Life Cycle
For non-human hosts, the life cycle of Oesophagostomum begins with the passing of eggs in the animal feces. From there the eggs develop into stage one larvae. These larvae then spend 6–7 days in the environment developing into stage two and then infectious stage three larvae. Infection begins with the ingestion of soil contaminated with stage three larvae. After ingestion the larvae end up in the small intestine, unsheathing and penetrating the intestinal wall to form nodules. The resulting adult worms that remain in the intestinal lumen copulate; the eggs from the female are then deposited in the feces. Females usually lay around 5,000 eggs per day, which is on par with reproductive rates of other nematodes within Strongyloidea.
For human hosts, the life cycle is very similar to that of Oesophagostomum in animals. It begins when an animal reservoir defecates into the soil, leaving feces infested with eggs that develop into rhabitiform larvae. These larve then develop into stage two and then infectious stage three larvae in the environment over the course of 6–7 days. Human infection occurs when soil or water containing the third-stage larvae is ingested, presumably via contaminated meat obtained from infected livestock or crops with contaminated soil. Once ingested, the filariform larvae migrate to the submucosa of the small or large intestine, then to the lumen of the colon. The developing worms then penetrate the intestinal tissues, causing nodular lesion formation in the intestines and colon; it is in these nodules that the larvae mature to stage four larvae. These larvae may then emerge from their nodules and migrate back to the intestinal lumen, where they mature into adults. But many larvae often do not complete development and remain in their colon nodules, as humans are generally unsuitable hosts for Oesophagostomum. The instances where Oesophagostomum have completed development in humans seem to be dependent on certain environmental and host factors that have yet to be identified.
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