Mitigation of PRRS Transmission with UV Light Treatment of Barn Inlet Air: Proof-of-Concept

Drive sustainable Production’ is one of the NBP’s key goals for 2015-2020 and the Swine Health Committee. This research helped address one key target, i.e., deployment of tools for a significant decrease of porcine reproductive and respiratory syndrome (PRRS) economic impact by 2020. The main objective was to test the efficiency of ultraviolet (UV) treatment of the airborne PRRS virus. Specifically, we tested and compared (in lab-scale) four types of UV lights: (1) conventional germicidal UV-C (254 nm), (2) UV-C’ excimer’ (222 nm), (3) UV-A (365 nm) fluorescent, and (4) UV-A (365 nm) LED for inactivation of PRRS virus using treatment times that are consistent with fast-moving barn inlet air. The key advancement was testing of the never-tested before excimer UV-C light that is by far less toxic to people and livestock while being very recently proven to be bactericidal for MSRA and for the H1N1 influenza virus. No data existed on how effective the excimer UV-C is for the treatment of PRRS. Similarly, no data existed on how effective the UV-A (a.k.a. ‘black light’ and commonly used for artificial suntanning) is for PRRS treatment. Yet, there are concerns about using the UV 254 nm (conventional germicidal UV lamps) on farms due to its harm to both workers and animals. The experimental design consisted of PRRS virus propagation and storage, PRRSV aerosolization, UV treatment, PRRSV sampling and recovery, virus isolation, determination of surviving virus, estimation of UV dose, and cost analysis to achieve practical levels of virus load reduction. The results showed that UV-C (254 nm) and UV-C excimer (222 nm) could effectively inactivate the aerosolized PRRS virus. The UV-A (365 nm, both fluorescent and LED), however, did not yield obvious virus load reduction in this research for doses up to 4.11 mJ/cm2. UV inactivation models of four lamps were developed based on the experimental data to estimate UV doses for target virus load reduction. A UV dose needed for 2-log (99%), 3-log (99.9%) aerosolized PRRS virus reduction was 0.0872 and 0.0958 mJ/cm2, respectively, for UV-C (254 nm). This finding is also important because the value for the 3-log (99.9%) PRRS virus reduction was over 12x lower than the one and only previously reported 3-log (99.9%) airborne (not in plate study) PRRS virus reduction by 1.21 mJ/cm2 for UV-C (254 nm) (Cutler et al., 2012). The practical significance is that the UV-C (254 nm) doses (and therefore the cost) might be lower than previously estimated. The dose needed for 2-log (99%), 3-log (99.9%) aerosolized PRRS virus reduction was 0.0429 and 0.0489 mJ/cm2, respectively, for UV-C (222 nm, excimer). This finding is important because the 222 nm ‘excimer’ UV doses are ~50% lower than the conventional 254 nm for the same level of PRRS virus kill. However, the cost of 222-nm excimer lamps is still economically prohibitive to consider them for the scaling-up trials. Pilot-scale testing of UV-C treatment of aerosolized PRRS large volumes of air simulating barn ventilation rates are recommended based on the high effectiveness and reasonable cost estimates comparable to HEPA filtration.