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Trichinosis, also called trichinellosis, is a parasitic disease caused by eating raw or undercooked pork and wild game products infected with the larvae of a species of roundworm Trichinella spiralis, commonly called the trichina worm. Infection is common where raw or undercooked pork, such as ham or sausage, is regularly consumed as part of the diet. more...

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Signs and symptoms

Symptoms can be divided into two types: symptoms caused by worms in the intestine, and symptoms caused by worms elsewhere.

In the intestine, infection can cause:

  • Nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort

Later, as the worms encyst in different parts of the body, other symptoms occur such as:

  • Headaches, fevers, chills, cough, eye swelling, aching joints and muscle pains, pinpoint hemorrhages, itchy skin, and heightened numbers of white blood cells.

If worms penetrate nervous tissue, they cannot survive, but patients may experience difficulty coordinating movements, and respiratory paralysis. In severe cases, death may occur. Heart infection can also cause death.

For mild to moderate infections, most symptoms subside within a few months. Fatigue, weakness, and diarrhea may last for months.

Incubation time

Abdominal symptoms can occur 1-2 days after infection. Further symptoms usually start 2-8 weeks after eating contaminated meat. Symptoms may range from very mild to severe and relate to the number of infectious worms consumed in meat. Often, mild cases of trichinosis are never specifically diagnosed and are assumed to be the flu or other common illnesses.

Life cycle

The worm can infect any species of mammal (including humans) that consumes its encysted larval stages. When an animal eats meat that contains infective Trichinella cysts, the acid in the stomach dissolves the hard covering of the cyst and releases the worms. The worms pass into the small intestine and, in 1-2 days, become mature. After mating, adult females produce larvae, which break through the intestinal wall and travel through the lymphatic system to the circulatory system to find a suitable cell. Larvae can penetrate any cell, but can only survive in skeletal muscle. Within a muscle cell, the worms curl up and direct the cells functioning much as a virus does. The cell is now called a nurse cell. Soon, a net of blood vessels surround the nurse cell, providing added nutrition for the larva inside.

Risk factors

Eating raw or undercooked meats, particularly pork, bear, wild feline (such as a cougar), fox, dog, wolf, horse, seal, or walrus puts one at risk for trichinosis. This is the only way that infection can occur. It is not transmitted from one person to another, except through cannibalism. Even ingesting infected feces will not cause trichinosis because adults and unencysted larvae cannot survive in the stomach.


A blood test or muscle biopsy can identify trichinosis. Stool studies can identify adult worms, with females being about 3 mm long and males about half that size.


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Outbreak of trichinellosis associated with eating cougar jerky - Idaho, 1995
From Morbidity and Mortality Weekly Report, 3/15/96

On March 3, 1995, the Idaho Department of Health and Welfare received a report from the North Central District Health Department (NCDHD) of trichinellosis in a man residing in idaho County, Idaho (1994 population: 14,938). This report summarizes the epidemiologic and laboratory investigations of this index case and the related outbreak by NCDHD, the U.S. Department of Agriculture (USDA), and CDC.

During the second week of January, the index patient shot and killed a cougar (Felis concolor) near Elk City, Idaho. During January 15-18, he prepared jerky from the cougar meat by first soaking the meat in a brine solution made from table salt, then smoking the meat; however, he later reported the smoker never became more than warm. During the next 4 weeks, he distributed the meat to 14 other persons, all of whom ate the meat within days to 1 month after receipt.

On January 26, the man had onset of illness characterized by fever, myalgia, arthralgia, facial swelling, and fatigue. On examination by his physician, his total white blood cell count was 8500/[mm.sup.3] (normal: 5000-lea,000/[mm.sup.3]) with 48% eosinophils, 32% segmented neutrophils, 17% lymphocytes, and 3% monocytes. Based on these findings, trichinellosis was suspected, and he was referred to an infectious disease consultant.

Samples of cougar jerky examined at the Sacred Heart Medical Center Department of Laboratory Medicine in Spokane, Washington, on February 22 contained Trichinella larvae. Examination of a muscle biopsy obtained from the patient on February 23 revealed granulomatous myositis with eosinophils. Serum obtained March 9 tested positive for Trichinella antibody by bentonite flocculation (1:160) and enzyme-linked immunosorbent assay (ELISA) (3.707) at CDC. Trichinella larvae were identified in specimens of jerky and fresh frozen cougar muscle submitted to the USDA in March. Polymerase chain reaction was performed on live larvae recovered from the fresh frozen tissue, and results were consistent with the sylvatic genotypes T. nativa and Trichinella T6.

During March 3-April 10, NCDHD interviewed the 14 persons who had received jerky. A case of trichinellosis was defined as 1) a Trichinella-positive muscle biopsy or positive serologic test for trichinellosis in a patient with eosinophilia, fever, myalgia, and/or periorbital edema; or 2) either a positive serologic test for trichinellosis or eosinophilia, fever, myalgia, and/or periorbital edema in a person who had eaten the cougar jerky. Based on these criteria, nine additional cases were identified. Manifestations among the 10 cases included myalgia (seven), fever (six), rash (three), weakness (three), and arthralgia (two). Seven of these persons were men; case-patients ranged in age from 25 to 52 years.

The index patient and seven others were treated with mebendazole. Persons who had received the jerky were educated by NCDHD on trichinellosis prevention. Reported by: A Vollbrecht, D Sokolowski, North Central District Health Dept, Lewiston; W Hollipeter, MD, Grangeville" R Sigler MD, Cottonwood, J Greenblatt, MD, State Epidemiologist, idaho Dept of Health and Welfare. DE Anderson, Jr, Phd, Sacred Heart Medical Center PJ Tennican, Infectious Diseases Northwest, Spokane, Washington. HR Gamble, Phd, D Zarlenga, Parasite Biology and Epidemiology Laboratory, US Dept of Agriculture. Div of Parasitic Diseases, National Center for infectious Diseases; Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note: Since trichinellosis was designated a reportable condition in 1947, the number of cases reported annually by state health departments has declined from an average of 400 cases per year in the late 1940s to 32 cases in 1994 (1,2). The proportion of cases associated with eating contaminated commercial pork has been declining since 1975, most likely because of laws prohibiting feeding offal to hogs, the increased use of home freezers, and the practice of thoroughly cooking pork (2).

Trichinella species are found in virtually all warm-blooded animals. As domestic swine-associated cases have decreased, the proportion of cases associated with eating wild game has increased, and cases have resulted from consumption of bear, wild boar, and walrus (3-5). This report is the first to document cougar as the source of trichinellosis in the United States. in this investigation, viable larvae were recovered from meat that had been frozen. Although most species of Trichinella are killed by freezing, results of the genomic DNA amplification performed at USDA suggest that the cougar isolate was either T nativa or Trichinella T6, both freeze-resistant strains that have not been previously reported in Idaho.

To ensure that Trichinella are destroyed, meat should be thoroughly cooked. A temperature of 170 F (77 C) exceeds the thermal death point of the trichinae and usually is achieved if the meat is cooked until the color changes from pink or red to gray. Some brine solutions used for preparing jerky also may kill Trichinella; however, curing temperature and total duration of time at this temperature are important determinants in this process (6). Physicians should be aware of the continued presence of Trichinella sp. in commercial pork and wild game in the United States and should consider the diagnosis in any patient with an illness compatible with trichinosis and whose dietary preferences pose a risk for infection (2).


[1.] Schantz PM. Trichinosis in the United States, 1947-1981. Food Technol 1983;37:83-6. [2.] CDC. Trichinella spiralis infection--United States, 1990. MMWR 1991;40:57-60. [3.] Bailey TM, Schantz PM. Trends in the incidence and transmission patterns of human trichinosis in the United States, 1982-1986. Rev Infect Dis 1990;12:5-11. [4.] MacLean JD, Viallet J, Law C, et al. Trichinosis in the Canadian arctic: report of five outbreaks and a new clinical syndrome. J Infect Dis 1989;160:513-20. [5.] Woodard TL. An outbreak of trichinosis traced to Alaskan black bear meat. Alaska Medicine 1988;30:41-4. [6.] Zimmerman WJ. Salt cure and drying time and temperature on viability of Trichinella spiralis in dry cured hams. J Food Sci 1971;36:58-65.

COPYRIGHT 1996 U.S. Government Printing Office
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