Vibrio in seafood - FAO.org

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The approach being taken is to use the United States FDA Draft Risk Assessment on the PublicHealth Impacts of V. parahaemolyticus in Raw Molluscan Shellfish model (FDA-VPRA) (Anonymous,2001) as the base and further develop it to accommodate data inputs from other countries. The FDA-VPRA contains several key linkages between prevalence of V. parahaemolyticus in oysters andtemperature, most notably temperature of harvest waters and of oysters throughout the post-harvest-retailconsumptioncontinuum. Temperature profiles in the oyster industry of other countries e.g. New Zealandand Australia indicated the opportunity for growth of pathogenic V. parahaemolyticus to potentiallydangerous numbers. However, the public health statistics of these countries do not reflect any impact dueto this organism in oysters. Accordingly, an exposure assessment will be undertaken onV. parahaemolyticus in oysters using data from Australia, Canada, Japan, New Zealand and the UnitedStates.The model incorporates all phases in the harvest - post-harvest - consumption continuum using amodular approach. A schematic representation of the pathway to be modelled is presented in Figure 2.1.Much of the information presented in the following pages is based on the FDA-VPRA. Data from othercountries for the exposure assessment have and continue to be obtained via a call for data issued by FAOand WHO. The data are then being analysed for incorporation into the risk assessment model. Thisprocess is ongoing and will be completed in 2002.Thus the objectives of this exposure assessment are;• to quantify the exposure of consumers to pathogenic V. parahaemolyticus fromconsumption of raw oysters, and• to take a model that was developed for one particular country scenario and extend it toconsumers in other countries that have oyster industries.2.2.1 Microbial ecologyVibrio parahaemolyticus is found in the estuarine environment in the tropical to temperate zones.Several studies have been published on the concentration of V. parahaemolyticus in shellfish growingareas (Davis & Sizemore. 1982; DePaola et al., 1990; Kaneko & Colwell, 1978; Kaysner et al., 1990a;Kaysner et al., 1990b; Kaysner & Weagant, 1982: Kelly, 1999; Levine et al., 1993). The organism hasbeen isolated from a number of fish species and is associated primarily with the intestinal contents (Nair etal., 1980).areas:There are several pathways by which V. parahaemolyticus strains may enter into shellfish growing• It may be introduced by terrestrial and aquatic animals, some of which may harbour virulentstrains and act as intermediate hosts (Sarkar et al., 1985).• It may be introduced through “relaying” shellfish or by release of ballast water. Cargo vesselscarry substantial quantities (10 6 litres) of ballast water from the body of water where the voyageoriginates. This water is retained until the ship is about to load cargo, when it is discharged.Thus, if present, V. parahaemolyticus is also released into the loading port. A report that strains ofVibrio cholerae, indistinguishable from the Latin American epidemic strain, were found in nonpotablewater taken from a cargo ship docked in the Gulf of Mexico indicate that ballast watermay have been responsible for the spread of an epidemic strain of V. cholerae to the Gulf ofMexico (McCarthy & Khambaty, 1994). A similar mechanism could account for the spread ofV. parahaemolyticus.Once introduced, a number of factors influence the establishment of V. parahaemolyticusincluding:6
• Interactions of environmental conditions;• Species and physiology of the shellfish;• Genetics of the micro-organism.Certain areas may have more favourable environmental conditions that support establishment,survival and growth of the organism such as temperature, salinity, zooplankton, tidal flushing (includinglow tide exposure of shellfish) and dissolved oxygen (Amako et al., 1987; Garay et al., 1985; Kaneko &Colwell, 1978; Venkateswaran et al., 1990).Regional, seasonal andyearl y vari ationWatertemperatureWatersalinityTotalV.parahaemolyticus./gPathogenicV.parahaemolyticus./gV.parahaemolyticus./gat har vestTime to re frigerationV.parahaemolyticus./gat 1 st refrigerationAir temperatureV.parahaemolyticus./gat c ool downV.parahaemolyticus./gat consumptionCooldown timeStorage timeFigure 2.1. A schematic representation of the process pathway to be modeled in the exposureassessment of V. parahaemolyticus in oysters.7
Page 1 and 2: Food and Agriculture Organization o
Page 3: 4.2.5 Simulation Results...........
Page 6 and 7: United States prior to 1997 illness
Page 8 and 9: 2 RISK ASSESSMENT OF VIBRIO PARAHAE
Page 12 and 13: 2.2.2 Growth and survival character
Page 14 and 15: given average temperature and predi
Page 16 and 17: strains have been identified as a p
Page 18 and 19: 2001) and so this assumption may ha
Page 20 and 21: States. The study was undertaken on
Page 22 and 23: The estimated relationships between
Page 24 and 25: Clearly, in order to predict the di
Page 26 and 27: expected. Differences in these dist
Page 28 and 29: measurements were recorded for any
Page 30 and 31: egions of the country the average p
Page 32 and 33: etained. A corresponding air temper
Page 34 and 35: Frequency of duration of oysterharv
Page 36 and 37: 2.2.5.4.5 Die-off of V. parahaemoly
Page 38 and 39: V. parahaemolyticus cause illness -
Page 40 and 41: and four of those patients died. Pa
Page 42 and 43: Vomiting 52 17-79Headache 42 13-56F
Page 44 and 45: 2.3.3.2 Dose-response model2.3.3.2.
Page 46 and 47: While these assumptions are not rep
Page 48 and 49: Bean, N. H., Maloney, E. K., Potter
Page 50 and 51: Gjerde, E.P. and Bøe, B. 1981. Isp
Page 52 and 53: Levine, W. C., Griffin, P. M., and
Page 54 and 55: Abstract of the National Shellfishe
Page 56 and 57: 3.1.2 Prevalence in foodAlthough li
Page 58 and 59: The concentration of V. parahaemoly
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Figure 3.3. Schematic representatio
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3.2.4 Preparation and consumption m
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• Frequency of consumption of raw
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Sarkar, B. L., G. B. Nair, et al..
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foodborne case has been associated
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(Cook and Ruple, 1992). However, th
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4.2.4.1 HarvestLike V. parahaemolyt
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Although not incorporated in the pr
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increase in log of Vv density32.521
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Figure 4.6 shows typical distributi
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1.5Probability Density0.7501 2 3 4
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Table 4.6. Prevalence rates of V. v
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4.3.3 Dose-response relationship4.3
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Dec 15 0.76 0.61 1,841,000 1,025,00
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• Does virulence vary by season,
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ICMSF. 1996. Microorganisms in Food
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Appendix.Analytica 2.0.5 Model Simu
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The chance nodes representing varia
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5.2.2.2 Death or inactivationV. cho
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Table 5.3. Instances of fish implic
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Shrimp harvested fromcoastal areas
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O1 through poor quality water, and
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5.3.1.2 Characteristics of the host
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5.3.3.1.4 Probability of death give
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Resampled Beta-Poisson dose-respons
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De Paola, A. 1981. Vibrio cholerae
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Reilly, L.A. and Hackney, C.R. 1985
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