Diseases caused by parasitic roundworms that are widespread in tropical regions
Parasitic worms that infest humans are most common in tropical and subtropical regions. Both poor sanitation and poor personal hygiene contribute to the spread of parasites among people, especially children. In the UK, tropical worm infestations are very rare and usually occur only in people who have visited or lived in the tropics.
There are four main types of roundworm infestation that normally affect only people in tropical and subtropical regions, such as Central and South America, Africa, and Southeast Asia.
This disease is caused by a tiny worm called Trichinella spiralis. People usually become infested by eating undercooked pork containing cysts (larval stages of the worm). In severe cases, symptoms may include vomiting, diarrhoea, abdominal and muscle pains, and fever. In some cases, trichinosis can cause acute heart failure or an illness similar to meningitis.
The minute worm Strongyloides stercoralis causes this condition. Infestation is usually a result of walking barefoot on soil contaminated with larvae. If severe, infestation may result in abdominal pain and diarrhoea between periods of constipation and weight loss. Infestations may be present for years without causing symptoms, but symptoms will appear if immunity becomes reduced due to conditions such as HIV infection (see HIV infection and AIDS).
Various types of worm or their larvae cause filariasis. The parasites are transmitted to people by certain bloodsucking insects. Different parts of the body are affected, depending on the type of worm. A severe infestation with some types may lead to a massive, painful, disfiguring swelling in the limbs or in the scrotum known as elephantiasis. Infestation with a type of worm known as Onchocerca volvulus sometimes results in blindness.
This infestation is due to Trichuris trichuria, also known as whipworm, and it is most common in children. People become infested when they ingest worm eggs. Adult worms live in the intestines, and a severe case of trichuriasis may cause bloody diarrhoea, abdominal pain, and weight loss.
The diagnosis depends on the type of worm but is usually confirmed when eggs, larvae, or adult worms are found in a sample of faeces, blood, or tissue. Treatment also varies with the infestation, but anthelmintic drugs are commonly prescribed. Most people make a full recovery if treated early, but reinfection is common in tropical countries. Preventive measures include not walking barefoot on soil, not eating undercooked meat or other foods that may be contaminated, and using insect repellents and mosquito nets.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.