Ascaris lumbricoides is the largest human intestinal parasitic roundworm (nematode) that causes an infectious disease called Ascariasis. Ascariasis is particularly common in tropical regions and in areas with inadequate sanitation where prevalence can exceed 90%. A. lumbricoides infection follows ingestion of eggs in contaminated food or by fecal-oral contact.
courtesy of DPDx
The majority of infected patients are asymptomatic. In a small number of patients with a heavy infectious dose, symptoms develop as the worms migrate from the intestine. Early symptoms could include cough and wheezing; later, abdominal pain can develop as well as malnutrition in chronically infected children.
The diagnosis of A. lumbricoides infection requires identifying eggs or adult worms in stool, recognizing adult worms that migrate from the nose or mouth, or larvae in sputum during the early infection phase. Curative therapy requires antihelmintic drugs, such as albendazole, mebendazole, or pyrantel pamoate.
Alfred is a 12-year-old male living in a tropical region developed nocturnal fever (maximum 38.6°C). After 3 weeks of periodic nocturnal fever episodes accompanied by a non-productive cough and wheezing, the patient developed anorexia and experienced a weight loss of 2 kg. His family took him to see a physician.
The patient presented with pallor of anemia and urticaria. The physical exam was unremarkable, but the patient continued to complain of diffuse abdominal pain.
About 25% of the world's population is infected. Globally, 12 million acute cases and 10,000 deaths occur annually.
Prevalence is high wherever there is poor hygiene and sanitation or where human feces are used as fertilizer. Household transmission, agricultural spread, and sporadic travel-related cases are also described. Risk factors for infection include living in an endemic area, dog/cat ownership, presence of pets within the house, and a history of geophagia. Children are thought to be infected more frequently due to greater contact with soil. Due to similarities in the means of infection, many individuals infected with A. lumbricoides are also co-infected with other intestinal parasites.
Infective eggs are ingested with consumption of feces-contaminated food or soil. The eggs hatch in the small intestine and the larvae are released.
During the larval phase, the larvae invade the intestinal mucosa and migrate through the circulation to the lungs. The larvae then break into the alveoli, ascend the bronchial tree, and return via swallowing to the small intestine, where they develop into adult worms. Larval invasion induces an immune response, which can further contribute to symptoms.
During the adult phase, the worms reach a length of 10-30 cm as they attach to the lumen of the small intestine for up to 2 years. The mature A. lumbricoides copulate and lay eggs in the intestine. These eggs are then released into the stool.
In the adult phase, the worms may migate to the appendix, hepatobiliary system, pancreatic ducts, and rarely other organs such as kidneys or brain, where they can cause local symptoms due to their size and induction of a host immune response. If there are a large number of worms, they may cause partial or complete bowel obstruction.
It takes approximately 2-3 months from the initial infection for new egg release to take place. A. lumbricoides eggs are remarkably resistant to environmental stresses. They become infective after 3 weeks of maturation in the soil and can remain infective for years.
Eggs may be killed by heat and direct sunlight or can be removed by hand washing and good hygiene practices.
Most infections are asymptomatic. Adult worms may migrate and be coughed up, vomited, or may emerge through the nose or anus.
During the Larval Phase, migration of the worms may cause:
Ascaris passed by one child in Kenya.
courtesy of CDC PHIL, #9813
During the Adult Phase, mature worms may migrate to a variety of locations and cause:
A high density infection may cause intestinal obstruction, volvulus, intussusception, and death.
Ascaris egg (fertilized), 400x
courtesy of DPDX
The most common method for diagnosing intestinal ascariasis is light microscopy using direct wet mount examination or formalin-ethyl acetate sedimentation. Ascariasis may be diagnosed after adult worms emerge from the mourth, nose, or anus.
A complete blood count may show marked eosinophilia during worm migration (larval phase) but may be absent during intestinal infection (adult phase).
The differential diagnosis of Ascariasis includes:
All cases of A. lumbricoides infection require treatment.
In the early infection (larval phase), inhaled β-agonists may be used for symptom control; however, this phase is rarely serious and antihelmintic therapy is the only definitive treatment.
During established infection (Adult Phase), the antihelmintic agents of choice are:
These drugs are normally well tolerated but may cause nausea and vomiting. Mild diarrhea and abdominal pain are uncommon side effects. They are considered safe for children above 1 year of age and in pregnancy, although use in the first trimester is best avoided.
Partial intestinal obstruction should be managed with nasogastric suction, IV fluid administration, and instillation of piperazine through the nasogastric tube. Complete intestinal obstruction and its severe complications are rare but require immediate surgical intervention.
Knopp S et al. Diagnosis of soil-transmitted helminths in the era of preventive chemotherapy: effect of multiple stool sampling and use of different diagnostic techniques. PLoS Negl Trop Dis. 2008;2(11):e331.