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Trichinosis

Trichinosis

Definition

Trichinosis is a disease caused by a roundworm (nematode) called Trichinella spiralis. An individual worm of this species is called a trichina, from the Greek word meaning "hairlike." Trichinae can be readily avoided by proper handling and cooking of certain meats, particularly pork products.

Description

The life cycle of T. spiralis includes several different stages. The adult trichina lives in the intestinal lining of such meat-eating animals as swine, bears, walrus, and rodents. After mating, the male worm dies while the female goes on to produce the offspring.

Roundworms have a stage of development called the embryonic stage, which in many species occurs after birth. In trichinae, however, this embryonic stage occurs within the uterus of the female, so the offspring that are ultimately discharged into the host's intestinal lining are in the larval second stage of life. These larvaeabout 1500 from each female wormtravel through the circulatory system to the heart, then through the blood vessels leading to striated muscle (the muscle of the skeletal system and the heart). Most larvae that cannot find suitable locations in striated muscle will die.

Those larvae that reach striated muscle will grow to a length of about one millimeter, coil themselves, and enclose themselves within a protective wall called a cyst. This process is referred to as encysting. The worms in the cysts can live for up to ten years in this form.

A pig that has been infected with T. spiralis, then, has thousands of cysts lying dormant within its musclesthe very muscles that humans look forward to consuming in the form of pork chops, ham, barbecued ribs, etc. When humans sit down to a delicious meal of undercooked, trichina-infected pig dinner, they are ingesting T. spiralis cysts. The cyst walls are broken down by the usual process of food digestion in the stomach, allowing the larvae to escape into the new host's intestines. There the larvae mature to become adult worms, capable of producing a new crop of larvae. When these new larvae hatch, they begin their migration throughout the human host's bloodstream to his or her muscles, where they live for a short while before encysting.

Causes and symptoms

Human hosts who eat meat infested with trichinae may experience symptoms in varying degrees. If the meat ingested has only a few cysts, then the human host's load of parasites (worm burden) is said to be relatively small, and symptoms will be moderate. In fact, many trichinosis infections are subclinical, which means that the symptoms are so mild that the infection remains undiagnosed. In a host with a greater worm burden, the initial symptoms will be caused by the presence of the adult worms in the intestine. These symptoms usually include fever, diarrhea, abdominal pain, and perhaps vomiting. The symptoms begin about one to two days after eating the contaminated meat, and may last for a week or so.

When the larvae begin their migration through the blood vessels, the host will begin to experience symptoms that affect the whole body (systemic symptoms), such as fever; swelling of the face and the area around the eyes; rash; bleeding into the nail beds, retina, and whites of the eyes; and cough. In very severe cases of trichinosis, inflammation of the heart muscle (myocarditis ), lungs (pneumonitis), or brain (encephalitis) may occur. These symptoms can lead to the few deaths caused by trichinosis.

The larvae begin to burrow into the host's muscles and form cysts within two to three weeks of the initial infection. This encysting produces signs of muscle inflammation (myositis) including swelling of the affected muscle groups, pain, and weakness. The most frequently affected muscles are the muscles outside the eye (extraocular muscles) that control eye movements; the muscles of the jaw, neck, and upper arm (biceps muscle); the muscles of the lower back (lumbar region); and the diaphragm, which is the muscle that separates the abdominal and chest cavities and aids in breathing.

The symptoms of trichinosis are at their most severe at about three weeks after infection, and decrease very slowly in their severity. Recovery is extremely gradual, and symptoms may last for as long as three months. Fatigue and muscle pain (myalgia) may take several more months to subside.

Diagnosis

An initial diagnosis of trichinosis relies heavily on the presence of its classic symptomsswelling around the eyes, muscle inflammation, fever, and high levels of a certain type of white blood cell (eosinophils)coupled with the patient's history. If the patient reports having eaten undercooked meat from an animal known to be a potential carrier of trichinosis, the doctor may order a muscle biopsy to confirm the diagnosis. By the third or fourth week of infection, muscle biopsies usually indicate the presence of larvae. Stool tests rarely reveal adult worms, although larvae can sometimes be found in blood or duodenal washings after the second week of infection. The blood test that is the most specific for trichinosis is the bentonite flocculation (BF) test.

T. spiralis can infect a number of different animal species used for food. The most common food culprit in the United States has been pork sausage, while outbreaks in Europe have caused by wild boar and horse meat. Outbreaks of trichinosis in Asia and Africa have been traced to dog meat, and outbreaks in Northern Canada have resulted from consumption of walrus and bear meat.

Treatment

Supportive care

Treatment of trichinosis is primarily aimed at decreasing the severity of the symptoms. Symptomatic relief includes bed rest and medications to relieve fever and muscle pain. The medications most commonly given are aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs). Steroids such as prednisone (Deltasone, Meticorten) are reserved for the most severe cases of muscle inflammation, or for complicated cases that include myocarditis.

Anthelminthic medications

In addition to medications for pain relief, trichinosis can be treated with drugs that are called anti-worm medications or anthelminthics. Two related anti-worm medications, mebendazole (Vermox) and thiabendazole (Mintezol), have been reported to be effective against intestinal larvae, but not against larvae encysted in the muscles. In particular, thiabendazole has worked best when given to patients who knew within 24 hours that they had eaten infested meat. Thiabendazole has, however, anti-inflammatory properties that can relieve some of the pain during the muscle stage of trichinosis.

Prognosis

The prognosis for recovery from trichinosis is generally good. Most people with the disease are unaware that they have even been infected. It is estimated that between 150,000 and 300,00 people in the United States become infected yearly, so that at any given time, 1.5 million people have T. spiralis infections. Most of these people have such light cases that trichinosis is never identified. Worm burden is measured in larvae per gram of muscle tissue; people with 10 or fewer larvae per gram of muscle tissue usually have no significant symptoms. When the number climbs to 100 larvae per gram of muscle tissue, the symptoms become noticeable. People with over 1000 larvae per gram of muscle tissue are usually extremely ill, and often die. The mortality rate of trichinosis is about 1%.

Prevention

Prevention of trichinosis is relatively simple. Swine should be fed only grain or cooked garbage because uncooked garbage may contain contaminated pork scraps. Meat from animals prone to trichinosis infection should be cooked or smoked thoroughly until it is no longer pink. Freezing meat at an adequately low temperature (5°F/-15°C for three weeks) can kill most encysted larvae, except for species which infect such arctic mammals as walrus or bear.

Resources

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. http://www.cdc.gov.

KEY TERMS

Anthelminthic A type of medication that is given to destroy or eliminate parasitic worms.

Cyst In the life cycle of the round worm, a protective, walled-off capsule in which the larvae lie dormant.

Embryonic In the life cycle of the round worm, a very early life stage occurring within the uterus of the female round worm.

Host The animal within which a parasite lives, and from which the parasite receives its nutrition.

Inflammation A reaction within the body to an invader (virus, bacteria, fungus, worm, etc.) or to tissue injury. The classic signs of inflammation include redness, heat, pain, and loss of function.

Larva In the life cycle of the round worm, the second stage of life, sometimes considered the "adolescent" stage.

Nematode A type of roundworm with a long, unsegmented body, usually parasitic on animals or plants.

Striated muscle Also known as striped muscle; it includes muscles of the skeletal system and of the heart.

Trichina An individual example of Trichinella spiralis.

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Carson-DeWitt, Rosalyn. "Trichinosis." Gale Encyclopedia of Medicine, 3rd ed.. 2006. Encyclopedia.com. 24 Aug. 2016 <http://www.encyclopedia.com>.

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Carson-DeWitt, Rosalyn. "Trichinosis." Gale Encyclopedia of Medicine, 3rd ed.. 2006. Retrieved August 24, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3451601656.html

Trichinosis

TRICHINOSIS

Trichinosis is a disease caused by the invasion of the human body by the larval stage of the parasitic nematode worm Trichinella spiralis. Characteristically, humans are infected by eating poorly cooked pork, but infection sometimes follows eating the flesh of other carnivores such as bears or herbivores such as horses. The several varieties of trichinella all have the same life cycleinfection occurs when the larvae, encysted in muscle tissue ("red meat"), are ingested. The cyst wall is dissolved by gastric juices and the larvae are released into the intestine, where they undergo several developmental stages before reaching sexual maturity. Female adult worms may live for some years, continuing to produce newborn larvae that migrate through the intestinal wall and invade many organs and tissues, including the heart, brain, eye, and muscle tissue.

Heavy infection can be lethal or have devastating clinical effects such as seizures, heart attack, or blindness if the brain, heart, or eyes are affected. Light and moderate infection (when only a few cysts are ingested) causes muscle pains, skin rashes, diarrhea, and other symptoms that may be so vague that the condition escapes detection. Sometimes it comes to light only years later when calcium deposits around dead cysts show up on an X-ray. As infection occurs only by ingesting meat containing live larvae, person-to-person transmission is not possible.

Control relies on prevention. Abattoirs must be regularly and rigorously inspected and all suspect meat must be condemned; hunters need to be aware that carnivorous game animals may be infected, and must therefore ensure that meat is thoroughly cooked for long enough to kill any cysts that it may contain.

John M. Last

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trichinosis

trichinosis (trĬk´Ĭnō´sĬs) or trichiniasis (trĬk´Ĭnī´əsĬs), parasitic disease caused by the roundworm Trichinella spiralis. It follows the eating of raw or inadequately cooked meat, especially pork. The larvae are released, reach maturity, and mate in the intestines, the females producing live larvae. The parasites are then carried from the gastrointestinal tract by the bloodstream to various muscles, where they become encysted. It is estimated that 10% to 20% of the adult population of the United States suffers from trichinosis at some time. In many people the disease exhibits no symptoms and is discovered only at autopsy. In others it causes diarrhea and other gastrointestinal symptoms as the worms multiply in the digestive tract. When the larvae circulate through the bloodstream, the patient experiences edema, irregular fever, profuse sweating, muscle soreness and pain, and prostration. There may be involvement of the central nervous system, heart, and lungs; death occurs in about 5% of clinical cases. Once the larvae have imbedded themselves in the muscle tissue, the cysts usually become calcified; however, the infestation usually causes no further symptoms except fatigue and vague muscular pains. There is no specific treatment.

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Trichinosis

Trichinosis

What Is Trichinosis?

How Common Is Trichinosis?

How Do People Know They Have Trichinosis?

How Do Doctors Diagnose and Treat Trichinosis?

How Can Trichinosis Be Prevented?

Resources

Trichinosis (trih-kih-NO-sis) is a parasitic infection that comes from eating raw or undercooked meat. It is caused by species of the roundworm Trichinella (trih-kih-NEH-luh).

KEYWORDS

for searching the Internet and other reference sources

Nematodes

Roundworms

Trichinella

What Is Trichinosis?

Also called trichinellosis (trih-kih-neh-LO-sis), trichinosis can occur when people eat meat that is infected with the larvae* of Trichinella roundworms (also called nematodes, NEE-muh-todes); Trichinella spiralis (spy-RAL-is) is the most common species that causes trichinosis. People can become infected only by eating infected meat; the disease is not spread through human contact. The parasite also can spread when animals eat the infected flesh of other animals. Most often, meat infected with the parasite comes from pigs or wild game, such as bear, horse, wolf, and fox.

*larvae
(LAR-vee) are the immature forms of an insect or worm that hatch from an egg.

Trichinella larvae form cysts (SISTS, shell-like sacs that contain the larvae in a resting stage) in meat. When an animal eats this meat, the animals stomach acid dissolves the cysts, and the worms are released into the body. They travel to the small intestine*, where they grow into adult worms and mate. After about a week, the mature female worm releases larvae, which travel through the bloodstream to the muscles. There they form the hard cysts that began the cycle. The cysts remain in the muscles, and people become infected when they eat these cysts in animal meat.

*small intestine
is the part of the intestinethe system of muscular tubes that food passes through during digestionthat directly receives the food when it passes through the stomach.

How Common Is Trichinosis?

According to the U.S. Centers for Disease Control and Prevention (CDC), there were 16 cases in 2000, down from an average of 38 cases per year from 1991 to 1996. The decline came about because people are now more aware of the dangers of eating raw or undercooked meat; better storage and freezing methods of meat are being used; and laws prohibiting the feeding of raw meat to pigs have been passed. Most trichinosis cases now are associated with eating wild game.

How Do People Know They Have Trichinosis?

The length of the period between eating the infected meat and the first symptoms of illness depends on the number of parasites in the meat and how much a person has eaten. It can range from 1 to 45 days, but symtoms often surface in 10 to 14 days. Symptoms can be mild and even go unnoticed, but they usually start with fever, diarrhea (dye-uh-REEuh), belly pain, nausea (NAW-zee-uh), vomiting, and extreme tiredness. Other symptoms may follow, such as headache, cough, chills, muscle and joint pain, eye swelling, and constipation. If the infection is severe, a person may have trouble with coordination as well as heart and breathing problems.

How Do Doctors Diagnose and Treat Trichinosis?

A blood test or muscle biopsy* can be done to determine whether a person has trichinosis. The blood test can detect antibodies* working to destroy the parasite, and the biopsy shows the presence of cysts in the muscles. Asking if a person has recently eaten game or traveled outside of the United States may provide information useful in making the diagnosis.

*biopsy
(BI-op-see) is a test in which a small sample of skin or other body tissue is removed and examined for signs of disease.
*antibodies
(AN-tih-bah-deez) are protein molecules produced by the bodys immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.

The infection can be treated with various medications to kill the worms in the intestine, but the medication does not get rid of the larvae that have produced cysts in the muscles. These larvae remain in a dormant (inactive) state in the muscle tissue. If the infection is mild, symptoms usually go away after a few months. Muscle aches and weakness may last longer. Some people require only bed rest; others need to be hospitalized and receive oxygen and intravenous (in-tra-VEE-nus) fluids (fluids injected directly into a vein). Severe complications of trichinosis include inflammation of the heart muscle, heart failure, lung problems, delirium*, and coma*. The disease can be fatal if it is not treated.

*delirium
(dih-LEER-e-um) is a condition in which a person is confused, is unable to think clearly, and has a reduced level of consciousness.
*coma
(KO-ma) is an unconscious state in which a person cannot be awakened and cannot move, see, speak, or hear.

How Can Trichinosis Be Prevented?

The best way to prevent infection is to eat only thoroughly cooked meat. Curing, drying, salting, and microwaving meat may not kill Trichinella larvae. When cooking meat, the juices must be clear (not bloody) and the meat must reach an internal temperature of 170 degrees Fahrenheit. Freezing meat at subzero temperatures for several weeks also should kill any larvae in cysts. Raw meat can contaminate work surfaces, so it must not touch surfaces used to prepare food, and grinders and other utensils used with raw meat must be cleaned thoroughly and not used to prepare cooked meat.

See also

Intestinal Parasites

Zoonoses

Resources

Book

Gittleman, Ann Louise. Guess What Came to Dinner? Parasites and Your Health. New York: Avery Penguin Putnam, 2001.

Organizations

National Institute of Allergy and Infectious Diseases (NIAID), Building 31, Room 7A-50, 31 Center Drive MSC 2520, Bethesda, MD 20892. The NIAID, part of the National Institutes of Health, posts information about trichinosis and other roundworm infections at its website.

http://www.niaid.nih.gov

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC is the U.S. government authority for information about infectious and other diseases. It has a fact sheet about trichinosis at its website.

Telephone 800-311-3435 http://www.cdc.gov

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trichinosis

trichinosis (trichiniasis) (trik-i-noh-sis) n. a disease caused by larvae of the nematode worm Trichinella spiralis, contracted by eating imperfectly cooked infected meat. Symptoms include diarrhoea, nausea, fever, vertigo, delirium, and pains in the limbs. The larvae eventually settle within cysts in the muscles, which may result in pain and stiffness.

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trichinosis

trich·i·no·sis / ˌtrikəˈnōsis/ • n. a disease caused by trichinae (usually Trichinella spiralis), typically from infected meat, esp. pork, characterized by digestive disturbance, fever, and muscular rigidity.

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trichinosis

trichinosis (trichinellosis, trichiniasis) Disease that can arise from eating under‐cooked pork or pork sausage meat; due to Trichinella spiralis, a worm that is a parasite in pork muscle.

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DAVID A. BENDER. "trichinosis." A Dictionary of Food and Nutrition. 2005. Encyclopedia.com. 24 Aug. 2016 <http://www.encyclopedia.com>.

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trichinosis

trichinosis disease due to trichinae (parasitic worms) in the alimentary canal. XIX. f. modL. trichina, f. Gr. tríkhinos of hair, f. thrix, trikh- hair; see -INE2, -OSIS.

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T. F. HOAD. "trichinosis." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 24 Aug. 2016 <http://www.encyclopedia.com>.

T. F. HOAD. "trichinosis." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (August 24, 2016). http://www.encyclopedia.com/doc/1O27-trichinosis.html

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trichinosis

trichinosisglacis, Onassis •abscess •anaphylaxis, axis, praxis, taxis •Chalcis • Jancis • synapsis • catharsis •Frances, Francis •thesis • Alexis • amanuensis •prolepsis, sepsis, syllepsis •basis, oasis, stasis •amniocentesis, anamnesis, ascesis, catechesis, exegesis, mimesis, prosthesis, psychokinesis, telekinesis •ellipsis, paralipsis •Lachesis •analysis, catalysis, dialysis, paralysis, psychoanalysis •electrolysis • nemesis •genesis, parthenogenesis, pathogenesis •diaeresis (US dieresis) • metathesis •parenthesis •photosynthesis, synthesis •hypothesis, prothesis •crisis, Isis •proboscis • synopsis •apotheosis, chlorosis, cirrhosis, diagnosis, halitosis, hypnosis, kenosis, meiosis, metempsychosis, misdiagnosis, mononucleosis, myxomatosis, necrosis, neurosis, osmosis, osteoporosis, prognosis, psittacosis, psychosis, sclerosis, symbiosis, thrombosis, toxoplasmosis, trichinosis, tuberculosis •archdiocese, diocese, elephantiasis, psoriasis •anabasis • apodosis •emphasis, underemphasis •anamorphosis, metamorphosis •periphrasis • entasis • protasis •hypostasis, iconostasis

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