Trichinosis overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Danitza Lukac

Overview

Trichinosis, also called trichinellosis or trichiniasis, is a parasitic disease caused by eating raw or undercooked pork and wild game products infected with the larvae of Trichinella species. Based on the severity of signs and larval density, trichinosis may be classified into asymptomatic, abortive, mild, pronounced, and severe. Trichinella spp. is usually transmitted to the human host by eating undercooked meat containing cysts of Trichinella spp. Following ingestion, exposure to gastric acid and pepsin release the larvae from the cysts and invade the small bowel mucosa. When an individual eats meat from an infected animal, Trichinella cysts break open in the intestines and grow into adult roundworms. These organisms tend to invade muscle tissues, including the heart and diaphragm. They can also affect the lungs and brain. Trichinosis must be differentiated from influenza virus, salmonella, shigella, eosinophilia-myalgia syndromes, tissular parasitosis, glomerulonephritis, serum sickness, infectious meningitis and encephalitis, leptospirosis, bacterial endocarditis and typhus exanthematicus. Worldwide, an estimated 10,000 cases of trichinosis occur every year. Common risk factors in the development of trichinosis disease are consuming raw or undercooked meat, informal meat transportation, age, antimicrobial free/organic pork and hunting practices. If left untreated, infected patients develop manifestations within 1-2 days of infection. Infected patients with trichinosis may progress to develop periorbital edema, muscle pain, and fever. Complications of trichinosis affect the cardiovascular, neurological, ocular, respiratory, and digestive systems. Most people with trichinosis have no symptoms, the infection is usually self-limited. The prognosis of trichinosis is good with adequate treatment. The diagnosis of trichinosis is based on the European Center for Disease Control criteria, which include a combination of clinical, laboratory and epidemiological criteria. The mainstay of therapy for trichinosis are anthelmintics drugs, such as albendazole or mebendazole. The optimal way to prevent trichinosis is to cook meat to safe temperatures. Using food thermometers can make sure the temperature inside the meat is high enough to kill the parasites.

Historical Perspective

Trichinella spiralis was first discovered by James Paget, an English first-year medical student, in 1835. In 1846, Joseph Leidy, an American paleontologist, was the first to discover the association between undercooked meat and development of trichinosis. There have been several outbreaks of trichinosis, most of them for consuming infected pork, wild boar and bear.

Classification

Based on the severity of signs and larval density, trichinosis may be classified into asymptomatic, abortive, mild, pronounced, and severe.

Pathophysiology

Trichinella spp. is usually transmitted to the human host by eating undercooked meat containing cysts of Trichinella spp. Following ingestion, exposure to gastric acid and pepsin release the larvae from the cysts and invade the small bowel mucosa. When an individual eats meat from an infected animal, Trichinella cysts break open in the intestines and grow into adult roundworms. Females are approximately 2.2 mm in length; males 1.2 mm. The life span in the small intestine is approximately four weeks. After 1 week, the females release more larvae that migrate through the bloodstream to voluntarily controlled muscles where they encyst. These organisms tend to invade muscle tissues, including the heart and diaphragm. They can also affect the lungs and brain. Characteristic findings on microscopic histopathological analysis of the muscle, the nurse cell has a collagen capsule with larvae inside and is surrounded by cellular infiltrates.

Causes

Common cause of trichinosis include Trichinella spiralis. Less common causes of trichinosis include T. britovi, T. nativa, T. pseudospiralis, T. papuae, T. nelsoni, T. murrelli, and T. zimbabwensis.

Differential Diagnosis

Trichinosis must be differentiated from influenza virus, salmonella, shigella, eosinophilia-myalgia syndromes, tissular parasitosis, glomerulonephritis, serum sickness, infectious meningitis and encephalitis, leptospirosis, bacterial endocarditis and typhus exanthematicus.

Epidemiology and Demographics

Worldwide, an estimated 10,000 cases of trichinosis occur every year. Trichinosis is rare in developed countries, but it is still common in developing countries.

Risk Factors

Common risk factors in the development of trichinosis disease are consuming raw or undercooked meat, informal meat transportation, age, antimicrobial free/organic pork, and hunting practices.

Natural History, Complications and Prognosis

If left untreated, infected patients develop manifestations within 1-2 days of infection. Infected patients with trichinosis may progress to develop periorbital edema, muscle pain, and fever. Complications of trichinosis affect the cardiovascular, neurological, ocular, respiratory, and digestive systems. Most people with trichinosis have no symptoms, the infection is usually self-limited. The prognosis of trichinosis is good with adequate treatment.

Diagnosis

Diagnostic Criteria

The diagnosis of trichinosis is based on the European Center for Disease Control criteria, which include a combination of clinical, laboratory and epidemiological criteria.

History and Symptoms

Trichinosis initially involves the intestines. Symptoms include nausea, heartburn, dyspepsia, and diarrhea. The severity of symptoms depends on the number of worms ingested. As the worms encyst in different parts of the human body, other manifestations may occur, such as headache, fever, chills, cough, eye swelling, joint pain and muscle pain, and itching. A positive history of gastroenteritis symptoms, muscle pain and fever and recent ingestion of undercooked meat such as pork, wild boar or bear is suggestive of trichinosis.

Physical Examination

Common physical examination findings of trichinosis include periorbital edema and splinter hemorrhage.

Laboratory Findings

Laboratory findings suggestive of trichinosis include eosinophilia, elevated muscle enzymes and anti trichinella IgG. Muscle biopsy is diagnostic of trichinosis.

Treatment

Medical Therapy

The mainstay of therapy for trichinosis are anthelmintics drugs such as albendazole or mebendazole.

Primary Prevention

The optimal way to prevent trichinosis is to cook meat to safe temperatures. Using food thermometers can make sure the temperature inside the meat is high enough to kill the parasites.