This nematode is distributed in tropical and subtropical areas including the Nansei Islands of Japan. Its life cycle is complex, with switching between free-living and parasitic cycles. In the parasitic cycle, all adults are female, parasitic in the small intestines of humans and dogs. Human infection is asymptomatic when the parasite load is low, but in large numbers they cause severe diarrhea and stomach-ache; in an immunodeficient host, there may be much more serious symptoms.
The rhabditiform larvae grow into free-living adult males and females. These adults mate and produce eggs in the soil. In unfavorable environments, they transform into infective filariform larvae, which penetrate the host’s skin, and migrate to, and mature in, the small intestine. Hatched rhabditiform larvae become filariform larvae in the small intestine, and then may penetrate the wall of the large intestine and spread into the body.
