Ascaris lumbricoides
From IDWiki
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
