What is the extraordinary life cycle of the intestinal threadworm?
The female worm lives in the intestine of the host where it lays eggs. Remarkably, the eggs can develop even though they have not been fertilized by a male. In fact, there are no adult male worms. The eggs hatch into larvae in the intestine and are passed out in the feces. These larvae can either develop into infective parasitic larvae or into free-living worms of either sex. The parasitic larvae enter a new host by penetrating the skin. They then migrate to the lungs, travel up the trachea and are swallowed. The free-living larvae mate but do not produce more free-living larvae, only infective larvae that must enter a host to survive. What determines whether the larvae passed in the feces develop into parasitic or free-living forms? It is believed that the severity and length of infection, the species, age of the host, and the status of the host’s immune system affect the development of the larvae. Some migrating larvae may remain in the tissues of a dog. In a bitch, these larvae can
