Food Safety Magazine, February/March 2013

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SEAFOOD(infectious and noninfectious virus particles) in foods; however,there are no internationally recognized standard methods todate. In an effort to develop standardized procedures, the EuropeanCommittee for Standardization established a TechnicalAdvisory Group for Viruses to develop and publish standard virusextraction and assay procedures for food surfaces, soft fruitand salad vegetables, bottled water and bivalve molluscan shellfish.11 After many years of work, their results should be availablesoon. Virus isolation from foods, either through a rinsingprocedure or by extraction, must be followed by analysis of theInadequacies of Norovirus SurrogateResearchThe quest for an assay to detect infectious noroviruses infood and water has been hampered by the inability to propagatehuman noroviruses in cell or tissue culture systems and theinability to infect common laboratory animals. Consequently,other viruses that can be assayed for infectivity are often used asnorovirus surrogates. One of the earliest viruses to stake a claimas a norovirus surrogate was feline calicivirus, which produceseasily quantified plaques in feline kidney cell culture. A morerecent entry in the search for a surrogate is murine norovirus,which is genetically more similar to human norovirus than isfeline calicivirus and produces plaques in a mouse macrophagecell line. To date, over 400 papers have been published on the“Several methods have been developed to extract and test fortotal norovirus contamination...in foods; however, there are nointernationally recognized standard methods to date.”viruses. In spite of improvements in our ability to extract virusesfrom foods, the analysis of rinses and extracts leaves muchto be desired. Assay methods are almost exclusively based onreverse-transcription polymerase chain reaction (RT-PCR), amolecular-based procedure that amplifies viral RNA into complementaryDNA (cDNA) copies. RT-PCR-based assays have anumber of limitations. Perhaps the most significant is that theydetect total virus presence (both infectious and noninfectiousvirus particles). Thus, viruses inactivated by chlorine, other disinfectants,sunlight, heat, high pressure, etc. can still test positiveby RT-PCR. Other limitations of RT-PCR are that the assayis subject to laboratory contamination and is frequently inhibitedby compounds in the extracts of shellfish or other foods.Various controls must be included in both virus extraction andassay to demonstrate the effectiveness of the extraction and thelack of inhibitors or contaminants in the assay. Such controlsincrease the time and complexity of the procedures but are necessaryfor accurate interpretation of the results.Determining Norovirus Infectivity. For over 40 years, researchershave attempted to propagate noroviruses in culture. Unlikemany human viruses, which can be assayed and quantified incell culture, norovirus propagation has not been successful, inspite of some reports to the contrary. Plaque assays and cytopathogenicityassays are the basis for quantitative assessmentfor many viruses, but are ineffective for human noroviruses.Animal models are another way to monitor the infectivity ofsome viruses, but human noroviruses are incapable of replicationin laboratory animals. Recent advances suggest it will soonbe possible to separate inactive from potentially active norovirususing magnetic beads coated with molecules that mimic thecellular receptors to which noroviruses bind. It would then be12, 13possible to extract potentially infectious norovirus particles.use of feline calicivirus and murine norovirus to determine theeffectiveness of chemical disinfectants and processing technologieson norovirus inactivation. Other norovirus surrogates havebeen proposed; however, it has become abundantly clear thatnone of the surrogates tested to date perfectly mimics humannorovirus. 14 In many cases, human noroviruses may be morepersistent than the surrogates. Such variability in inactivationrates between the surrogate and the pathogen itself might havebeen anticipated, because different strains of even the same viruscan have widely varying inactivation kinetics. For instance,different strains of feline calicivirus showed differences in theirinactivation by chemicals, heat and pH, 15, 16 whereas differentstrains of hepatitis A virus showed substantial differences in inactivationby heat and HPP. 17 Since human norovirus illnessesare caused by any of a wide variety of norovirus strains, it isunlikely that surrogate testing in itself will provide accurate dataor data useful for the promulgation of regulations for the foodindustry. Currently, only human volunteer studies with the actualpathogens can definitively determine norovirus infectivityor the efficacy of sanitation interventions. 14The Need for Clinical TrialsClinical trials have been performed on human norovirusfor decades, but the perceptions that they may be too risky orexpensive have dissuaded some governments from fundingsuch trials. In the United States, clinical trials are still fundedby some agencies, and the information provided in respect tonorovirus inactivation is essential to developing methods applicableto food processing. However, as a practical matter, thehigh cost and complexity of human trials limit the scope of thistype of research. As previously mentioned, the results to date ofsurrogate-based studies are of limited value. Human clinical trialsare needed to evaluate the effectiveness of disinfectants andprocessing technologies on human norovirus inactivation andto identify true norovirus surrogates. 14 Only then will definitiveinformation be available to properly evaluate the retention anddisinfection of infectious noroviruses in foods.60 F o o d S a f e t y M a g a z i n e
SEAFOODConclusionsStrategies to reduce human noroviruses in the food chaininvolve: (a) pre- and postharvest interventions to precludenoroviruses from food or food contact surfaces; (b) processingtechniques to inactivate viruses on or within the products and(c) product analyses. Cooking, washing and peeling could havea significant effect on eliminating human noroviruses in somefoods, but viruses tend to persist in molluscan shellfish. Effortsusing norovirus surrogates identified to date have not resultedin new disinfectants or processing techniques, and have not significantlyadvanced food safety. Currently, human clinical trials4. McIntyre, L., E. Galanis, K. Mattison, O. Mykytczuk, E. Buenaventura, J.Wong, N. Prystajecky, M. Ritson, J. Stone, D. Moreau and A. Youssef. 2012.Multiple clusters of norovirus among shellfish consumers linked to symptomaticoyster harvesters. J Food Prot 75:1715–1720.5. DiGirolamo, R., J. Liston and J. Matches. 1970. Survival of virus in chilled,frozen, and processed oysters. Appl Microbiol 20:58–63.6. Richards, G.P., C. McLeod and F.S. Le Guyader. 2010. Processing strategiesto inactivate enteric viruses in shellfish. Food Environ Virol 2:183–193.7. Provost, K., B.A. Dancho, G. Ozbay, R.S. Anderson, G.P. Richards and D.H.Kingsley. 2011. Hemocytes are sites of enteric virus persistence in oysters.Appl Environ Microbiol 77:8360–8369.“Human clinical trials are needed to evaluate the effectiveness ofdisinfectants and processing technologies on human norovirusinactivation and to identify true norovirus surrogates.”remain the only method to conclusively show the effectivenessof processing techniques on virus persistence. Over the nextdecade, technological advancements may lead to simple, quantitativeassays for human noroviruses. In the meantime, clinicaltrials will provide the best opportunity to identify processinginterventions to reduce noroviruses in foods. The food industry,regulatory agencies and the public face many challenges inregard to norovirus contamination of the food supply, but witha concerted effort, obstacles that compromise food safety willbe overcome.Mention of trade names or commercial products in this publication issolely for the purpose of providing specific information and does notimply recommendation or endorsement by the USDA, which is anequal opportunity provider and employer.•Gary Richards, Ph.D. (right), and David Kingsley, Ph.D. (left),are research microbiologists at the USDA Agricultural ResearchService’s Microbial Safety of AquacultureProducts Center of Excellence in Dover,DE. Their research involves the developmentof food safety and intervention technologies toreduce bacterial and viral contaminants in foods with emphasison molluscan shellfish.References1. Scallan, E., R.M. Hoekstra, F.J. Angulo, R. V. Tauxe, M.A. Widdowson, S.L.Roy, J.L. Jones and P.M. Griffin. 2011. Foodborne illness acquired in theUnited States — major pathogens. Emerg Infec Dis 17:7–15.2. Richards, G.P. 2001. Enteric virus contamination of foods through industrialpractices: A primer on intervention strategies. J Indust MicrobiolBiotechnol 27:117–125.3. Kohn, M.A., T.A. Farley, T. Ando, M. Curtis, S.A. Wilson, Q. Jin, S.S. Monroe,R.C. Baron, L.M. McFarland and R.I. Glass. 1995. An outbreak ofNorwalk virus gastroenteritis associated with eating raw oysters. Implicationsfor maintaining safe oyster beds. JAMA 273:466–471.8. Kingsley, D.H., D.G. Hoover, E. Papafragkou and G.P. Richards. 2002. Inactivationof hepatitis A virus and a calicivirus by high hydrostatic pressure.J. Food Prot 65:1605–1609.9. Kingsley, D.H., D.R. Holliman, K.R. Calci, H. Chen and G.J. Flick. 2007.Inactivation of a norovirus by high pressure processing. Appl EnvironMicrobiol 73:581–585.10. Leon, J.S., D.H. Kingsley, J.S. Montes, G.P. Richards, G.M. Lyon, G.M. Abdulhafid,S.R. Seitz, M.L. Fernandez, P.F. Teunis, G.J. Flick and C.L. Moe. 2011.Randomized, double-blinded clinical trial for human norovirus inactivationin oysters by high hydrostatic pressure processing. Appl Environ Microbiol77:5476–5482.11. Lees, D. and CEN-WG6-TAG4. 2010. International standardisation of amethod for detection of human pathogenic viruses in molluscan shellfish.Food Environ Virol 2:146–155.12. Dancho, B.A., H. Chen and D.H. Kingsley. 2012. Discrimination betweeninfectious and non-infectious human norovirus using porcine gastric mucin.Int J Food Microbiol 155:222–226.13. Tian, P., A. Engelbrektson and R. Mandrell. 2008. Two-log increase insensitivity for detection of norovirus in complex samples by concentrationwith porcine gastric mucin conjugated to magnetic beads. Appl EnvironMicrobiol 74:4271–4276.14. Richards, G.P. 2012. Critical review of norovirus surrogates in food safetyresearch: rationale for considering volunteer studies. Food Environ Virol4:6–13.15. Di Martino, B., C. Ceci, F. Di Profio and F. Marsilio. 2010. In vitro inactivationof feline calicivirus (FCV) by chemical disinfectants: Resistance variationamong field strains. Arch Virol 155:2047–2051.16. Lee, K.M. and H.H. Gillespie. 1973. Thermal and pH stability of felinecalicivirus. Infect Immun 7:678–679.17. Shimasaki, N., T. Kiyohara, A. Totsuka, K. Nojima, Y. Okada, K. Yamaguchi,J. Kajioka, T. Wakita and T. Yoneyama. 2009. Inactivation of hepatitis Avirus by heat and high hydrostatic pressure: variation among laboratorystrains. Vox Sanguinis 96:14–19.To read more about seafood safety, please visitwww.foodsafetymagazine.com/signature-series/.F e b r u a r y • M a r c h 2 0 1 3 61
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February/March 2013Vol. 19, No. 1FE
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Editor’s LetterWe at Food Safety
Page 10 and 11: USDA Seeks Comments on ProposedFroz
Page 12: TestingBy Katerina Mastovska, Ph.D.
Page 15 and 16: Testingheat treatment, the toxins c
Page 17 and 18: staying connectedto your data hasne
Page 19 and 20: PROCESS CONTROL1. Scope2. Normative
Page 21 and 22: SANITATIONapproach, 1, 2 while effe
Page 23 and 24: SANITATIONis a matter of legal liab
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Page 27 and 28: AccreditationFood Microbiological L
Page 29 and 30: MANAGEMENTcertain spices. As no acc
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Page 37 and 38: AccuracyQualitySafetyHACCP Monitori
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Page 54 and 55: INGREDIENTSBy Rupa Das, M.Sc.Qualit
Page 56 and 57: SEAFOODBy Gary P. Richards, Ph.D.,
Page 58 and 59: SEAFOODfoods is essential to reduci
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