Parasitic Nematodes

 There are a great many species of parasitic nematodes and they attack virtually all groups of animals and plants. Parasitic forms include ascarids, hookworms, Guinea worms, trichina worms, pinworms, and filarial worms.

Heartworm

Heartworms may be a parasite you’re all too familiar with if you’ve been unfortunate enough to own a dog or cat that was diagnosed with this disease. Heartworms can live in a dog’s heart and lungs for years and can be fatal to the animal. Another species of nematode can cause the condition known as elephantiasis. These parasitic worms reside in human lymph nodes and obstruct the flow of fluid, which causes severe and sometimes debilitating swelling.

                           Ascaris lumbricoides: large roundworm of humans

It’s estimated that worldwide as many as 1.4 billion people are infected with Ascaris lumbricoides which lives in the small intestine. Infection occurs when parasite eggs are eaten with uncooked food or when soiled fingers are put into the mouth.

 Hookworms

Hookworms are named for the dorsal curve in their anterior end. Hookworms are quite small, the commonest species Necator americanus is only 11mm long.  However, because they feed on blood a heavy infection can produce severe anemia. Large plates in the hookworm’s mouth are used to cut the intestinal lining of the host according to Bird and Bird (2012).  The parasite then pumps blood through its gut, partially digesting it before excreting it. Because hookworms suck more blood than they use, they can cause debilitating anemia. In children a hookworm infection can stunt growth and cause a general lack of energy. Infection occurs after a larva hatches from an egg and penetrates the skin of a person.  It then makes its way to the lungs where eventually it is coughed up and swallowed and travels to the intestines.

                                                             Guinea worms

Guinea worm infections (also referred to as Dracunculiasis) are now confined to sub-Saharan Africa.  Adults are threadlike nematode worms that can grow to 1 meter in length. The adult lives in humans and the intermediate host is tiny crustaceans. Humans become infected when they drink water containing the crustaceans. (Bird, 2012)

Filarial worms

Filarial worms are thread-like nematodes of which there are at least 8 species for which humans, especially in tropical regions, are the definitive host.  Approximately 250 million people worldwide are infected with these worms which are spread by mosquitoes.  Different species inhabit different locations in the body.  Some live in the lymphatic system, others subcutaneously and others in the abdominal cavity.

Trichina worms

Trichinella spiralis is a tiny nematode that causes the potentially fatal disease trichinosis. Humans typically become infected by eating undercooked pork.  Trichinella lives in cysts formed in individual muscle cells of the host. Trichinella, just as a virus does, manipulates the host cell’s DNA.  It causes the cell to recruit a blood supply to supply food to the cell and also produce collagen to form a cyst around the cell. (Sikora, Coyne, Hallmann & Timper, 2018).