Epizootiological surveillance of porcine circoviruses in free-ranging wild boars in China

Identification and genetic analysis of new ephemeroviruses in wild boars in China

Ephemeroviruses (EVs) are arthropod-borne rhabdoviruses and were isolated exclusively from cattle and haematophagous arthropods until two new ephemeroviruses were first identified from domestic pigs most recently. Here we report the identification of newer EVs in wild boar by meta-transcriptomic (MTT) sequencing. Further screening by specific RT-nPCR of tissue samples of 459 free-ranging wild boars collected between 2018 and 2023 from 26 provinces across China confirmed five positive wild boars in four provinces. Interestingly, two ticks especially collected from two positive wild boars were also EV positive. Finally, four complete genome sequences of wild boar ephemeroviruses (WbEVs) were obtained with two strains belonging to a new EV species, and the rest two falling into porcine ephemerovirus 2 (PoEV2) species identified from domestic pigs. Our study has further extended EV host range and demonstrated natural circulations of divergent EVs in wild boars, in which ticks may play roles. Biological implications of EV infection in wild boars should be interesting topics for future investigations.

The single-cell transcriptional landscape of lung cells from PCV2d-infected mice

Introduction

Porcine Circovirus (PCV2) infection is prevalent in pig farming and causes significant economic losses. In recent years, the PCV2d subtype has become the most prevalent genotype worldwide, exhibiting higher virulence, leading to more severe viremia and organ damage. Therefore, studying the biological characteristics of the PCV2d subtype is of great significance.

Methods

We established a PCV2d infection model using BALB/c mice and employed single-cell RNA sequencing (scRNA-seq) to systematically analyze the transcriptome of 10 cell types in the lung tissues of infected mice. We developed a comprehensive marker gene catalog for these cell types.

Results

Compared to uninfected mice, PCV2d infection induced extensive viral replication and immunosuppressive responses in most cell types. Monocyte macrophages with high levels of viral replication, pro-inflammatory cytokines, and various cell population interactions occurring through CD40-CD40L and CXCL14-CXCR4 were identified. These cells predominantly mediate antigen presentation and processing pathways in vivo, contributing to PCV2d-driven inflammatory lung injury.

Discussion

Our data uncovered a complex unique immune response scenario in the lung tissue of mice after PCV2d infection, deciphering the potential mechanisms underlying PCV2d-driven inflammatory responses in mice. Furthermore, this study provides a rich database for the molecular basis of different cell types' responses to PCV2d infection.

Geographical distribution and characterization of Jingmen tick virus in wild boars in China

•JMTV RNA was identified in 9 out of 26 provinces with an average wild boar infection rate of 5.45% (25/459). •Phylogenetic analysis indicated that JMTV strains could be divided into two groups, but have a complex evolutionary history. •Wild boars are a potential reservoir host for JMTV.

The C3d-fused Porcine circovirus type 2d virus-like particle induced early and enhanced immune response and protected pigs against challenge

Porcine circovirus type 2 (PCV2) is an economically significant pathogen affecting the global swine industry. Vaccination is considered the most effective and best way to prevent PCV2-associated disease. The PCV2d genotype has become predominant by replacing the previous PCV2b genotype. The potential increase in the virulence of PCV2d has drawn attention, spurring the development of PCV2d vaccines. Virus-like particle (VLP) is an ideal vaccine candidate for its safety and potent immunogenicity. C3d is a molecular adjuvant that can be used to promote the protective efficacy of the PCV2 vaccine. In this study, we expressed PCV2d Cap protein fused with C3d epitope using E. coli expression system. The purified recombinant Cap protein assembled into VLP, which was designated as PCV2d-C3d-VLP. Through assessments in mice and piglets, we demonstrated that the PCV2d-C3d-VLP elicited robust humoral responses, notably accelerating antibody production one week earlier compared to a commercial PCV2d subunit vaccine. Furthermore, vaccination substantially reduced PCV2d viral load in piglets. These results present an innovative strategy for developing a more efficacious and cost-effective PCV2d VLP vaccine.

Molecular epidemiological surveillance and complete genome analysis of porcine circoviruses in wild boars (Sus scrofa) in Gyeongnam Province, South Korea

IMPORTANCE

Porcine circovirus (PCV) is a global concern due to its financial impact on the pig industry. Molecular epidemiology of PCV2 and PCV3 in wild boars is essential for understanding viral dispersal and evolution in the wild boar population.

OBJECTIVE

This study aimed to assess the prevalence and genotypic traits of PCV2 and PCV3 in wild boars in the Gyeongnam region.

METHODS

Serum samples from wild boars in Gyeongnam Province were screened for PCV2 and PCV3, and polymerase chain reaction-positive samples were further subjected to genotyping and whole-genome sequencing of PCV2 and PCV3.

RESULTS

Thirty-eight samples tested positive for PCV2, 7 for PCV3, and 2 for PCV2 and PCV3 (coinfection). PCV2d and PCV3b are the dominant genotypes, causing PCV2 and PCV3 coinfections. Wild boar PCV2 and PCV3 viruses closely resemble their corresponding genotypic strains circulating in South Korea.

CONCLUSIONS AND RELEVANCE

The circulation of PCV2 and/or PCV3 in wild species poses an additional challenge for commercial pig farming due to potential contact with infected wild boars. Our findings highlight the necessity for active monitoring and surveillance of wild boars and the enforcement of stringent biosecurity measures on commercial swine farms to mitigate the risk of PCV spillover to the domestic pig population.

Genetic diversity of porcine circoviruses 2 and 3 circulating among wild boars in the Moscow Region of Russia

Porcine circoviruses (PCVs) are widely distributed in swine herds. PCV2, the significant swine pathogen, causes infections characterized by growth and development disorders, skin lesions, and respiratory distress. PCV3 has been circulating worldwide and can be associated with various clinical signs and disease developments. Wild boars are the main reservoir of these pathogens in wildlife and can create an alarming threat to pig farming. In Russia, three PCV2 genotypes (PCV2a, PCV2b, and PCV2d) were identified in pig farms. Additionally, PCV3 was observed in pig herds during the monitoring studies in the country. However, data considering the circulation of PCVs in herds of wild boars in Russia is scant. For this purpose, we performed PCR assays of the samples from 30 wild boars hunted in the Moscow Region of Russia in 2021-2023. The ratios of wild boars positive for PCV2, PCV3, or coinfected were 50, 10, and 13.3%, respectively. Additionally, we sequenced 15 PCV2 and four PCV3 complete genomes and conducted phylogenetic analysis, which divided PCV2 isolates into two groups: PCV2d and PCV2b. The study showed a high infection rate of PCV2 among wild boars, with PCV2d dominance. Simultaneously, PCV3 also circulates among wild boars. The obtained results can provide a basis for the development of preventive measures to support infection transmission risks between farm and wild animals.

Both recombinant Bacillus subtilis Expressing PCV2d Cap protein and PCV2d-VLPs can stimulate strong protective immune responses in mice

Porcine circovirus type 2 (PCV2) is one of the most serious pathogens in pig herds worldwide. The Capsid protein (Cap), a structural protein of PCV2, is involved in the host's immune response; it induces neutralizing-antibody production and has good immunogenicity. The main PCV2 subtype currently prevalent in the Chinese pig herd is PCV2d. In this study, We constructed a recombinant Bacillus subtilis (B. subtilis) capable of secreting Cap protein, named pHT43-Cap/B. subtilis; we concentrated the supernatant of the recombinant bacteria and observed virus-like particles (VLPs) of PCV2d formed by Cap protein under transmission electron microscopy, named PCV2d-VLPs. The immunocompetence of the pHT43-Cap/B. subtilis and PCV2d-VLPs were then assessed by oral administration and by intramuscular injection into mice, respectively. The results showed that the levels of PCV2d-Cap protein-specific IgG in the serum and of PCV2d-Cap protein-specific sIgA in the small intestinal fluid of pHT43-Cap/B. subtilis immunized mice were elevated compared to the control group, both of them highly significant (p < 0.01), and the corresponding serum-specific IgG antibodies were effective in neutralizing PCV2d virulence. The virus load in the liver of the immunized mice was significantly lower than that in the control group (p < 0.01), as was the virus load in the spleen and lungs of the immunized mice (p < 0.05). In addition, the serum levels of PCV2d-Cap-specific IgG in mice immunized with PCV2d-VLPs by intramuscular injection were significantly elevated compared to the control group (p < 0.05), and the viral load in all tissues was significantly lower in immunized mice (p < 0.05). In conclusion, the recombinant bacterium pHT43-Cap/B. subtilis can induce effective mucosal and humoral immunity in mice, PCV2d-VLPs can induce humoral immunity in mice, and both vaccines have good immunogenicity; these results provide a theoretical and material basis for the development of a new vaccine against PCV2d.