Trichinella

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Trichinella
Trichinella larv1 DPDx.JPG
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Nematoda
Class: Enoplea
Order: Trichocephalida
Family: Trichinellidae
Genus: Trichinella
Railliet, 1895
Species

Trichinella britovi
Trichinella murrelli
Trichinella nativa
Trichinella nelsoni
Trichinella papuae
Trichinella pseudospiralis
Trichinella spiralis
Trichinella zimbabwensis

Trichinella is the genus of parasitic roundworms of the phylum Nematoda that cause trichinosis (also known as trichinellosis). Members of this genus are often called trichinella or trichina worms. A characteristic of Nematoda is the one-way digestive tract, with 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 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 cyst- or larvae-contaminated tissue is the usual route of infection, but congenital and mammary transmission can occur in rats. [1]

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. zimbabwensis) that does not.

The nonencapsulated group infects saurians, crocodilians, and other nonavian archosaurs (T. papuae, T. zimbabwensis) and birds (T. pseudospiralis). The encapsulated group infects 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

A microscope for Trichinella detection (from 1847). 1847 "Praepariermikroskop" First simple microscope for Trichinella detection by Carl Zeiss Jena (7039026859).jpg
A microscope for Trichinella detection (from 1847).

Trichinella species can infect swine, wild omnivores (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:

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, [2] [3] 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.[ citation needed ] Other herbivores, such as moose may also be a potential host and source of Trichinella, however data is inconclusive. [4]

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. [5]

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. By 2010, only eight known human infections had been reported in Finland since the 1800s, with the last one more than three decades before. [6]

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. [7]

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. [8]

Detection

Artificial digestion is used to detect the presence of encysted trichinella larvae in suspected muscle tissue. The meat sample is dissolved by a digestive solution and the remains are examined for the presence of larvae.

Treatment

Treatment is by either thiabendazole or mebendazole.

Prevention

Trichinella infection can be prevented by cooking pork meat properly, or by freezing pork. However, freezing pork is not an effective method for killing larvae.

One way to prevent trichinellosis is to cook meat to a safe temperature (at least 145 °F, 63 °C internal temperature as measured by a food thermometer, followed by a three-minute rest for fresh pork). [9] The meat is not safe until cooking is completed. To help prevent Trichinella infection in animal populations, pigs or wild animals should be prevented from eating uncooked meat, scraps, or carcasses of any animals, including rats, which may be infected with Trichinella, [10] in order to break the oral ingestion cycle of infection.

Related Research Articles

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Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or months of mild, flu-like illness such as muscle aches and tender lymph nodes. In a small number of people, eye problems may develop. In those with a weak immune system, severe symptoms such as seizures and poor coordination may occur. If a woman becomes infected during pregnancy, a condition known as congenital toxoplasmosis may affect the child.

<span class="mw-page-title-main">Trichinosis</span> Parasitic disease due to invasion by Trichinella spp.

Trichinosis, also known as trichinellosis, is a parasitic disease caused by roundworms of the Trichinella type. During the initial infection, invasion of the intestines can result in diarrhea, abdominal pain, and vomiting. Migration of larvae to muscle, which occurs about a week after being infected, can cause swelling of the face, inflammation of the whites of the eyes, fever, muscle pains, and a rash. Minor infection may be without symptoms. Complications may include inflammation of heart muscle, central nervous system involvement, and inflammation of the lungs.

<i>Toxoplasma gondii</i> Type of protozoan parasite

Toxoplasma gondii is a parasitic protozoan that causes toxoplasmosis. Found worldwide, T. gondii is capable of infecting virtually all warm-blooded animals, but felids are the only known definitive hosts in which the parasite may undergo sexual reproduction.

Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms, ingestion takes place by absorbing a substance through the cell membrane.

<span class="mw-page-title-main">Cysticercosis</span> Tissue infection caused by the young form of the pork tapeworm

Cysticercosis is a tissue infection caused by the young form of the pork tapeworm. People may have few or no symptoms for years. In some cases, particularly in Asia, solid lumps of between one and two centimetres may develop under the skin. After months or years these lumps can become painful and swollen and then resolve. A specific form called neurocysticercosis, which affects the brain, can cause neurological symptoms. In developing countries this is one of the most common causes of seizures.

<span class="mw-page-title-main">Natural reservoir</span> Type of population in infectious disease ecology

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<i>Trichinella spiralis</i> Species of roundworm

Trichinella spiralis is a viviparous nematode parasite, occurring in rodents, pigs, bears, hyenas and humans, and is responsible for the disease trichinosis. It is sometimes referred to as the "pork worm" due to it being typically encountered in undercooked pork products. It should not be confused with the distantly related pork tapeworm.

<i>Taenia</i> (tapeworm) Genus of flatworms

Taenia is the type genus of the Taeniidae family of tapeworms. It includes some important parasites of livestock. Members of the genus are responsible for taeniasis and cysticercosis in humans, which are types of helminthiasis belonging to the group of neglected tropical diseases. More than 100 species are recorded. They are morphologically characterized by a ribbon-like body composed of a series of segments called proglottids; hence the name Taenia. The anterior end of the body is the scolex. Some members of the genus Taenia have an armed scolex ; of the two major human parasites, Taenia saginata has an unarmed scolex, while Taenia solium has an armed scolex.

Artificial digestion is a laboratory technique that reduces food to protein, fat, carbohydrates, fiber, minerals, vitamins, and non-nutrient compounds for analytical or research purposes. Digestive agents such as pepsin and hydrochloric acid are typically used to accomplish artificial digestion.

<span class="mw-page-title-main">Pig</span> Domesticated omnivorous even-toed ungulate

The pig, also called swine or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus Sus. It is considered a subspecies of Sus scrofa by some authorities, but as a distinct species by others. Pigs were domesticated in the Neolithic, both in East Asia and in the Near East. When domesticated pigs arrived in Europe, they extensively interbred with wild boar but retained their domesticated features.

Spirometra erinaceieuropaei is a parasitic tapeworm that infects domestic animals and humans. The medical term for this infection in humans and other animals is sparganosis. Morphologically, these worms are similar to other worms in the genus Spirometra. They have a long body consisting of three sections: the scolex, the neck, and the strobilia. They have a complex life cycle that consists of three hosts, and can live in varying environments and bodily tissues. Humans can contract this parasite in three main ways. Historically, humans are considered a paratenic host; however, the first case of an adult S. erinaceieuropaei infection in humans was reported in 2017. Spirometra tapeworms exist worldwide and infection is common in animals, but S. erinaceieuropaei infections are rare in humans. Treatment for infection typically includes surgical removal and anti-worm medication.

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<i>Capillaria hepatica</i> Species of roundworm

Capillaria hepatica is a parasitic nematode which causes hepatic capillariasis in rodents and numerous other mammal species, including humans. The life cycle of C. hepatica may be completed in a single host species. However, the eggs, which are laid in the liver, must mature outside of the host body prior to infecting a new host. So the death of the host in which the adults reach sexual maturity, either by being eaten or dying and decomposing, is necessary for completion of the life cycle.

<i>Dirofilaria repens</i> Species of roundworm

Dirofilaria repens is a filarial nematode that affects dogs and other carnivores such as cats, wolves, coyotes, foxes, and sea lions, as well as muskrats. It is transmitted by mosquitoes. Although humans may become infected as aberrant hosts, the worms fail to reach adulthood while infecting a human body.

<i>Trichinella britovi</i> Species of roundworm

Trichinella britovi is a nematode parasite responsible for a zoonotic disease called trichinellosis. Currently, eight species of Trichinella are known, only three of which cause trichinellosis, and Trichinella britovi is one of them. Numerous mammal species, as well as birds and crocodiles, can harbor the parasite worldwide, but the sylvatic cycle is mainly maintained by wild carnivores.

Trichinella nativa is a nematode worm, one of the species of the genus Trichinella, found in arctic and subarctic regions.

<i>Alaria</i> (flatworm) Genus of flukes

Alaria is a genus of flatworms, or trematodes, in the family Diplostomidae.

Trichinella papuae is a nematode parasite responsible for a zoonotic disease called trichinellosis, predominantly in Thailand. Currently, eight species of Trichinella are known.

<span class="mw-page-title-main">Cat worm infections</span> Worm infections in cats

Cat worm infections, the infection of cats (Felidae) with parasitic worms, occur frequently. Most worm species occur worldwide in both domestic and other cats, but there are regional, species and lifestyle differences in the frequency of infestation. According to the classification of the corresponding parasites in the zoological system, infections can be divided into those caused by nematode and flatworms - in the case of the latter, mainly cestoda and trematoda - while other strains are of no veterinary significance. While threadworms usually do not require an intermediate host for their reproduction, the development cycle of flatworms always proceeds via alternate hosts.

<span class="mw-page-title-main">Nematode infection in dogs</span> Threadworm infections of dogs are frequent

Nematode infection in dogs - the infection of dogs with parasitic nemamotodes - are, along with tapeworm infections and infections with protozoa, frequent parasitoses in veterinary practice. Nematodes, as so-called endoparasites, colonize various internal organs - most of them the digestive tract - and the skin. To date, about 30 different species of nematode have been identified in domestic dogs; they are essentially also found in wild dog species. However, the majority of them often cause no or only minor symptoms of disease in adult animals. The infection therefore does not necessarily have to manifest itself in a worm disease (helminthosis). For most nematodes, an infection can be detected by examining the feces for eggs or larvae. Roundworm infection in dogs and the hookworm in dogs is of particular health significance in Central Europe, as they can also be transmitted to humans (zoonosis). Regular deworming can significantly reduce the frequency of infection and thus the risk of infection for humans and dogs.

References

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