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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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Trichinellosis Outbreaks — Northrhine-Westfalia, Germany, 1998-1999
From Morbidity and Mortality Weekly Report, 6/18/99

From November 1998 through January 1999, 52 cases of trichinellosis were identified by the public health surveillance systems in 11 cities and districts of the state of Northrhine-Westfalia (NRW), Germany. In comparison, zero to 10 cases were reported annually in Germany during 1987-1997. This report summarizes the investigation of these cases, which indicated the existence of two simultaneous outbreaks-one caused by contaminated ground meat and the other by a commercially prepared raw smoked sausage.

A case of trichinellosis was defined as a positive serologic test for Trichinella antibodies (IgG and/or 1gM) in a NRW resident after September 1, 1998. Preliminary investigations indicated that 22 of 23 case-patients from 10 cities and districts in NRW had eaten a specific brand of raw smoked sausage made by company A; however, none of eight case-patients in Mettmann-Langenfeld (ML) had eaten this product. To identify the cause of each outbreak, two separate case-control studies were conducted. Case-patients and controls were interviewed by telephone using a standardized questionnaire. For case-patients, information about food consumption was gathered for the 4 weeks before onset of illness; for controls, information was gathered from September 1, 1998, to the date of the interview. For each case-control study, controls were selected randomly from the same town using random-digit dialing. Analyses by individual cases and family clusters yielded similar results. Only data by individual cases are presented in this report.


Case-Control Study

Eight case-patients from ML were compared with 29 controls from the same area. Case-patients included a resident of another town who had eaten with ML case-patients. The seven symptomatic case-patients became ill during November 4-24, 1998 (Figure 1). Symptoms included myalgia (six patients [75%]), fever (five 163%]), headache (five [63%]), facial edema (four [50%]), and diarrhea (two [25%]). Seven case-patients received medical care; none was hospitalized. One control reported symptoms consistent with trichinellosis (i.e., myalgia, fever, and fatigue). Among the eight case-patients and 28 controls who had histories of eating ground pork, seven case-patients (88%) and 11(39%) controls reported having eaten ground pork (odds ratio [OR]=10.8; p=0.02). Among the seven case-patients and 29 controls who had histories of eating ground mixed meat (beef and pork), all case-patients and 21 (72%) controls reported having eaten the product (OR=[infinity], p=0.3). No case-patients or controls reported having eaten raw smoked sau sage produced by company A. The location where the mixed meat and ground pork had been bought was available for six case-patients; all had obtained meat from supermarket A. In comparison, nine of 21 controls who had eaten mixed meat (OR=[infinity], p=0.02) and three of 11 controls who had eaten ground pork (OR=[infinity], p=0.009) had bought it from supermarket A.

Environmental Investigation

Frozen samples of ground meat bought in early November at supermarket A were collected from three case-families in ML. Larvae of Trichinella were detected in one sample of ground mixed meat. Supermarket A belongs to a chain of supermarkets with a central meat distribution station. During the week in which the contaminated meat was processed, the company had bought pork from nine different abattoirs in Germany, Belgium, and the Netherlands that had received pigs from approximately 40 producers. It was not possible to determine which producer provided the contaminated meat.


Case-Control Study

Forty-four cases were identified from 10 cities in NRW other than ML. The 38 symptomatic case-patients with known dates of symptom onset became ill during October 6-December 8, 1998 (Figure 1). Additional data were obtained from 39 of the 44 case-patients and from 44 controls from the same area. Symptoms included myalgia (30 [77%]), fever (28 [72%]), headache (21 [54%]), diarrhea (19 [49%]), and facial edema (17 [44%]). One control reported typical symptoms of trichinellosis (i.e., diarrhea, headache, fever, myalgia, and leg edema). Of 39 case-patients, 32(82%) received medical care, and 15 (38%) were hospitalized for a median of 13 days (range: 1-64 days). Among the 38 case-patients and 43 controls who had histories of eating smoked sausage, all case-patients and 30 (47%) controls reported having eaten raw smoked sausage (OR=[infinity]; p[less than]0.000l). Of 38 case-patients, 34 reported having eaten raw smoked sausage produced by company A (OR=[infinity]; p[less than]0.0001); no controls reported eating the product. Case-patients were more likely than controls to have eaten ground pork (OR=6.2; p=0.001), mixed ground meat (OR=7.0; p=O.0002), and sandwiches with raw ground meat (OR=4.7; p=O.0O2). To control for possible confounding by smoked sausage consumption, a stratified analysis was conducted using only case-patients and controls who had eaten smoked sausage. The strength of association between consumption of ground pork (OR=2.6; p=0.2), ground mixed meat (OR=2.7; p=0.2), or sandwiches with raw ground meat (OR=2.0; p=0.3) and illness was lower among these persons.

Environmental Investigation

Because the usual incubation period of trichinellosis is 8-15 days, the environmental investigation focused on the meat that had been used for sausage production during the last week of September. During this week, company A had produced its sausages from deep frozen pork from Belgium and Germany and from 1650 lbs (750 kg) of fresh pork neck from Spain. Samples from neither the meat nor the sausages remained for investigation. Samples from later production lots were negative for trichinellosis.

The meat from Belgium and Germany had been frozen at 5 F (--15 C) for at least 20 days. The trichinellosis control certificates for the fresh pork neck provided by the abattoir in Spain had control numbers that did not match the control numbers on the meat. Further investigations are ongoing.

Reported by: S Rehmet, G Sinn, O Robstad, A Ammon Dept of Infectious Disease Epidemiology, Robert Koch Institute; K Noeckler, National Veterinary Reference Laboratory for Trichinellosis, Federal Institute for Health Protection of Consumers and Veterinary Medicine, Berlin; D Lesser, Ministry of Women, Youth, Family and Health; H David, Ministry of Environment, Environmental Planning and Agriculture, Northrhine-Westfalia; G Scherholz, Health Dept; D Stegemann, Veterinary Dept, Bonn; K-D Erkrath, Health Dept. Bottrop; D Pechmann, Health Dept. Dssseldorf; R Kundt, Health Dept; W Lotz, Veterinary Dept, Essen; G Qltmans, Health Dept, Gelsenkirchen; R Lange, Health Dept M Steigert, D Franke, P Hagelschur, Veterinary Dept, Mettmann-Langenfeld; J Laumen, Health Dept, Neuss; U Nogay, Health Dept, Recklinghausen; M Dixius, Health Dept. Rhein-Sieg-Kreis; J Eichenberg, Health Dept. Solingen; F Dinse, Health Dept, Viersen. Office of the Director, National Center for Infectious Diseases, CDC.

Editorial Note: The findings in this report indicate the existence of two outbreaks of trichinellosis. Because the exact source of the meat from either outbreak could not be determined, it is unclear whether the outbreaks were related. The large outbreak from the smoked sausage could have heightened awareness of trichinellosis in NRW, which resulted in the identification of the small outbreak that may have been otherwise unnoticed.

The 52 cases identified in these outbreaks may represent only a fraction of persons actually infected. The severity of trichinellosis varies from asymptomatic infection to death; however, only persons ill enough to seek medical care or their family members were identified in this investigation. In addition, the approximately 1650 lbs (750 kg) of fresh pork was sufficient to produce an estimated 10,000--40,000 sausages (W. Lotz, Veterinary Department, Essen, personal communication, 1999), which were distributed in at least 10 cities and districts with approximately 2 million inhabitants. As a result, hundreds of persons potentially were exposed. Approximately 2% of controls had symptoms compatible with trichinellosis.

Trichinellosis outbreaks in Europe typically are caused by meat or meat products distributed locally from a single infected animal [1-6]. In comparison, the smoked sausage outbreak described in this report was caused by a widely distributed commercial product made from domestically produced meat and meat imported from several countries. The nature of this outbreak reflects a new foodborne outbreak scenario in which localized outbreaks are replaced by diffuse outbreaks spread over wide areas [7]. These diffuse outbreaks, which result from low-level contamination of commercial food products, may not become apparent immediately unless the pathogen is unusual, such as occurred in this outbreak, or unless specific surveillance systems are designed to detect them [7].

In Germany, trichinellosis screening of all pork has been mandatory since 1937. The extremely low prevalence of Trichinella in pigs--three or fewer infected pigs identified among approximately 40 million pigs slaughtered each year in Germany--has led to debate about the need for continued routine testing of all slaughtered pigs. This outbreak indicates that it may be difficult to maintain a sufficient sensitivity of screening to prevent all outbreaks under routine conditions. Screening of meat for Trichinella involves visual identification of the larvae. The extremely low prevalence of trichinellosis among pigs may lead to a lack of experience in identifying positive samples, worker fatigue, and complacency. Nevertheless, this outbreak demonstrates that Modern mass food production can produce large outbreaks of trichinellosis when screening is absent or fails.


(1.) Frongillo RF, Baldelli B, Pozio E, et al. Report on an outbreak of trichinellosis in central Italy. Eur J Epidemiol 1992;8:283-8.

(2.) Kociecka W, Pielok L, Pietrzak H, Gustowska L. Detection of Trichinella sp.: invasion and clinical appraisal of patients in the late stage of trichinellosis in a new epidemic focus in Wielkopoiska. Proceedings of the International Commission of Trichinellosis No. XXIV. Wiadomosci Parazytologiczne 1997;43:257-63.

(3.) Ban C DI, Santagada G, Pozio E, Schiraldi O. Epidemiological research on trichinellosis in Apulia and Basilicata (southern Italy). Eur J Epidemiol 1990;6:412-5.

(4.) Egbering O. Observations on the origin and course of a trichinellosis epidemic [German]. Giessen, German Federal Republic: Department of Veterinary Medicine, Justus-Liebig University, 1988.

(5.) Ancelle T, Dupouy-Camet J, Desenclos JC, et al. A multifocal outbreak of trichinellosis linked to horse meat imported from North America to France in 1993. Am J Trop Med Hyg 1998;59:615-9.

(6.) Ancelle T. History of trichinellosis outbreaks linked to horse meat consumption, 1975-1998. Eurosurveillance 1998;3:86-9.

(7.) Tauxe R. Emerging foodborne diseases: an evolving public health challenge. Emerg Infect Dis 1997;3:425-34.

COPYRIGHT 1999 U.S. Government Printing Office
COPYRIGHT 2004 Gale Group

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