USAID's NTD Program
Roundworm: Ascariasis
- Overview
- Epidemiology
- Distribution of Roundworm
- Life Cycle of A. lumbricoides
- Symptoms
- Diagnosis
- Treatment, Prevention, and Control
Overview
Ascariasis is a soil-transmitted helminthiasis (STH) infection caused by the roundworm Ascaris lumbricoides (A. lumbricoides). Ascariasis, one of the most common STH infections, affects an estimated 1 billion people worldwide. About half of the populations in tropical and subtropical areas are infected with this parasite, which causes an estimated 20,000 deaths each year. While mild cases of ascariasis often show no symptoms, heavy infections can cause intestinal blockage and impair growth in children.
Epidemiology
Ascariasis infection is highly prevalent and geographically widespread. Many factors, including the large number of eggs produced by a female worm, the properties of the eggs, environmental conditions, and poor socioeconomic settings facilitate the spread of the parasite and thus determine the geographic distribution of the disease.
Children, especially those suffering from malnutrition, are infected more often than adults, with the most common age group being 3 to 8 year olds. Children often become infected by playing in contaminated soil, but eating uncooked food grown in contaminated soil or irrigated with inadequately treated wastewater is another frequent avenue of infection.
Distribution of Roundworm
| Estimated Number of Roundworm Infections (in millions) by Age Group, 2003 | |||||
|---|---|---|---|---|---|
| WHO Region | 0-4 Years |
5-9 Years |
10-14 Years |
≥ 15 Years |
Total |
| Africa | 28 | 28 | 25 | 92 | 173 |
| Americas | 8 | 10 | 10 | 56 | 84 |
| E. Mediterranean | 3 | 3 | 3 | 14 | 23 |
| South-East Asia | 28 | 33 | 30 | 145 | 237 |
| Western Pacific | 55 | 69 | 76 | 505 | 705 |
| Total | 122 | 143 | 144 | 812 | 1,222 |
Source: World Health Organization
Life Cycle of A. lumbricoides
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| Source: CDC |
Step 1: Adult worms live and mate in the lumen of the small intestine. Eggs are passed in the stool of an infected person.
Steps 2 and 3: Fertile eggs develop into embryos and, depending on the environmental conditions (optimum being moist, warm, and shaded soil), become infective after 18 days to several weeks, but the eggs may remain viable in soil for years.
Step 4: Humans are infected when they ingest soil containing infective eggs.
Step 5: The eggs hatch into larvae within the infected person’s intestine.
Step 6: The larvae penetrate the intestine wall and travel through the bloodstream to the lungs.
Step 7: The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Once the larvae return to the small intestine, they develop into adult worms and mate. The female adult worm, which can grow to more than 30 cm in length, may produce up to 200,000 eggs per day. An adult ascaris may live up to 1 and a half years.
Symptoms
Most cases of ascariasis are asymptomatic. The clinical effects of heavier infections include a wide range of manifestations with symptoms associated with the migration of juvenile or adult worms in infected organs. Most potential and common complications include pneumonitis due to passage of worms in the lungs, with pulmonary eosinophilia (Loeffler’s syndrome); intestinal obstruction by masses of worms; and biliary and pancreatic obstruction by worms.
The intensity of clinical signs is usually related to the worm burden in infected individuals. Serious, even fatal, but less common complications of ascariasis result from the infiltration of the larvae into sensitive tissues, such as the brain, and from the migration of the adult worms into various body structures, where they produce abscesses and toxic manifestations. Infection with A. limbricoides may contribute substantially to child morbidity when associated with malnutrition, pneumonia, enteric diseases, and vitamin A deficiency. Ascariasis adversely affects children's growth and development.
Diagnosis
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Diagnosis requires careful examination under a microscope of a fecal sample for eggs. Common methods for eggs search and count include the direct examination of stool mixture with 0.85 percent NaCl and the Kato-Katz technique.
Stool samples for eggs might be negative in the case of pneumonitis from A. lumbricoides in a newly infected individual. Chest radiographs usually reveal infiltrates, and examination of sputum could reveal Charcot-Leyden crystals.
Ultrasonography and radiology are the most appropriate tools to diagnose intestinal and biliary obstruction due to A. lumbricoides as well as to detect other abdominal localization of the worms.
Treatment, Prevention, and Control
Anthelminthic drugs are used to treat complications of intestinal ascariasis. Mebendazole and albendazole are currently the drugs of choice to treat adult worms. Ascariasis is treated with a single dose of 300 mg to 500 mg of mebendazole or 100 mg of mebendazole twice a day for 3 consecutive days. Albendazole is given at a single dose of 400 mg. The surgical treatment is often indicated for severe intestinal complications with peritonitis.
Control measures for ascariasis are similar to those for other STHs and include:
- Availability of water for use in personal hygiene
- Sanitation and education to promote using latrines
- Education on hand washing and washing of food
- Avoiding the use of uncomposted human feces as fertilizer
- Mass chemotherapy: Modern anthelminthics, such as mebendazole and albendazole, administered in a single dose, are safe and relatively inexpensive and effective for several months. The association of albendazole to ivermectine and to diethylcarbamazine in community-wide drug distribution to eliminate lymphatic filariasis in many areas also will reduce the number of eggs released in the environment and, consequently, decrease the intensity and prevalence of A. lumbricoides infection.
Although ascariasis is not eradicable, it can be better controlled if the above measures are implemented in areas of high prevalence.
References
- Crompton D.W.T. Ascaris and ascariasis. Adv Parasitol. 48:285, 2001.
- Crompton D.W.T, Nesheim M.C. Nutritional impact of intestinal helminthiasis during the human life cycle. Ann Rev Nutr. 22:35, 2002.
- De Silva N., Guyatt H., Bundy D. Morbidity and mortality due to Ascaris-induced intestinal obstruction. Trans R Soc Trop Med Hyg. 91:31, 1997.
- Ferreyra N.P., Cerri G.G. Ascariasis of the alimentary tract, liver, pancreas and biliary system: Its diagnosis by ultrasonography. Hepatogastroenterology. 45:932, 1998.
- O’Lorcain P., Holland C.V. The public health importance of Ascaris lumbricoides. Parasitology. 121:S51, 2000.
- Wasadikar P.P., Kulkarni A.B. Intestinal obstruction due to ascariasis. Br J Surg. 84:410, 1997.
- World Health Organization. First WHO report on neglected tropical diseases 2010: Working to overcome the global impact of neglected tropical diseases. World Health Organization, 2010.
- World Health Organization. Prevention and control of schistosomiasis and soil transmitted helminthiasis. Report of a WHO expert committee, WHO Technical Report Series 912. World Health Organization, 2002.
- World Health Organization. Preventive chemotherapy in human helminthiasis – October 2006 [PDF, 1.6MB].
- World Health Organization. Report of the WHO informal consultation on the use of praziquantel during pregnancy/lactation and albendazole/mebendazole in children under 24 months. World Health Organization, 2003.