Epidemiological monitoring and genetic variation analysis of pathogens associated with porcine viral diarrhea in southern China from 2021 to 2023

Large-scale outbreaks of virus-associated severe diarrhea have occurred in pig populations since 2010. To investigate the prevalence and genetic evolution of the diarrhea-associated viruses responsible for the outbreaks, we tested 1,791 diarrhea samples collected from 213 pig farms in five provinces in southern China between 2021 and 2023. The test results showed that porcine epidemic diarrhea virus (PEDV) was the most frequently detected virus. The prevalence rates ranged from 47.40 to 52.22% in samples and 76.06% (162/213) in pig farms. Porcine rotavirus (PoRV) was the second common virus, with prevalence rates ranging from 25.81 to 50.81% in samples and 72.77%(155/213) in pig farms. Porcine delta coronavirus (PDCoV) was the third common virus, with prevalence rates ranging from 16.33 to 17.48% in samples and 38.50% (82/213) in pig farms. The detection rates of both transmissible gastroenteritis virus (TGEV) and porcine acute diarrheal syndrome coronavirus (SADS-CoV) were very low, less than 1.01% in samples and less than 3.76% in pig farms. In this study, we found SADS-CoV only in piglet diarrhea samples from Jiangxi, Guangdong, and Guangxi provinces in China, with a prevalence rate of 5.16% (11/213) in pig farms. Co-infection with these diarrhea-associated viruses is a common occurrence. The most common co-infections were PEDV and PoRV, with a prevalence rate of 6.64% (119/1,791), followed by PDCoV and PoRV, with a prevalence rate of 4.19% (75/1,791). Phylogenetic analyses showed that PEDV and PEDV variants prevalent in southern China during the past three years clustered into genotype GIIb and recombinant PEDV subtypes. Among the currently endemic PEDV, the most common mutations occurred in the collagenase equivalent (COE) and epitope regions of the spike gene. PoRV strains were mainly dominated by the G9 subtype, followed by the G5, G3 and G4 subtypes. Our results suggest that variant PEDV, PDCoV and PoRV are the main pathogens of swine diarrhea, and singular- or co-infection with pathogenic enteric CoV is common in pig herds in southern China. Therefore, prevention and control of porcine viral diarrhea should be given high attention.

SADS-CoV nsp1 inhibits the STAT1 phosphorylation by promoting K11/K48-linked polyubiquitination of JAK1 and blocks the STAT1 acetylation by degrading CBP

The newly discovered zoonotic coronavirus swine acute diarrhea syndrome coronavirus (SADS-CoV) causes acute diarrhea, vomiting, dehydration, and high mortality rates in newborn piglets. Although SADS-CoV uses different strategies to evade the host's innate immune system, the specific mechanism(s) by which it blocks the interferon (IFN) response remains unidentified. In this study, the potential of SADS-CoV nonstructural proteins (nsp) to inhibit the IFN response was detected. The results determined that nsp1 was a potent antagonist of IFN response. SADS-CoV nsp1 efficiently inhibited signal transducer and activator of transcription 1 (STAT1) phosphorylation by inducing Janus kinase 1 (JAK1) degradation. Subsequent research revealed that nsp1 induced JAK1 polyubiquitination through K11 and K48 linkages, leading to JAK1 degradation via the ubiquitin-proteasome pathway. Furthermore, SADS-CoV nsp1 induced CREB-binding protein degradation to inhibit IFN-stimulated gene production and STAT1 acetylation, thereby inhibiting STAT1 dephosphorylation and blocking STAT1 transport out of the nucleus to receive antiviral signaling. In summary, the results revealed the novel mechanisms by which SADS-CoV nsp1 blocks the JAK-STAT signaling pathway via the ubiquitin-proteasome pathway. This study yielded valuable findings on the specific mechanism of coronavirus nsp1 in inhibiting the JAK-STAT signaling pathway and the strategies of SADS-CoV in evading the host's innate immune system.

Research Advances on Swine Acute Diarrhea Syndrome Coronavirus

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a virulent pathogen that causes acute diarrhea in piglets. The virus was first discovered in Guangdong Province, China, in 2017 and has since emerged in Jiangxi, Fujian, and Guangxi Provinces. The outbreak exhibited a localized and sporadic pattern, with no discernable temporal continuity. The virus can infect human progenitor cells and demonstrates considerable potential for cross-species transmission, representing a potential risk for zoonotic transmission. Therefore, continuous surveillance of and comprehensive research on SADS-CoV are imperative. This review provides an overview of the temporal and evolutionary features of SADS-CoV outbreaks, focusing on the structural characteristics of the virus, which serve as the basis for discussing its potential for interspecies transmission. Additionally, the review summarizes virus-host interactions, including the effects on host cells, as well as apoptotic and autophagic behaviors, and discusses prevention and treatment modalities for this viral infection.

Prevention and Control of Swine Enteric Coronaviruses in China: A Review of Vaccine Development and Application

Swine enteric coronaviruses (SECs) cause significant economic losses to the pig industry in China. Although many commercialized vaccines against transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are available, viruses are still widespread. The recent emergence of porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), for which no vaccines are available, increases the disease burden. In this review, we first introduced the genomic organization and epidemiology of SECs in China. Then, we discussed the current vaccine development and application in China, aiming to provide suggestions for better prevention and control of SECs in China and other countries.

Generation and Characterization of Monoclonal Antibodies against Swine Acute Diarrhea Syndrome Coronavirus Spike Protein

Swine acute diarrhea syndrome coronavirus (SADS-CoV), a member of the family Coronaviridae and the genus Alphacoronavirus, primarily affects piglets under 7 days old, causing symptoms such as diarrhea, vomiting, and dehydration. It has the potential to infect human primary and passaged cells in vitro, indicating a potential risk of zoonotic transmission. In this study, we successfully generated and purified six monoclonal antibodies (mAbs) specifically targeting the spike protein of SADS-CoV, whose epitope were demonstrated specificity to the S1A or S1B region by immunofluorescence assay and enzyme-linked immunosorbent assay. Three of these mAbs were capable of neutralizing SADS-CoV infection on HeLa-R19 and A549. Furthermore, we observed that SADS-CoV induced the agglutination of erythrocytes from both humans and rats, and the hemagglutination inhibition capacity and antigen-antibody binding capacity of the antibodies were assessed. Our study reveals that mAbs specifically targeting the S1A domain demonstrated notable efficacy in suppressing the hemagglutination phenomenon induced by SADS-CoV. This finding represents the first instance of narrowing down the protein region responsible for SADS-CoV-mediated hemagglutination to the S1A domain, and reveals that the cell attachment domains S1A and S1B are the main targets of neutralizing antibodies.

Furin cleavage is required for swine acute diarrhea syndrome coronavirus spike protein-mediated cell-cell fusion

Swine acute diarrhea syndrome coronavirus (SADS-CoV) was reported in China in 2017 and is a causative agent of porcine enteric disease. Recent studies indicate that cells from various hosts are susceptible to SADS-CoV, suggesting the zoonotic potential of this virus. However, little is known about the mechanisms through which this virus enters cells. In this study, we investigated the role of furin in SADS-CoV spike (S)-mediated cell-cell fusion and entry. We found that the SADS-CoV S protein induced the fusion of various cells. Cell-cell fusion was inhibited by the proprotein convertase inhibitor dec-RVKR-cmk, and between cells transfected with mutant S proteins resistant to furin cleavage. These findings revealed that furin-induced cleavage of the SADS-CoV S protein is required for cell-cell fusion. Using mutagenesis analysis, we demonstrated that furin cleaves the SADS-CoV S protein near the S1/S2 cleavage site, ₄₄₆RYVR₄₄₉ and ₅₄₃AVRR₅₄₆. We used pseudotyped viruses to determine whether furin-induced S cleavage is also required for viral entry. Pseudotyped viruses expressing S proteins with a mutated furin cleavage site could be transduced into target cells, indicating that furin-induced cleavage is not required for pseudotyped virus entry. Our data indicate that S cleavage is critical for SADS-CoV S-mediated cell-cell fusion and suggest that furin might be a host target for SADS-CoV antivirals.

Genomewide CRISPR knockout screen identified PLAC8 as an essential factor for SADS-CoVs infection

Zoonotic transmission of coronaviruses poses an ongoing threat to human populations. Endemic outbreaks of swine acute diarrhea syndrome coronavirus (SADS-CoV) have caused severe economic losses in the pig industry and have the potential to cause human outbreaks. Currently, there are no vaccines or specific antivirals against SADS-CoV, and our limited understanding of SADS-CoV host entry factors could hinder prompt responses to a potential human outbreak. Using a genomewide CRISPR knockout screen, we identified placenta-associated 8 protein (PLAC8) as an essential host factor for SADS-CoV infection. Knockout of PLAC8 abolished SADS-CoV infection, which was restored by complementing PLAC8 from multiple species, including human, rhesus macaques, mouse, pig, pangolin, and bat, suggesting a conserved infection pathway and susceptibility of SADS-CoV among mammals. Mechanistically, PLAC8 knockout does not affect viral entry; rather, knockout cells displayed a delay and reduction in viral subgenomic RNA expression. In a swine primary intestinal epithelial culture (IEC) infection model, differentiated cultures have high levels of PLAC8 expression and support SADS-CoV replication. In contrast, expanding IECs have low levels of PLAC8 expression and are resistant to SADS-CoV infection. PLAC8 expression patterns translate in vivo; the immunohistochemistry of swine ileal tissue revealed high levels of PLAC8 protein in neonatal compared to adult tissue, mirroring the known SADS-CoV pathogenesis in neonatal piglets. Overall, PLAC8 is an essential factor for SADS-CoV infection and may serve as a promising target for antiviral development for potential pandemic SADS-CoV.

The Roles of Apoptosis in Swine Response to Viral Infection and Pathogenesis of Swine Enteropathogenic Coronaviruses

Apoptosis is a tightly regulated mechanism of cell death that plays important roles in various biological processes including biological evolution, multiple system development, anticancer, and viral infections. Swine enteropathogenic coronaviruses invade and damage villous epithelial cells of the small intestine causing severe diarrhea with high mortality rate in suckling piglets. Transmissible gastroenteritis virus (TGEV), Porcine epidemic diarrhea virus (PEDV), Porcine deltacoronavirus (PDCoV), and Swine acute diarrhea syndrome coronavirus (SADS-CoV) are on the top list of commonly-seen swine coronaviruses with a feature of diarrhea, resulting in significant economic losses to the swine industry worldwide. Apoptosis has been shown to be involved in the pathogenesis process of animal virus infectious diseases. Understanding the roles of apoptosis in host responses against swine enteropathogenic coronaviruses infection contribute to disease prevention and control. Here we summarize the recent findings that focus on the apoptosis during swine coronaviruses infection, in particular, TGEV, PEDV, PDCoV, and SADS-CoV.