Control and Prevention
International Commission on Trichinellosis
Control and Prevention in Pork and Other Meat From Food Animals
Post-harvest prevention of human exposure
Many countries require that pigs (and horses) sold as food animals be tested for Trichinella infection. These requirements are in the form of regulations governing slaughter inspection. The European Union (EU) outlines these requirements in SANCO 2075/2005. Other countries have similar regulations and proof of freedom from Trichinella infection must accompany products sold for interstate commerce. As stated in the OIE Terrestrial Animal Health Code, importing countries should require that an international health certificate accompany imported pork products. The sanitary certificate should attest that the product has: 1) been tested for Trichinella infection at slaughter and was shown to be negative; 2) originated from a Trichinella free country or territory; or 3) been processed to ensure destruction of Trichinella larvae. In the same document, it is specified that horsemeat sold for human consumption should be submitted to slaughter inspection or be processed by methods known to kill Trichinella larvae.
Some countries, including the United States, have relied primarily on further processing (cooking, freezing and curing) of ready-to-eat pork products and advice to consumers regarding the safe preparation of fresh pork. Commercial processing methods which have been proven experimentally to render pork free from infective Trichinella larvae are described in the U.S. Code of Federal Regulations (9CFR 318.10). Pork meat must be heated to 58° C or frozen at one of several time temperature combinations. For flash freezing, Trichinella larvae are killed instantaneously at -35° C. The effectiveness of curing depends on a combination of salt concentration, temperature, and time. Each method should be tested experimentally to determine effectiveness as no model for curing conditions has been devised. Consumers of fresh product are advised to cook pork, and other meat products that might serve as a source of Trichinella, to an internal temperature of 70° C.
Pre-harvest prevention of Trichinella infection in pigs
Prevention of exposure of domestic pigs to Trichinella, requires implementation of sanitary management practices which: 1) prohibit feeding of animal products (without proper cooking); and 2) preventing exposure to rodents or other potentially infected mammals either directly, or through contamination of feed. Production practices which are free from risk or have minimal risk for exposure to Trichinella should be monitored periodically (by testing blood samples from live animals or by sampling slaughtered animals) to verify the absence of infection.
Several regulations support programs for certifying pigs free from risk of exposure to Trichinella including, in the EU, SANCO 2075/2005 and, in the U.S., the National Trichinae Herd Certification Program (http://www.aphis.usda.gov/vs/trichinae/docs/prog_stds.htm).
The OIE Terrestrial Animal Health Code specifies that absence of Trichinella infection in pigs can be documented by declaring a country or territory as "Trichinella-free" based on certain criteria. These criteria include: 1) the disease is compulsorily notifiable; 2) waste food feeding is officially regulated; 3) a surveillance program is in place to detect Trichinella infection at a very low prevalence in the disease free area; 4) surveillance is intensified where infection was last reported; and 5) any outbreaks of infection in swine or humans are fully investigated to determine the source. Establishing a country or region as free from Trichinella is difficult since the parasite circulates in so many species of wildlife.
Analytical methods
Trichinella spp. may be identified by direct or indirect methods. The oldest method of direct detection of Trichinella, and one which is still frequently used, is the compression method. Small pieces of pork, or tissue from other animals, collected from the pillars (crus muscle) of the diaphragm, or alternative sites, are compressed between two thick glass slides (a compressorium) and examined microscopically. A minimum of 1 gram must be examined to allow a theoretical sensitivity of 1 larva per gram (a number frequently cited as the threshold of infection posing a public health risk). In practice, the compression method has an approximate sensitivity of > 3 larvae per gram of tissue. The compression method is suitable for testing small numbers of samples and should be used to test carcasses of wild carnivores destined for human consumption.
An improvement in direct testing methods for Trichinella infection is the digestion method. Samples of tissue collected from sites of parasite predilection (diaphragm, cheek muscle, tongue) are subjected to digestion in acidified pepsin. Larvae, freed from their muscle cell capsules, are recovered by a series of sedimentation steps, then visualized and enumerated under a microscope. Requirements for performing the digestion test are found in the Directives of the European Union (SANCO 2075/2005), in the U.S. Code of Federal Regulations (9CFR 318.10) and in the OIE Manual of Standards for Diagnostic Tests and Vaccines.
Using methods of inspection testing as practiced on pig carcasses, the sensitivity of the digestion method is approximately 3 LPG. This level of detection is considered effective for identifying pork that poses a significant public health risk. Although there is insufficient information to determine the exact number of larvae which are necessary to cause clinical human disease (and these figures will be affected by the type of Trichinella, the amount of meat eaten, and the health of the individual), it is generally considered that infections > 1 LPG are a public health risk. Thus, most infections which could cause clinical human disease would be detected by currently employed direct testing methods.
Trichinella spp. infection can also be detected by the presence of antibodies to the parasites in serum, blood or tissue fluid samples. The enzyme linked immunosorbent assay (ELISA) has been used extensively for testing in both pre- and post-slaughter applications. Based on the use of an excretory-secretory antigen collected from short-term in vitro cultivation of Trichinella spiralis, the ELISA has proven to be highly sensitive and specific; no known cross-reactions occur using this test. Since the ELISA is not in widespread use for the detection of trichinellosis in pigs at slaughter, the reader is referred to the OIE Manual of Standards for Diagnostic Test and Vaccines for specific methodologies involving this test.
Further reading
Gamble, H.R., Boireau, P., Noeckler, K. and Kapel, C.M.O. 2007. Prevention of Trichinella infection in the domestic pig. In, (Dupouy-Camet, J and Murrell, K.D. eds.), FAO/WHO/OIE Guidelines for the Surveillance, Management, Prevention and Control of Trichinellosis, Rome, pp. 101-110.
Nöckler, K. and Kapel, C.M.O. 2007. Detection and surveillance for Trichinella: meat inspection, hygiene and legislation. In, (Dupouy-Camet, J and Murrell, K.D. eds.), FAO/WHO/OIE Guidelines for the Surveillance, Management, Prevention and Control of Trichinellosis, Rome, pp. 69-98.
Post-harvest prevention of human exposure
Many countries require that pigs (and horses) sold as food animals be tested for Trichinella infection. These requirements are in the form of regulations governing slaughter inspection. The European Union (EU) outlines these requirements in SANCO 2075/2005. Other countries have similar regulations and proof of freedom from Trichinella infection must accompany products sold for interstate commerce. As stated in the OIE Terrestrial Animal Health Code, importing countries should require that an international health certificate accompany imported pork products. The sanitary certificate should attest that the product has: 1) been tested for Trichinella infection at slaughter and was shown to be negative; 2) originated from a Trichinella free country or territory; or 3) been processed to ensure destruction of Trichinella larvae. In the same document, it is specified that horsemeat sold for human consumption should be submitted to slaughter inspection or be processed by methods known to kill Trichinella larvae.
Some countries, including the United States, have relied primarily on further processing (cooking, freezing and curing) of ready-to-eat pork products and advice to consumers regarding the safe preparation of fresh pork. Commercial processing methods which have been proven experimentally to render pork free from infective Trichinella larvae are described in the U.S. Code of Federal Regulations (9CFR 318.10). Pork meat must be heated to 58° C or frozen at one of several time temperature combinations. For flash freezing, Trichinella larvae are killed instantaneously at -35° C. The effectiveness of curing depends on a combination of salt concentration, temperature, and time. Each method should be tested experimentally to determine effectiveness as no model for curing conditions has been devised. Consumers of fresh product are advised to cook pork, and other meat products that might serve as a source of Trichinella, to an internal temperature of 70° C.
Pre-harvest prevention of Trichinella infection in pigs
Prevention of exposure of domestic pigs to Trichinella, requires implementation of sanitary management practices which: 1) prohibit feeding of animal products (without proper cooking); and 2) preventing exposure to rodents or other potentially infected mammals either directly, or through contamination of feed. Production practices which are free from risk or have minimal risk for exposure to Trichinella should be monitored periodically (by testing blood samples from live animals or by sampling slaughtered animals) to verify the absence of infection.
Several regulations support programs for certifying pigs free from risk of exposure to Trichinella including, in the EU, SANCO 2075/2005 and, in the U.S., the National Trichinae Herd Certification Program (http://www.aphis.usda.gov/vs/trichinae/docs/prog_stds.htm).
The OIE Terrestrial Animal Health Code specifies that absence of Trichinella infection in pigs can be documented by declaring a country or territory as "Trichinella-free" based on certain criteria. These criteria include: 1) the disease is compulsorily notifiable; 2) waste food feeding is officially regulated; 3) a surveillance program is in place to detect Trichinella infection at a very low prevalence in the disease free area; 4) surveillance is intensified where infection was last reported; and 5) any outbreaks of infection in swine or humans are fully investigated to determine the source. Establishing a country or region as free from Trichinella is difficult since the parasite circulates in so many species of wildlife.
Analytical methods
Trichinella spp. may be identified by direct or indirect methods. The oldest method of direct detection of Trichinella, and one which is still frequently used, is the compression method. Small pieces of pork, or tissue from other animals, collected from the pillars (crus muscle) of the diaphragm, or alternative sites, are compressed between two thick glass slides (a compressorium) and examined microscopically. A minimum of 1 gram must be examined to allow a theoretical sensitivity of 1 larva per gram (a number frequently cited as the threshold of infection posing a public health risk). In practice, the compression method has an approximate sensitivity of > 3 larvae per gram of tissue. The compression method is suitable for testing small numbers of samples and should be used to test carcasses of wild carnivores destined for human consumption.
An improvement in direct testing methods for Trichinella infection is the digestion method. Samples of tissue collected from sites of parasite predilection (diaphragm, cheek muscle, tongue) are subjected to digestion in acidified pepsin. Larvae, freed from their muscle cell capsules, are recovered by a series of sedimentation steps, then visualized and enumerated under a microscope. Requirements for performing the digestion test are found in the Directives of the European Union (SANCO 2075/2005), in the U.S. Code of Federal Regulations (9CFR 318.10) and in the OIE Manual of Standards for Diagnostic Tests and Vaccines.
Using methods of inspection testing as practiced on pig carcasses, the sensitivity of the digestion method is approximately 3 LPG. This level of detection is considered effective for identifying pork that poses a significant public health risk. Although there is insufficient information to determine the exact number of larvae which are necessary to cause clinical human disease (and these figures will be affected by the type of Trichinella, the amount of meat eaten, and the health of the individual), it is generally considered that infections > 1 LPG are a public health risk. Thus, most infections which could cause clinical human disease would be detected by currently employed direct testing methods.
Trichinella spp. infection can also be detected by the presence of antibodies to the parasites in serum, blood or tissue fluid samples. The enzyme linked immunosorbent assay (ELISA) has been used extensively for testing in both pre- and post-slaughter applications. Based on the use of an excretory-secretory antigen collected from short-term in vitro cultivation of Trichinella spiralis, the ELISA has proven to be highly sensitive and specific; no known cross-reactions occur using this test. Since the ELISA is not in widespread use for the detection of trichinellosis in pigs at slaughter, the reader is referred to the OIE Manual of Standards for Diagnostic Test and Vaccines for specific methodologies involving this test.
Further reading
Gamble, H.R., Boireau, P., Noeckler, K. and Kapel, C.M.O. 2007. Prevention of Trichinella infection in the domestic pig. In, (Dupouy-Camet, J and Murrell, K.D. eds.), FAO/WHO/OIE Guidelines for the Surveillance, Management, Prevention and Control of Trichinellosis, Rome, pp. 101-110.
Nöckler, K. and Kapel, C.M.O. 2007. Detection and surveillance for Trichinella: meat inspection, hygiene and legislation. In, (Dupouy-Camet, J and Murrell, K.D. eds.), FAO/WHO/OIE Guidelines for the Surveillance, Management, Prevention and Control of Trichinellosis, Rome, pp. 69-98.
