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Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically devastating pathogenic microorganism that greatly affects the pork industry in the world. The genetic variation and frequent emergence of novel strains greatly hinder the control efforts of PRRSV. Therefore, monitoring the evolutionary dynamics is long and rewarding work for PRRSV researchers and practitioners to make the control strategy. Here, three novel PRRSV strains named CHbj2101, CHbj2102, and CHbj2103 were isolated from different nursery barns with various mortality rates from 6% to 17%, belonging to the same farm, but at different periods of the outbreak. The genomic sequencing and phylogenetic analyses indicated that these three isolates were all clustered with NADC30-like virus CHsx1401, sharing higher genomic similarity from 87.3% to 89.8%, and having the same molecular marker of 131 amino acid residues deletion at their nsp2 coding region, but varied mutagenesis among the antigenic sites in the region of GP2 to GP5. Among the available PRRSV sequences in the GenBank, the isolates CHbj2101 and CHbj2102 display the highest genomic identity (90.1% and 89.8%) with NADC30-like recombinant strain 15LN3, and the rest CHbj2103 shows the highest genomic identity (90.8%) with NADC30-like virus strain 15SC3. The recombination analysis indicated that all three isolates are generated by multiple recombination events among the NADC30-like virus (major parent, Lineage 1), HP-PRRSV vaccine-like virus (minor parent, Lineage 8), and QYYZ-like virus (minor parent, Lineage 3). The isolates CHbj2101 and CHbj2102 shared a similar recombination pattern, but CHbj2103 has a different pattern in nonstructural protein coding regions. To further investigate the recombination characteristics of QYYZ-like strains, we analyzed all available whole genomic sequences of QYYZlike PRRSV, submitted during the year 1991 and 2021 (n = 83) in China. The result shows that almost all QYYZ-like strains were products of recombination and their immunogenicity or protective protein fragments (nsp2--nsp7 and GP2--GP4) were mainly from QYYZ. These results provide us with some better insight into the evolution process of PRRSV strains in the field and warn us to pay more attention to monitoring and reducing the PRRSV variant on farms to reduce the risk of novel emergence and outbreak. [ABSTRACT FROM AUTHOR]

Background: The highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) emerging in China exhibits high fatality to pigs. However, the mechanism related to the increased pathogenicity of the virus remains unclear. In the present study, the differences in tissue tropism between the highly pathogenic PRRSV strain (JXwn06) and the low pathogenic PRRSV strain (HB-1/3.9) were investigated using PRRSV-specific immunohistochemistry (IHC) staining to provide evidence for elucidating possible mechanism of the pathogenicity of Chinese highly pathogenic PRRSV. Findings: IHC examination showed that PRRSV antigen in the tissues including spleen, tonsil, thymus, kidney, cerebellum, stomach, small intestine, large intestine, turbinal bone and laryngeal cartilage was positive in more pigs inoculated with JXwn06 than HB-1/3.9, and the tissues including trachea, esophagus, liver, mandibular gland and thyroid gland were positive for viral antigen in the pigs inoculated with JXwn06, but not in the pigs inoculated with HB-1/3.9. Meanwhile, we observed that epithelium in tissues including interlobular bile duct in liver, distal renal tubule of kidney, esophageal gland and tracheal gland were positive for viral antigen only in JXwn06-inoculated pigs, and epithelium of gastric mucosa and fundic gland, and intestinal gland were positive for viral antigen in both JXwn06- and HB-1/3.9-inoculated pigs, using monoclonal antibodies to N and Nsp2 proteins. Conclusions: Taken together, these findings indicate that the highly pathogenic PRRSV JXwn06 displays an expanded tissue tropism in vivo, suggesting this may contribute to its high pathogenicity to pigs. [ABSTRACT FROM AUTHOR]

A total of 133 Salmonella isolates recovered from retail meats purchased in the United States and the People's Republic of China were assayed for antimicrobial susceptibility, the presence of integrons and antimicrobial resistance genes, and horizontal transfer of characterized antimicrobial resistance determinants via conjugation. Seventy-three (82%) of these Salmonella isolates were resistant to at least one antimicrobial agent. Resistance to the following antibiotics was common among the United States isolates: tetracycline (68% of the isolates were resistant), streptomycin (61%), sulfamethoxazole (42%), and ampicillin (29%). Eight Salmonella isolates (6%) were resistant to ceftriaxone. Fourteen isolates (11%) from the People's Republic of China were resistant to nalidixic acid and displayed decreased susceptibility to ciprofloxacin. A total of 19 different antimicrobial resistance genes were identified in 30 multidrug-resistant Salmonella isolates. The bla[sub CMY-2] gene, encoding a class A AmpC β-lactamase, was detected in all 10 Salmonella isolates resistant to extended-spectrum β-lactams. Resistance to ampicillin was most often associated with a TEM-1 family β-lactamase gene. Six aminoglycoside resistance genes, aadA1, aadA2, aacC2, Kn, aph(3)-Ila, and aac(3)-IVa, were commonly present in the Salmonella isolates. Sixteen (54%) of 30 Salmonella isolates tested had integrons ranging in size from 0.75 to 2.7 kb. Conjugation studies demonstrated that there was plasmid-mediated transfer of genes encoding CMY-2 and TEM-1-like β-lactamases. These data indicate that Salmonella isolates recovered from retail raw meats are commonly resistant to multiple antimicrobials, including those used for treating salmonellosis, such as ceftriaxone. Genes conferring antimicrobial resistance in Salmonella are often carried on integrons and plasmids and could be transmitted through conjugation. These mobile DNA elements have likely played an important role in transmission and dissemination of antimicrobial resistance determinants among Salmonella strains. [ABSTRACT FROM AUTHOR]