Ascaris lumbricoides has probably been infecting humans for thousands of years. It is the most common nematode parasite infecting humans and over 1 billion people are believed to be infected. Children who live in moist, warm climates are the most at risk to become infected. Ingesting embryonated eggs from contaminated soil is the primary means of infection. The eggs will hatch in either the stomach or small intestine where the larvae penetrate through the intestine wall. Larvae are carried to the heart and then to the lungs, where they stay for approximately 10 days. Larvae will then go into the alveoli and migrate via the bronchi to the trachea and pharynx. The larvae are coughed up, swallowed, and returned to the intestine where they mature and mate, eventually producing eggs. This process occurs over 8 – 12 weeks. Eggs will get passed into the environment via feces. Fertilized eggs will become infective within 2 weeks if they are kept in warm, moist soil. Adult worms usually live for about 1 year. Females are 20 – 35 cm long and can produce 200,000 eggs per day where as males are 15 – 31 cm long and have a curved posterior end. Pathogenisis in humans from Ascaris can be cause by the host’s immune response, effects of larvae migration, mechanical effects of adult worms, and also nutritional deficiencies caused by the adult worms being present in the body.

There are usually no symptoms involved with the initial passage of larvae through the liver and lungs unless the number of worms is high. Bronchial epithelium damage may result from larvae exiting lung tissue. When successive migrations of larvae occur, more intense tissue reactions may be observed. This could be accompanied by a dry or productive cough, fever, transient eosinophilia, dyspnea, and a chest x-ray that resembles viral pneumonia; this condition being referred to as Ascaris pneumonitis. The presence of adult worms in the intestine usually shows no symptoms unless the number of worms present is high. However, even a single worm can cause damage due to the worms tendency to migrate. Certain stimuli may result in migration such as fever, general anesthesia, as well as other abnormal body conditions. This can result in entry into the bile duct, liver or other small spaces as well as intestinal blockage. Worms have been known to spontaneously migrate out of the body through the mouth, nose or anus. Eighty-five percent of humans infected with Ascaris will exhibit no symptoms.

The primary means of preventing the spread of Ascaris infection is through the use of appropriate sanitation facilities and practices, such as frequent washing of the hands. The use of human feces, known as night soil, as fertilizer should be recognized as potentially hazardous. Any fruits or vegetables that are grown using night soil cannot be eaten raw. Even after fields using night soil have been processed and treated, Ascaris eggs may still remain viable and infective.