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

The demonstrated pathogenicity in PdCV may reflect an emergent property inherent in sequence changes from otherwise closely related CoVs. For example, PRCV, a deletion mutant of TGEV, shifted the tissue tropism from intestine to lung (4, 29) . Tropism for both respiratory and gastrointestinal tracts is also a feature of SARS-CoV. Although the respiratory tract is the main target for SARS-CoV infection, outbreaks in human patients were associated with gastrointestinal symptoms, and SARS-CoV was detected in the stool samples (30) (31) (32) . Subsequent histologic characterization found that intestinal epithelia and mucosal lymphoid tissue are infected by SARS virus (30, 31) . In contrast to SARS-CoV and PRCV, the gastrointestinal tract is the primary target for PdCV, whereas the respiratory tract is the minor target. PdCV shares the highest genomic homology with avian deltacoronaviruses, all of which were originally detected from the gastrointestinal tract via rectal swabs (15) (16) (17) . Presumably, all these avian deltacoronaviruses were capable of replicating in the gastrointestinal tract, although it is not known if infection also involves a respiratory component. Further studies on this important point are urgently needed, particularly in light of the SARS and Middle East respiratory syndrome (MERS) experiences in humans.