Survival of North American Genotypes of Trichinella in Frozen Pork

Abstract

North American genotypes of Trichinella spiralis (T-1), Trichinella nativa (T-2), Trichinella pseudospiralis (T-4), Trichinella murrelli (T-5), and Trichinella T-6 were examined for susceptibility to freezing in pork using time-temperature combinations that have been proven to inactivate T. spiralis. Infections were established in 3-month-old pigs of mixed sex and breed by oral inoculation of 10,000 muscle larvae (ML) (all genotypes, rodent-derived ML), 20,000 ML (T-1, T-4, and T-5; cat-derived ML), or 30,000 ML (T-2 and T-6; cat-derived ML). Pigs were euthanized 60 days postinoculation. Muscles from the tongue, masseter muscles, diaphragm, triceps, hams, neck, rump, and loins were ground, pooled, and mixed to ensure even distribution of larvae. Samples (20 g) containing each Trichinella species, genotype, and source combination were placed in heat-sealable pouches, transferred to a constant temperature refrigerant bath, and maintained according to defined time and temperature combinations. Larvae recovered from cold-treated pork samples were inoculated into mice to determine infectivity. Results indicated that the time-temperature combinations known to render pork safe for T. spiralis are sufficient to inactivate T. nativa and T-6 (the freeze-resistant isolates), T. murrelli (the most common sylvatic species in the United States excluding Alaska), and T. pseudospiralis (a species that lacks a muscle nurse cell). These data close a gap in knowledge about the effectiveness of freezing for inactivating these parasites in pork and should alleviate concern about the safety of frozen pork products from the United States.

Pathogens of Interest to the Pork Industry: A Review of Research on Interventions to Assure Food Safety

“…Using liquid nitrogen or liquid carbon dioxide was also found to be effective at destruction of the parasite when –29 °C was achieved (Rust and Zimmermann ). Recently there has been concern of freeze‐resistant strains of Trichinella ; however, these strains are not found in domestic pigs (Pozio and others ; Hill and others ). The Intl.…”

Cessation ofTrichinella spiralisTransmission Among Scavenging Mammals After the Removal of Infected Pigs From a Poorly Managed Farm: Implications for Trichinae Transmission in the US

“…Five of the sibling species, T. spiralis (T1), T. nativa (T2), T. pseudospiralis (T4), T. murrelli (T5) and Trichinella T6 occur in the continental US, and have been identified in a variety of mammalian species including but not limited to domestic swine and wild boar, black bear, opossum, raccoon, coyote, wolf, dog, fox, skunk, rat, bobcat and cougar (Pozio, 2007). Trichinella murrelli is the predominant genotype found in sylvatic carnivores in North America (Zarlenga et al., 1991; Pozio and La Rosa, 2000; Hill et al., 2008, 2009). The sylvatic genotypes are minimally infective to domestic pigs, and show poor persistence in pig tissues (Kapel and Gamble, 2000; Hill et al., 2009).…”

“…Trichinella murrelli is the predominant genotype found in sylvatic carnivores in North America (Zarlenga et al., 1991; Pozio and La Rosa, 2000; Hill et al., 2008, 2009). The sylvatic genotypes are minimally infective to domestic pigs, and show poor persistence in pig tissues (Kapel and Gamble, 2000; Hill et al., 2009).…”

“…Although T. spiralis probably separated from the non‐encapsulated clade millions of years ago (Zarlenga et al., 2006), it has only recently become established in North America, having been transported to the Western hemisphere in the tissues of infected swine brought from Europe during colonial era migrations (Rosenthal et al., 2008). Infection with T. spiralis less commonly occurs in sylvatic carnivores, which by contrast serve as important reservoirs for other species of Trichinella (Pozio and Murrell, 2006; Hill et al., 2008, 2009; Pozio et al., 2009).…”

“…Whether some scavenging mammals maintain transmission cycles of T. spiralis in the absence of infected pigs remains unknown. Recent surveys have failed to demonstrate T. spiralis cycling independently in scavenging mammals in North America, while T. murrelli is common; more research is needed to decide this issue (Zarlenga et al., 1991; Pozio, 2000; Pozio and La Rosa, 2000; Burke et al., 2008; Hill et al., 2008, 2009; Masuoka et al., 2009).…”