Infectious Disease · Helminthic Infections
The facts most likely to be tested
Ascariasis is caused by the soil-transmitted helminth Ascaris lumbricoides, the most common helminthic infection worldwide.
The Loeffler syndrome presentation involves transient pulmonary infiltrates and eosinophilia caused by larval migration through the lungs.
Small bowel obstruction is a common complication caused by a bolus of adult worms typically located in the ileocecal valve area.
Diagnosis is confirmed by identifying characteristic oval, bile-stained eggs with a thick, mammillated shell on stool ova and parasite (O&P) exam.
Adult worms may be visualized as long, tubular filling defects on abdominal ultrasound or barium swallow studies.
Albendazole or mebendazole are the first-line pharmacologic treatments for symptomatic intestinal ascariasis.
Surgical intervention is indicated for patients who develop complete bowel obstruction, biliary obstruction, or appendicitis due to worm burden.
Vignette unlocked
A 6-year-old boy is brought to the clinic with a 3-day history of crampy abdominal pain, nausea, and vomiting. He recently immigrated from a rural area with poor sanitation. Physical examination reveals a distended abdomen with high-pitched bowel sounds. A stool study shows oval, bile-stained eggs with a mammillated shell. An abdominal radiograph demonstrates a whirlpool-like pattern of gas and fluid consistent with a small bowel obstruction.
What is the most appropriate next step in management for this patient?
Surgical consultation
While albendazole is the treatment for uncomplicated ascariasis, this patient has a complete bowel obstruction, which is a surgical emergency requiring immediate consultation.
Full handout
High yield triage
Etiology / Epidemiology
Caused by Ascaris lumbricoides; most common helminth infection worldwide, prevalent in poor sanitation areas.
Clinical Manifestations
Often asymptomatic; Loeffler syndrome (pulmonary phase) or small bowel obstruction (heavy worm burden).
Diagnosis
Stool ova and parasite (O&P) exam is the gold standard; look for characteristic oval, bile-stained eggs.
Treatment
Albendazole is the first-line treatment; teratogenic in pregnancy.
Prognosis
Generally excellent; biliary obstruction or intestinal perforation are rare but life-threatening complications.
Full handout
Epidemiology & Etiology
Infection occurs via ingestion of soil-contaminated food/water containing embryonated eggs. It is the most common human helminthic infection, particularly in tropical and subtropical regions with inadequate fecal waste disposal.
Pertinent Anatomy
Adult worms reside in the small intestine (jejunum). Their size and motility allow them to migrate into the biliary tree or pancreatic duct, causing mechanical obstruction.
Pathophysiology
Ingested eggs hatch in the intestine, larvae penetrate the wall, and migrate through the bloodstream to the lungs. After alveolar rupture, they are coughed up and swallowed, maturing into adult worms in the gut. This pulmonary migration phase triggers a hypersensitivity reaction.
Clinical Manifestations
Early pulmonary phase presents as Loeffler syndrome: non-productive cough, dyspnea, and eosinophilic pneumonitis. Intestinal phase is often asymptomatic, but high worm burden causes colicky abdominal pain and small bowel obstruction. Migration into the biliary tract causes biliary colic or cholangitis.
Diagnosis
Stool O&P exam is the diagnostic gold standard, revealing characteristic oval, bile-stained eggs with a thick, mammillated shell. During the pulmonary phase, peripheral eosinophilia is common, but eggs are not yet present in stool. Abdominal ultrasound is the preferred modality for detecting worms in the biliary tree.
Treatment
Albendazole (400 mg once) or Mebendazole are the first-line agents. Albendazole is teratogenic and contraindicated in the first trimester of pregnancy; use pyrantel pamoate for pregnant patients. Surgical intervention is required for intestinal obstruction or biliary duct perforation.
Prognosis
Prognosis is excellent with anthelmintic therapy. Intestinal obstruction is the most common surgical complication, while biliary obstruction and pancreatitis represent severe, acute emergencies requiring endoscopic or surgical extraction.
Differential Diagnosis
Hookworm: causes iron deficiency anemia
Strongyloides: causes hyperinfection syndrome in immunocompromised
Giardiasis: causes malabsorption and steatorrhea
Appendicitis: presents with acute RLQ pain without worm history
Biliary colic: usually associated with cholelithiasis