UV inactivation and model of UV inactivation of foot-and-mouth disease viruses in suspension.

Foot-and-mouth disease virus (FMDV) causes one of the most contagious diseases affecting cloven-hoofed animals (e.g., cattle and swine) and causes severe economic loss for many countries. The resistance to UV irradiation of FMDV strains isolated from outbreaks in Thailand was investigated in phosphate-buffered saline at 25 degrees C. Since the regression coefficients of linear regression were large and root mean square errors were small, UV inactivation could be appropriately summarized and fitted well by a linear equation. The first-order kinetics then could describe UV inactivation, which was experimentally and mathematically shown in this study to be an effective means to inactivate FMDV in suspension. The decimal inactivation dose (DID) was modified from D value in traditional thermal-inactivation kinetics. The DID was the amount of UV irradiation required to reduce the number of microorganisms by a factor of 10, or by 90%. DIDs of FMDV serotypes O189, A132, A-Sakol, and AS1 ranged from 19.66 to 31.31 mWs/cm2. FMDV serotype AS1 was the most UV-resistant, and FMDV serotype A132 was the least UV-resistant. UV resistance of FMDV did not vary significantly among strains and serotypes (P value > 0.05). DID raw data were used to determine the fitted probability distributions by simulation software @Risk. The fitted distributions suggested were Exponential, Logistic, Normal, and LogNormal. Exponential distribution was the best fit by Chi-square test, Kolmogorov-Smirnov test, and Anderson-Darling test (P value >0.10). The parameter beta of the Exponential distribution, equivalent to the mean DID, was 24.173 mWs/cm2 as a first-order model. Poisson probability distribution described the uncertainty of parameter beta for the second-order model. After running simulations of both first-order and second-order models, the curves of both first-order and second-order models were overlaid on the same graph, which indicated that both models were only slightly different. This study concluded that FMDV in suspension was effectively inactivated by UV irradiation, the fitted probability distribution for UV inactivation was Exponential, and source of total uncertainty of this UV-inactivation model was not the uncertainty component.