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Definition of Ascariasis
Ascariasis is a human disease caused by the parasitic roundworm Ascaris lumbricoides. Perhaps as many as one quarter of the world's people are infected, with rates of 45% in Latin America and 95% in parts of Africa. Ascariasis is particularly prevalent in tropical regions and in areas of poor hygiene. Other species of the genus Ascaris are parasitic and can cause disease in domestic animals. Certain genes have been identified in human populations that may increase the susceptibility to infection.
Symptoms of Ascariasis
Patients can remain asymptomatic for very long periods of time. As larval stages travel through the body, they may cause visceral damage, peritonitis and inflammation, enlargement of the liver or spleen, toxicity, and pneumonia. A heavy worm infestation may cause nutritional deficiency; other complications, sometimes fatal, include obstruction of the bowel by a bolus of worms (observed particularly in children) and obstruction of the bile or pancreatic duct. More than 796 Ascaris lumbricoides worms weighing up to 550 g (19 ounces) were recovered at autopsy from a 2-year-old South African girl. The worms had caused torsion and gangrene of the ileum, which was interpreted as the cause of death.
Ascaris takes most of its nutrients from the partially digested host food in the intestine. There is limited evidence that it can also pierce the intestinal mucous membrane and feed on blood, but this is not its usual source of nutrition. As a result, Ascaris infection does not produce the anemia associated with some other roundworm infections.
Causes of Ascariasis
Ascariasis is caused by consuming food or drink contaminated with roundworm eggs. Ascariasis is the most common intestinal worm infection. It is found in association with poor personal hygiene, poor sanitation, and in places where human feces are used as fertilizer.
Once consumed, the eggs hatch and release immature roundworms called larvae within the small intestine. Within a few days, the larvae then move through the bloodstream to the lungs, exit up through the large airways of the lungs, and are swallowed back into the stomach and reach the small intestine.
During movement through the lungs the larvae may produce an uncommon form of pneumonia called eosinophilic pneumonia. Once they are back in the small intestine, the larvae mature into adult roundworms. Adult worms live in the small intestine where they lay eggs that are present in feces. They can live 10 – 24 months.
Diagnosis of Ascariasis
The diagnosis is usually incidental when the host passes a worm in the stool or vomit. Stool samples for ova and parasites will demonstrate Ascaris eggs. Larvae may be found in gastric or respiratory secretions in pulmonary disease. Blood counts may demonstrate peripheral eosinophilia. On X-ray, 15–35 cm long filling defects, sometimes with whirled appearance (bolus of worms).
Treatment of Ascariasis
Pharmaceutical drugs that are used to kill roundworms are called ascaricides and include:
Prognosis of Ascariasis
Most people recover from symptoms of the infection, even without treatment, although they may continue to carry the worms in their body.
Complications may be caused by adult worms that move to certain organs such as the bile duct, pancreas, or appendix, or multiply and cause a blockage in the intestine.
Prevention of Ascariasis
Prevention includes: use of toilet facilities; safe excreta disposal; protection of food from dirt and soil; thorough washing of produce; and hand washing.
Food dropped on the floor should never be eaten without washing or cooking, particularly in endemic areas. Fruits and vegetables should always be washed thoroughly before consumption.
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