Trichinosis
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Trichinosis, also known as trichinellosis, is a
parasitic disease A parasitic disease, also known as parasitosis, is an infectious disease caused by parasites. Parasites are organisms which derive sustenance from its host while causing it harm. The study of parasites and parasitic diseases is known as parasitol ...
caused by roundworms of the '' Trichinella'' genus. During the initial infection, invasion of the
intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...
can result in
diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...
,
abdominal pain Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Since the abdomen contains most of the body's vital organs, it can be an indicator of a wide variety of diseases. Given th ...
, and
vomiting Vomiting (also known as emesis, puking and throwing up) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteritis, pre ...
. Migration of
larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...
to muscle, which occurs about a week after being infected, can cause swelling of the face, inflammation of the whites of the eyes,
fever Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...
, muscle pains, and a
rash A rash is a change of the skin that affects its color, appearance, or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracke ...
. Minor infection may be without symptoms. Complications may include inflammation of heart muscle,
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...
involvement, and inflammation of the lungs. Trichinosis is mainly spread when undercooked meat containing ''Trichinella''
cysts A cyst is a closed Wikt:sac, sac, having a distinct Cell envelope, envelope and cell division, division compared with the nearby Biological tissue, tissue. Hence, it is a cluster of Cell (biology), cells that have grouped together to form a sac ...
is eaten. Wild meat is more likely to contain the parasite. In North America this is most often bear, but infection can also occur from pork, boar, and dog meat. Several
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of ''Trichinella'' can cause disease, with ''T. spiralis'' being the most common. After the infected meat has been eaten, the larvae are released from their cysts in the stomach. They then invade the wall of the
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...
, where they develop into adult worms. After one week, the females release new larvae that migrate to voluntarily controlled muscles, where they form cysts. The diagnosis is usually based on symptoms and confirmed by finding specific antibodies in the blood, or larvae on
tissue biopsy A biopsy is a medical test commonly performed by a surgeon, an interventional radiologist, or an interventional cardiologist. The process involves the extraction of sample cells or tissues for examination to determine the presence or extent o ...
. The best way to prevent trichinosis is to fully cook meat. A food thermometer can verify that the temperature inside the meat is high enough. Infection is typically treated with antiparasitic medication such as
albendazole Albendazole is a broad-spectrum antihelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, hookworm infection, trichuri ...
or mebendazole. Rapid treatment may kill adult worms and thereby stop further worsening of symptoms. Both medications are considered safe but have been associated with side effects such as bone marrow suppression. Their use during pregnancy or in children under the age of 2 years is poorly studied but appears to be safe. Treatment with steroids is sometimes also required in severe cases. Without treatment, symptoms typically resolve within three months. Worldwide, about 10,000 infections occur a year. At least 55 countries including the United States, China, Argentina, and Russia have had recently documented cases. While the disease occurs in the tropics, it is less common there. Rates of trichinosis in the United States have decreased from about 400 cases per year in the 1940s to 20 or fewer per year in the 2000s. The risk of death from infection is low.


Signs and symptoms

The great majority of trichinosis infections have either minor or no symptoms and no complications. The two main phases for the infection are enteral (affecting the intestines) and parenteral (outside the intestines). The symptoms vary depending on the phase, species of ''Trichinella'', the quantity of encysted larvae ingested, age, sex, and host immunity.


Enteral phase

A large burden of adult worms in the intestines promotes symptoms such as
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...
,
heartburn Heartburn is a burning sensation felt behind the breastbone. It is a symptom that is commonly linked to acid reflux and is often triggered by food, particularly fatty, sugary, spicy, chocolate, citrus, onion-based and tomato-based products. Ly ...
,
dyspepsia Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, or upper abdominal pain. People may also experience feeling full earlier ...
, and
diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...
from two to seven days after infection, while small worm burdens generally are asymptomatic. Eosinophilia presents early and increases rapidly.


Parenteral phase

The severity of symptoms caused by larval migration from the intestines depends on the number of larvae produced. As the larvae migrate through tissue and vessels, the body's inflammatory response results in
edema Edema (American English), also spelled oedema (British English), and also known as fluid retention, swelling, dropsy and hydropsy, is the build-up of fluid in the body's tissue (biology), tissue. Most commonly, the legs or arms are affected. S ...
, muscle pain, fever, and weakness. A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by
vasculitis Vasculitis is a group of disorders that destroy blood vessels by inflammation. Both artery, arteries and veins are affected. Lymphangitis (inflammation of lymphatic vessels) is sometimes considered a type of vasculitis. Vasculitis is primarily c ...
. Splinter hemorrhage in the nails is also a common symptom.John D. and William A. Petri. Markell and Voge's Medical Parasitology. 9th ed. Philadelphia: Saunders, 2006. They may very rarely cause enough damage to produce serious neurological deficits (such as
ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...
or respiratory paralysis) from worms entering the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...
(CNS), which is compromised by trichinosis in 10–24% of reported cases of cerebral venous sinus thrombosis, a very rare form of stroke (three or four cases per million annual incidence in adults). Trichinosis can be fatal depending on the severity of the infection; death can occur 4–6 weeks after the infection, and is usually caused by
myocarditis Myocarditis is inflammation of the cardiac muscle. Myocarditis can progress to inflammatory cardiomyopathy when there is associated ventricular remodeling and cardiac dysfunction due to chronic inflammation. Symptoms can include shortness of bre ...
,
encephalitis Encephalitis is inflammation of the Human brain, brain. The severity can be variable with symptoms including reduction or alteration in consciousness, aphasia, headache, fever, confusion, a stiff neck, and vomiting. Complications may include se ...
, or
pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...
.


Cause

The classical agent is ''T. spiralis'' (found worldwide in many carnivorous and omnivorous animals, both domestic and sylvatic (wild), but seven primarily sylvatic species of ''Trichinella'' also are now recognized:


Species and characteristics

* ''T. spiralis'' is most adapted to swine, most pathogenic in humans, and is cosmopolitan in distribution. * ''T. britovi'' is the second-most common species to infect humans; it is distributed throughout Europe, Asia, and northern and western Africa, usually in wild carnivores, crocodiles, birds, wild boar, and domesticated pigs. * ''T. murrelli'' also infects humans, especially from black bear meat; it is distributed among wild carnivores in North America. * ''T. nativa'', which has a high resistance to freezing, is found in the Arctic and subarctic regions; reservoir hosts include polar bears, Arctic foxes, walruses, and other wild game. * ''T. nelsoni'', found in East African predators and scavengers, has been documented to cause a few human cases. * '' T. papuae'' infects both mammals and reptiles, including crocodiles, humans, and wild and domestic pigs; this species, found in Papua New Guinea and Thailand, is also nonencapsulated. * ''T. pseudospiralis'' infects birds and mammals, and has demonstrated infection in humans; it is a nonencapsulated species. * ''T. zimbabwensis'' can infect mammals, and possibly humans; this nonencapsulated species was detected in crocodiles in Africa.


Taxonomy

* Kingdom: Animalia * Phylum: Nematoda * Class: Adenophorea * Order: Trichurida * Family: Trichinellidae * Genus: ''Trichinella''


Lifecycle

The typical lifecycle for ''T. spiralis'' involves humans, pigs, and rodents. A pig becomes infected when it eats infectious cysts in raw meat, often porcine
carrion Carrion (), also known as a carcass, is the decaying flesh of dead animals. Overview Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...
or a
rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...
( sylvatic cycle). A human becomes infected by consuming raw or undercooked infected pork (domestic cycle). In the stomach, the
cyst A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubb ...
s from infected undercooked meat are acted on by
pepsin Pepsin is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pe ...
and
hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
, which help release the larvae from the cysts into the
stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
. The larvae then migrate to the
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...
, and burrow into the intestinal mucosa, where they molt four times before becoming adults. Thirty to 34 hours after the cysts were originally ingested, the adults mate, and within five days produce larvae. Adult worms can only reproduce for a limited time because the
immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...
eventually expels them from the small intestine. The larvae then use their piercing mouthpart, called the "stylet", to pass through the intestinal mucosa and enter the
lymphatic vessel The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessel ...
s, and then enter the bloodstream. The larvae travel by
capillaries A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the in ...
to various organs, such as the
retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
,
myocardium Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall o ...
, or
lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that includ ...
s; however, only larvae that migrate to
skeletal muscle Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...
cells survive and encyst. The larval host cell becomes a nurse cell, in which the larva will be encapsulated, potentially for the life of the host, waiting for the host to be eaten. The development of a capillary network around the nurse cell completes encystation of the larva. Trichinosis is not soil-transmitted, as the
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
does not lay eggs, nor can it survive long outside a host.


Diagnosis

Diagnosis of trichinosis is confirmed by a combination of exposure history, clinical diagnosis, and laboratory testing.


Exposure history

An epidemiological investigation can be done to determine a patient's exposure to raw infected meat. Often, an infection arises from home preparation of contaminated meat, in which case microscopy of the meat may be used to determine the infection. Exposure determination does not have to be directly from a laboratory-confirmed infected animal. Indirect exposure criteria include the consumption of products from a laboratory-confirmed infected animal or sharing of a common exposure with a laboratory-confirmed infected human.


Clinical diagnosis

Clinical presentation of the common trichinosis symptoms may also suggest infection. These symptoms include eye puffiness, splinter hemorrhage, nonspecific
gastroenteritis Gastroenteritis, also known as infectious diarrhea, is an inflammation of the Human gastrointestinal tract, gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of ...
, and muscle pain. The case definition for trichinosis at the European Center for Disease Control states, "at least three of the following six:
fever Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...
, muscle soreness and pain, gastrointestinal symptoms, facial
edema Edema (American English), also spelled oedema (British English), and also known as fluid retention, swelling, dropsy and hydropsy, is the build-up of fluid in the body's tissue (biology), tissue. Most commonly, the legs or arms are affected. S ...
, eosinophilia, and subconjunctival, subungual, and retinal hemorrhages."


Laboratory testing

Blood tests and
microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical mic ...
can be used to aid in the diagnosis of trichinosis. Blood tests include a complete blood count for eosinophilia, creatine phosphokinase activity, and various immunoassays such as
ELISA The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of ...
for larval antigens. In some cases, muscle biopsies are performed, where "0.2 to 0.5 grams of human or animal skeletal muscle tissue is collected and examined for Trichinella larvae via artificial digestion or histological analysis."


Prevention


Legislation

Laws and rules for food producers may improve food safety for consumers, such as the rules established by the
European Commission The European Commission (EC) is the primary Executive (government), executive arm of the European Union (EU). It operates as a cabinet government, with a number of European Commissioner, members of the Commission (directorial system, informall ...
for inspections, rodent control, and improved hygiene. A similar protocol exists in the United States, in the
USDA The United States Department of Agriculture (USDA) is an United States federal executive departments, executive department of the Federal government of the United States, United States federal government that aims to meet the needs of commerc ...
guidelines for farms and slaughterhouse responsibilities in inspecting pork.


Education and training

Public education about the dangers of consuming raw and undercooked meat, especially pork, may reduce infection rates. Hunters are also an at-risk population due to their contact and consumption of wild game, including bears. As such, many states, such as New York, require the completion of a course in such matters before a hunting license can be obtained.


Meat testing

Testing methods are available for both individual carcasses and monitoring of the herds. Artificial digestion method is usually used for the testing of individual carcasses, while the testing for specific antibodies is usually used for herd monitoring.


Food preparation

Larvae may be killed by the heating or irradiation of raw meat. Freezing is normally only effective for ''T. spiralis'', since other species, such as ''T. nativa'', are freeze-resistant and can survive long-term freezing. * All
meat Meat is animal Tissue (biology), tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of vertebrates, including chickens, sheep, ...
(including pork) can be safely prepared by cooking to an internal temperature of or higher for 15 seconds or more. * Wild game: Wild game meat must be cooked thoroughly (see meat preparation above). Freezing wild game does not kill all trichinosis larval worms, because the worm species that typically infests wild game can resist freezing. *
Pork Pork is the culinary name for the meat of the pig (''Sus domesticus''). It is the most commonly consumed meat worldwide, with evidence of pig animal husbandry, husbandry dating back to 8000–9000 BCE. Pork is eaten both freshly cooke ...
: Freezing cuts of pork less than 6 inches thick for 20 days at 5 °F (−15 °C) or three days at −4 °F (−20 °C) kills ''T. spiralis'' larval worms; but this will not kill other trichinosis larval worm species, such as ''T. nativa'', if they have infested the pork food supply (which is unlikely, due to geography). Pork can be safely cooked to a slightly lower temperature, provided that the internal meat temperature is at least as hot for at least as long as listed in the
USDA The United States Department of Agriculture (USDA) is an United States federal executive departments, executive department of the Federal government of the United States, United States federal government that aims to meet the needs of commerc ...
table below. Nonetheless, allowing a
margin of error The margin of error is a statistic expressing the amount of random sampling error in the results of a Statistical survey, survey. The larger the margin of error, the less confidence one should have that a poll result would reflect the result of ...
for variation in internal temperature within a particular cut of pork, which may have bones that affect temperature uniformity, is prudent. In addition, kitchen thermometers have measurement errors that must be considered. Pork may be cooked for significantly longer and at a higher uniform internal temperature than listed below to be safe. Unsafe and unreliable methods of cooking meat include the use of microwave ovens, curing, drying, and smoking, as these methods are difficult to standardize and control.


Pig farming

Incidence of infection can be reduced by: * Keeping pigs in clean pens, with floors that can be washed (such as concrete) * Not allowing hogs to eat carcasses of other animals, including rats, which may be infected with ''Trichinella'' * Cleaning meat grinders thoroughly when preparing ground meats * Control and destruction of meat containing trichinae, e.g., removal and proper disposal of porcine diaphragms before public sale of meat The US
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...
makes the following recommendation: "Curing (salting), drying, smoking, or microwaving meat does not consistently kill infective worms." However, under controlled commercial food processing conditions, some of these methods are considered effective by the USDA. The USDA Animal and Plant Health Inspection Service (APHIS) is responsible for the regulations concerning the importation of swine from foreign countries. The Foreign Origin Meat and Meat Products, Swine section covers swine meat (cooked, cured, dried, and fresh). APHIS developed the National Trichinae Certification Program; this is a voluntary "preharvest" program for U.S. swine producers "that will provide documentation of swine management practices" to reduce the incidence of ''Trichinella'' in swine.USDA Animal and Plant Health Inspection Service APHIS – Veterinary Services. Retrieved February 11, 2009, The CDC reports 0.013% of U.S. swine are infected with ''Trichinella''.


Treatment

As with most diseases, early treatment is better and decreases the risk of developing the disease. If larvae do encyst in skeletal muscle cells, they can remain infectious for months to years.


Primary treatment

Early administration of
anthelmintics Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms ( helminths) and other internal parasites from the body by either stunning or killing them without causing significant damage to the host. They may als ...
, such as mebendazole or
albendazole Albendazole is a broad-spectrum antihelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, hookworm infection, trichuri ...
, decreases the likelihood of larval encystation, particularly if given within three days of infection. However, most cases are diagnosed after this time. In humans, mebendazole (200–400 mg three times a day for three days) or albendazole (400 mg twice a day for 8–14 days) is given to treat trichinosis. These drugs prevent newly hatched larvae from developing, but should not be given to pregnant women or children under two years of age. Medical references from the 1940s described no specific treatment for trichinosis at the time, but intravenous injection of calcium salts was found to be useful in managing symptoms related to severe toxemia from the infection.


Secondary treatment

After infection,
steroids A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter mem ...
, such as
prednisone Prednisone is a glucocorticoid medication mostly used to immunosuppressive drug, suppress the immune system and decrease inflammation in conditions such as asthma, COPD, and rheumatologic diseases. It is also used to treat high blood calcium ...
, may be used to relieve muscle pain associated with larval migration.


Vaccine research

Researchers trying to develop a vaccine for ''Trichinella'' have tried using either "larval extracts, excretory-secretory antigen, DNA, or recombinant antigen protein." Currently, no marketable vaccine is available for trichinosis, but experimental mouse studies have suggested possibilities. * In one study, microwaved ''Trichinella'' larvae were used to immunize mice (orally or intraperitoneally), which were subsequently infected. Depending on the dosage and frequency of immunization, results ranged from a decreased larval count to complete protection from trichinosis. * Another study used extracts and excretory-secretory products from first-stage larvae to produce an oral vaccine. To prevent gastric acids from dissolving the antigens before reaching the small intestine, scientists encapsulated the antigens in microcapsules. This vaccine significantly increased CD4+ cell levels, and increased antigen-specific serum IgGq and IgA, resulting in a statistically significant reduction in the average number of adult worms in the small intestines of mice. The significance of this approach is that, if the white blood cells in the small intestine have been exposed to ''Trichinella'' antigens (through vaccination) when an individual does get infected, the immune system will respond to expel the worms from the small intestine fast enough to prevent the female worms from releasing their larvae. * A DNA vaccine tested on mice "induced a muscle larva burden reduction in BALB/c mice by 29% in response to ''T. spiralis'' infection".


Epidemiology

About 11 million humans are infected with ''Trichinella''; ''T. spiralis'' is the species responsible for most of these infections. Infection was once very common, but this disease is now rare in the
developed world A developed country, or advanced country, is a sovereign state that has a high quality of life, developed economy, and advanced technological infrastructure relative to other less industrialized nations. Most commonly, the criteria for eval ...
, but two known outbreaks occurred in 2015. In the first outbreak, around 40 people were infected in Liguria, Italy, during a New Year's Eve celebration. The second outbreak in France was associated with pork sausages from
Corsica Corsica ( , , ; ; ) is an island in the Mediterranean Sea and one of the Regions of France, 18 regions of France. It is the List of islands in the Mediterranean#By area, fourth-largest island in the Mediterranean and lies southeast of the Metro ...
, which were eaten raw, affecting 14 people in total. The incidence of trichinosis in the U.S. has decreased dramatically in the past century from an average of 400 cases per year mid-20th century down to an annual average of 20 cases per year (2008–10). The number of cases has decreased because of legislation prohibiting the feeding of raw meat garbage to hogs, increased commercial and home freezing of pork, and the public awareness of the danger of eating raw or undercooked pork products. China reports around 10,000 cases every year and is the country with the highest number of cases. In China, between 1964 and 1998, over 20,000 people became infected with trichinosis, and more than 200 people died. Trichinosis is common in developing countries where meat fed to pigs is raw or undercooked, but infections also arise in developed countries in Europe where raw or undercooked pork, wild boar, and horse meat may be consumed as delicacies. In the
developing world A developing country is a sovereign state with a less-developed industrial base and a lower Human Development Index (HDI) relative to developed countries. However, this definition is not universally agreed upon. There is also no clear agreeme ...
, most infections are associated with undercooked pork. For example, in
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
, between 200 and 600 cases are reported annually around the Thai New Year. This is mostly attributable to a particular delicacy, '' larb'', which calls for undercooked pork as part of the recipe. In parts of Eastern Europe, the
World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...
reports, some swine herds have trichinosis infection rates above 50%, with correspondingly large numbers of human infections.


United States

Historically, pork products were thought to have the most risk of infecting humans with ''T. spiralis''. However, a trichinosis surveillance conducted between 1997 and 2001 showed a higher percentage of cases caused by consumption of wild game (the sylvatic transmission cycle). This is thought to be due to the Federal Swine Health Protection Act (Public Law 96-468) that was passed by Congress in 1980. Before this act, swine were fed garbage that could potentially be infected by'' T. spiralis''. This act was put in place to prevent trichinella-contaminated food from being given to swine. Additionally, other requirements were put in place, such as rodent control, limiting commercial swine contact with wildlife, maintaining good hygiene, and removing dead pigs from pens immediately. Between 2002 and 2007, 11 trichinosis cases were reported to the CDC each year on average in the United States, and 2008–10 averaged 20 cases per year; these were mostly the result of consuming undercooked game (sylvatic transmission) or home-reared pigs (domestic transmission).


Religious groups

The
kashrut (also or , ) is a set of Food and drink prohibitions, dietary laws dealing with the foods that Jewish people are permitted to eat and how those foods must be prepared according to halakha, Jewish law. Food that may be consumed is deemed ko ...
and
halal ''Halal'' (; ) is an Arabic word that translates to in English. Although the term ''halal'' is often associated with Islamic dietary laws, particularly meat that is slaughtered according to Islamic guidelines, it also governs ethical practices ...
dietary laws of
Judaism Judaism () is an Abrahamic religions, Abrahamic, Monotheism, monotheistic, ethnic religion that comprises the collective spiritual, cultural, and legal traditions of the Jews, Jewish people. Religious Jews regard Judaism as their means of o ...
and
Islam Islam is an Abrahamic religions, Abrahamic monotheistic religion based on the Quran, and the teachings of Muhammad. Adherents of Islam are called Muslims, who are estimated to number Islam by country, 2 billion worldwide and are the world ...
prohibit eating pork. In the 19th century, when the association between trichinosis and undercooked pork was first established, this association was suggested to be the reason for the prohibition, reminiscent of the earlier opinion of medieval
Jewish Jews (, , ), or the Jewish people, are an ethnoreligious group and nation, originating from the Israelites of History of ancient Israel and Judah, ancient Israel and Judah. They also traditionally adhere to Judaism. Jewish ethnicity, rel ...
philosopher
Maimonides Moses ben Maimon (1138–1204), commonly known as Maimonides (, ) and also referred to by the Hebrew acronym Rambam (), was a Sephardic rabbi and Jewish philosophy, philosopher who became one of the most prolific and influential Torah schola ...
that food forbidden by Jewish law was "unwholesome". This theory was controversial and eventually fell out of favor.


Reemergence

The disappearance of the pathogen from domestic pigs has led to a relaxation of legislation and control efforts by veterinary public health systems. Trichinosis has lately been thought of as a re-emerging
zoonosis A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a virus, bacterium, parasite, fungi, or prion) that can jump from a non-human vertebrate to a human. When ...
, supplemented by the increased distribution of meat products, political changes, a changing climate, and increasing sylvatic transmission. Major sociopolitical changes can produce conditions that favor the resurgence of ''Trichinella'' infections in swine and, consequently, in humans. For instance, "the overthrow of the social and political structures in the 1990s" in Romania led to an increase in the incidence rate of trichinosis.


History

As early as 1835, trichinosis was known to have been caused by a parasite, but the mechanism of infection was unclear at the time. A decade later, American scientist Joseph Leidy pinpointed undercooked meat as the primary vector for the parasite, and two decades afterward, this hypothesis was fully accepted by the scientific community.


Parasite

The circumstances surrounding the first observation and identification of ''T. spiralis'' are controversial, due to a lack of records. In 1835, James Paget, a first-year medical student, first observed the larval form of ''T. spiralis'', while witnessing an autopsy at St. Bartholomew’s Hospital in London. Paget took a special interest in the presentation of muscle with white flecks, described as a "sandy diaphragm". Although Paget is most likely the first person to have noticed and recorded these findings, the parasite was named and published in a report by his professor,
Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...
, who is now credited for the discovery of the ''T. spiralis'' larval form.


Lifecycle

A series of experiments conducted between 1850 and 1870 by the German researchers
Rudolf Virchow Rudolf Ludwig Carl Virchow ( ; ; 13 October 18215 September 1902) was a German physician, anthropologist, pathologist, prehistorian, biologist, writer, editor, and politician. He is known as "the father of modern pathology" and as the founder o ...
,
Rudolf Leuckart Karl Georg Friedrich Rudolf Leuckart (7 October 1822 – 22 February 1898) was a German zoologist born in Helmstedt. He was a pioneer of parasitology research and was widely known for developing a series of illustrated wall charts for use in zo ...
, and Friedrich Albert von Zenker, which involved feeding infected meat to a dog and performing the subsequent necropsy, led to the discovery of the lifecycle of ''Trichinella''. Through these experiments, Virchow was able to describe the development and infectivity of ''T. spiralis''.


Research

The International Commission on Trichinellosis (ICT) was formed in Budapest in 1958. Its mission is to exchange information on the epidemiology, biology, pathophysiology, immunology, and clinical aspects of trichinosis in humans and animals. Prevention is a primary goal. Since the creation of the ICT, its members (more than 110 from 46 countries) have regularly gathered and worked together during meetings held every four years: the International Conference on Trichinellosis.


See also

* List of parasites (human) * Nurse cell


References

* ''The text of the original version of this article was taken from the public domain resource at https://www.cdc.gov/ncidod/dpd/parasites/trichinosis/factsht_trichinosis.htm'' *
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...
. Trichinosis Surveillance, United States, 1987–1990, MMWR 1991;40:(SS-3)35-42. *
USDA regulations – Title 9 – Chapter 3 – Part 318 – includes "Prescribed treatment of pork and products containing pork to destroy trichinae."


External links





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