Trichinella
| Trichinella | |
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| Genus: | Trichinella Railliet, 1895
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Trichinella britovi | |
Trichinella is the genus of parasitic roundworms of the phylum Nematoda that cause trichinosis. Members of this genus are often called trichinella or trichina worms. A characteristic of nematoda are one-way digestive tract, and a pseudocoelom (body cavity made up of only an ectoderm and endoderm).
The genus was first recognised in a larval form in 1835. The L1 larvae live in a modified skeletal muscle cell. The adult worms occupy a membrane-bound portion of columnar epithelium, living as intramulticellular parasite. Infections with this genus have reported from more than 150 different naturally or experimentally infected hosts. It has been shown to have a worldwide distribution in domestic and/or sylvatic animals.
Phylogenetics
Eight species are currently recognized. Four additional genotypes require adequate description before they can be recognized as valid species.
Two main clades are recognized in the genus: one group (T. britovi, T. murrelli, T. nativa, T. nelsoni, T. spiralis) that encapsulates in host muscle tissue and a second (T. papuae, T. pseudospiralis, T. zimbabwensisi) that does not.
The non encapsulated group infect saurians, crocodilians and other nonavian archosaurs (T. papuae, T. zimbabwensis) and birds (T. pseudospiralis). The encapsulated group infect synapsid and mammalian hosts. T. spiralis and T. nelsoni appear to be basal in the encapsulated group and T. murrelli and T. nativa the most recently evolved.
Prevalence in Animals and Humans
Trichinella species can infect swine, horses, wild animals (foxes, wolves, bears, skunk, raccoons, rats, and other small mammals) and humans.
In swine, the prevalence varies from country to country, and regionally. Long standing meat inspection programs in some European countries have drastically lowered prevalence rates among domestic swine. Domestic swine can be exposed to the parasite by the following three ways:
- Feeding of animal waste products or other feed contaminated with Trichinella
- Exposure to infected rodents or other infected wildlife
- Cannibalism within an infected herd
In wild animals, Trichinella infection rates vary from region to region and seem to increase in colder climates. Foxes, wolves and bears have the highest infection rates, but small mammals such as skunks, raccoons and rats provide the highest risk to infecting the domestic pig. In horses, natural infections are rare; however, infected horses from Mexico and Romania have been identified.
Human infection caused by the domestic pig varies from country to country. While some countries do not report any human infection, other countries in Eastern Europe and Asia report hundreds or thousands of cases annually.
The United States, reported 25 cases per year from 1991-1996 with few implicating pork. Documented sources of human infection have also included game meats such as wild boar, bear, walrus, fox and cougar.
Trichinosis is often diagnosed in humans once the larvae invade the muscle tissue. Some symptoms include fever, myalgia, malaise and edema. Trichinosis treatment focuses on reducing inflammation, and corticosteroids are usually administered. This treatment often leads to complete recovery, but muscle pain and weakness may persist.[1]
Treatment: Treatment is by either Thiabendazole or Mebendazole
Notes and references
- ^ Smith, Tara (August 2008). "A Focus on Trichinella: A Nematode Parasite". National Agricultural Library, Food Safety Research Information Office. Retrieved December 17, 2008.