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Parasitic Nematodes

Parasitic Nematodes

Depending upon the species, the hosts for parasitic nematodes can be insects, plants, and animals. Approximately 60 species of nematodes (roundworms) are parasites in humans. This article provides information on the human and plant parasitic nematodes.
BiologyWise Staff
Last Updated: Apr 9, 2018
Nematodes are a group of pseudocoelomate animals, classified under the separate phylum Nematoda. Their digestive tract is a tube-like structure with openings at both ends, thus they are often described as organisms with a tube within a tube. Although there are beneficial species, the number of parasitic organisms is relatively more. Of the total 28,000 scientifically known pseudocoelomate animals, it is estimated that nearly 16,000 are harmful in some way or the other. Scientists are of the opinion that there might be around one hundred thousand pseudocoelomate animals.

Both parasitic (leech-like organism) and beneficial nematodes are characterized by the presence of pseudocoe (a false body cavity), which is why the term pseudocoelomate is used to define these invertebrates. The body encloses a false body cavity that is lined by three distinct layers. It is believed that the body cavity is lost as a result of mutation in successive generations. These invertebrates may attack insects, plants, or animals.

Humans
These parasites can attack the muscles, intestines, and other bodily tissues in humans. The modes of entry include bite by an infected vector, unintentional ingestion of eggs through consumables, and penetrative entry via skin. Examples are:
  • Roundworm: Represented scientifically as Ascaris lumbricoides, this is a pink-colored, large leech-like species (35 cm in length). Infection by roundworms occurs after ingesting contaminated food or through soil.
  • Whipworm: The whip-like species is known as whipworm (Trichuris trichiura). It is transmitted from contaminated soil. In case of mild intestinal infections, it might be asymptomatic.
  • Pinworm: Of the several parasitic species, pinworm (Enterobius vermicularis) causes the highest number of infections in the United States. This parasite is small in size (about 13 mm in length), and this infection occurs after ingestion of the eggs.
  • Hookworm: Under hookworm, there are two species called Ancylostoma duodenale and Necator americanus. As per medical data, they are the second leading intestinal parasites found in humans. At the time of infection, the larvae penetrate human skin.
  • Trichina: Infection of trichina (Trichinella spiralis) is called trichinosis. This parasite might be present in pork, and the person is infected by the consumption of undercooked pork. The larvae from the stomach later migrate to the muscular tissues.
Plants
A scoop of garden soil contains hundreds of nematodes. Thus, the damage to the plants usually occurs in the underground root system, as the roots are in direct contact with the parasitic organisms in the soil. They may make their way to the upper portion and feed on different plant parts. Common nematodes for plants are:
  • Root-knot: This is the most destructive invertebrate genus (Meloidogyne), in which some species are capable of infecting more than 1,000 plants. After infection in lawn grass and other plants, they feed in specific root areas and cause formation of root galls.
  • Stem and Bulb: Unlike the root-knot, this group affects the upper plant parts such as leaves, bulbs, and stems. They are classified under the genus Ditylenchus, and the name of the species vary according to the strain.
  • Cyst: In comparison to the root-knot, this invertebrate is parasitic in a narrow range of host plants. A commonly identified cyst invertebrate is Globodera pallida that exclusively attacks potato plants.
  • Lesion: Classified under the taxonomic genus Pratylenchus, this parasitic organism causes necrotic lesions in various part of ornamental plants, fruits, coffee, corn, and other crops.
  • Citrus Nematode: Identified by the scientific name, Tylenchulus semipenetrans, this parasitic organism affects citrus fruit plants. In severe cases, its symptoms mimic nutritional deficiency, and it causes a slow decline in the fruit yield.
The life cycle of nematodes differs according to the species. In general, the life cycle of the beneficial and the parasitic organism encompasses six stages. Starting with the egg stage, it hatches into larva, followed by three other immature stages, before entering the matured adult stage.

Disclaimer: This article is for informative purposes only and does not in any way attempt to replace the advice offered by an expert on the subject.