Early infection of Streptococcus suis serotype 2 increases the virulence of highly pathogenic porcine reproductive and respiratory syndrome MLV-like virus in pigs

• Published in: Research in veterinary science 2020-06, Vol.130, p.68-72
• Main Authors: Sun, Ying-Feng, Jiang, Xuan, Zhang, Ao, Ma, Ji-Fei, Yu, Xiao-Xue, Li, Liu-An, Yu, Hai
• Format: Article
• Language: English
• Subjects: Amino acids; Animal diseases; Anorexia; Antibodies; Bacteria; Bacterial diseases; Bacterial infections; Early bacterial infection; Epidemics; Experiments; Fever; Genome characterization; Genomes; Hogs; Homology; HP-PRRSV; Immunization; Infections; Inflammation; MLV-like; Mortality; Pathogenicity; Pathogens; Phylogenetics; Pneumonia; Respiratory diseases; Software; Strains (organisms); Streptococcus infections; Streptococcus suis; Swine; Vaccines; Veterinary medicine; Viral diseases; Virulence; Viruses
• ISSN: 0034-5288; 1532-2661
• DOI: 10.1016/j.rvsc.2020.02.010

Modified-live virus (MLV) vaccines derived from highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) were wildly used in China, which resulted in the emergence of MLV-like strains in pigs. Previous studies demonstrated that secondary bacterial infection could enhance HP-PRRSV infection-mediated inflammatory responses, but it is unknown whether early bacterial infection could enhance the HP-PRRSV MLV-like infection-mediated pathological reaction. In this paper, to gain the evidence for infection of pigs with MLV-like strains in China, we firstly analyzed the genetic characterization of the HP-PRRSV MLV-like isolate (TJxq1701) and further evaluated whether the early Streptococcus suis infection synergizes HP-PRRSV MLV-like infection-mediated pathological reaction. Our results showed that the whole genome of TJxq1701 shared the highest homology with JXA1-P80 and a total of 16 amino acids residues unique to JXA1-P80 in ORF1a, ORF1b, GP2, GP3, GP4, and GP5 were found in the corresponding locations. The results of infection experiments in pigs revealed that TJxq1701 caused transitional fever, moderate respiratory clinical sign and microscopic lung lesions in piglets, but early infection with low virulence Streptococcus suis serotype 2 (SS2) exhibited seriously clinical signs, including high fever, anorexia, and respiratory distress, leading to 60% mortality within four weeks in comparison with alone infected group. Taken together, our findings reveal that early bacterial infection could enhance the HP-PRRSV MLV-like infection-mediated pathological reaction, which provide an important clue for understanding that streptococcus infection increases the pathogenicity of MLV-like virus and a new thought for prevention and control of PRRSV. •The TJxq1701 isolate shared similar phylogenetic properties with the MLV vaccine (JXA1-P80).•A total of 16 amino acids unique to JXA1-P80 are found in the TJxq1701.•Infection experiments showed that the TJxq1701 isolates was low pathogenic.•Early infection of Streptococcus suis enhances the TJxq1701 infection-mediated pathological reaction.