Cause
Horses become infected when they ingest feces containing strongyles at the infective larval stage, or L3. Once the larvae are swallowed, they travel to the small intestine, cecum and colon. From here, the larvae ultimately develop into sexually mature adults and return to the intestines to produce eggs that are passed into the horse's feces -- into the environment, where they can infect other horses. The eggs can then develop into the infective stage of the larvae, or L3, over a period of one to three weeks. Under certain conditions, these eggs can survive in the environment for up to two years. In moist conditions, L3 larvae can survive for approximately five weeks to several months.