Ascaris

Ascaris is a genus of parasitic nematodes that inhabit the gastrointestinal tract of humans and other animals. The species most commonly associated with human disease is Ascaris lumbricoides; Ascaris suum infects pigs and can occasionally infect humans. Together they are among the largest intestinal nematodes.

Transmission occurs by ingesting eggs present in soil-contaminated food or water. After ingestion, fertilized eggs hatch in the small intestine, and larvae migrate through the intestinal wall to the liver and lungs, then are coughed up and swallowed back into the intestine where they mature into adult worms. Adults can reach up to 30 cm in length and live for a year or more.

Clinical features range from asymptomatic to prominent. In light infections, few symptoms; in heavy infections, abdominal pain, malnutrition, and intestinal obstruction can occur. Migration of larvae through the lungs can cause cough, wheeze, and transient eosinophilia (Loeffler’s pneumonia). Chronic heavy infections may impair growth in children and cause nutritional deficiencies.

Diagnosis relies on detection of Ascaris eggs in stool samples, using microscopy or concentration techniques; serology and imaging are used in certain contexts. Treatment typically involves antihelminthic medications such as albendazole or mebendazole; pyrantel pamoate is another option. In large infestations, retreatment may be required.

Prevention focuses on sanitation and hygiene to prevent fecal contamination of soil and food, proper washing of produce, and safe storage of human waste. Ascaris is globally distributed, with highest prevalence in regions with poor sanitation.