The outbreak of 2019-nCoV in the central Chinese city of Wuhan at the end of 2019 poses unprecedent public health challenges to both China and the rest world ¹ . The new coronavirus shares high sequence identity to SARS-CoV and a newly identified bat coronavirus ² . While bats may be the reservoir host for various coronaviruses, whether 2019-nCoV has other hosts is still ambiguous. In this study, one coronavirus isolated from Malayan pangolins showed 100%, 98.2%, 96.7% and 90.4% amino acid identity with 2019-nCoV in the E, M, N and S genes, respectively. In particular, the receptor-binding domain of the S protein of the Pangolin-CoV is virtually identical to that of 2019-nCoV, with one amino acid difference. Comparison of available genomes suggests 2019-nCoV might have originated from the recombination of a Pangolin-CoV-like virus with a Bat-CoV-RaTG13-like virus. Infected pangolins showed clinical signs and histopathological changes, and the circulating antibodies reacted with the S protein of 2019-nCoV. The isolation of a coronavirus that is highly related to 2019-nCoV in the pangolins suggests that these animals have the potential to act as the intermediate host of 2019-nCoV. The newly identified coronavirus in the most-trafficked mammal could represent a continuous threat to public health if wildlife trade is not effectively controlled.

Gammacoronavirus infectious bronchitis virus (IBV) causes a highly contagious disease in chickens and seriously endangers the poultry industry. The emergence and co-circulation of diverse IBV serotypes and genotypes with distinct pathogenicity worldwide pose a serious challenge to the development of effective intervention measures. In this study, we report the epidemic trends of IBV in China from 2019 to 2023 and a comparative analysis on the antigenic characteristics and pathogenicity of isolates among major prevalent lineages. Phylogenetic and recombination analyses based on the nucleotide sequences of the spike (S) 1 gene clustered a total of 205 isolates into twelve distinct lineages, with GI-19 as a predominant lineage (61.77 ± 4.56%) exhibiting an overall increasing trend over the past five years, and demonstrated that a majority of the variants were derived from gene recombination events. Further characterization of the growth and pathogenic properties of six representative isolates from different lineages classified four out of the six isolates as nephropathogenic types with mortality rates in one-day-old SPF chickens varying from 20–60%, one as a respiratory type with weak virulence, and one as a naturally occurring avirulent strain. Taken together, our findings illuminate the epidemic trends, prevalence, recombination, and pathogenicity of current IBV strains in China, providing key information for further strengthening the surveillance and pathogenicity studies of IBV.

In this study, a specific and simple method based on the dual priming oligonucleotide (DPO) system was developed to simultaneously detect transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine rotavirus A (PRV-A), porcine delta coronavirus (PDCoV), and swine acute diarrhea syndrome coronavirus (SADS-CoV), associated with the major enteric RNA viruses in pigs. The DPO system-based multiplex RT-PCR method simplified the primer design and did not require optimization of the annealing temperature. Specificity analysis revealed that the method could specifically detect TGEV, PEDV, PRV-A, PDCoV, and SADS-CoV without any cross-amplification of other circulating swine viruses. The limit of detection of the method was as low as 10³–10⁴ copies/μL plasmid of each virus. The method also had good repeatability, and obvious results were seen in three repeat experiments with an interval of 45 days. This optimized multiplex RT-PCR method was used to evaluate 181 clinical swine samples that were collected from four provinces of China between September 2016 and August 2018. The results showed that the positive detection rates of PEDV, PDCoV, SADS-CoV, PRV-A, and TGEV were 30.94% (56/181), 17.67% (32/181), 11.6% (21/181), 9.39% (17/181), and 0.55% (1/181), respectively. Mixed infection of two or more viruses was also common. The DPO system-based multiplex RT-PCR could be a useful tool for detecting enteric virus infections. This method has the advantages of easy operation, low cost, high detection efficiency, and short running time for early diagnosis in clinical cases.

Coronavirus nonstructural protein 3 (nsp3) is a multi-functional protein, playing a critical role in viral replication and in regulating host antiviral innate immunity. In this study, we demonstrate that nsp3 from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and avian coronavirus infectious bronchitis virus (IBV) directly interacts with melanoma differentiation-associated gene 5 (MDA5), rendering an inhibitory effect on the MDA5-mediated type I interferon (IFN) response. By the co-expression of MDA5 with wild-type and truncated nsp3 constructs, at least three interacting regions mapped to the papain-like protease (PLpro) domain and two other domains located at the N- and C-terminal regions were identified in SARS-CoV-2 nsp3. Furthermore, by introducing point mutations to the catalytic triad, the deubiquitylation activity of the PLpro domain from both SARS-CoV-2 and IBV nsp3 was shown to be responsible for the suppression of the MDA5-mediated type I IFN response. It was also demonstrated that both MDA5 and nsp3 were able to interact with ubiquitin and ubiquitinated proteins, contributing to the interaction between the two proteins. This study confirms the antagonistic role of nsp3 in the MDA5-mediated type I IFN signaling, highlighting the complex interaction between a multi-functional viral protein and the innate immune response.

Porcine enteric coronaviruses are pathogens that cause viral diarrhea in pigs and are widely prevalent worldwide. Moreover, studies have shown that some porcine enteric coronaviruses can infect humans and poultry. In order to effectively monitor these viruses, it is necessary to establish a multiple detection method to understand their prevalence and conduct in-depth research. Common porcine enteric coronaviruses include Porcine epidemic diarrhea virus (PEDV), Porcine transmissible gastroenteritis virus (TGEV), Porcine delta coronavirus (PDCoV), and Swine acute diarrhea syndrome coronavirus (SADS-CoV). Pigs infected with these viruses have the common clinical symptoms that are difficult to distinguish. A quadruplex RT-PCR (reverse transcription-polymerase chain reaction) method for the simultaneous detection of PEDV, PDCoV, TGEV and SADS-CoV was developed. Four pairs of specific primers were designed for the PEDV M gene, PDCoV N gene, TGEV S gene and SADS-CoV RdRp gene. Multiplex RT-PCR results showed that the target fragments of PDCoV, SADS-CoV, PEDV and TGEV could be amplified by this method. and the specific fragments with sizes of 250 bp, 368 bp, 616 bp and 801 bp were amplified, respectively. This method cannot amplify any fragment of nucleic acids of Seneca Valley virus (SVV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and Atypical Porcine Pestivirus (APPV), and has good specificity. The lowest detection limits of PDCoV, PEDV, TGEV and SADS-CoV were 5.66 × 10⁵ copies/μL, 6.48 × 10⁵ copies/μL, 8.54 × 10⁵ copies/μL and 7.79 × 10⁶ copies/μL, respectively. A total of 94 samples were collected from pig farms were analyzed using this method. There were 15 positive samples for PEDV, 3 positive samples for mixed infection of PEDV and PDCoV, 2 positive samples for mixed infection of PEDV and TGEV, and 1 positive sample for mixed infection of PEDV, TGEV, and PDCoV. Multiplex RT-PCR method could detect four intestinal coronaviruses (PEDV, PDCoV, TGEV, and SADS-CoV) in pigs efficiently, cheaply and accurately, which can be used for clinical large-scale epidemiological investigation and diagnosis.