Porcine reproductive and respiratory syndrome (PRRS) is an infectious swine disease that causes significant economic loss to swine producers every year. PRRSV aerosols are an important route of transmission. Proper treatment of infectious aerosols could potentially mitigate the spread of the disease from one barn to another.
The battle against PRRS has been somewhat effective recently. The annual economic losses due to PRRS dropped from $664 million in 2012 (Holtkamp et al., 2013), to $580 million in 2016 (Pork Checkoff Report, 2017). Yet, the issue of biosecurity is still a top priority for producers and veterinarians.
PRRSV can be transmitted via indirect contact (such as aerosol and fomites) or direct contact (such as pig-to-pig). Given its airborne features and survivability of resisting a few miles of air travel, proper treatment of PRRSV aerosols could effectively reduce the transmission of the disease.
Dr. Jacek Koziel of Iowa State University built a team of interdisciplinary scholars and investigated the mitigation of airborne PRRS virus using ultraviolet (UV) light at a lab-scale with fast-moving air.
This project was inspired and funded by one of the National Pork Board's key goals for 2015-2020, and the Swine Health Committee, specifically, one key target of deployment of tools for a significant decrease of PRRS economic impact by 2020.
Previous work in the Koziel team has proven that UV-A (near-visible “blacklight”) can effectively reduce odor and odor-causing gases. This research expanded upon it by adding conventional germicidal UV-C light and novel excimer UV-C light and comparing the effectiveness in killing airborne PRRS virus.
The main objective was to test and compare (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 a recently developed "excimer" UV-C light (222 nm) that is by far less harmful to people and livestock while being proven to be germicidal for MSRA and for the H1N1 influenza virus. No data existed on how effective the excimer UV-C or UV-A is for the treatment of PRRS. This research bridged this knowledge gap by comparing UV of three wavelengths.
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. A closeup of the system is shown in Figure 1.
Dr. Koziel’s team found that UV-C (254 nm) and UV-C excimer (222 nm) could effectively inactivate the aerosolized PRRS virus. The UV-A (365 nm, blacklight), however, did not yield obvious virus load reduction for doses up to 4.11 mJ/cm2. This was expected because UV-A is not used for disinfection.
A UV-C dose (at 254 nm) needed for 2-log (99%), 3-log (99.9%) aerosolized PRRS virus reduction was 0.0872 and 0.0958 mJ/cm2, respectively. This finding is 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%) aerosolized (not 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.
A UV-C (222 nm) dose needed for 2-log (99%), 3-log (99.9%) aerosolized PRRS virus reduction was 0.0429 and 0.0489 mJ/cm2, respectively. 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 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.
Cutler, T.D., Wang, C., Hoff, S.J., Zimmerman, J.J. (2012). Effect of temperature and relative humidity on ultraviolet (UV 254) inactivation of airborne porcine respiratory and reproductive syndrome virus. Vet Microbiol. 159(1-2):47-52. doi: 10.1016/j.vetmic.2012.03.044
Holtkamp, D. J., Kliebenstein, J. B., Neumann, E., Zimmerman, J. J., Rotto, H., Yoder, T. K., Haley, C. A. (2013). Assessment of the economic impact of porcine reproductive and respiratory syndrome virus on United States pork producers. Journal of Swine Health and Production, 21(2), 72.
Miller, M. (2017). Annual PRRS Costs Fall $83.3 Million. Pork Checkoff Report, 2017, pp. 38–39.
Sources: Jacek Koziel, Peiyang Li, Jeff Zimmerman, William Jenks, Jianqiang Zhang, Ting-Yu Cheng, Iowa State University, who are solely responsible for the information provided, and wholly own the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.