Trichinosis
Encyclopedia
Trichinosis, also called trichinellosis, or trichiniasis, is a parasitic disease
caused by eating raw or undercooked pork
or wild game infected with the larva
e of a species of roundworm Trichinella spiralis
, commonly called the trichina worm. There are eight Trichinella species; five are encapsulated and three are not. Only three Trichinella species are known to cause trichinosis: T. spiralis, T. nativa, and T. britovi
. The few cases in the United States are mostly the result of eating undercooked game, bear meat, or home-reared pigs. It is common in developing countries where meat fed to pigs is raw or undercooked, but many cases also come from developed countries in Europe and North America, where raw or undercooked pork and wild game may be consumed as delicacies.
, 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 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
, who is now credited for the discovery of the T. spiralis larval form.
, Rudolf Leuckart
and Friedrich Albert von Zenker
, which involved feeding infected meat to a dog and performing the subsequent necropsy, led to the discovery of the life cycle of Trichinella. Through these experiments, Virchow was able to describe the development and infectivity of T. spiralis.
The great majority of trichinosis infections have either minor or no symptoms and no complications. http://www.medicinenet.com/trichinosis/page3.htm There are two main phases for the infection: enteral (affecting the intestines) and parenteral (outside the intestines). The symptoms vary depending on the phase, species of Trichinella, amount of encysted larvae ingested, age, gender, and host immunity.
, heartburn
, dyspepsia
, and diarrhea
from two to seven days after infection, while small worm burdens generally are asymptomatic. Eosinophilia
presents early and increases rapidly.
, muscle pain, fever, and weakness. A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by vasculitis
. Splinter hemorrhage
in the nails is also a common symptom.
The most dangerous case is worms entering the central nervous system
(CNS). They cannot survive there, but they may cause enough damage to produce serious neurological deficits (such as ataxia
or respiratory paralysis), and even death
. The CNS is compromised by trichinosis in 10-24% of reported cases of a rare form of stroke
. 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
, encephalitis
, or pneumonia
.
). Humans become infected when they eat raw or undercooked infected pork (domestic cycle). After humans ingest the cyst
s from infected undercooked meat, pepsin and hydrochloric acid help free the larvae in the cysts in the stomach. The larvae then migrate to the small intestine, 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. The worms can only reproduce for a limited time because the immune system will eventually expel 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 vessels, and then enter the bloodstream. The larvae travel by capillaries to various organs, such as the retina, myocardium, or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst. The larval host cell becomes a nurse cell
in which the larvae will encapsulate. The development of a capillary network around the nurse cell completes encystation of the larvae.
, nonspecific gastroenteritis
, and muscle pain. The case definition for trichinosis at the European Center for Disease Control states "at least three of the following six: fever
, muscle soreness and pain, gastrointestinal symptoms, facial edema, eosinophilia
, and subconjuctival, subungual, and retinal hemorrhages."
can be used to confirm a diagnosis of trichinosis. Serological tests include a blood test for eosinophilia, increased levels of creatine phosphokinase, IgG, and antibodies against newly hatched larvae. Immunoassays, such as ELISA
, can also be used.
or albendazole
, decreases the likelihood of larval encystation, particularly if given within three days of infection Unfortunately, most cases are diagnosed after this time.
Mebendazole
(200–400 mg three times a day for three days) or albendazole
(400 mg twice a day for 8–14 days) are 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.
and pyrantel
, may be used to relieve muscle pain associated with larval migration.
Another study, Dea-Ayuela et al. (2006) used extracts and excretory-secretory products from first stage larvae to produce an oral vaccine. To prevent the gastric acids from dissolving the antigens before reaching the small intestine, scientists encapsulated the antigens in a microcapsule made of copolymers. This vaccine significantly increased CD4+ cells and increased antigen-specific serum IgGq and IgA, resulting in a statistically significant reduction in the average number of adult worms in the small intestine 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) then, when an individual gets 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. Yuan Gu et al. (2008) tested a DNA vaccine on mice which “induced a muscle larvae burden reduction in BALB/c mice by 29% in response to T. spiralis infection”. Researchers trying to develop a vaccine for Trichinella have tried to using either “larval extracts, excretory-secretory antigen, DNA vaccine, or recombinant antigen protein.”
scientist Joseph Leidy
pinpointed undercooked meat as the primary vector for the parasite, and it was not until two decades afterwards that this hypothesis was fully accepted by the scientific community.http://www.ansp.org/museum/leidy/other/parasitology.php
About 11 million individuals are infected with Trichinella; Trichinella spiralis is the species responsible for most of these infections. Infection was once very common, but is now rare in the developed world
. The incidence of trichinosis in the U.S. has decreased dramatically in the past century. From 1997 to 2001, an annual average of 12 cases per year were reported in the United States. 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.
In the developing world
, most infections are associated with undercooked pork. For example, in Thailand
, 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 (WHO
) reports some swine herds have trichinosis infection rates above 50%, and there are correspondingly large numbers of human infections. http://www.emedicine.com/emerg/topic612.htm
transmission.
It is also important to keep in mind major socio-political changes can produce conditions that favor the resurgence of Trichinella infections in swine and, consequently, 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. There is also a high incidence of trichinosis among refugees from Southeast Asia. China reports approximately 10,000 cases every year, and is therefore the country with the highest numbers of cases. In China, between 1964-1998 over 20,000 people were infected with Trichinosis and over 200 people died.
The kashrut
and halal
dietary laws of Judaism
and Islam
prohibit eating pork. In the 19th century, when the association between trichinosis and undercooked pork was first established, it was suggested this association was the reason for the prohibition, reminiscent of the earlier opinion of the medieval Jewish
philosopher Maimonides
that food forbidden by Jewish law was "unwholesome". This theory was controversial and eventually fell out of favor.
(ICT) was created in 1958 in Budapest and is aiming to exchange information on the biology, the physiopathology, the epidemiology, the immunology, and the clinical aspects of trichinellosis 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
.
for inspections, rodent control, and improved hygiene. Similar protocol exists in the United States in the USDA guidelines for establishment responsibilities in inspecting pork.
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.
The Centers for Disease Control and Prevention
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 United States Department of Agriculture
(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 and 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. The CDC reports 0.013% of U.S. swine is infected with Trichinella.
Parasitic disease
A parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases. Parasitic diseases can affect practically all living organisms, including plants and mammals...
caused by eating raw or undercooked pork
Pork
Pork is the culinary name for meat from the domestic pig , which is eaten in many countries. It is one of the most commonly consumed meats worldwide, with evidence of pig husbandry dating back to 5000 BC....
or wild game infected with the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of a species of roundworm Trichinella spiralis
Trichinella spiralis
Trichinella spiralis is a nematode parasite, occurring in rats, pigs, bears and humans, and is responsible for the disease trichinosis. It is sometimes referred to as the "pork worm" due to it being found commonly in undercooked pork products...
, commonly called the trichina worm. There are eight Trichinella species; five are encapsulated and three are not. Only three Trichinella species are known to cause trichinosis: T. spiralis, T. nativa, and T. britovi
Trichinella britovi
Trichinella britovi is a nematode parasite responsible for a zoonotic disease called trichinellosis. There are currently eight known species of Trichinella. Only three of the Trichinella species cause trichinellosis, and Trichinella britovi is one of them...
. The few cases in the United States are mostly the result of eating undercooked game, bear meat, or home-reared pigs. It is common in developing countries where meat fed to pigs is raw or undercooked, but many cases also come from developed countries in Europe and North America, where raw or undercooked pork and wild game may be consumed as delicacies.
Agent
The disease-causing agents include the eight species of Trichinella, but T. spiralis is the most important to humans due to its worldwide distribution and high pathogenicity.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.
- 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. pseudospiralis infects birds and mammals, and has demonstrated infection in humans; it is a nonencapsulated species.
- T. papuae infects both mammals and reptiles, including crocodiles, humans, and pigs; this species, found in Papua New Guinea and Thailand, is also nonencapsulated.
- T. nelsoni, found in eastern Africa, has been documented to cause a few human cases.
- T. murrelli also infects humans, especially from black bear meat; it is distributed among wild carnivores in North America.
- T. zimbabwensis can infect mammals and possibly humans; this nonencapsulated species was detected in reptiles of Africa.
Taxonomy
- Kingdom: Animalia
- Phylum: Nematoda
- Class: Adenophorea
- Order: Trichurida
- Family: Trichinellidae
- Genus: Trichinella
Discovery of the parasite
The circumstances surrounding the first observation and identification of Trichinella spiralis are controversial due to a lack of medical records. In 1835, James PagetJames Paget
Sir James Paget, 1st Baronet was a British surgeon and pathologist who is best remembered for Paget's disease and who is considered, together with Rudolf Virchow, as one of the founders of scientific medical pathology. His famous works included Lectures on Tumours and Lectures on Surgical Pathology...
, 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 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
Richard Owen
Sir Richard Owen, FRS KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
, who is now credited for the discovery of the T. spiralis larval form.
Discovery of the life cycle
A series of experiments conducted between 1850 and 1870 by the German researchers Rudolf VirchowRudolf Virchow
Rudolph Carl Virchow was a German doctor, anthropologist, pathologist, prehistorian, biologist and politician, known for his advancement of public health...
, Rudolf Leuckart
Rudolf Leuckart
Karl Georg Friedrich Rudolf Leuckart was a German zoologist who was born in Helmstedt. He was a nephew to naturalist Friedrich Sigismund Leuckart ....
and Friedrich Albert von Zenker
Friedrich Albert von Zenker
Friedrich Albert von Zenker was a German pathologist and physician, celebrated for his discovery of trichinosis. He was born in Dresden, and was educated in Leipzig and Heidelberg. Attached to the city hospital of Dresden in 1851, he added, in 1855, the duties of professor of pathological...
, which involved feeding infected meat to a dog and performing the subsequent necropsy, led to the discovery of the life cycle of Trichinella. Through these experiments, Virchow was able to describe the development and infectivity of T. spiralis.
Signs and symptoms
Enteral phase
A large burden of adult worms in the intestines promote symptoms such as nauseaNausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, heartburn
Heartburn
Heartburn, also known as pyrosis or acid indigestion is a burning sensation in the chest, just behind the breastbone or in the epigastrium...
, dyspepsia
Dyspepsia
Dyspepsia , also known as upset stomach or indigestion, refers to a condition of impaired digestion. It is a medical condition characterized by chronic or recurrent pain in the upper abdomen, upper abdominal fullness and feeling full earlier than expected when eating...
, and diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
from two to seven days after infection, while small worm burdens generally are asymptomatic. Eosinophilia
Eosinophilia
Eosinophilia is a condition in which the eosinophil count in the peripheral blood exceeds 0.45×109/L . A marked increase in non-blood tissue eosinophil count noticed upon histopathologic examination is diagnostic for tissue eosinophilia. Several causes are known, with the most common being...
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 edemaEdema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
, muscle pain, fever, and weakness. A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by vasculitis
Vasculitis
Vasculitis refers to a heterogeneous group of disorders that are characterized by inflammatory destruction of blood vessels. Both arteries and veins are affected. Lymphangitis is sometimes considered a type of vasculitis...
. Splinter hemorrhage
Splinter hemorrhage
Splinter hemorrhages are tiny lines that run vertically under nails. Splinter hemorrhage is a nonspecific finding and can be associated with subacute bacterial endocarditis, scleroderma, trichinosis, Systemic lupus erythematosus , rheumatoid arthritis, psoriatic nails, antiphospholipid syndrome,...
in the nails is also a common symptom.
The most dangerous case is worms entering the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
(CNS). They cannot survive there, but they may cause enough damage to produce serious neurological deficits (such as ataxia
Ataxia
Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
or respiratory paralysis), and even death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
. The CNS is compromised by trichinosis in 10-24% of reported cases of a rare form of stroke
Cerebral venous sinus thrombosis
Cerebral venous sinus thrombosis is a rare form of stroke that results from thrombosis of the dural venous sinuses, which drain blood from the brain. Symptoms may include headache, abnormal vision, any of the symptoms of stroke such as weakness of the face and limbs on one side of the body, and...
. 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
Myocarditis is inflammation of heart muscle . It resembles a heart attack but coronary arteries are not blocked.Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi or Trypanosoma cruzi, or as a...
, encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
, or pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
.
Life cycle
The typical life cycle for T. spiralis involves humans, pigs, and rodents. Pigs become infected when they eat infectious cysts in raw meat, often pork or rats (sylvatic cycleSylvatic cycle
The sylvatic cycle, also enzootic or sylvatic transmission cycle, is a portion of the natural transmission cycle of a pathogen. The sylvatic cycle is the fraction of the pathogen population's lifespan spent cycling between wild animals and vectors. Humans are usually an incidental or dead-end host,...
). Humans become infected when they eat raw or undercooked infected pork (domestic cycle). After humans ingest the cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s from infected undercooked meat, pepsin and hydrochloric acid help free the larvae in the cysts in the stomach. The larvae then migrate to the small intestine, 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. The worms can only reproduce for a limited time because the immune system will eventually expel 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 vessels, and then enter the bloodstream. The larvae travel by capillaries to various organs, such as the retina, myocardium, or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst. The larval host cell becomes a nurse cell
Nurse cell
-Human physiology:Nurse cells are specialized macrophages residing in the bone marrow that assist in the development of red blood cells. They absorb the nuclei of immature red blood cells and may provide growth factors to help the red blood cells mature...
in which the larvae will encapsulate. The development of a capillary network around the nurse cell completes encystation of the larvae.
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 can be used to determine the infection. However, exposure does not have to be directly from an infected animal. Other exposure includes the consumption of products from a laboratory-confirmed infected animal or by sharing a common exposure as a laboratory-confirmed infected human.Clinical diagnosis
Clinical presentation of the common trichinosis symptoms may also suggest infection. These symptoms include circumorbital edema, splinter hemorrhageSplinter hemorrhage
Splinter hemorrhages are tiny lines that run vertically under nails. Splinter hemorrhage is a nonspecific finding and can be associated with subacute bacterial endocarditis, scleroderma, trichinosis, Systemic lupus erythematosus , rheumatoid arthritis, psoriatic nails, antiphospholipid syndrome,...
, nonspecific gastroenteritis
Gastroenteritis
Gastroenteritis is marked by severe inflammation of the gastrointestinal tract involving both the stomach and small intestine resulting in acute diarrhea and vomiting. It can be transferred by contact with contaminated food and water...
, 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
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, muscle soreness and pain, gastrointestinal symptoms, facial edema, eosinophilia
Eosinophilia
Eosinophilia is a condition in which the eosinophil count in the peripheral blood exceeds 0.45×109/L . A marked increase in non-blood tissue eosinophil count noticed upon histopathologic examination is diagnostic for tissue eosinophilia. Several causes are known, with the most common being...
, and subconjuctival, subungual, and retinal hemorrhages."
Laboratory testing
Serological tests and microscopyMicroscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
can be used to confirm a diagnosis of trichinosis. Serological tests include a blood test for eosinophilia, increased levels of creatine phosphokinase, IgG, and antibodies against newly hatched larvae. Immunoassays, such as ELISA
ELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
, can also be used.
Treatment and vaccines
As is desirable with most diseases, early treatment is better and decreases the risk of developing disease. If larvae do encyst in skeletal muscle cells, they can remain infectious for months to years.Primary treatment
Early administration of anthelmintics, such as mebendazoleMebendazole
Mebendazole or MBZ is a benzimidazole drug developed by Janssen Pharmaceutica and marketed as Vermox, Ovex, Antiox, and Pripsen...
or albendazole
Albendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
, decreases the likelihood of larval encystation, particularly if given within three days of infection Unfortunately, most cases are diagnosed after this time.
Mebendazole
Mebendazole
Mebendazole or MBZ is a benzimidazole drug developed by Janssen Pharmaceutica and marketed as Vermox, Ovex, Antiox, and Pripsen...
(200–400 mg three times a day for three days) or albendazole
Albendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
(400 mg twice a day for 8–14 days) are 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.
Secondary treatment
After infection, steroids, such as prednisonePrednisone
Prednisone is a synthetic corticosteroid drug that is particularly effective as an immunosuppressant drug. It is used to treat certain inflammatory diseases and some types of cancer, but has significant adverse effects...
and pyrantel
Pyrantel
Pyrantel is an antinematodal thiophene. It is often prescribed by veterinarians to treat and prevent the occurrence of intestinal parasites in small animal pets.-Mechanism of Action:Pyrantel is a nicotinic receptor agonist...
, may be used to relieve muscle pain associated with larval migration.
Vaccine research
There are currently no vaccines for trichinosis, although experimental mice studies have suggested a possibility. In one study, microwaved Trichinella larvae were used to immunize mice which were subsequently infected. Depending on dosage and frequency of immunization, results ranged from a decreased larval count to complete protection from trichinosis.Another study, Dea-Ayuela et al. (2006) used extracts and excretory-secretory products from first stage larvae to produce an oral vaccine. To prevent the gastric acids from dissolving the antigens before reaching the small intestine, scientists encapsulated the antigens in a microcapsule made of copolymers. This vaccine significantly increased CD4+ cells and increased antigen-specific serum IgGq and IgA, resulting in a statistically significant reduction in the average number of adult worms in the small intestine 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) then, when an individual gets 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. Yuan Gu et al. (2008) tested a DNA vaccine on mice which “induced a muscle larvae burden reduction in BALB/c mice by 29% in response to T. spiralis infection”. Researchers trying to develop a vaccine for Trichinella have tried to using either “larval extracts, excretory-secretory antigen, DNA vaccine, or recombinant antigen protein.”
Epidemiology
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, AmericanUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
scientist Joseph Leidy
Joseph Leidy
Joseph Leidy was an American paleontologist.Leidy was professor of anatomy at the University of Pennsylvania, and later was a professor of natural history at Swarthmore College. His book Extinct Fauna of Dakota and Nebraska contained many species not previously described and many previously...
pinpointed undercooked meat as the primary vector for the parasite, and it was not until two decades afterwards that this hypothesis was fully accepted by the scientific community.http://www.ansp.org/museum/leidy/other/parasitology.php
About 11 million individuals are infected with Trichinella; Trichinella spiralis is the species responsible for most of these infections. Infection was once very common, but is now rare in the developed world
First World
The concept of the First World first originated during the Cold War, where it was used to describe countries that were aligned with the United States. These countries were democratic and capitalistic. After the fall of the Soviet Union and the end of the Cold War, the term "First World" took on a...
. The incidence of trichinosis in the U.S. has decreased dramatically in the past century. From 1997 to 2001, an annual average of 12 cases per year were reported in the United States. 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.
In the developing world
Third World
The term Third World arose during the Cold War to define countries that remained non-aligned with either capitalism and NATO , or communism and the Soviet Union...
, most infections are associated with undercooked pork. For example, in Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, between 200 and 600 cases are reported annually around the Thai New Year
Thai New Year
The Songkran festival is celebrated in Thailand as the traditional New Year's Day from 13 to 15 April. It coincides with the New Year of many calendars of South and Southeast Asia....
. This is mostly attributable to a particular delicacy, larb
Larb
Larb is a type of Laotian and Isan meat salad that is regarded as the national dish of Laos. Larb is a creation of the Lao people, with 20 million living in the Isan region of Thailand, and 4.5 million in Laos. Larb originated in Laos and is one of the most famous dishes from Laos...
, which calls for undercooked pork as part of the recipe. In parts of Eastern Europe, the World Health Organization (WHO
Who
Who may refer to:* Who , an English-language pronoun* who , a Unix command* Who?, one of the Five Ws in journalism- Art and entertainment :* Who? , a 1958 novel by Algis Budrys...
) reports some swine herds have trichinosis infection rates above 50%, and there are correspondingly large numbers of human infections. http://www.emedicine.com/emerg/topic612.htm
Reemergence
The disappearance of the pathogen from domestic pigs has led to a relaxation of legislation and control efforts by veterinary public health systems. It has since been thought of as a reemerging zoonosis supplemented by the increased distribution of meat products, political changes, a changing climate, and increasing sylvaticSylvatic
Sylvatic is a scientific term referring to diseases or pathogens affecting only wild animals. In the context of animal research, its opposite is domestic, which refers to pets, farm animals or other animals which do not dwell in the wild.*Examples: sylvatic rabies; sylvatic and domestic bacterial...
transmission.
It is also important to keep in mind major socio-political changes can produce conditions that favor the resurgence of Trichinella infections in swine and, consequently, 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. There is also a high incidence of trichinosis among refugees from Southeast Asia. China reports approximately 10,000 cases every year, and is therefore the country with the highest numbers of cases. In China, between 1964-1998 over 20,000 people were infected with Trichinosis and over 200 people died.
The kashrut
Kashrut
Kashrut is the set of Jewish dietary laws. Food in accord with halakha is termed kosher in English, from the Ashkenazi pronunciation of the Hebrew term kashér , meaning "fit" Kashrut (also kashruth or kashrus) is the set of Jewish dietary laws. Food in accord with halakha (Jewish law) is termed...
and halal
Halal
Halal is a term designating any object or an action which is permissible to use or engage in, according to Islamic law. The term is used to designate food seen as permissible according to Islamic law...
dietary laws of Judaism
Judaism
Judaism ) is the "religion, philosophy, and way of life" of the Jewish people...
and Islam
Islam
Islam . The most common are and . : Arabic pronunciation varies regionally. The first vowel ranges from ~~. The second vowel ranges from ~~~...
prohibit eating pork. In the 19th century, when the association between trichinosis and undercooked pork was first established, it was suggested this association was the reason for the prohibition, reminiscent of the earlier opinion of the medieval Jewish
Jewish philosophy
Jewish philosophy , includes all philosophy carried out by Jews, or, in relation to the religion of Judaism. Jewish philosophy, until modern Enlightenment and Emancipation, was pre-occupied with attempts to reconcile coherent new ideas into the tradition of Rabbinic Judaism; thus organizing...
philosopher Maimonides
Maimonides
Moses ben-Maimon, called Maimonides and also known as Mūsā ibn Maymūn in Arabic, or Rambam , was a preeminent medieval Jewish philosopher and one of the greatest Torah scholars and physicians of the Middle Ages...
that food forbidden by Jewish law was "unwholesome". This theory was controversial and eventually fell out of favor.
International Commission on Trichinellosis
The International Commission on TrichinellosisInternational Commission on Trichinellosis
The International Commission on Trichinellosis was created in 1958 in Budapest and is aiming to exchange information on the biology, the pathophysiology, the epidemiology, the immunology, and the clinical aspects of trichinellosis in humans and animals...
(ICT) was created in 1958 in Budapest and is aiming to exchange information on the biology, the physiopathology, the epidemiology, the immunology, and the clinical aspects of trichinellosis 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
International Conference on Trichinellosis
The International Commission on Trichinellosis was created in 1958 in Budapest and is aiming to exchange information on the biology, the physiopathology, the epidemiology, the immunology, and the clinical aspects of trichinellosis in humans and animals. Prevention is a primary goal...
.
Legislation
Laws and rules required of food producers may improve food safety for consumers, such as the rules established by the European CommissionEuropean Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
for inspections, rodent control, and improved hygiene. Similar protocol exists in the United States in the USDA guidelines for establishment 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 bear. As such, many states, such as New York, require the completion of a course in such matters before a hunting license can be obtained.Food preparation
Larvae may be inactivated by the heating, freezing (caution), or irradiation of raw meat. Freezing may only be effective for T. spiralis, since some other species, such as T. nativa, are freeze resistant and can survive long-term freezing.- Cooking meatMeatMeat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
products to an internal temperature of 165 °FFahrenheitFahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
(74 °CCelsiusCelsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
) for a minimum of 15 seconds. - Cooking porkPorkPork is the culinary name for meat from the domestic pig , which is eaten in many countries. It is one of the most commonly consumed meats worldwide, with evidence of pig husbandry dating back to 5000 BC....
to a minimum uniform internal temperature per USDA Title 9 section 318.10 Table below. It is prudent to use a margin of error to allow for variation in internal temperature and error in the thermometer.°F FahrenheitFahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...°C CelsiusCelsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...Minimum Time 120 49 21 hours 122 50.0 9.5 hours 124 51.1 4.5hours 126 52.2 2 hours 128 53.4 1 hours 130 54.5 30 minutes 132 55.6 15 minutes 134 56.7 6 minutes 136 57.8 3 minutes 138 58.9 2 minutes 140 60.0 1 minute 142 61.1 1 minute 144 62.2 Instant
- Freezing porkPorkPork is the culinary name for meat from the domestic pig , which is eaten in many countries. It is one of the most commonly consumed meats worldwide, with evidence of pig husbandry dating back to 5000 BC....
less than 6 inches thick for 20 days at 5 °F (−15 °C) or three days at −4 °F (−20 °C) kills larval worms. - Cooking wild game meat thoroughly. Freezing wild game meats, unlike freezing pork products, even for long periods of time, may not effectively kill all worms. This is because the species that typically infects wild game is more resistant to freezing than the species that infects pigs.
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.
Hygienic pig farming
- Cooking all meat fed to pigs or other wild animals
- Keeping pigs in clean pens with floors that can be washed (such as concrete)
- Not allowing hogs to eat uncooked 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 prior to public sale of meat
The Centers for Disease Control and Prevention
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...
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 United States Department of Agriculture
United States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...
(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 and 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. The CDC reports 0.013% of U.S. swine is infected with Trichinella.