The question addressed in this dissertation is whether ultraviolet could be used to inactivate airborne PRRS virus. Specifically, the aim of this research was to determine if ultraviolet could be used to prevent the airborne transmission of PRRS virus. This problem was addressed in the logical series of experiments described below.

Chapter 2 addressed the problem of quantifying the concentration of airborne infectious PRRS virus at levels sufficient to infect pigs, but below the threshold of microinfectivity assays. This study explored the application of the "continuous-stirred tank reactor (CSTR) model" to this problem and validated the CSTR approach using rhodamine B dye as a surrogate for aerosolized microbial pathogens in a dynamic aerosol toroid (DAT).

In Chapter 3, the median infectious dose (ID50) of PRRS virus isolate MN-184 via aerosol exposure was estimated. This information was needed to determine the level of ultraviolet inactivation necessary to stop transmission of PRRS virus. Infection occurred at virus concentrations too low to quantify by microinfectivity assays. Therefore, exposure dose was determined using two indirect methods ("calculated" and "theoretical"). "Calculated" virus dose was derived from the concentration of rhodamine B monitored over the exposure sequence. "Theoretical" virus dose was based on the continuous stirred-tank reactor model. The estimation of ID50 was modeled on the proportion of pigs that became infected using the probit and logit link functions for both "calculated" and "theoretical" exposure doses.

Chapter 4 established UV254 inactivation constants for: influenza virus Type A, porcine respiratory and reproductive syndrome virus (PRRS virus), bovine virus diarrhea virus (BVDV), and reovirus. Viruses were exposed to various UV254 doses then titrated for infectious virus. Analysis showed that virus inactivation by UV254 was more accurately described by a two-stage inactivation model, rather than the traditional one-stage inactivation model. These results provided insight into the dose of ultraviolet required to inactivate airborne pathogens (Chapter 5).

Chapter 5 described the effects of temperature and relative humidity on the inactivation of PRRS virus by ultraviolet. Viral aerosols were exposed to four doses of UV254 under three temperature ranges and three relative humidity ranges. This study allowed for calculating the dose of UV254 required to inactivate airborne PRRS virus under various conditions.