Ascaris lumbricoides is a large parasitic roundworm that infects the intestines of humans. It can grow up to 35 centimeters long and is one of the most common human parasites worldwide. Infection occurs when a person ingests eggs from contaminated food, water, or soil. Once inside the body, the eggs hatch in the intestines, and the larvae migrate through the bloodstream to the lungs before returning to the intestines to mature. Symptoms of infection can include abdominal pain, malnutrition, and respiratory issues. Proper sanitation and hygiene practices are essential to prevent Ascaris lumbricoides infections.