Ascaris lumbricoides

Background

Life Cycle

• Female worm releases egg into small intestine, which are passed in feces
• They develop to become infectious eggs over 2 to 6 weeks, depending on environmental conditions
• The eggs are then ingested, releasing the contained larva into the small intestine
• Larvae penetrate the intestinal wall, enter the venous blood, and deposit into the lungs, where they climb the bronchial tree and are swallowed
  • It matures in some way in the lungs
• They reach the small intestine (again), where they develop into adults
• Egg production starts about 2 months after initial ingestion
• Adult worms live 10 to 24 months

Epidemiology

• Likely the most common helminth infection worldwide, with a global distribution
• Promoted by poor sanitation and by using human waste as fertilizer
• Children often become infected when playing in contaminated soil
• Ova can remain viable in soil for up to 6 years
• It is unclear if it's still endemic in parts of the US, include Appalachia

Clinical Manifestations

• Mostly asymptomatic
• After 2 week incubation period, may develop pulmonary symptoms from a hypersensitivity response
  • Non-productive cough, chest discomfort, low-grade fever, and eosinophilia
  • Resolves by the time the worms mature
  • Can rarely develop Löffler syndrome (eosinophilic pneumonia)
• Once in the abdomen, the symptoms are usually mild
  • May include mild abdo discomfort, dyspepsia, anorexia, or nausea
  • If heavier worm burden, it can cause malnutrition
• Can migrate, with adult worms exiting per rectum, mouth, tear duct, or nose (though all rare)

Complications

• Malnutrition leading to intellectual stunting, poor school performance, and decreased growth
• Can cause intestinal obstruction and intestinal performation when they amass
• Can cause cholangitis, liver abscesses, pancreatitis, and appendicitis when they enter small orifices
  • More common in adults

Diagnosis

• Stool for ova, which should be easy to find due to the large amount of eggs released
• Can also find larvae in sputum and gastric aspirates
• PCR can detect them in stool
• May appear as filling defects on bowel imaging

Management

• Albendazole 400 mg po once, or mebendazole 500 mg po once, or mebendazole 100 mg po daily for 3 days, or pyrantel pamoate 11 mg/kg po once (max 1 g)
• Ivermectin can also treat ascariasis 150 to 200 mcg/kg po once
• In pregnancy and in children, albendazole and mebendazole can be used