Roundworm eggs - ascariasis

Roundworms are the most common type of worm infection. It is estimated that there are 4,000,000 cases in the United States at any time. Infection is more common in warm climates. Eggs are passed in the stool of infected animals and contaminate the soil. Ingestion of contaminated soil then leads to roundworm infection. (Image courtesy of the Centers for Disease Control and Prevention.)