pubis, lives in the pubic hair. Crab lice also cause itching, with scratch marks susceptible to secondary infection. The hair of the armpits and eyebrows may become involved if infestation is severe. The body is washed in a special solution for three consecutive days to kill the lice and their eggs. Bed bugs are parasites which live where there is a dirty environment, particularly in the crevices of old walls, bedsteads and floors. They emerge at night and suck blood of humans, causing irritation and restlessness and leaving a small red bite. Some people are more susceptible to flea bites than others. Animal fleas sometimes infest human beings and, like other parasites, they live by sucking blood. They can be destroyed by ordinary cleanliness and the use of insecticides.

Threadworm or pinworm infestation is probably the most common intestinal worm, especially in young children. Infestation, known medically as ascariasis, occurs by eating raw vegetables or other foodstuffs handled by an infected person whose unwashed hands or fingernails retain the eggs. The worms inhabit the lower part of the gut and appear like fine white threads in faeces. Female worms lay their eggs around the anus and buttocks and cause intense irritation, sleeplessness and, in some cases, convulsions. After medical treatment with a drug such as piperazine extreme cleanliness must be maintained to prevent re-infestation. Threadworms and pinworms are examples of nema- todes, or roundworms. Other types include hook-worms, which cause an infestation known medically as ankylostomiasis. Its symptoms include a rash, cough and sometimes abdominal pain and anaemia because of blood loss. Whipworms, causing trichuriasis, also live in the intestine, but seldom produce symptoms. Tapeworms are segmented cestode worms, usually contracted by eating undercooked meat, particularly pork, beef or fish. They reveal their presence when segments break off and are passed in the faeces. Drug treatment is usually effective. Disorders caused by infestation wit parasitic flukes are rare outside tropical countries. Two common ones are Schsistosoma, found in impure water and the cause of schistosomiasis or bilharzia, and the lung fluke Paragonimus, which occurs in undercooked crab meat and causes paragonimiasis. Most types of parasitic worm infestation can be avoided by making sure that all food, particularly meat and fish, is thoroughly cooked before eating.

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