Co-infection of porcine deltacoronavirus and porcine epidemic diarrhoea virus alters gut microbiota diversity and composition in the colon of piglets

The highly pathogenic strain of porcine deltacoronavirus disrupts the intestinal barrier and causes diarrhea in newborn piglets

Porcine deltacoronavirus (PDCoV) is increasingly prevalent in newborn piglets with diarrhea. With the development of research on the virus and the feasibility of PDCoV cross-species transmission, the biosafety and the development of pig industry have been greatly affected. In this study, a PDCoV strain CH/LNFX/2022 was isolated from diarrheal newborn piglets at a farm in China. A genome-wide based phylogenetic analysis suggests that 97.5% to 99.2% homology existed in the whole genomes of other strains. Five amino acid mutations are seen for the first time in the S protein. By constructing 3D models, it was found that the S1-NTD/CTD and S2-HR-C regions produced structural alterations. Protein functional analysis showed that the structural changes of the three regions changed the epitope of S protein, the O-GalNAc glycosylation site and the 3C-like protease cleavage site. In addition, oral administration of 107 TCID50 CH/LNFX/2022 to newborn piglets successfully reproduced obvious clinical signs of piglets, such as diarrhea and dehydration. Meanwhile, PDCoV antigen was detected by immunofluorescence in the small intestine, and microscopic lesions and intestinal mucosal barrier destruction were detected by histological observation and scanning electron microscopy. Our study confirmed that porcine coronavirus strains increased pathogenicity through evolution, damaged the intestinal barrier of newborn piglets, and caused diarrhea in pigs. This study provided the candidate strains and theoretical basis for establishing the prevention and control system of vaccine and diagnostic methods for piglet diarrhea.

Gut microbiota contributes to protection against porcine deltacoronavirus infection in piglets by modulating intestinal barrier and microbiome

BACKGROUND

Gut microbiota plays a critical role in counteracting enteric viral infection. Our previous study demonstrated that infection of porcine deltacoronavirus (PDCoV) disturbs gut microbiota and causes intestinal damage and inflammation in piglets. However, the influence of gut microbiota on PDCoV infection remains unclear.

RESULTS

Firstly, the relationship between gut microbiota and disease severity of PDCoV infection was evaluated using 8-day-old and 90-day-old pigs. The composition of gut microbiota was significantly altered in 8-day-old piglets after PDCoV infection, leading to severe diarrhea and intestinal damage. In contrast, PDCoV infection barely affected the 90-day-old pigs. Moreover, the diversity (richness and evenness) of microbiota in 90-day-old pigs was much higher compared to the 8-day-old piglets, suggesting the gut microbiota is possibly associated with the severity of PDCoV infection. Subsequently, transplanting the fecal microbiota from the 90-day-old pigs to the 3-day-old piglets alleviated clinical signs of PDCoV infection, modulated the diversity and composition of gut microbiota, and maintained the physical and chemical barrier of intestines. Additionally, metabolomic analysis revealed that the fecal microbiota transplantation (FMT) treatment upregulated the swine intestinal arginine biosynthesis, FMT significantly inhibited the inflammatory response in piglet intestine by modulating the TLR4/MyD88/NF-κB signaling pathway.

CONCLUSIONS

PDCoV infection altered the structure and composition of the gut microbiota in neonatal pigs. FMT treatment mitigated the clinical signs of PDCoV infection in the piglets by modulating the gut microbiota composition and intestinal barrier, downregulating the inflammatory response. The preventive effect of FMT provides novel targets for the development of therapeutics against enteropathogenic coronaviruses. Video Abstract.

Epidemiological Study and Genetic Diversity Assessment of Porcine Epidemic Diarrhea Virus (PEDV) in Yunnan Province, China

Porcine epidemic diarrhea virus (PEDV) is a highly contagious pathogen responsible for devastating enteric disease and lethal watery diarrhea, leading to significant economic losses in the global swine industry. Understanding the epidemiology and genetic diversity of PEDV over the past decade is crucial for the effective prevention and treatment of porcine epidemic diarrhea. In this study, 1851 fecal samples were collected from pigs exhibiting diarrhea symptoms across 11 cities in Yunnan Province between 2013 and 2022. The prevalence of PEDV, along with other common swine diarrhea viruses, including porcine transmissible gastroenteritis virus (TGEV), porcine rotavirus (PoRV), porcine Sapporo virus (PoSaV), porcine stellate virus (PaStV), and porcine delta coronavirus (PDCoV) was assessed using a polymerase chain reaction (PCR) assay. The results revealed a total detection rate of 52.94% (980/1851) for the six viruses, with PEDV accounting for 25.93% (480/1851) of cases. Further analysis showed that weaned piglets were more susceptible to PEDV than fattening pigs, with the highest prevalence observed in spring (61.52%, 275/447) and the lowest in summer (12.68%, 97/765). Dual infections were also identified, with PEDV + PoSaV being the most common combination (2.81%, 52/1851), followed by PEDV + PoRV, with a detection rate of 1.67% (31/1851). Phylogenetic analysis of the PEDV S genes revealed that the 28 epidemic strains in Yunnan Province shared a nucleotide sequence homology from 91.4% to 98.4% and an amino acid sequence homology ranging from 85.6% to 99.3%. All strains were classified as GII variant strains. This study provides a comprehensive overview of the epidemiology of PEDV and its co-infection patterns with other common diarrhea-causing viruses in the swine herds of Yunnan Province over the past decade. These findings offer valuable insights for the development of effective prevention and control strategies to mitigate the impact of PEDV and other enteroviruses on the swine industry in Yunnan Province.

Development and Clinical Application of a Molecular Assay for Four Common Porcine Enteroviruses

Porcine epidemic diarrhea virus (PEDV), porcine transmissible gastroenteritis virus (TGEV), porcine deltacoronavirus (PDCoV), and porcine rotavirus-A (PoRVA) are the four main pathogens that cause viral diarrhea in pigs, and they often occur in mixed infections, which are difficult to distinguish only according to clinical symptoms. Here, we developed a multiplex TaqMan-probe-based real-time RT-PCR method for the simultaneous detection of PEDV, TGEV, PDCoV, and PoRVA for the first time. The specific primers and probes were designed for the M protein gene of PEDV, N protein gene of TGEV, N protein gene of PDCoV, and VP7 protein gene of PoRVA, and corresponding recombinant plasmids were constructed. The method showed extreme specificity, high sensitivity, and excellent repeatability; the limit of detection (LOD) can reach as low as 2.18 × 102 copies/μL in multiplex real-time RT-PCR assay. A total of 97 clinical samples were used to compare the results of the conventional reverse transcription PCR (RT-PCR) and this multiplex real-time RT-PCR for PEDV, TGEV, PDCoV, and PoRVA detection, and the results were 100% consistent. Subsequently, five randomly selected clinical samples that tested positive were sent for DNA sequencing verification, and the sequencing results showed consistency with the detection results of the conventional RT-PCR and our developed method in this study. In summary, this study developed a multiplex real-time RT-PCR method for simultaneous detection of PEDV, TGEV, PDCoV, and PoRVA, and the results of this study can provide technical means for the differential diagnosis and epidemiological investigation of these four porcine viral diarrheic diseases.

An isothermal nucleic acid amplification-based enzymatic recombinase amplification method for dual detection of porcine epidemic diarrhea virus and porcine rotavirus A

Viral diarrhea is the predominant digestive tract sickness in piglings, resulting in substantial profit losses in the porcine industry. Porcine rotavirus A (PoRVA) and porcine epidemic diarrhea virus (PEDV) are the main causes of grave gastroenteritis and massive dysentery, especially in piglets. PoRVA and PEDV have high transmissibility, exhibit similar clinical symptoms, and frequently co-occur. Therefore, to avoid financial losses, a quick, highly efficient, objective diagnostic test for the prevention and detection of these diseases is required. Enzymatic recombinase amplification (ERA) is a novel technology based on isothermal nucleic acid amplification. It demonstrates high sensitivity and excellent specificity, with a short processing time and easy operability, compared with other in vitro nucleic acid amplification technologies. In this study, a dual ERA method to detect and distinguish between PEDV and PoRVA nucleic acids was established. The method shows high sensitivity, as the detection limits were 101 copies/μL for both viruses. To test the usefulness of this method in clinical settings, we tested 64 swine clinical samples. Our results were 100% matched with those acquired using a commercially available kit. Therefore, we have successfully developed a dual diagnostic ERA nucleic acids method for detecting and distinguishing between PEDV and PoRVA.

Establishment and application of a quadruplex real-time RT-qPCR assay for differentiation of TGEV, PEDV, PDCoV, and PoRVA

Porcine viral diarrhea is a common ailment in clinical settings, causing significant economic losses to the swine industry. Notable culprits behind porcine viral diarrhea encompass transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), and porcine rotavirus-A (PoRVA). Co-infections involving the viruses are a common occurrence in clinical settings, thereby amplifying the complexities associated with differential diagnosis. As a consequence, it is therefore necessary to develop a method that can detect and differentiate all four porcine diarrhea viruses (TGEV, PEDV, PDCoV, and PoRVA) with a high sensitivity and specificity. Presently, polymerase chain reaction (PCR) is the go-to method for pathogen detection. In comparison to conventional PCR, TaqMan real-time PCR offers heightened sensitivity, superior specificity, and enhanced accuracy. This study aimed to develop a quadruplex real-time RT-qPCR assay, utilizing TaqMan probes, for the distinctive detection of TGEV, PEDV, PDCoV, and PoRVA. The quadruplex real-time RT-qPCR assay, as devised in this study, exhibited the capacity to avoid the detection of unrelated pathogens and demonstrated commendable specificity, sensitivity, repeatability, and reproducibility, boasting a limit of detection (LOD) of 27 copies/μL. In a comparative analysis involving 5483 clinical samples, the results from the commercial RT-qPCR kit and the quadruplex RT-qPCR for TGEV, PEDV, PDCoV, and PoRVA detection were entirely consistent. Following sample collection from October to March in Guangxi Zhuang Autonomous Region, we assessed the prevalence of TGEV, PEDV, PDCoV, and PoRVA in piglet diarrhea samples, revealing positive detection rates of 0.2 % (11/5483), 8.82 % (485/5483), 1.22 % (67/5483), and 4.94 % (271/5483), respectively. The co-infection rates of PEDV/PoRVA, PEDV/PDCoV, TGEV/PED/PoRVA, and PDCoV/PoRVA were 0.39 %, 0.11 %, 0.01 %, and 0.03 %, respectively, with no detection of other co-infections, as determined by the quadruplex real-time RT-qPCR. This research not only established a valuable tool for the simultaneous differentiation of TGEV, PEDV, PDCoV, and PoRVA in practical applications but also provided crucial insights into the prevalence of these viral pathogens causing diarrhea in Guangxi.

Establishment and application of a TaqMan-based multiplex real-time PCR for simultaneous detection of three porcine diarrhea viruses

Introduction

Porcine viral diarrhea is a common clinical disease, which results in high mortality and economic losses in the pig industry. Porcine epidemic diarrhea virus (PEDV), porcine rotavirus (PoRV), and porcine deltacoronavirus (PDCoV) are important diarrhea viruses in pig herds. The similarities of their clinical symptoms and pathological changes make it difficult to distinguish these three viruses clinically. Therefore, there is a need for a highly sensitive and specific method to simultaneously detect and differentiate these viruses.

Methods

A multiplex real-time PCR assay using TaqMan probes was developed to simultaneously detect PEDV, PoRV, and PDCoV. To assess the efficacy of the established assay, 30 clinical samples with diarrhea symptoms were used to compare the results obtained from the multiplex real-time PCR assay with those obtained from commercial singleplex real-time PCR kit. Importantly, a total of 4,800 diarrhea samples were tested and analyzed to validate the utility of the assay.

Results

This multiplex real-time PCR assay showed high sensitivity, specificity, and excellent repeatability with a detection limit of 1 × 102 copies/μL. Comparing the results of the commercial singleplex real-time PCR kit and the multiplex real-time PCR method for detecting PEDV, PoRV, and PDCoV, there was complete agreement between the two approaches. Clinical data revealed single infection rates of 6.56% for PEDV, 21.69% for PoRV, and 6.65% for PDCoV. The co-infection rates were 11.83% for PEDV + PoRV, 0.29% for PEDV + PDCoV, 5.71% for PoRV + PDCoV, and 1.29% for PEDV + PDCoV + PoRV, respectively.

Discussion

The multiplex real-time PCR method established in this study is a valuable diagnostic tool for simultaneously differentiating PEDV, PoRV, and PDCoV. This method is expected to significantly contribute to prevent and control the spread of infectious diseases, as well as aid in conducting epidemiological investigations.

Serial passage of PDCoV in cell culture reduces its pathogenicity and its damage of gut microbiota homeostasis in piglets

Porcine deltacoronavirus (PDCoV) is an enteropathogenic coronavirus that mainly causes diarrhea in suckling piglets, and also has the potential for cross-species transmission. However, there are still no commercial vaccines available to prevent and control PDCoV infection. In this study, PDCoV strain HNZK-02 was serially propagated in vitro for up to 150 passages and the amino acid changes have mainly occurred in the S protein during serial passage which caused structure change. PDCoV HNZK-02-passage 5 (P5)-infected piglets exhibited acute and severe watery diarrhea, an obvious intestinal damage, while the piglets infected with PDCoV HNZK-02-P150 showed no obvious clinical signs, weak intestinal lesions, and lower viral loads in rectal swabs and various tissues. Compared with the PDCoV HNZK-02-P5 infection, HNZK-02-P150 infection resulted in a decrease in intestinal mucosal permeability and pro-inflammatory cytokines. Moreover, PDCoV HNZK-02-P5 infection had significantly reduced bacterial diversity and increased relative abundance of opportunistic pathogens, while PDCoV HNZK-02-P150 infection did not significantly affect the bacterial diversity, and the relative abundance of probiotics increased. Furthermore, the alterations of gut microbiota were closely related to the change of pro-inflammatory factor. Metagenomics prediction analysis demonstrated that HNZK-02-P150 modulated the tyrosine metabolism, Nucleotide-binding and oligomerization domain (NOD)-like receptor signaling pathway, and lipopolysaccharide biosynthesis, which coincided with lower inflammatory response and intestinal permeability in the piglets infected with HNZK-02-P150. In conclusion, the PDCoV HNZK-02 was successfully attenuated by serial passage in vitro, and the changes of S gene, metabolic function, and gut microbiota may contribute to the attenuation. The PDCoV HNZK-02-P150 may have the potential for developing live-attenuated vaccine.IMPORTANCEPorcine deltacoronavirus (PDCoV) is an enteropathogen causing severe diarrhea, dehydration, and death in nursing piglets, devastating great economic losses for the global swine industry, and has cross-species transmission and zoonotic potential. There are currently no approved treatments or vaccines available for PDCoV. In addition, gut microbiota has an important relationship with the development of many diseases. Here, the PDCoV virulent HNZK-02 strain was successfully attenuated by serial passage on cell cultures, and the pathogenesis and effects on the gut microbiota composition and metabolic function of the PDCoV HNZK-02-P5 and P150 strains were investigated in piglets. We also found the genetic changes in the S protein during passage in vitro and the gut microbiota may contribute to the pathogenesis of PDCoV, while their interaction molecular mechanism would need to be explored further.

Evaluation of the immunoprotective effects of porcine deltacoronavirus subunit vaccines

Porcine deltacoronavirus (PDCoV), a new porcine enteric coronavirus, has seriously endangered the pig breeding industry and caused great economic losses. However, a PDCoV vaccine is not commercially available. Therefore, new and efficient PDCoV vaccines must be developed without delay. In this study, we used the ExpiCHO eukaryotic expression system to express and purify the following 3 structural proteins of PDCoV: S, N and M. Subsequently, the level of humoral and cellular immunity induced by the S protein (immunization with the S protein alone) and a protein mixture (immunization with a mixture of S, N and M proteins) were evaluated in mice and piglets, respectively, and the performances of the 2 immunizations in a challenge protection test were assessed in piglets. The results showed that both the S protein and the protein mixture induced the production of high levels of specific IgG antibodies and neutralizing antibodies and effectively neutralized PDCoV-infected LLC-PK cells in vitro. Furthermore, compared with the S protein, the N and M proteins in the protein mixture promoted the expression of CD8+ T cells and IFN-γ, induced a stronger cellular immune response, and effectively protected 4/5 of the piglets from PDCoV infection. In conclusion, the results of this study showed that the N and M proteins play important roles in inducing an immunoprotective response. Using N and M antigens as effective antigenic components in the development of PDCoV vaccines in the future will effectively increase the immune efficacy of the vaccines.

Isolation and Pathogenicity of a Chinese Porcine Astrovirus Type 5 Strain HNPDS-01 and Its Influence on Cecum Microbiota in Piglets

Astroviruses have frequently been found in mammals and poultry, but only a few have been successfully isolated for extensive research. Here, we isolated a strain of porcine astrovirus type 5 (PAstV 5) on LLC-porcine kidney (LLC-PK) cells, from the intestinal contents of diarrhea piglets, namely PAstV 5-HNPDS-01. The complete genome sequence length of this strain was 6,419 nt, which has 77.2%-91.1% nucleotide homology with other PAstV 5 strains and 45.0%-50.0% nucleotide homology with other mammalian astroviruses. The recombination analysis indicated that the recombination events were occurred in ORF 2 region (4,444-5,323 nt) in PAstV 5-HNPDS-01 strain. Subsequently, the pathogenicity of PAstV 5-HNPDS-01 was evaluated in 5-day-old piglets. It showed that the PAstV 5-HNPDS-01 could cause mild diarrhea, growth retardation, minor damage to intestinal villi clinically. Meanwhile, PAstV 5-HNPDS-01 infection could affect the microbiota diversity and composition of cecum in piglet from phylum to genus level. After infected with PAstV 5, there was a significant downregulation of beneficial bacteria, including Faecalibacterium, Bacteroides, Lactobacillus, and Prevotella, while harmful bacteria such as Subdoligranulun showed a significant upregulation. These results provided a research basis for pathogenic mechanisms, vaccine development, and beneficial symbiotic bacteria development for PAstV 5 infection.

Establishment and Application of a Triplex Real-Time RT-PCR Assay for Differentiation of PEDV, PoRV, and PDCoV

Porcine viral diarrhea is very common in clinical practice and has caused huge losses to the pig industry. Porcine epidemic diarrhea virus (PEDV), porcine rotavirus (PoRV), and porcine deltacoronavirus (PDCoV) are important pathogens of porcine viral diarrhea. Co-infection situations among these three viruses in clinics are common, which increases the difficulty of differential diagnosis. Currently, polymerase chain reaction (PCR) is commonly used to detect pathogens. TaqMan real-time PCR is more sensitive than conventional PCR and has better specificity and accuracy. In this study, a triplex real-time RT-PCR assay based on TaqMan probes was developed for differential detection of PEDV, PoRV, and PDCoV. The triplex real-time RT-PCR assay developed in this study could not detect unrelated pathogens and showed satisfactory specificity, sensitivity, repeatability, and reproducibility with a limit of detection (LOD) of 6.0 × 10¹ copies/μL. Sixteen clinical samples were used to compare the results of the commercial RT-PCR kit and the triplex RT-PCR for PEDV, PoRV, and PDCoV detection, and the results were completely consistent. A total of 112 piglet diarrhea samples collected from Jiangsu province were next used to study the local prevalence of PEDV, PoRV, and PDCoV. The positive rates of PEDV, PoRV, and PDCoV detected by the triplex real-time RT-PCR were 51.79% (58/112), 59.82% (67/112), and 2.68% (3/112), respectively. The co-infections of PEDV and PoRV were frequent (26/112, 23.21%), followed by the co-infections of PDCoV and PoRV (2/112, 1.79%). This study established a useful tool for simultaneous differentiation of PEDV, PoRV, and PDCoV in practice and provided valuable information on the prevalence of these diarrhea viral pathogens in Jiangsu province.