Roundworm (Ascariasis) Infection
Roundworm (Ascariasis) Infection
Disease History, Characteristics, and Transmission
Introduction
Ascariasis (as-kuh-RYE-uh-sis), or roundworm infection, is an infection caused by the parasitic helminth, or roundworm Ascaris lumbricoides. It is considered to be the largest roundworm that infects the intestines of humans. A. lumbricoides infects humans and other mammals when embryonated eggs are ingested with contaminated food or water.
The parasite, which is commonly called the giant intestinal roundworm, can grow up to a length of 6–12 in (15–30 cm) by a diameter of 0.12–0.32 in (0.3–0.8 cm) in males and 8–14 in (20–35 cm) by 0.2 in (0.5 cm) in females. The embryonated eggs are the infectious part of the disease.
It is estimated that up to one-fourth of the world's population is infected with the roundworm A. lumbricoides. The National Institutes of Health (NIH) estimates that, generally, over one billion people are infected worldwide, with children being affected more seriously and more frequently than adults.
Disease History, Characteristics, and Transmission
Infection occurs via the fecal-oral route, most often when contaminated food is eaten that contains fertilized eggs within fecal material. The larvae hatch and burrow into the moist lining (mucosa) of the intestines. They then travel to the lungs where they further mature—usually for 10 to 14 days. They eventually travel through the respiratory tract and up into the throat where they are swallowed and sent to the small intestines. They mature as worms while attached to the walls of the small intestines.
A mature female can produce about 200,000 eggs per day. Roundworms live approximately one to two years. The time from egg ingestion to egg egression with feces is between two and three months. Upon egress from a host, the eggs become infectious within 18 days to several weeks—with the range dependent on soil conditions such as temperature.
Symptoms are usually few, and sometimes not even evident, especially when the worms are immature and small. Noticeable symptoms usually occur between four and 16 days of ingestion. Common symptoms include diarrhea, fever, inflammation, wheezing, and nonproductive cough. Other serious problems develop whenever the worms live within the lungs (pulmonary symptoms) or throughout the body (neurological disorders). The final symptoms are gastrointestinal distress, nausea, vomiting, fever, nutritional insufficiencies, peritonitis (inflammation of abdominal wall), enlargement of the liver or spleen, and observation of live worms in stools. In rare cases, worms may obstruct the intestines, cause pneumonitis (inflammation of the lungs), or cause eosinophilia (increase in white blood cells).
Humans become infected by direct contact of the worms to skin and through the ingestion of soil and vegetation that contain fecal matter contaminated with eggs. Transmission can also occur when wastewater is recycled onto crop fields as fertilizer—a practice that is common in developing countries.
Scope and Distribution
Roundworm infection is found throughout the world, but especially in tropical regions and among the poorest areas with the worst of hygiene conditions. It is pronounced along the rural areas of the Gulf Coast within the United States; in Africa, especially Nigeria; and in Southeast Asia, especially Indonesia. About 2 percent of people in the United States are estimated to be infected with roundworms. High-risk groups include visitors and travelers to third-world countries.
Treatment and Prevention
The diagnosis is easily made when the infected person actually observes worms in his/her stool or vomit. If that does not happen, stool samples can be taken to medically show the presence of eggs. Blood counts can also diagnosis eosinophilia; and respiratory samples can find pneumonitis and other pulmonary diseases.
WORDS TO KNOW
EMBRYONATED: When an embryo has been implanted in a female animal, that animal is said to be embryonated.
HELMINTH: A representative of various phyla of worm-like animals.
FECAL-ORAL-ROUTE: The spread of disease through the transmission of minute particles of fecal material from one organism to the mouth of another organisms. This can occur by drinking contaminated water, eating food that was exposed to animal or human feces (perhaps by watering plants with unclean water), or by the poor hygiene practices of those preparing food.
PARASITE: An organism that lives in or on a host organism and that gets its nourishment from that host. The parasite usually gains all the benefits of this relationship, while the host may suffer from various diseases and discomforts, or show no signs of the infection. The life cycle of a typical parasite usually includes several developmental stages and morphological changes as the parasite lives and moves through the environment and one or more hosts. Parasites that remain on a host's body surface to feed are called ectoparasites, while those that live inside a host's body are called endoparasites. Parasitism is a highly successful biological adaptation. There are more known parasitic species than nonparasitic ones, and parasites affect just about every form of life, including most all animals, plants, and even bacteria.
Treatment involves medicines that commonly combat parasitic worms such as albendazole (Albenza ®), mebendazole (Ovex ®, Vermox ®), piperazine (Entacyl ®), pyrantel pamoate (Antiminth ®, Pin-Rid ®, Pin-X ®), and thiabendazole (Mintezol®). Corticosteroid medicine is sometimes given to counter inflammation.
Roundworm infection is prevented by using careful and comprehensive hygiene techniques such as protecting food from soil and dirt, thoroughly washing vegetables and fruits, washing hands especially after using the toilet, and other similar sanitary measures.
Impacts and Issues
Ascariasis dominates in areas with poor sanitation. According to the Office of Laboratory Security at the Public Health Agency of Canada, roundworm infection is concentrated in moist tropical areas of the world. Within these regions, its incidence can be over 50 percent. The highest group infected in these areas is children aged three to eight years. It adds to iron-deficiency anemia, malnutrition, and impairment of growth and intelligence among the people it affects.
Complications that occur as a direct result of roundworm infection occur in many cases. The most common complication is intestinal tract obstruction. Although complications are only fatal in a small number of cases, according to the NIH, an estimated 8,000 to 10,000 deaths occur annually in the world, primarily in children. Male children are thought to more likely get the disease because of amount of time that they play in dirt.
The disease has generally been neglected in the past because it occurs primarily in poor, rural areas of the world. The affliction has been around for thousands of years. However, aggressive treatment has been recently attempted in some regions.
According to a 2005 paper published in the journal PLoS Medicine, ascariasis is considered one of thirteen neglected tropical diseases in Africa. The authors contend that even though HIV (human immunodeficiency virus), TB (tuberculosis), and malaria are the most serious of the tropical diseases, others such as ascariasis are also major medical problems in need of attention throughout the world. Even though neglected in the past, recent attempts to remedy the affects of ascariasis have been successful though affordable and effective means.
See AlsoFood-borne Disease and Food Safety; Globalization and Infectious Disease; Handwashing; Helminth Disease; Travel and Infectious Disease.
BIBLIOGRAPHY
Books
Handbook of Diseases. Philadelphia, Penn.: Lippincott Williams & Wilkins, 2004.
Holland, Celia V., and Malcolm W. Kennedy. The Geohelminths: Ascaris, Trichuris, and Hookworm. Boston, Mass.: Kluwer Academic Publishers, 2002.
Infectious Diseases Sourcebook, edited by Karen Bellenir. Detroit, Mich.: Omnigraphics, 2004.
Tamparo, Carol D. Diseases of the Human Body. Philadelphia, Penn.: F.A. Davis Co., 2005.
Web Sites
MedlinePlus, National Institutes of Health. “Ascariasis.” October 9, 2006. <http://www.nlm.nih.gov/medlineplus/ency/article/000628.htm> (accessed May 21, 2007).
Office of Laboratory Security, Public Health Agency of Canada. “Ascaris lumbricoides.” January 23, 2001. <http://www.phac-aspc.gc.ca/msds-ftss/msds9e.html> (accessed May 21, 2007). PLoS Medicine, Public Library of Science. “Rapid-Impact
Interventions: How a Policy of Integrated Control for Africa's Neglected Tropical Diseases Could Benefit the Poor.” October 11, 2005. <http://medicine.plosjournals.org/perlserv/?request=get-documentdoi=10.1371/journal.pmed.0020336#JOURNAL-PMED-0020336-T001> (accessed May 21, 2007).