Canine adenovirus (CAdV) has a high prevalence in canine populations. High affinity neutralizing antibodies against conserved epitopes can provide protective immunity against CAdV and protect against future outbreaks. In this study, we identified two CAdV-2-specific neutralizing monoclonal antibodies (mAbs), 2C1 and 7D7, which recognized two linear-dependent epitopes. MAb 2C1 potently neutralized CAdV-2 with a 50% neutralization titer (NT50) of 4096, and mAb 7D7 partially neutralized CAdV-2 with a 50% NT50 of 64. Immunoprecipitation, Western blot and protein spectral analysis indicated that both neutralizing mAbs recognized the hexon protein (Hex) of CAdV-2. Through a 12-mer random peptide phage display and synthetic peptides analysis, we finely mapped the neutralizing epitopes to two 10-amino acid (aa) peptides within the CAdV Hex: ⁶³⁴RIKQRETPAL⁶⁴³ located on the surface region; and ⁷³⁶PESYKDRMYS⁷⁴⁵ located in the inner region of the expected 3D structure of trimeric Hex. Importantly, the two epitopes are highly conserved among all CAdV isolates by sequence alignment analysis. Thus, these results provide insights into the interaction between virus and mAbs at the aa level and may have potential applications in the development of novel therapeutic or epitope-based vaccines, antibody therapeutics and a diagnostic method suitable for the rapid detection of all CAdVs.

Serological testing is an important method for the diagnosis of pseudorabies virus (PRV) infection. We aimed to investigate the envelope glycoprotein I (gI) of PRV, a strong immunogen, and its potential as an efficient and low-cost diagnostic reagent. In this study, the DNA of the PRV SC strain was used as the template, and the recombinant fragment of gI (633 bp) was amplified via PCR using synthetic primers, and was then ligated into the pET-30a expression vector. The constructs were transferred into Escherichia coli (E. coli) for prokaryotic expression, and the antigenicity of the expression products was identified by Western blot analysis with pig positive serum against PRV. The recombinant protein was purified by a Ni column, and BALB/c mice were immunized with purified gI protein to obtain anti-gI-positive serum. After PK-15 cells had been infected by PRV for 48 h, the immunogenicity of purified gI protein was identified with a fluorescence immunoassay using anti-gI mouse serum. The recombinant plasmid (pET-30a-gI) was expressed, and the native gI protein was obtained after denaturation by urea and renaturation by dialysis. A small-scale ELISA test containing 1.0 µg/mL of purified gI protein was designed to evaluate pig serum (80 samples), and the results of the ELISA test were compared to those of competitive ELISA (cELISA) tests using IDEXX Kits, which resulted in 97.5% consistency. The results suggested that the truncated gI protein may be a potential diagnostic reagent.

Streptococcus suis (S. suis) is a major pathogen in pigs and an emerging zoonotic agent which causes serious infections in humans. It is also an immunosuppressive pathogen that exerts detrimental effects on the thymus, spleen, lymph nodes, and macrophages, impairing their ability to perform their normal physiological functions. S. suis induces thymic atrophy, splenomegaly, and lymphadenectasis and triggers apoptosis in T cells and B cells, as well as pyroptosis in macrophages within immune organs. Subsequently, T cell subsets in peripheral blood become abnormal, and the expression of cytokines becomes dysregulated, which leads to host immunosuppression, suggesting a new virulence mechanism of S. suis.

In China, the national-level protected pig, the Min pig, is characterized by the development of secondary hairs and hair follicles in winter. Factors that dominate the genotype in the growth of secondary hairs are not clear through the concrete cell signaling pathways. This study compared hair phenotypes based on morphological structure, transcriptomics, and potential targeting molecules in the breeds of Min, Berkshire, and Yorkshire pigs. The results indicated that Min pigs have specific characteristics for the growth of secondary hairs compared with the Berkshire and Yorkshire pigs. The transcriptome analyses and quantitative reverse transcription-polymerase chain reaction results revealed that secondary hair growth was activated by follicle stem cells. The specific inhibitors of Wnt and BMP were studied using respective signals. The density of follicles, activity of follicle stem cells, and relative gene expression results have shown that Wnt and BMP stimulate the activity of follicle stem cells, and the Wnt signaling molecule has a significantly better effect than the BMP signaling molecule on stem cells. Wnt and BMP can promote the growth of local secondary hair and gene expression. Therefore, this study was conducted to verify the development mechanisms of secondary hairs, which have potential applications in laboratory animals and comparative medicine.

Hepatitis E virus (HEV) is an emerging zoonotic pathogen capable of both human-to-human and animal-to-human transmission. However, limited data are available regarding HEV infections in pigs in Heilongjiang Province, China. To investigate the prevalence of HEV in pigs in this region, liver samples from diseased or deceased pigs and fecal samples from healthy pigs were collected and analyzed. A total of 82 liver samples and 86 fecal samples were obtained from 13 farms and tested for HEV genotypes 3 and 4 using nested RT-PCR assays targeting the ORF2 gene. Samples with high viral loads were further subjected to direct sequencing and phylogenetic analysis. Overall, 32 samples tested positive for HEV RNA and were classified as genotype 3 or 4, with genotype 4 being the most prevalent. The identified subtypes included 3a, 4a, and 4d, among which subtype 4d was the most common. Phylogenetic analysis revealed that swine HEV genotype 3 (subtype 3a) and genotype 4 (subtypes 4a and 4d) clustered closely with reference sequences 3a/AB089824/JA10, 4a/JX9974449/NJ6, and 4d/JX997439/NJ5. These strains exhibited close genetic similarity to human HEV isolates previously reported in Tokyo, Japan, and eastern China. These findings indicate that HEV genotypes 3 and 4 are distributed in pig farms across Heilongjiang Province and suggest that zoonotic transmission between pigs and humans is frequent in China.