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Trichinella in pork: current knowledge on the suitability of freezing as a public health measure

November 22, 2006 — E Pozio1, CMO Kapel2, AA Gajadhar3, P Boireau4, J Dupouy-Camet5, HR Gamble6

Nematodes of the genus Trichinella are the causative agents of trichinellosis, a potentially severe disease in humans. Raw or undercooked pork, horse and game meat (predominantly wild boar and bear) poses a health risk to consumers.

Various European and international regulations and guidelines have been developed to protect consumers from exposure to this parasite [1-3]; these regulations and guidelines cover both slaughter inspection and post-slaughter processing (e.g., freezing, cooking). Scientific studies have been conducted to validate these methods in pork, including an international study, which described the time and temperature requirements for the freezing process to inactivate Trichinella spiralis, the species of Trichinella most commonly associated with pork [4]. Results of this study have been widely used to develop regulations governing the commercial freezing of pork and pork products [1, 3].

However, recent scientific information on the geographical distribution of species of Trichinella, other than T. spiralis, which can infect pigs, and the ability of some of these species to tolerate freezing, have raised doubts about the effectiveness of commercial freezing methods to kill trichinella larvae in pork intended for human consumption [5].

Recommendations Considering the moderate infectivity of T. britovi for pigs, the regular isolation of this species from the domestic pig in Europe, and the uncertainty of freezing as a method to inactivate this species, pork from areas where T. britovi is endemic should not be treated by freezing alone as a method to protect human health until further research has been conducted. In the interim, pork from areas where T. britovi is endemic should be inspected using reliable detection methods [2].

Research on freezing pork as a method to inactivate T. britovi should account for all the factors which may influence the susceptibility of this parasite, such as intra-specific variation of isolates from and within different geographic regions. Furthermore, studies investigating the susceptibility of T. britovi, or other trichinella species in different hosts to various freezing conditions should be conducted with the same rigour as applied in earlier studies [4], as these results will influence future regulations on meat safety.

[Note: The authors are members of the International Commission on Trichinellosis (http://monsite.wanadoo.fr/intcomtrichinellosis) and provide information and recommendations based on recent recognition of gaps in knowledge on this parasite which may impact regulatory decisions. Additional information on the subject of freeze tolerant Trichinella can be found in an opinion paper from the European Food Safety Authority [12]].

Source:
Eurosurveillance Weekly

1Department of Infectious, Parasitic and Immunomediated Diseases, Istituto Superiore di Sanita, Rome, Italy; 2Lab. of Zoology, Department of Ecology, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark; 3Centre for Food-borne and Animal Parasitology, Canadian Food Inspection Agency, Saskatoon, Canada; 4UMR BIPAR INRA AFSSA ENVA UPVM, Maisons-Alfort, France; 5Parasitologie, Hopital Cochin, Universite Descartes, Paris, France; 6National Research Council, Washington, USA