Erysipelothrix rhusiopathiae is the causative agent of animal erysipelas and, to a fewer occurrences, human erysipeloid. It is ubiquitous in nature and commensal in diverse species of animals, wild or domestic, from mammals and birds to reptiles and fish. Mechanisms of its virulence and pathogenicity are poorly understood.

Background: Porcine reproductive and respiratory syndrome virus (PRRSV) is largely responsible for heavy economic losses in the swine industry worldwide because of its high mutation rate and subsequent emergence of virulent strains. However, the immunological and pathological responses of pigs to PRRSV strains with different virulence have not been completely elucidated.Methods: Twenty-four piglets were divided into 4 groups (n = 6 each) and inoculated with highly pathogenic PRRSV isolate BB0907 (HP), low pathogenic PRRSV NT0801 (LP), LP derivative strain NT0801-F70 (LP-der), and DMEM medium (control), respectively. The changes in TLR2, 3, 7, and 8 gene expression and TNF-α, IL-1β, IL-6, IFN-γ, and IL-10 secretion were evaluated using real-time PCR and ELISA at 6, 9, and 15 days post inoculation (d.p.i.). The cytokine levels were evaluated in the supernatants of porcine alveolar macrophages (PAMs) and peripheral blood mononuclear cells (PBMCs) following stimulation with LTA, poly(I:C), CL097, and PRRSV individually.Results: HP caused more severe clinical signs and pathological lesions in swine than LP and LP-der had almost no virulence compared with LP. The serum levels of IL-1β, IL-6, TNF-α, and IFN-γ were increased in HP-infected piglets, which were greater than in those infected with LP or LP-der. The mRNA levels of TLR3, 7, and 8 were significantly up-regulated in PAMs in HP-infected pigs compared to those in groups LP and LP-der. Furthermore, TNF-α and IL-1β secretion in PAMs from group LP was statistically greater than those from the control group after stimulation with either poly(I:C) or CL097. Meanwhile, TNF-α, IL-1β, and IL-6 levels in CL097-stimulated PBMCs from HP-infected pigs were markedly higher than those from the LP- and LP-der-infected groups.Conclusions: We found that HP was a stronger inducer of TLR 3, 7, and 8 expression and IL-1β, IL-6, TNF-α, and IFN-γ production compared to LP and LP-der. HP enhanced production of TNF-α, IL-1β, and IL-6 in PBMCs following CL097-stimulation more than LP and LP-der, whereas LP enhanced the secretion of TNF-α and IL-1β in poly(I:C)- and CL097-stimulated PAMs. Our data regarding cellular reactivity to different isolates should be useful in the development of more efficacious vaccines.

Recently, a series of acute swine erysipelas outbreaks occurred in Eastern China. Eight strains isolated from cases of septicemia were determined as serotype 1a, and 4 of the isolates were resistant to acriflavine. One isolate strain named HX130709 was attenuated on agar media containing acriflavine dye. The 432-bp hypervariable region in spaA gene of the field and attenuated strains were amplified and sequenced. It was further compared with the vaccine strain G4T10, and thus, the eight field strains can be divided into four spaA-types. The partial spaA gene analysis also showed that no point mutations occurred among different archived passages of HX130709 during the attenuation. Results of pulsed-field gel electrophoresis showed that eight distinct patterns with 22 to 30 DNA fragment bands were produced from field strains, and twelve distinct patterns with 23 to 27 DNA fragment bands were produced from different passages of the attenuated strains. Mouse pathogenicity test showed that the mortality of the mice infected with 10(4) CFU field strains was 100% and the attenuation of strain HX130709 occurred between 46 and 50 passages. All the field and attenuated strains were highly sensitive to β-lactam antibiotics, tetracyclines and macrolides. So, we can make conclusions that the acute swine erysipelas outbreaks in Eastern China were caused by serotype 1a E. rhusiopathiae strains with different biochemical characteristics, and the virulence of serotype 1a E. rhusiopathiae strains is unrelated with some point mutations in 432-bp hypervariable region of the spaA gene.

Porcine circovirus 3 (PCV3), a recently discovered virus, has spread widely in pigs throughout the world. In order to investigate the possibility of mice used to study the infection of PCV3, commercially sourced Balb/C and ICR mice were screened for PCV3 infection. Blood samples were collected from 20 mice (10 each of Balb/c and ICR), DNA was extracted, and subjected to PCR with PCV3 specific primers. We found all 20 serum samples tested positive for PCV3 DNA. From four mice, the complete genomes of PCV3 were amplified and sequenced, and a phylogenetic tree was constructed. The results showed that the amplified genome was 2000 bp, and sequence comparison showed that the homology of the complete genome and ORF2 gene with those of porcine PCV3 are 97.9%–98.8% and 96.9%–98.3%, respectively. Amino acids alignment results showed that the Cap protein of the mouse PCV3 isolates share 90.7%–96.3% amino acid homology with that of the references strains derived from pigs. Phylogenetic analysis based on ORF2 sequences showed that all PCV3 strains clustered together and were clearly separate from other circovirus species. We detected PCV3 in experimental mice in China for the first time, which is an opportunity to use mice to study the infection of PCV3 and a potential hazard to swine industry.