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Ascaris Lumbricoides
Updated: Feb 14, 2007
Introduction
Background
Intestinal nematode infections affect one fourth to one third of the world's population. Of these, the intestinal roundworm Ascaris lumbricoides is the most common. While the vast majority of these cases are asymptomatic, infected persons may present with pulmonary or gastrointestinal complaints. Ascariasis predominates in areas of poor sanitation and is associated with malnutrition, iron-deficiency anemia, and impairments of growth and cognition.
Pathophysiology
A lumbricoides is the largest of the intestinal nematodes affecting humans, measuring 15-35 cm in length. Infection begins with the ingestion of embryonated (infective) eggs in feces-contaminated soil. Once ingested, eggs hatch, releasing small larvae that penetrate the intestinal wall. Larvae migrate to the pulmonary bed via the portal veins, during which time they may cause pulmonary symptoms (eg, cough, wheezing). After migrating up the respiratory tract and being swallowed, they mature, copulate, and lay eggs in the intestines. Adult worms may live in the gut for 6-24 months, where they can cause partial or complete bowel obstruction in large numbers, or they can migrate into the appendix, hepatobiliary system, or pancreatic ducts. From egg ingestion to new egg passage takes approximately 9 weeks, with an additional 3 weeks needed for egg molting before they are capable of infecting a new host.
Frequency
United States
In the United States, approximately 4 million people are believed to be infected. High-risk groups include international travelers, recent immigrants (especially from Latin America and Asia), refugees, and international adoptees. Ascariasis is indigenous to the rural southeast, where cross-infection by pigs with the nematode Ascaris suum is thought to occur.
International
Worldwide, 1.4 billion people are infected with A lumbricoides, with prevalence among developing countries as low as 4% in Mafia Island, Zanzibar, to as high as 90% in some areas of Indonesia. Local practices (eg, termite mound–eating in Kenya) may predispose to ascariasis in some populations.
Mortality/Morbidity
The rate of complications secondary to ascariasis ranges from 11-67%, with intestinal and biliary tract obstruction representing the most common serious sequelae. Although infection with A lumbricoides is rarely fatal, it is responsible for an estimated 8,000-100,000 deaths annually, mainly in children.
Race
No racial predilection is known. A genetic predisposition has been described in a study of families from Nepal.
Sex
Male children are thought to be infected more frequently, owing to a greater propensity to eat soil.
Age
Children, because of their habits (eg, directly or indirectly consuming soil), are more commonly and more heavily infected than adults. Neonates may be infected by transplacental infection.
Clinical
History
Most patients are asymptomatic. When symptoms occur, they are divided in 2 categories: early (larval migration) and late (mechanical effects).
- In the early phase (4-16 d after egg ingestion), respiratory symptoms result from the migration of larvae through the lungs. Classically, these symptoms occur in the setting of eosinophilic pneumonia (Löffler syndrome).
- Fever
- Nonproductive cough
- Dyspnea
- Wheezing
- In the late phase (6-8 wk after egg ingestion), gastrointestinal symptoms occur.
- Passage of worms (from mouth, nares, anus)
- Diffuse or epigastric abdominal pain
- Nausea, vomiting
Physical
- General
- Fever
- Jaundice (in biliary obstruction)
- Cachexia (due to malnutrition)
- Mental retardation
- Pulmonary
- Wheezing
- Rales
- Diminished breath sounds
- Abdominal
- Abdominal tenderness, which may be diffuse (in obstructive infections), or localized to the right lower (appendicitis) or right upper quadrant (hepatobiliary infections)
- Peritoneal signs in cases of bowel perforation
- Migrating larvae may transmit other organisms, causing bacterial pneumonia. Rare cases of airway obstruction have also been reported. Other much less common presentations include lacrimal drainage obstruction, acute interstitial nephritis, and encephalopathy.
Causes
Symptoms are typically associated with early larval migration, heavy intestinal burdens of adult worms, or aberrant worm migration. Worm migration may be stimulated by anesthetic agents or subtherapeutic anthelmintic treatment or by use of certain anthelmintics (eg, pyrantel pamoate).
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References
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Further Reading
Keywords
Ascaris lumbricoides, A lumbricoides, roundworm, intestinal roundworm, human parasite, nematode infection, ascariasis, malnutrition, iron-deficiency anemia, bowel obstruction, Ascaris suum, eosinophilic pneumonia, Löffler syndrome
