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

Interestingly, disease associated with PdCV has not been reported in China and other Asian countries in spite of being geographically closer to Hong Kong than is the United States. In 2012, Woo et al. analyzed a total of 169 pig rectal swabs, 17 of which were positive for PdCV HKU15 (15) . However, clinical signs were not described in their study. Aside from Woo's study, further outbreaks of HKU15-associated diseases in pigs have not been documented in Hong Kong and Asia, raising the possibility that HKU15 may not be a significant pathogen within its region of origin. Since PEDV is the dominant enteric disease in Asia and PdCV causes clinical signs indistinguishable from those of PEDV, it is also possible that clinically significant PdCV-induced disease has been overlooked. In contrast to the Asian experience, U.S. PdCV strains are associated with significant mortality (40 to 60%) in the field (18) (19) (20) and severe clinical disease and pathological changes in experimentally infected Gn and conventional piglets of the present study. In April 2014, PdCV was first identified in feces from diarrheic piglets in South Korea (22) . The PdCV South Korean strain is more (99.7% homology) closely related to U.S. isolates than Hong Kong strains, suggesting that the South Korean strain may be virulent to piglets. Sequence analysis in the current work suggests that U.S. PdCV originated from Hong Kong strains. Unique amino acid substitutions exist in U.S. PdCV isolates that may account for the increased virulence of this virus in U.S. swine, a possibility that should be addressed in future studies.