Causal Agent:
Bursate nematodes in the genus, Oesophagostomum.  Oesophagostomum bifurcum is the most-common species infecting humans in Africa.

Life Cycle:

Common livestock such as sheep, goats, and swine, as well as non-human primates, are the usual definitive hosts for Oesophagostomum spp., but other animals, including humans and cattle, may also serve as definitive hosts.  Eggs are shed in the feces of the definitive host , and may be indistinguishable from the eggs of Necator and Ancylostoma.  Eggs hatch into rhabditiform (L1) larvae in the environment , given appropriate temperature and level of humidity.  In the environment, the larvae will undergo two molts and become infective filariform (L3) larvae .  Worms can go from eggs to L3 larvae in a matter of a few days, given appropriate environmental conditions.  Definitive hosts become infected after ingesting infective L3 larvae .  After ingestion, L3 larvae burrow into the submucosa of the large or small intestine and induce cysts.  Within these cysts, the larvae molt and become L4 larvae.  These L4 larvae migrate back to the lumen of the large intestine, where they molt into adults .  Eggs appear in the feces of the definitive host about a month after ingestion of infective L3 larvae.

Geographic Distribution:
Oesophagostomum spp. are widely distributed wherever livestock is raised, but more common in the tropics and subtropics.  The highest incidence in humans is in the northern regions of Togo and Ghana, where O. bifurcum (primarily a monkey parasite) appears to cycle naturally in the human populations.  Sporadic cases in humans have also been recorded in Brazil, Malaysia, Indonesia, French Guiana, and West Africa.