A Getah virus (GETV) outbreak occurred in a swine farm in Hunan, China, between June and July 2017. Approximately 200 piglets died 5-10 days after birth, and more than 150 pregnant sows had stillbirths or foetal mummies in this outbreak. GETV HuN1, isolated from the cerebrum of an infected piglet, shared a close evolutionary relationship with the Kochi/01/2005 strain, isolated from pigs in Japan. GETV was detected in the cerebral cortices of a dead foetus and in various organs of two infected piglets, thereby demonstrating that GETV can be transmitted through the placenta to infected newborn piglets with multiple tissue tropisms. Seroepizootiologic investigation of GETV revealed that a wide infection of GETV had been persisting in the farm between June 1 and July 17. In conclusion, clinical and laboratory diagnostics of the diseased pigs in this outbreak were consistent with GETV being the causative agent. To the best of our knowledge, this is the first unequivocal report of GETV in pigs in China.

Porcine sapeloviruses (PSVs) are widely distributed in pig populations; however, little information on their evolutionary history and the mechanisms driving their divergence is available. Therefore, in the present study, 241 fecal samples and 91 intestinal contents collected from pigs at 26 farms in Hunan, China, were tested for the presence of PSVs. The overall PSV positivity rate was 46.39 %, with a particularly high infection rate detected in nursery and fattening pigs. A total of 29 PSV strains (PSV-HuNs) were isolated, with these showing high genetic diversity based on phylogenetic and pairwise distance analyses of the capsid-protein gene sequences. Incongruence between phylognetic trees of the capsid-protein and 3CD regions indicated frequent recombination within the PSV-HuNs, and a putative recombinant hotspot near the 3' end of the P1 region was identified. Our results suggested that recombination played an important role in driving PSV genetic diversity and evolution.

Streptococcus suis is a zoonotic pathogen that harbors anti-oxidative stress genes, which have been reported to be associated with virulence. Serial passage has been widely used to obtain phenotypic variant strains to investigate the functions of important genes. In the present study, S. suis serotype 9 strain DN13 was serially passaged in mice 30 times. The virulence of a single colony from passage 10 (SS9-P10) was found to increase by at least 140-fold as indicated by LD50 values, and the increased virulence was stable for single colonies from passage 20 (SS0-P20) and 30 (SS0-P30). Compared to the parental strain, the mouse-adapted strains were more tolerant to oxidative and high temperature stress. Genome-wide analysis of nucleotide variations found that reverse mutations occurred in seven genes, as indicated by BLAST analysis. Three of the reverse mutation genes or their homologs in other bacteria were reported to be virulence-associated, including ideSsuis in S. suis, a homolog of malR of Streptococcus pneumoniae, and a homolog of the prepilin peptidase-encoding gene in Legionella pneumophila. However, these genes were not involved in the stress response. Another gene, srtR (stress response transcriptional regulator), encoding an XRE family transcriptional regulator, which had an internal stop in the parental strain, was functionally restored in the adapted strains. Further analysis of DN13 and SS9-P10-background srtR-knock-out and complementing strains supported the contribution of this gene to stress tolerance in vitro and virulence in mice. srtR and its homologs are widely distributed in Gram-positive bacteria including several important human pathogens such as Enterococcus faecium and Clostridioides difficile, indicating similar functions in these bacteria. Taken together, our study identified the first member of the XRE family of transcriptional regulators that is involved in stress tolerance and virulence. It also provides insight into the mechanism of enhanced virulence after serial passage in experimental animals.

No abstract

ABSTRACTA double-antigen sandwich enzyme-linked immunosorbent assay (ELISA) is described for detection of porcine circovirus 2 (PCV2) antibodies using the well-characterized recombinant PCV2 capsid protein. In a comparative test of 394 pig sera against an indirect immunofluorescence (IIF) test and a commercial ELISA kit (also based on the recombinant PCV2 capsid protein), the results showed that the diagnostic sensitivity, specificity, and accuracy of the assay were, respectively, 90.61, 94.02, and 91.62% compared with IIF and 94.38, 95.28, and 94.67% compared with the commercial ELISA kit. Assay of 12 PCV-free pigs over a 5-week period produced only PCV2-negative titers by all 3 methods. These results and the seroprofiles of 4 pig farms obtained by both the commercial ELISA kit and the double-antigen sandwich ELISA indicate that the sandwich ELISA is a reliable method for detection of antibodies to PCV2. Additionally, the method described here permits the use of undiluted test serum samples simultaneously loaded with horseradish peroxidase (HRP)-conjugated antigen into the test well, and the complete test procedure can be performed in less than 90 min. This double-antigen sandwich ELISA should be a useful tool to aid swine industry professionals in deciding the intervention strategies for the control of PCV2-associated diseases.