page_title: Trichinella
section_title: Prevalence in animals and humans
hierarchical_section_title: Trichinella / Prevalence in animals and humans
caption_attribution_description: September 1847: With skill, experience, vigor, and ideas of his own, Carl Zeiss starts making microscopes on his new premises at Wagnergasse 32 in Jena. These are simple microscopes, consisting of one lens only and intended mainly for dissecting work. During the first year, Zeiss sells as many as 23 of them, an indication that they do well in comparison to other makes. Nevertheless, they undergo many improvements during the following years. www.musoptin.com Images donated as part of a GLAM collaboration with Carl Zeiss Microscopy - please contact Andy Mabbett for details.
context_page_description: 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 is the one-way digestive tract, with a pseudocoelom.
  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 parasites of animals, including humans. Infections with this genus have been 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.
  Trichinella is the smallest human nematode parasite, yet it is also the largest of all intracellular parasites.
  Oral ingestion of larvae-contaminated tissue is the usual route of infection, but congenital and mammary transmission can occur in rats.
context_section_description: Trichinella species can infect swine, 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:
  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, horses from Mexico and Romania have been found to be infected.
  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 to 1996, with few implicating raw or undercooked pork. Documented sources of human infection have also included game meats, such as wild boar, bear, walrus, fox, and cougar. From 1997 to 2001 meats other than pork were the most common source of infection, with more cases associated with home-raised pork than commercial. The decreased incidence of trichinellosis in the United States has resulted from changes in pork industry management standards and government regulations.
  In Finland, meat inspection revealed a small but worrisome number of swine infections in the early 1980s, peaking in 1996. However, due to the swine industry's modernization process, the number of cases decreased, with the last infected swine diagnosed in 2004. As of 2010 only eight known human infections had been reported in Finland since the 1800s, with the last one more than three decades before.
  A study of the sera from 197 wild boars from 25 farms slaughtered in Finland between 2007 and 2008 found four (2.0%) of the sera, originating from three (12.0%) farms, to be Trichinella-seropositive.
  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.
  Knowledge on the epidemiology, host range and transmission of Trichinella species occurring in wildlife in sub-Saharan Africa is limited. However, hypothetical transmission cycles have been proposed for Trichinella zimbabwensis, Trichinella T8 and Trichinella nelsoni; these cycles consider the role of Lions and Spotted Hyenas as apex predators.
caption: A microscope for Trichinella detection (from 1847).
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