Ascariasis is caused by Ascaris lumbricoides, a large intestinal roundworm that infects humans through ingestion of fertilized eggs. The larvae hatch in the intestine, migrate through the bloodstream to the lungs, and then return to the intestine to mature. This lifecycle leads to symptoms such as abdominal pain, intestinal obstruction, and malnutrition. Diagnosis is confirmed by identifying characteristic eggs in stool samples. Effective treatment typically includes anthelmintics like albendazole or mebendazole. Recognizing Ascaris lumbricoides as the causative agent is essential for targeted therapy and prevention of complications.

Reference: Harrison's Principles of Internal Medicine, Kasper et al., 20th Edition.