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As PED is an enteric disease, fecal samples from clinical pigs are considered to be the ‘gold standard’ for viral testing. Yet, such a sample presents a challenge to monitoring the presence and circulation of virus in a population when not clinical. Recently oral fluid sampling has been recognized as a cost effective tool for surveillance of numerous pathogens notably PRRSV and SIV. The objective of the present study was to assess the utility of oral fluid sampling and testing in monitoring viral shedding in comparison to fecal samples under experimental conditions.
Ninety six 4-week-old pigs with no previous exposure to PEDV and antibody negative for TGE and PRRS viruses were randomly allocated into control (n = 40) and challenge (n = 56) groups. Groups were housed separately and fed ad libitum. Pigs in the challenge group were randomly distributed in 4 pens, and control pigs were in 2 pens. Pigs were inoculated orally with 1ml of PEDV isolate (US/Iowa/18984/2013) 4,1 × 103 PFU/ml. Control pigs were sham inoculated with 1ml of cell culture media. Individual fecal swabs and pen-based oral fluids were collected every 24 hours for the first week, and twice a week thereafter for 56 days post inoculation (DPI) with periodic necropsies. Serum samples were also collected periodically. All oral fluids and fecal swabs were tested for PEDV nucleic acid using real-time RT-PCR5 and compared for correlation in test results.
Clinical diarrhea was developed in the inoculated pigs 3-5 DPI, which subsided by 10 DPI. Virus infection of the pigs was evident based on gross and microscopic lesions and positive IHC staining for PEDV in their intestinal tissues. According to PCR results on both oral fluids and fecal swabs, viral shedding began on day 1 and reached its peak during 3-4 DPI. Although no clinical signs of virus infection were present after 10 DPI, viral nucleic acid continued to be detected at levels near the limit of detection in oral fluids and fecal swabs after 10 through 35 DPI. A slight increase of viral shedding was detected from DPI 14-17 in oral fluids, though this increase was not seen as a general trend in the fecal swabs. No PEDV nucleic acid was detected in fecal and oral fluid samples collected at day 0 and in any of samples col- lected from control group thereafter.
In this study, oral fluids were collected, in addition to fecal swabs, from animals inoculated with the PEDV, in order to monitor viral shedding over the course of seven weeks. It was surprising to discover viral shedding continued for nearly 30 days after clinical symptoms of PEDV infection ceased. This information is vitally important for producers who are moving clinically normal animals among herds that have previously tested positive for PEDV.
PCR results on both fecal swab and oral fluid samples from the challenged groups showed good correlation, both in the duration of viral shedding as well as relative quantitation of viral shedding over time. Thus, oral fluids can be used as a sample type to accurately detect the presence and circulation of PEDV in pig herds. Though oral fluids do not yield comparative information between individuals in a herd, this specimen can accurately detect the presence of PEDV for surveillance of herd health.
Leslie Bower, Darin Madson, Hai Hoang, Dong Sun, Luis Gimenez-Lirola, Drew Magstadt, Paulo Arruda, Bailey Wilberts, Kyoungjin Yoon. Utility of oral fluid sampling and testing for monitoring PEDV in herds. 2014 AASV Annual Meeting.
