Parasitic Nematodes


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 Part A shows a foot with a guinea worm extending from a blister. The end of the worm is wrapped around a stick. Part B shows the life cycle of the guinea worm, which begins when a person drinks unfiltered water containing copepods infected with guinea worm larvae. Larvae, which are released when the copepods die, penetrate the wall of the stomach and intestine. The worms mature and reproduce. Fertilized females migrate to the surface of the skin, where they discharge larvae into the water. Copepods consume the larvae. The copepods are consumed by humans, completing the cycle. About a year after infection, the female worm emerges from the skin.
Life cycle of the guinea worm. The guinea worm Dracunculus medinensis infects about 3.5 million people annually, mostly in Africa. (a) Here, the worm is wrapped around a stick so it can be slowly extracted. (b) Infection occurs when people consume water contaminated by infected copepods, but this can easily be prevented by simple filtration systems. (credit: modification of work by CDC)

OpenStax Biology 2e

A number of common parasitic nematodes serve as prime examples of parasitism (endoparasitism). These economically and medically important animals exhibit complex life cycles that often involve multiple hosts, and they can have significant medical and veterinary impacts. Here is a partial list of nasty nematodes: Humans may become infected by Dracunculus medinensis, known as guinea worms, when they drink unfiltered water containing copepods, an intermediate crustacean host. Hookworms, such as Ancylostoma and Necator, infest the intestines and feed on the blood of mammals, especially of dogs, cats, and humans. Trichina worms (Trichinella) are the causal organism of trichinosis in humans, often resulting from the consumption of undercooked pork; Trichinella can infect other mammalian hosts as well. Ascaris, a large intestinal roundworm, steals nutrition from its human host and may create physical blockage of the intestines. The filarial worms, such as Dirofilaria and Wuchereria, are commonly vectored by mosquitoes, which pass the infective agents among mammals through their blood-sucking activity. One species, Wuchereria bancrofti, infects the lymph nodes of over 120 million people worldwide, usually producing a non-lethal but deforming condition called elephantiasis. In this disease, parts of the body often swell to gigantic proportions due to obstruction of lymphatic drainage, inflammation of lymphatic tissues, and resulting edema. Dirofilaria immitis, a blood-infective parasite, is the notorious dog heartworm species.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: