Multiple antiviral approaches of (-)-epigallocatechin-3-gallate (EGCG) against porcine reproductive and respiratory syndrome virus infection in vitro.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains an economically important pathogen in the global pig industry, effective measures to control the virus are still lacking. (-)-Epigallocatechin-3-gallate (EGCG), the most abundant and bioactive catechin in green tea, has been reported to have antiviral effect against the diverse groups of viruses. In this study, the comprehensive anti-PRRSV activity of EGCG was investigated using various in vitro assays. EGCG effectively inhibited PRRSV infection and replication in porcine alveolar macrophages (PAMs), regardless of whether it was administrated pre- or post-infection, and the cytotoxicity to PAMs was low. Next, anti-PRRSV approaches of EGCG were characterized in MARC-145 cells. EGCG was demonstrated to be able to significantly prevent PRRSV from infecting MARC-145 cells either through blocking of EGCG-treated viruses docking to susceptible cells involving a direct virus-EGCG interaction or by blocking of the infective virus binding to EGCG pre-treated cells via triggering down-regulation of viral receptors and/or related proteins required for infection. In addition, PRRSV replication was suppressed in MARC-145 cells treated with EGCG post-infection, likely because of down-regulation of pro-inflammatory cytokines, such as TNF-α, IL-6 and IL-8. Taken together, these data showed that treatment of primary PAMs with EGCG can inhibit PRRSV infection and revealed that multiple antiviral approaches of EGCG operate in PRRSV-susceptible MARC-145 cells.

Molecular characterization and recombination analysis of porcine reproductive and respiratory syndrome virus emerged in southwestern China during 2012-2016.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important swine pathogen causing tremendous economic losses to the swine industry. To investigate the prevalence of PRRSV of genotype 2 (North American type, NA-type) in southwestern China, the Nsp2 hypervariable region (Nsp2 HV) and ORF5 of 61 PRRS viruses collected during 2012-2016 were sequenced and analyzed. All the virus detected clustered into the JXA1-like (52/61), VR-2332-like (7/61), and NADC30-like (2/61) sub-genotypes. Five deletions in Nsp2 HV were detected in addition to the typical 30aa discontinuous deletion in HP-PRRSV, and two of these five were not reported previously. Strikingly, two PRRS virus (SCnj16 and SCcd16) isolated in 2016 contained the classic HP-PRRSV molecular marker in the Nsp2-coding region, but belonged to the NADC30-like sub-genotype on the ORF5 gene. Further recombination and phylogenetic analysis on the two complete genomic sequences revealed that they may have originated from recombination events between the NADC30 and Chinese HP-PRRSV strains. The present study suggests that the endemic PRRSVs in the region have continuously evolved and new vaccine strategies are necessary for more efficient control of the virus.

Investigation on host susceptibility of Tibetan pig to infection of porcine reproductive and respiratory syndrome virus through viral challenge study.

Previous reports showed that infection of porcine reproductive and respiratory syndrome virus (PRRSV) stimulated a variable host response and pig susceptibility to PRRSV was largely dependent on its genetic composition. In the present study, host susceptibility of Tibetan pig to PRRSV was compared with other two pig breeds, ZangMei black and Large White, by challenge of them with highly pathogenic PRRSV (HP-PRRSV). In the first challenge test, each eight piglets of the three breeds were inoculated with HP-PRRSV and clinical symptoms, viremia and animal mortality were examined up to 28 days post inoculation (DPI). In the secondary pathological study, each twelve piglets of the three breeds were challenged and three pigs of each breed were sacrificed on 4, 7, and 14 DPI for examination of gross damage and lung microscopic lesions. The results showed that no typical clinical signs such as cough, diarrhea and high fever were observed in challenged Tibetan pigs, which however all occurred in Large White accompanied with ∼40% mortality (3/8). In addition, a significant low and short viremia was detected specifically in Tibetan pigs. Based on histopathological analysis of lung sections, a mild to moderate interstitial pneumonia in Tibetan pigs and a much severe pneumonia in Large White were identified on 7-14 DPI. In summary, the study demonstrated that three genetically different pig breeds exhibited a differential host susceptibility to HP-PRRSV and Tibetan pig was much less susceptible to the virus in the three tested pig breeds.

Propagation of field highly pathogenic porcine reproductive and respiratory syndrome virus in MARC-145 cells is promoted by cell apoptosis.

Infection of porcine reproductive and respiratory syndrome virus (PRRSV) induces cell apoptosis both in vivo and in vitro. However, the correlation between host cell apoptosis and PRRSV replication is unclear. Here, the promotion of PRRSV propagation by cell apoptosis in MARC-145 cells was reported. The observation on propagation of field highly pathogenic PRRSV (HP-PRRSV) in MARC-145 cells showed that infection of overgrown MARC-145 cells obviously elevated virus production and cell apoptosis was triggered in these cells before virus inoculation. The investigation on propagation of field HP-PRRSV in apoptosis induced MARC-145 cells displayed that induction of apoptosis further increased the virus production and a vigorous viral RNA replication accompanied by fast virus release in these cells was detected in the initial 24h post infection. In addition, when field HP-PRRSV was serially passed in drug-treated MARC-145 cells, the progeny viruses kept a stable viral titer and infectivity to its native target cells in the tested generations. In summary, these findings demonstrated that apoptotic MARC-145 cells were more susceptible to field HP-PRRSV and propagation of the virus was promoted by effective replication and cell-to-cell transmission of the virus in these cells.