Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2009
Publication Date: 12/15/2009
Citation: Hill, D.E., Forbes, L., Zarlenga, D.S., Urban Jr, J.F., Gajadhar, A.A., Gamble, H. 2009. Survival of North American Genotypes of Trichinella in Frozen Pork. Journal of Food Protection. 72(12):2565-2570.
Interpretive Summary: International market access for frozen pork has been limited and trading partners frequently require individual carcass testing in addition to cold treatment. In recent negotiations, trading partners agreed to accept frozen pork from the U.S. as part of the WTO agreement. This agreement was reached in spite of objections raised by international veterinary experts regarding a risk posed by cold tolerant species of Trichinella, some of which are found in the U.S. and Canada. The recent interest in issues surrounding international standards for the cold treatment of pork led members of the International Commission on Trichinellosis to review the current status of the problem and point out the need for additional research on this topic. The presence of sylvatic isolates in North America which are freeze tolerant (T-2 and T-6) is of concern to trading partners, and represents a barrier to increased trade of frozen pork products. The purpose of the current study was to fill the current gap in knowledge about susceptibility to cold treatment of sylvatic isolates of Trichinella which occur naturally in North America (T-2, T-4, T-5, and T-6), and increase confidence in the strategies currently used to eliminate the risk of Trichinella infection from frozen pork. Demonstrating the effectiveness of freezing methods against sylvatic genotypes of Trichinella in the U.S. closes this gap in our current knowledge. Demonstration of susceptibility to currently used freezing methods should eliminate concern about the safety of frozen pork products from these Trichinella genotypes in pork.
Technical Abstract: North American genotypes of Trichinella (T. nativa (T-2), T. pseudospiralis (T-4), T. murrelli (T-5), and Trichinella (T-6)) were examined for susceptibility to freezing in pork using established parameters for control of T. spiralis. Pig infections with these Trichinella genotypes were established by oral inoculation of 10,000 infective larvae in 3 month old pigs of mixed sex and breed. Infected pigs were humanely sacrificed 60 days following infection. Muscles from the tongue, masseters, diaphragm, triceps, hams, neck, rump, and loins were ground, pooled, and mixed to assure even distribution of larvae in tissue samples. Pork samples (20 grams) containing each species/genotype were placed in heat-sealable pouches, transferred to a constant temperature refrigerant bath, and maintained according to the time and temperature combinations described. Larvae recovered by digestion of cold treated pork samples were inoculated into mice to determine larval infectivity. Results demonstrated that the freezing parameters described for T. spiralis (T-1) in pork products are sufficient to render pork safe with respect to T. nativa, T. psuedospiralis, T. murrelli, and Trichinella T-6. Trichinella nativa and Trichinella T-6 have extremely low infectivity for domestic pigs, and where that risk remains, freezing pork at proscribed temperatures is sufficient to destroy these larvae.