Aims:  The objective of this study was to estimate UV₂₅₄ inactivation constants for four viral pathogens: influenza virus type A, porcine respiratory and reproductive syndrome virus (PRRSV), bovine viral diarrhoea virus (BVDV) and reovirus.

Methods and Results:  Viruses in culture medium were exposed to one of nine doses of UV₂₅₄ and then titrated for infectious virus. Analysis showed that viral inactivation by UV₂₅₄ was more accurately described by a two-stage inactivation model vs a standard one-stage inactivation model.

Conclusions:  The results provided evidence for the existence of two heterogeneous viral subpopulations among the viruses tested, one highly susceptible to UV₂₅₄ inactivation and the other more resistant. Importantly, inactivation constants based on the one-stage inactivation model would have underestimated the UV₂₅₄ dose required for the inactivation of these viruses under the conditions of the experiment.

Significance and Impact of the Study:  To improve the accuracy of estimates, it is recommended that research involving the inactivation of micro-organisms evaluates inactivation kinetics using both one-stage and two-stage models. These results will be of interest to persons responsible for microbial agents under laboratory or field conditions.