Search

North American genotypes of Trichinella spiralis (T-l), 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-I, 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. [ABSTRACT FROM AUTHOR]

A tissue digestion assay using a double separatory funnel procedure for the detection of Trichinella larvae in horse meat was validated for application in food safety programs and trade. The assay consisted of a pepsin-HC1 digestion step to release larvae from muscle tissue and two sequential sedimentation steps in separatory funnels to recover and concentrate larvae for detection with a stereomicroscope. With defined critical control points, the assay was conducted within a quality assurance system compliant with International Organization for Standardization--International Electrotechnical Commission (ISO/IEC) 17025 guidelines. Samples used in the validation were obtained from horses experimentally infected with Trichinella spiralis to obtain a range of muscle larvae densities. One-, 5-, and 10-g samples of infected tissue were combined with 99, 95, and 90 g, respectively, of known negative horse tissue to create a 100-g sample for testing. Samples of 5 and 10 g were more likely to be positive than were l-g samples when larval densities were less than three larvae per gram (lpg). This difference is important because ingested meat with 1 lpg is considered the threshold for clinical disease in humans. Using a 5-g sample size, all samples containing 1.3 to 2 lpg were detected, and 60 to 100% of samples with infected horse meat containing 0.1 to 0.7 lpg were detected. In this study, the double separatory funnel digestion assay was efficient and reliable for its intended use in food safety and trade. This procedure is the only digestion assay for Trichinella in horse meat that has been validated as consistent and effective at critical levels of sensitivity. [ABSTRACT FROM AUTHOR]

Retail meat cuts of pork are frequently enhanced with salt solutions to improve flavor and texture and to extend shelf life through reductions in microbial contamination. A study of the effect of commonly used meat enhancement solutions on the viability of Toxoplasma gondii tissue cysts was performed using tissues from experimentally infected mice and pigs. Brains of T. gondii-infected mice were injected to 110% of the original weight of the brain with solutions containing sodium chloride (1 and 2%), sodium diacetate (0.1 and 0.2%), sodium tripolyphosphate (0,25 and 0.5%), potassium lactate (1.4 and 1.96%), or sodium lactate (1.4, 1.5, and 2.0%) alone or in combination and stored at 4°C for 7 days before feeding to T. gondii--seronegative cats. Loins were collected from pigs experimentally infected with T. gondii and injected as above and stored for 7, 28, or 45 days at 4°C before feeding to T. gondii-seronegative cats. Cat feces were examined for 14 days to assess oocyst shedding. The present study demonstrated that injection of mouse brains or pork loins with solutions containing 2% sodium chloride or ⩾ 1.4% potassium or sodium lactate, alone or in combination with other components, prevented transmission of T. gondii to cats. [ABSTRACT FROM AUTHOR]

Treatment by hydrodynamic pressure is an attractive alternative for meat tenderization and might also have an effect on foodborne pathogens. Numbers of Trichinella spiralis recovered from infected pork were significantly reduced by treatment with the Hydrodyne process, as compared with untreated, infected pork. However, treatment with the hydrodynamic force described in this paper (55 to 60 MPa) did not eliminate the infectivity of this parasite when the larvae from Hydrodyne-treated meat were inoculated into mice.

Forty-seven pigs were infected with varying doses of Trichinella spiralis and tested for evidence of infection by serology, using an enzyme immunoassay (EIA), and by artificial digestion methods. Using a 1-g sample, as prescribed in accordance with European Union (EU) directives, the sensitivity of the pooled-sample artificial digestion method was between three and five larvae per gram (LPG) of tissue. Using a 5-g sample size, in accordance with methods described in the U.S. Code for Federal Regulations, and as required for the inspection of horses exported to the EU, the sensitivity of the test was increased to approximately 1 LPG. Serological testing by EIA detected pigs with as few as 0.02 LPG, but detection times varied from 4 to 8 weeks after infection. Mean postinoculation times for detection by serology were 32 to 42 days. On the basis of these results, it is clear that digestion testing using a 5-g sample size is the only method of those tested here that is completely reliable for detection of trichinae infection at a level that will protect public health. Both digestion testing using a 1-g sample and EIA have drawbacks. However, EIA remains a highly effective tool for epidemiological purposes and for monitoring trichinae infection on the farm.

Two enzyme immunoassays (EIA) for trichinellosis in swine (a research version and a commercial kit obtained from LMD Agro-Vet) were used to test pig whole blood, serum, and tissue fluids as sample sources. Five pigs inoculated with 2,500 Trichinella spiralis were bled weekly and then sacrificed after 42 days. Blood and serum samples from each sampling time and tissue fluids collected at slaughter were tested in both EIA formats. Whether samples were undiluted or diluted, blood could be used as effectively as serum for detecting pigs infected with T. spiralis . Further, it was as effective to use tissue fluids as either blood or serum. With both tests, the research and commercial versions, it is possible to detect infected pigs by 28 days following infection. The results of this study suggest that a rapid EIA test such as the LMD Agro-Vet Trichinella Serology Microwell ELISA can be used as an effective tool for testing pigs for trichinellosis on the farm. Additionally, because it can enable the detection of antibodies in tissue fluids, this test could be used effectively to determine trichinellosis in meat samples following slaughter.

The objective of this study was to demonstrate the reliability of current and proposed methods for the inspection of swine and other species for infection with the parasite Trichinella spiralis. Five groups of pigs were infected with doses of 2500, 500, 100, 50, and 20 T. spiralis larvae to establish moderate and low-level infections. Pigs were bled periodically during the study for samples to be tested by enzyme immunoassay (EIA). At the conclusion of the study, pigs were slaughtered and tissues collected for analyses of worm burdens and for comparison of digestion testing methods. Comparisons of pooled sample digestion methods were made using inspection methods prescribed by European Union Directives and the USDA, Code of Federal Regulations. Pooled sample digestion testing using 1-g samples was effective for detecting pigs with larval densities of > 10 larvae per gram (LPG) of tissue but only partially effective for pigs with infections of <3 LPG. Pooled sample digestion testing using 5-g samples detected all pigs with infection levels > 1 LPG. The EIA detected all T. spiralis-infected pigs, but did not detect infections in some pigs until 49 days after inoculation. These results demonstrate that the pooled sample digestion method using a 5-g sample size is the most effective inspection method for reducing the risk of human exposure to T. spiralis in pork.

This research was carried out to determine the time/temperature exposure of Trichinella spiralis to freezing conditions necessary to destroy the infectivity of the trichinae. Experimentally infected pork was subjected to temperatures of -1 to -193°C for one sec to 182 d and the treated pork samples, which contained about 1000 larvae per gram of tissue, were subjected to rat bioassay to determine infectivity of the larvae. A linear regression equation, log 10 t = 5.98 + 0.40T where t = required inactivation time in hours and T = temperature in degrees Celsius, described the exposure necessary to destroy the trichinae. The correlation for that relationship was r = 0.942. The predicted thermal death times (+7 min) at -20, -15, and -10°C were 8 min, 64 min, and 4.0 d, respectively. The predicted upper confidence limits (99%) for the thermal death times (+7 min) for exposure at -20, -15, and - 10°C, were 48 min, 63 h, and 266 d, respectively. These data provide a continuum of definitive times and temperatures necessary to destroy T. spiralis by freezing and are of value to the meat industry and the regulatory agencies.