It's one of the most common infections in tropical zones like Southeast Asia and affects people of all age and particularly children, yet soil-transmitted worm infections - soil-transmitted helminth infections as they are called in medical terms - are surprisingly cheap and easy to cure and prevent.
The result mainly of poor sanitation, poverty and low awareness, these infections, if left untreated, can seriously impact child development.
These diseases are part of the so-called Neglected Tropical Diseases (NGT), a group of 17 infections prevalent in the world' tropical areas that get much less attention from health authorities than Aids, malaria and tuberculosis.
The 3 main soil-transmitted illnesses are caused by intestinal roundworms. Ascariasis is caused by Ascaris lumbricoides, a 15cm-long-worm, trichuriasis, which comes from 4cm whipworm (Trichuris trichiura) and hookworms (Ancylostoma duodenale and Necator americanus) that are even smaller at 0.5 to 1cm. These parasites are well adapted to their human host and usually produce symptoms only when the infection is massive.
Although the lifecycle of these parasites varies depending on the species, all adult worms live in the intestine for several years and release thousands of eggs daily through the faeces into the environment. Healthy people become infected when they absorb food or water that has been contaminated by these eggs as a result of unhygienic practices or inappropriate food preparation. Eggs of hookworms also hatch in humid soil releasing larvae that can penetrate the skin when walking barefoot. The larva then travels through the bloodstream to different organs and ends up in the gastro-intestinal tract.
Ascaris and whipworm feed on absorbed nutrients while hookworms are blood-sucking worms that cling to the inner lining of the intestine. The parasites compete with the host for essential nutrients such as iron and some vitamins and produce inflammation of the intestinal mucosa leading to malabsorption of food. Prolonged hookworm infection can lead to a significant loss of blood or anaemia.
As symptoms tend to be mild or non-existent, the majority of soil-transmitted worm infections go undetected. When the contamination is severe and/or repeated, victims may suffer from diarrhoea with possible bloody stools, faecal incontinence during sleep, abdominal pain or discomfort, loss of appetite and fatigue. Sometimes ascaris worms can be expelled through vomiting or passing stools. Children are at higher risk of chronic parasitic infection and may progressively develop malnutrition, become more sensitive to other infectious illnesses and suffer from impaired physical and intellectual development. Although rare, complications can be serious and include intestinal occlusion, inflammation of gallbladder or the pancreas (ascaris) or the damaging consequences of anaemia (hookworm).
Diagnosis is confirmed by stool tests that reveals the presence of eggs in the faeces.
In practice, three successive stool exams are needed before concluding of the absence of infection.
Treatment with oral anti-worm medications, referred as anti-helminthics, is simple, highly effective and inexpensive. The main agents used are Albendazole and Mebendazole. They are given when diagnosis is confirmed by the stool exam or more often in a systematic deworming approach where they are suspicious symptoms or as a general health preventive policy among children at risk.
Prevention relies on providing clean water and improving sanitation in underprivileged settlements, increasing awareness and education on worm-transmitted infections and in promoting proper hygiene.
When travelling in endemic areas, use only bottled water, always wash your hands before handling food and carefully clean fruits and vegetables if eaten raw.
You should also exert caution when buying food at local street food stalls and never let children walk barefoot on humid soil where hookworm infection is obviously common.
Dr Gerard Lalande is managing director of CEO-Health, which provides medical referrals for expatriates and customised executive medical check-ups in Thailand. He can be contacted at firstname.lastname@example.org