A 3-year-old girl is seen in the emergency depament with acute abdominal pain. She has a 5-day history of vomiting and abdominal distension. She has not passed stool during this time, and during the past day, has been vomiting bilious material. On physical examination, she is lethargic, with a firm and tender abdomen, and peritoneal signs are present. She is immediately referred for laparotomy for suspected diagnosis of intussusception vs. volvulus. At surgery, approximately 20 cm of small intestine is found to be markedly distended, and is resected. The section contains a tightly knotted ball of nematodes that are about 15 to 35 cm in length. The worms have tapered ends without hooks. Pa of the life cycle of this patient’s parasite is a filarial stage in which larvae, hatched in the duodenum, penetrate the wall of the small intestine. The passage of migrating larvae most commonly produces symptomatic disease in which of the following organs?
Correct Answer: Lungs
Description: Ascaris infection is acquired by ingestion of the eggs, usually from contaminated soil. The ingested eggs hatch in the duodenum to produce larvae, which cross the small intestinal wall to enter the bloodstream. They then pass through the hea to lodge in the lungs. They leave the lung capillary bed to enter the airspaces. They then ascend the bronchial tree into the oropharynx, where they are again swallowed. This time, they return to the small intestine where they develop into mature worms that can live in the host for up to two years. A gravid female worm may produce up to 250,000 eggs daily, which are shed in stool. The passage of the larvae through the lungs often produces cough and/or wheezing, and may, in severe cases, produce fever, dyspnea, fleeting patchy pulmonary infiltrates (Loeffler pneumonitis with prominent eosinophilia), and rarely hemoptysis. Passage through the hea is usually asymptomatic, as the larvae are small. A single adult worm, but not usually larval forms, can migrate into the biliary tree, leading to biliary colic, cholangitis, or gallstone formation; obstructive jaundice uncommonly occurs. The pancreas and stomach are not common sites for complications of ascariasis. Ref: Levinson W. (2012). Chapter 56. Nematodes. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.
Category:
Microbiology
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