Efficacy of two porcine reproductive and respiratory syndrome (PRRS) modified-live virus (MLV) vaccines against heterologous NADC30-like PRRS virus challenge.

The emergence of novel and variant porcine reproductive and respiratory syndrome virus (PRRSV) strains has made controlling this disease a challenge in China. Several NADC30-like PRRSV outbreaks have occurred in mainland China since 2013. The objective of the present study was to evaluate the cross-protection efficacy of two commercial PRRS modified-live virus (MLV) vaccines, derived from classical PRRSV (VR2332) and highly pathogenic (HP) PRRSV (TJM-F92), against an increasingly circulating NADC30-like lineage in pigs. Thirty-five PRRSV- and antibody-free pigs were randomly divided into the following four groups: strict control (SC), negative control (NC), Boehringer control (BC), and Zoetis control (ZC) groups. The NADC30-like PRRSV used in this study caused fever, clinical respiratory signs, and gross and microscopic lung lesions in inoculated pigs in the NC group. Vaccination with the VR2332 vaccine significantly reduced the percentage of viremic pigs as well as gross lung lesions and improved average daily weight gain compared to the ZC and NC groups, suggesting that this MLV vaccine provides cross-protection against the NADC30-like virus. There were no significant differences in the efficacy of the two MLV vaccines based on clinical scores, immunological responses, or pathological outcomes. This study demonstrated that VR2332 MLV was effective against circulating NADC30-like PRRSV and could be used to control NADC30-like virus infections in the field.

[Biologic characteristics of eight Podoviridae Stx2-converting phage].

OBJECTIVE: We studied biologic characteristics of Stx2-converting phage induced from Escherichia coli O157 by mitomycin C. METHODS: Eight Stx2-converting phages were isolated from E. coli O157 and identified by PCR. The phage particles were purified and phage DNA was extracted. Random priming digoxin (DIG)-labeled stx2-specific gene probe was prepared for Southern blot. The morphology of these phages were studied by electron microscopy. Protein profiles were analyzed by Sodium Dodecyl Sulphate PolyAcrylamide Gel Electrophoresis (SDS-PAGE). Restriction fragment length polymorphism (RFLP) was used to confirm the size, type, and polymorphism of the purified phage genome. RESULTS: These 8 phages were confirmed Stx2-converting phage and DIG-labeled probe was highly specific. All phages had a regular hexagonal head and a short tail, belonging to Podoviridae phage families. The Stx2 phages had genome sizes in the range of 48 to 65.3kb, consisting of double-stranded DNA. The restriction fragment length polymorphism of these phages showed different groups, although the SDS-PAGE protein profiles of these phages were similar. CONCLUSION: These 8 Stx2-converting phages with similar morphology belonged to Podoviridae phage families. The protein profiles were highly identical. We could differentiate these Stx2-converting phages according to their restriction fragment length polymorphism patterns.