Trichinella spiralis
Encyclopedia
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. Its draft genome became available during early 2011.
s of an intermediate host such as a pig. Each adult female produces batches of live larva
e, which bore through the intestinal wall, enter the blood (to feed on it) and lymphatic system
, and are carried to striated muscle
Once in the muscle, they encyst
, or become enclosed in a capsule.
Humans can be infected by eating infected pork or wild carnivores such as fox, cat or bear.
(due to stomach pH) and migrate to the intestine, where they burrow into the intestinal mucosa, mature, and reproduce . Interestingly, juveniles within nurse cells have an anaerobic or facultative anaerobic metabolism, but when they become activated, they adopt an aerobic metabolism characteristics of the adult.
Female Trichinella worms live for about six weeks, and in that time can produce up to 1,500 larvae; when a spent female dies, she passes out of the host. The larvae can then gain access to the circulation and migrate around the body of the host . The migration and encystment of larvae can cause fever and pain brought upon by the host inflammatory response. In some cases, migration to specific organ tissues can cause myocarditis
and encephalitis
that can result in death.
formation in skeletal muscle tissue is mediated by the hypoxic
environment surrounding the new vessel formation. The hypoxic environment stimulates cells in the surrounding tissue to regulate up and secrete angiogenic cytokines, such as VEGF
. This allows for the newborn T. spinalis larvae to enter and form the nurse cells. Interestingly, VEGF expression is detected surrounding the nurse cell right after nurse cell formation, and the continued secretion of VEGF can maintain the constant state of hypoxia. Previous studies have shown VEGF can stimulate proliferation of synthesis of collagen type 1 in activated myofibroblast-like cells.
can cause traumatic damage to the host tissue, and the waste products they excrete can provoke an immunological reaction. The resulting inflammation can cause symptoms such as nausea, vomiting, sweating and diarrhea. Five to seven days after the appearance of symptoms, facial edema
and fever may occur. After 10 days, intense muscular pain, difficulty breathing, weakening of pulse and blood pressure, heart damage and various nervous disorders may occur, eventually leading to death due to heart failure, respiratory complications or kidney malfunction.
In pigs, infection is usually subclinical but large numbers of worms can be fatal in some cases.
or albendazole
, but efficacy of such products are uncertain. Symptoms can be relieved by use of analgesics and corticosteroids.
In pigs, ELISA
testing is possible as a method of diagnosis. Anthelmintics can treat and prevent Trichinella infections.
(also trichinellosis) is a disease caused by tissue-dwelling roundworms of the species Trichinella spiralis. In the United States, the national trichinellosis surveillance system has documented a steady decline in the reported incidence of this disease. During 1947 to 1951, a median of 393 cases was reported annually, including 57 trichinellosis-related deaths. During 1997-2001, the incidence decreased to a median of 12 cases annually, with no reported deaths. The decline of infection was largely associated with changes implemented by the U.S. pork industry that have resulted in reduced prevalence of Trichinella among domestic swine. In the United States, Congress passed the Federal Swine Health Protection Act restricting the use of uncooked garbage as feed stock for pigs and creating a voluntary Trichinae Herd Certification Program . The Trichinae Herd Certification Program is a voluntary preharvest pork safety program that provides documentation of swine management practices to minimize Trichinella exposure. The goal of the program is to establish a system under which pork production facilities that follow good production practices might be certified as Trichinella-safe.
In addition to the reduction in Trichinella prevalence in commercial pork, processing methods also have contributed to the dramatic decline in human trichinellosis associated with pork products. Through the U.S. Code of Federal Regulations, USDA has created guidelines for specific cooking temperatures and times, freezing temperatures and times, and curing methods for processed pork products to control postharvest human exposure to Trichinella. Pork products meeting these guidelines are designated certified pork.
In most abattoirs, the diaphragm of pigs is routinely sampled to detect Trichinella infection.
Trichinosis
Trichinosis, also called trichinellosis, or trichiniasis, is a parasitic disease caused by eating raw or undercooked pork or wild game infected with the larvae of a species of roundworm Trichinella spiralis, commonly called the trichina worm. There are eight Trichinella species; five are...
. It is sometimes referred to as the "pork worm" due to it being found commonly in undercooked pork products. Its draft genome became available during early 2011.
Description
Trichinella species are the smallest nematode parasite of humans, have an unusual life cycle and are one of the most widespread and clinically important parasites in the world. The small adult worms mature in the intestineIntestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s of an intermediate host such as a pig. Each adult female produces batches of live 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, which bore through the intestinal wall, enter the blood (to feed on it) and lymphatic system
Lymphatic system
The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...
, and are carried to striated muscle
Striated muscle
Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...
Once in the muscle, they encyst
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...
, or become enclosed in a capsule.
Humans can be infected by eating infected pork or wild carnivores such as fox, cat or bear.
Morphology
Males of T. spiralis measure between 1.4 mm and 1.6 mm long and are flat anteriorly than posteriorly. The anus can be found in the terminal (side) and they have a large copulatory pseudobursa on each side. The females of T. spiralis are about twice the size of the males and have an anus found terminally. The vulva is located near the esophagus. The single uterus of the female is filled with developing eggs in the posterior portion, while the anterior portion contained the fully developed juveniles.Life cycle
Trichinella spiralis is a parasitic nematode that has a direct life cycle, meaning it completes all stages of development in one host. The larval forms are encapsulated as a small cystic structure within the infected host. Humans typically become infected when they eat improperly cooked pork or Trichinella infected meat. When a human eats the infected meat, the larvae are released from the nurse cellNurse 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...
(due to stomach pH) and migrate to the intestine, where they burrow into the intestinal mucosa, mature, and reproduce . Interestingly, juveniles within nurse cells have an anaerobic or facultative anaerobic metabolism, but when they become activated, they adopt an aerobic metabolism characteristics of the adult.
Female Trichinella worms live for about six weeks, and in that time can produce up to 1,500 larvae; when a spent female dies, she passes out of the host. The larvae can then gain access to the circulation and migrate around the body of the host . The migration and encystment of larvae can cause fever and pain brought upon by the host inflammatory response. In some cases, migration to specific organ tissues can cause 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...
and 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...
that can result in death.
Nurse cell formation
Nurse cellNurse 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...
formation in skeletal muscle tissue is mediated by the hypoxic
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
environment surrounding the new vessel formation. The hypoxic environment stimulates cells in the surrounding tissue to regulate up and secrete angiogenic cytokines, such as VEGF
Vascular endothelial growth factor
Vascular endothelial growth factor is a signal protein produced by cells that stimulates vasculogenesis and angiogenesis. It is part of the system that restores the oxygen supply to tissues when blood circulation is inadequate....
. This allows for the newborn T. spinalis larvae to enter and form the nurse cells. Interestingly, VEGF expression is detected surrounding the nurse cell right after nurse cell formation, and the continued secretion of VEGF can maintain the constant state of hypoxia. Previous studies have shown VEGF can stimulate proliferation of synthesis of collagen type 1 in activated myofibroblast-like cells.
Symptoms
The first symptoms may appear between 12 hours and two days after ingestion of infected meat. The migration of worms in the intestinal epitheliumEpithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
can cause traumatic damage to the host tissue, and the waste products they excrete can provoke an immunological reaction. The resulting inflammation can cause symptoms such as nausea, vomiting, sweating and diarrhea. Five to seven days after the appearance of symptoms, facial edema
Edema
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...
and fever may occur. After 10 days, intense muscular pain, difficulty breathing, weakening of pulse and blood pressure, heart damage and various nervous disorders may occur, eventually leading to death due to heart failure, respiratory complications or kidney malfunction.
In pigs, infection is usually subclinical but large numbers of worms can be fatal in some cases.
Diagnosis and treatment
Muscle biopsy is used for trichinosis detection. Several immunodiagnostic tests are also available. Typically, patients are treated with either 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...
, but efficacy of such products are uncertain. Symptoms can be relieved by use of analgesics and corticosteroids.
In pigs, 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...
testing is possible as a method of diagnosis. Anthelmintics can treat and prevent Trichinella infections.
Prevention and control
TrichinosisTrichinosis
Trichinosis, also called trichinellosis, or trichiniasis, is a parasitic disease caused by eating raw or undercooked pork or wild game infected with the larvae of a species of roundworm Trichinella spiralis, commonly called the trichina worm. There are eight Trichinella species; five are...
(also trichinellosis) is a disease caused by tissue-dwelling roundworms of the species Trichinella spiralis. In the United States, the national trichinellosis surveillance system has documented a steady decline in the reported incidence of this disease. During 1947 to 1951, a median of 393 cases was reported annually, including 57 trichinellosis-related deaths. During 1997-2001, the incidence decreased to a median of 12 cases annually, with no reported deaths. The decline of infection was largely associated with changes implemented by the U.S. pork industry that have resulted in reduced prevalence of Trichinella among domestic swine. In the United States, Congress passed the Federal Swine Health Protection Act restricting the use of uncooked garbage as feed stock for pigs and creating a voluntary Trichinae Herd Certification Program . The Trichinae Herd Certification Program is a voluntary preharvest pork safety program that provides documentation of swine management practices to minimize Trichinella exposure. The goal of the program is to establish a system under which pork production facilities that follow good production practices might be certified as Trichinella-safe.
In addition to the reduction in Trichinella prevalence in commercial pork, processing methods also have contributed to the dramatic decline in human trichinellosis associated with pork products. Through the U.S. Code of Federal Regulations, USDA has created guidelines for specific cooking temperatures and times, freezing temperatures and times, and curing methods for processed pork products to control postharvest human exposure to Trichinella. Pork products meeting these guidelines are designated certified pork.
In most abattoirs, the diaphragm of pigs is routinely sampled to detect Trichinella infection.
External links
- The Trichinella Page @ Trichinella.org, Columbia UniversityColumbia UniversityColumbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...
- Trichina life cycle, Centers for Disease Control and PreventionCenters for Disease Control and PreventionThe 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...
- Trichina agent, Washington University
- Fluorescence image of Trichina