Christine Dubray, Sharon Roy
Ascaris lumbricoides (roundworm), Ancylostoma duodenale (hookworm), Necator americanus (hookworm), and Trichuris trichiura (whipworm) are helminths (parasitic worms) that infect the intestine and are transmitted via contaminated soil.
Eggs are passed in feces from an infected person. Hookworm eggs are not infective—the eggs must hatch and release larvae that need to mature in the soil before they become infective. Infection with roundworm and whipworm occurs when eggs in soil have become infective and are ingested. Hookworm infection (see the Cutaneous Larva Migrans section in this chapter) usually occurs when larvae penetrate the skin of people walking barefoot on contaminated soil. However, the hookworm Ancylostoma duodenale can also be transmitted when larvae are ingested.
A large part of the world’s population is infected with 1 or more of these helminths, and the prevalence is highest in tropical and subtropical countries where water supplies and sanitation are poor. Travelers to these countries should be at low risk of infection if preventive measures are taken. Infections in the United States are typically seen in immigrant and refugee populations. Since these worms do not multiply in hosts, reinfection occurs only as a result of additional contacts with the infective stages.
Most infections are asymptomatic, especially when few worms are present. Pulmonary symptoms (Löffler syndrome) occur in a small percentage of patients when roundworm larvae pass through the lungs. Löffler syndrome is associated with fever and marked eosinophilia. Roundworms can also cause intestinal discomfort, obstruction, and impaired nutritional status. Hookworm infection can lead to anemia due to blood loss and chronic protein deficiency. Whipworm infection can cause chronic abdominal pain, diarrhea, blood loss, dysentery, and rectal prolapse. However, travelers are rarely at risk, because these more severe manifestations are generally associated with high worm burdens seen in indigenous populations.
The standard method for diagnosing soil-transmitted helminths is by identifying eggs in a stool specimen using a microscope.
The drugs most commonly used are albendazole and mebendazole.
Food and water precautions (see Chapter 2, Food & Water Precautions). To avoid hookworm infection, travelers should not walk barefoot in areas where hookworm is common and where there may be human fecal contamination of the soil. In general, avoid ingesting soil that may be contaminated with human feces, including where human fecal matter or wastewater is used to fertilize crops.
CDC website: www.cdc.gov/parasites/sth
- Bethony J, Brooker S, Albonico M, Geiger SM, Loukas A, Diemert D, et al. Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookworm. Lancet. 2006 May 6;367(9521):1521–32.
- Brooker S, Bundy DAP. Soil-transmitted helminths (geohelminths). In: Cook GC, Zumla A, editors. Manson’s Tropical Diseases. 22nd ed. London: Saunders; 2009. pp. 1515–48.
- Brooker S, Clements AC, Bundy DA. Global epidemiology, ecology and control of soil-transmitted helminth infections. Adv Parasitol. 2006;62:221–61.