Nematodes (roundworms) have elongated, bilaterally long cylindrical bodies which contain an intestinal system and a large body cavity. Parasitic nematodes vary in length from several millimetres to approximately 2 metres and have larval stages and adult worms of both sexes. Approximately 60 species of roundworms are parasites of humans.
Some nematode infections can be transmitted directly from person to person but, in others, the nematode eggs must mature outside the host. The parasites may spend a part of their life cycle in the soil before becoming infective to humans. Nematodes commonly parasitic on humans include (click links for separate articles which provide more detail):
- Ascaris Lumbricoides.
- Hookworm Infections.
- Guinea Worm Disease (Dracunculiasis).
- Filariasis, which is caused by thread-like filarial nematodes (roundworms) in the family Filarioidea (also known as 'filariae'). There are eight known filarial nematodes which use humans as the host. These are divided into three groups:
- Trichuriasis (Whipworm).
Cutaneous larva migrans is caused by skin penetration and subsequent migration of larvae of various nematode parasites.
- A report by the World Health Organization (WHO) in 2005 stated that approximately 0.807-1.221 billion humans have ascariasis, 604-795 million have trichuriasis, and 576-740 million have hookworm infections worldwide.
- The bowel of a child living in poverty in a developing country is likely to be parasitised with at least one nematode and, in many cases, multiple infection (eg, whipworms, ascaris, and hookworms), with resultant impairments in physical, intellectual, and cognitive development.[1, 3]
- The prevalence of nematode infections throughout the world is generally increasing but varies according to levels of poverty, natural disasters and human conflicts. The spread of infection is also increasing in line with increased travel and mobility (eg, angiostrongyliasis and anisakiasis). However, some eradication programmes (notably for guinea worm disease) have been effective in reducing the burden of infection.
Control of nematode infections is based on drug treatment, improved sanitation and health education.
- Antihelmintic drugs (eg, mebendazole, albendazole and tiabendazole) are often used for both symptomatic infections and for large-scale prevention of morbidity in children living in endemic areas. This has resulted in improvements in child health and education after deworming.
- Concerns about the sustainability of periodic deworming with available drugs and the emergence of resistance mean that a great deal more needs to be done in terms of new drugs and developing effective vaccines, as well as education and alleviating poverty.
Further reading and references
Roundworm; NICE CKS, December 2011 (UK access only)
Parasites A-Z; Centers for Disease Control and Prevention
Cox FEG; History of Human Parasitology
Stepek G, Buttle DJ, Duce IR, et al; Human gastrointestinal nematode infections: are new control methods required? Int J Exp Pathol. 2006 Oct87(5):325-41.
Hökelek M et al; Nematode Infections, Medscape, Dec 2011
Bethony J, Brooker S, Albonico M, et al; Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookworm. Lancet. 2006 May 6367(9521):1521-32.
Beyrer C, Villar JC, Suwanvanichkij V, et al; Neglected diseases, civil conflicts, and the right to health. Lancet. 2007 Aug 18370(9587):619-27.