Characterization of the Cross-Species Transmission Potential for Porcine Deltacoronaviruses Expressing Sparrow Coronavirus Spike Protein in Commercial Poultry.

Avian species often serve as transmission vectors and sources of recombination for viral infections due to their ability to travel vast distances and their gregarious behaviors. Recently a novel deltacoronavirus (DCoV) was identified in sparrows. Sparrow deltacoronavirus (SpDCoV), coupled with close contact between sparrows and swine carrying porcine deltacoronavirus (PDCoV) may facilitate recombination of DCoVs resulting in novel CoV variants. We hypothesized that the spike (S) protein or receptor-binding domain (RBD) from sparrow coronaviruses (SpCoVs) may enhance infection in poultry. We used recombinant chimeric viruses, which express S protein or the RBD of SpCoV (icPDCoV-SHKU17, and icPDCoV-RBDISU) on the genomic backbone of an infectious clone of PDCoV (icPDCoV). Chimeric viruses were utilized to infect chicken derived DF-1 cells, turkey poults, and embryonated chicken eggs (ECEs) to examine permissiveness, viral replication kinetics, pathogenesis and pathology. We demonstrated that DF-1 cells in addition to the positive control LLC-PK1 cells are susceptible to SpCoV spike- and RBD- recombinant chimeric virus infections. However, the replication of chimeric viruses in DF-1 cells, but not LLC-PK1 cells, was inefficient. Inoculated 8-day-old turkey poults appeared resistant to icPDCoV-, icPDCoV-SHKU17- and icPDCoV-RBDISU virus infections. In 5-day-old ECEs, significant mortality was observed in PDCoV inoculated eggs with less in the spike chimeras, while in 11-day-old ECEs there was no evidence of viral replication, suggesting that PDCoV is better adapted to cross species infection and differentiated ECE cells are not susceptible to PDCoV infection. Collectively, we demonstrate that the SpCoV chimeric viruses are not more infectious in turkeys, nor ECEs than wild type PDCoV. Therefore, understanding the cell and host factors that contribute to resistance to PDCoV and avian-swine chimeric virus infections may aid in the design of novel antiviral therapies against DCoVs.

Pathogenic evaluation of a turkey coronavirus isolate (TCoV NC1743) in turkey poults for establishing a TCoV disease model.

Turkey coronavirus (TCoV) can cause a highly contagious enteric disease in turkeys with severe economic losses in the global turkey industry. To date, no commercial vaccines are available for control of the disease. In the present study, we isolated a field strain (NC1743) of TCoV and evaluated its pathogenicity in specific-pathogen-free (SPF) turkey poults to establish a TCoV disease model. The results showed that the TCoV NC1743 isolate was pathogenic to turkey poults with a minimal infectious dose at 106 EID50/bird. About 50 % of one-day-old SPF turkeys infected with the virus's minimal infectious dose exhibited typical enteric disease signs and lesions from 6 days post-infection (dpi) to the end of the experiment (21 dpi). In contrast, fewer than 20 % of older turkeys (1- or 2-week-old) infected with the same amount of TCoV displayed enteric disease signs, which disappeared after 15-18 dpi. Although all infected turkeys, regardless of age, shed TCoV, the older turkeys shed less virus than the younger birds, and 50 % of the 2-week-old birds even cleared the virus at 21 dpi. Furthermore, the viral infection caused day-old turkeys more body-weight-gain reduction than older birds. The overall data demonstrated that the TCoV NC1743 isolate is a highly pathogenic strain and younger turkeys are more susceptible to TCoV infection than older birds. Thus, one-day-old turkeys infected with the minimal infectious dose of TCoV NC1743 could be used as a TCoV disease model to study the disease pathogenesis, and the TCoV NC1743 strain could be used as a challenge virus to evaluate a vaccine protective efficacy.