Effect of porcine epidemic diarrhea virus infectious doses on infection outcomes in naïve conventional neonatal and weaned pigs
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Porcine epidemic diarrhea virus (PEDV) has been an important pathogen in Europe and Asia for several decades. It was identified in the United States (U.S.) swine population for the first time in April 2013, and spread rapidly across country and into Canada and Mexico. However, no information has been published regarding the minimum infectious dose (MID) of PEDV in different pig models. The main objective of this study was to determine the oral minimum infectious dose of PEDV in naïve conventional neonatal piglets and weaned pigs. A U.S. virulent PEDV prototype isolate (USA/IA19338/2013) with known infectious titer was serially ten-fold diluted in virus-negative cell culture medium, and inoculated into 5-day-old and 3-week-old pigs. Our data showed that PEDV is infectious in an age-dependent manner with a significantly lower MID for neonatal pigs compared to weaned pigs. Furthermore, it showed that, once an infection was established in pigs, the initial dose of PEDV administered did not affect the extent of fecal viral shedding, severity of histopathologic lesions, or magnitude of antibody titer subsequently developed. This information should be taken into consideration when interpreting clinical relevance of PEDV PCR results, designing a PEDV bioassay model, as well as emphasizes the importance of strict biosecurity and thorough cleaning/disinfection on sow farms.