Origin, Evolution, and Virulence of Porcine Deltacoronaviruses in the United States

Ma, Yuanmei; Zhang, Yu; Liang, Xueya; Lou, Fangfei; Oglesbee, Michael; Krakowka, Steven; Li, Jianrong

Factors that may influence the severity of PdCV-associated disease. Clinically, Ohio CVM1 caused more severe disease in Gn piglets than the cell-adapted MI strain, despite the fact that the inoculation dose of Ohio CVM1 (10 6 genomic RNA copies) was less than that of the MI strain (10 6 PFU, equivalent to 10 9 genomic RNA copies). The reduced virulence of the MI strain may reflect a degree of attenuation secondary to cell culture adaptation. PdCV MI caused more severe disease in conventional piglets than in Gn piglet at the same inoculation dose. Conventional piglets developed severe sudden-onset diarrhea (score of 3) on day 1 p.i., whereas Gn piglets required 2 days of incubation time to develop diarrhea (score of 2). This finding raises the possibility that the gut microbial flora in conventional piglets facilitates development of diarrhea upon PdCV infection. The contributions of gut microflora or other physiological factors to virus-induced diarrhea are also supported by the finding that the severity of diarrhea in conventional piglets was not correlated with the kinetics of viral RNA shedding in feces (Fig. 8) . Findings in the current study also indicate that PdCV is highly transmissible among Gn piglets, most likely via aerosolized particles. Two uninoculated Gn piglets developed typical clinical signs and shed high levels of virus in feces despite the fact that they were physically separated from three virus-inoculated piglets. Viral RNA was detected in feces and in the ileum at day 21 p.i., suggesting that PdCV can be persistent in conventional piglets for a long time period, a fact that would enhance the potential for viral transmission. Collectively, these data demonstrated that PdCV is highly virulent and transmissible in piglets.