Roundworms (medical)
Roundworms, also known as nematodes, are a diverse group of worm-shaped animals that can function as parasites in both plants and animals, including humans. They inhabit various environments worldwide, with some species being free-living while others are internal parasites. Among these, notable human parasites include Ascaris lumbricoides, which can cause severe pneumonia and intestinal blockages, and Enterobius vermicularis, the pinworm, which leads to itching and discomfort due to egg deposits in the perianal area. The life cycles of these roundworms can be complex, often involving intermediate hosts and various transmission routes, such as through contaminated food or skin exposure.
Symptoms of roundworm infections can vary greatly and may include malnutrition, anemia, and in severe cases, death. Treatment typically involves species-specific medications and is most effective when combined with preventive measures like improved sanitation and access to clean water. Despite advancements in medical treatments, roundworm infections continue to pose significant health challenges, particularly in tropical regions where sanitation may be inadequate. Understanding the biology and life cycles of these parasites is essential for managing their impact on human health.
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Subject Terms
Roundworms (medical)
ALSO KNOWN AS: Nematodes
ANATOMY OR SYSTEM AFFECTED: Blood vessels, circulatory system, gastrointestinal system, intestines, lungs, lymphatic system
DEFINITION: Worm-shaped animals that act as parasites of plants and animals
CAUSES: Parasitic infection transmitted through skin exposure or ingestion
SYMPTOMS: Depends on type; may include severe pneumonia, malnutrition, intestinal blockages, anemia, itching, elephantiasis, severe pain, and sometimes death
DURATION: Often chronic
TREATMENTS: Species-specific drugs
Causes and Symptoms
Roundworms are tube-shaped animals in the phylum Nemotoda. They are a highly diverse group, numbering twelve thousand named species, but some taxonomists suggest that fifty thousand more species have yet to be discovered and named. Roundworms occur from the tropics to the tundra and are found in virtually all habitats. Most are free-living animals, but some are parasites of plants and animals. At least fifty are important internal parasites of humans.
Structurally and organizationally, roundworms are very simple animals; most are composed of fewer than one thousand cells. The circular, long body of a is covered by a tough, protective cuticle. Inside is a tubular digestive tract and simplified nervous system. Its is capable of producing enormous numbers of eggs.
Ascaris lumbricoides is a common intestinal of humans and also one of the largest of the nematodes, with a length of 30 centimeters or more. A female can produce two hundred thousand eggs per day for several months, which are secreted into intestinal fluids and voided with the feces. If the eggs are ingested, then they pass through the stomach and into the digestive system and hatch in the intestines. The juveniles burrow through the intestinal wall and are carried via the circulatory system to the lungs. They are reswallowed and returned to the via the esophagus, where they mature. Large numbers of juveniles in the can produce a severe pneumonia, while heavy infestations of adults can cause malnutrition and intestinal blockages.
More than half a billion people in tropical regions may be infected by hookworms, which feed on the blood contents of the gut rather than intestinal fluids. Hookworm life cycles differ from that of Ascaris lumbricoides, in that eggs hatch on the ground and juveniles burrow into the skin of the feet or hands and are carried via the blood to the lungs. From the lungs, the juveniles migrate to the and are then carried to the intestines, where they cause serious blood and tissue damage including and malnutrition.
Pinworms are the most common of the parasitic roundworms. Infection by the human pinworm, Enterobius vermicularis, occurs when a female pinworm deposits its eggs at night in the perianal region, causing irritation. Scratching lodges eggs under the fingernails which, if put in the mouth, cause infection or reinfection.
A number of roundworm parasites have an intermediate host in their life cycle. For example, Trichinella spiralis, the trichina worm, which causes trichinosis in humans, has two hosts in its life cycle; humans are the primary hosts, while pigs are the intermediate hosts. Juveniles lodge in the muscle tissue of pigs as calcified cysts. If contaminated meat is ingested by humans, then the juveniles hatch and migrate into the intestines. Infection with trichina produces severe pain and sometimes death as juveniles and adults burrow through body tissues.
The most spectacular of the roundworm parasites is the dracunculoid guinea worm (Dracunculus medinensis), which lives in and may reach 2 to 3 feet in length. A female discharges its eggs directly into standing water through an ulcerated sore in a human’s skin, often on the feet. The larvae are eaten by freshwater copepods (water fleas) called Cyclops and embed in their tissues. Larvae gain entry to humans when a human drinks water containing the nearly microscopic Cyclops, thus beginning the life cycle again.
The filaroid roundworm parasites such as Wuchereria bancrofti of Africa and Asia are spread by means of a blood-feeding arthropod vector. All eight species of filaroids live in lymph nodes and associated ducts and feed on lymph. The female produces larvae, called microfilariae, which are carried to the skin via the circulatory system. Blood-feeding insects suck up blood containing the larvae, which are injected into another person during the next blood meal. Heavy infestations of male and female worms block the lymph vessels, which enlarge to produce the condition called elephantiasis.
Treatment and Therapy
Parasitic roundworm infection continues to be a global medical health problem of great concern, especially in the warmer regions of the world. Modern medicine has greatly reduced the pathologies associated with heavy parasitic infections, which can be detected by blood or samples, and treatment with species-specific drugs can very effectively eliminate most species. The best prevention method remains adequate sanitation and access to clean water.
Bibliography
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Parker, Philip M., and James N. Parker. Roundworms: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, Calif.: Icon Health, 2004.
Roberts, Larry S., and John Janovy, Jr., eds. Gerald D. Schmidt and Larry S. Roberts’ Foundations of Parasitology. 8th ed. Boston: McGraw-Hill Higher Education, 2010.
"Roundworms." Cleveland Clinic, 18 May 2021, my.clevelandclinic.org/health/diseases/15240-roundworms#. Accessed 8 Apr. 2024.
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