Porcine epidemic diarrhea virus (PEDV) is a causative agent of diarrhea in pigs. It recently caused significant economic damage worldwide. The disease is characterized by severe diarrhea, vomiting and dehydration, resulting in up to 100 % mortality in young piglets. While vaccines are available in market, low to moderate efficacy of vaccines have been a concern. One of the reasons implicated for vaccine failures has been genetic differences between vaccine and field strains. Thus, finding effective ways to prevent transmission of PEDV is critical to minimize outbreaks of this disease. However, very little is known about indirect transmission of the virus via personnel movement, and virus stability on fomite materials under different environmental condition. The work described in this dissertation, aims to assess contribution of fomites in indirect transmission events, and study PEDV stability on different fomites at varying temperatures.
Personnel movement across pig rooms caused rapid transmission of the PEDV when low biosecurity (LB) procedures were practiced. Donning contaminated personal protective equipment (PPE) was sufficient to transmit infection to naïve pigs resulting in virus shedding, and providing proof of the contagious nature of PEDV. Also, compared to direct-contact transmission which occurred within 24 hours, indirect transmission via personnel movement happened surprisingly rapidly, similar to direct contact. In addition, we found that PEDV transmission through contaminated body surfaces on personnel in medium biosecurity (MB) group may be possible based on detection of viral RNA on the surfaces of their face and hands. This indicates that given adequate exposure, there is an increased risk for PEDV transmission when procedures like taking a shower or changing PPE between rooms are not followed. On further investigation of contaminated fomites under different environmental conditions, we tested the stability of cell cultured PEDV on various fomite materials at two different temperatures, 4ºC and room temperature (25ºC). PEDV remained viable at 4°C, for over 20 days post application on fomites, specifically Styrofoam, Tyvek® coverall, metal and plastic. However, PEDV viability decreased rapid when stored at room temperature on the fomite surfaces we tested, rendering it undetectable using infectious virus assays. However, viral RNA copy numbers could be detected on all surfaces by real-time RT-PCR, which do not correlate well with cell-based assays demonstrating presence of infectious virus.
This data reinforces the fragile nature of this enveloped virus, suspecting effect changes of envelope without RNA degradation over time. These studies are the evidences that indirect transmission of PEDV through contaminated personnel, which occurs rapidly, and how fomite material and temperature impact viral stability over time. These observations provide an increased understanding of indirect transmission of PEDV through personnel movement on contaminated PPEs and fomites. This information can help improve the implementation of biosecurity procedures in controlling PEDV transmission and to prevent new outbreaks.
Kim, Yonghyan. (2016). Indirect transmission and stability of porcine epidemic diarrhea virus on fomites. Retrieved from the University of Minnesota Digital Conservancy, http://hdl.handle.net/11299/183297.