Appendix 15 Virus Inactivation Kinetics Soren Alexandersen Danish Institute for Food and Veterinary Research, Department of Virology, Lindholm, DK-4771 Kalvehave, Denmark At the session of the Research Group of the Standing Technical Committee of the European Commission for the Control of Foot-and-Mouth Disease in Gerzensee, Berne, Switzerland in September 2003 a review of methods for describing the effect of temperature and time upon virus survival in products was presented (Have, 2003). The Research Group recommended that “specific studies on heat inactivation should be designed to support further risk assessments for those identified as “high” risk commodities. These studies should make use of existing experimental data on D and Z-values or involve further experiments to fill any gaps” and that “the available data on inactivation of FMDV in milk and milk products should be reviewed in the light of current international trade standards. If necessary, additional studies on inactivation by heat treatment or lowering pH should be carried out”. It was decided to develop study plans for assessing D-values and Z-values for heat treatment of milk and pork from FMD-infected animals and to consult the industry in regard to the planning and funding of such studies. As mentioned by Have (2003) the scientific literature regarding inactivation kinetics of FMDV from relevant sources and under relevant conditions is fragmented and sporadic and the difficulties of making quantitative assessments from various data sources on virus inactivation e.g. in the environment has been reviewed by Bartley et al (2002). As explained (Have, 2003); the effect of heating is determined by a combination of time and temperature and the inactivation kinetics are often assumed to be first-order although this is not always the case. The decimal reduction time DT is the time needed to reduce the viable population by 90% at the temperature T. Semi-log plots of Dvalues against temperature often yield linear relationships, from which z-values can be calculated as the number of degrees temperature required to change D by one log unit. The z-value is often considered to be constant for a given strain of microorganism in a given product. Heat treatment includes a heating phase and a cooling phase and to account for the combined effect during heating and cooling, the temperature/time relationship data can be used to calculate lethal rates over the entire process and integrating into a cumulated lethal effect, expressed relative to a standard treatment at a chosen reference temperature and taking advantage of knowing the value of z (Peleg, 2003). In regard to FMDV, clearly also other conditions, apart from the temperature, such as product type, pH, ionic strength and a number of other factors are also of importance for the kinetics of inactivation. Conclusions • Inactivation studies of FMDV need to be done in a systematic way employing kinetic data under relevant conditions. Recommendations • The recommendations of the 2003 meeting need to be taken immediately forward. It is suggested to make a small working group with the responsibility of urgently drawing up a study plan and to take this plan to the industry for consultation in regard to the practical planning and funding of such studies. References Bartley, L. M., Donnelly, C.A. & Anderson, R.M. 2002. Review of foot-and-mouth disease virus survival in animal excretions and on fomites. Vet. Rec. 151:667-669. Have, P. An assessment of guidelines for treatment of meat from a FMD vaccination zone. Session of the Research Group of the Standing Technical Committee, European Commission for the Control of Foot-and-Mouth Disease 2003: 149-152. Peleg, M. 2003. Calculation of the non-isothermal inactivation patterns of microbes having sigmoidal isothermal semi-logarithmic survival curves. Crit Rev. Food Sci. Nutr. 43:645-658
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