PCR assay for specific detection of PRRSGard vaccine-like virus

 Transbound Emerg Dis

. 2021 Mar 24.

 doi: 10.1111/tbed.14084. Online ahead of print.

Development and validation of a reverse transcription real-time PCR assay for specific detection of PRRSGard vaccine-like virus

Gaurav Rawal 1, Wannarat Yim-Im 1, Fabian Chamba 2, Chad Smith 2, Jeff Okones 2, Charles Francisco 2, Jianqiang Zhang 1

Affiliations 

• PMID: 33763963
 
• DOI:10.1111/tbed.14084

Abstract

Increasing use of modified live virus (MLV) vaccines presents challenges to interpret positive results of porcine reproductive and respiratory syndrome virus (PRRSV) screening PCR that can detect both wild-type and vaccine strains. Instead, vaccine-specific PCR provides a convenient tool to detect vaccine-like virus from a sample. Here we report the development and validation of a real-time RT-PCR specific for PRRSGard® , a newly available commercial PRRSV-2 MLV vaccine. Analytical specificity, sensitivity, and diagnostic performance of PRRSGard PCR were evaluated and compared to a commercial PRRSV screening PCR (reference PCR). PRRSGard and reference PCRs did not cross-react with any of the 27 non-PRRSV swine pathogens. PRRSGard PCR did not cross-react with other PRRSV-2 vaccine viruses and 31 laboratory and field PRRSV-2 isolates representing various genetic lineages of PRRSV-2. PRRSGard and reference PCRs consistently detected up to 10-6 and 10-5 dilutions of PRRSGard vaccine virus, respectively. Based on testing serial dilutions of in vitro transcribed RNA, the 95% limit of detection of PRRSGard PCR was 16 genomic copies/reaction with CT cut-off value of 36 and 7 genomic copies/reaction with CT cut-off value of 37. Diagnostic performance of PRRSGard PCR was evaluated using 846 clinical samples (684 serum and 162 oral fluid samples). Compared to the reference screening PCR, diagnostic sensitivity, specificity, and agreement of PRRSGard PCR were 95.34%, 98.85%, and 97.52% with cut-off CT value of 36 and 98.14%, 96.56%, and 97.16% with cut-off CT value of 37. In addition, PRRSGard PCR was able to detect PRRSGard vaccine virus in a sample even with the co-presence of another PRRSV strain. In summary, in contrast to a reference screening PCR that detects both vaccine and field PRRSV strains, PRRSGard PCR provides a convenient tool to specifically detect PRRSGard vaccine-like virus and to inform PRRSV vaccination protocols.

Keywords: PRRSGard; PRRSV; Porcine reproductive and respiratory syndrome virus; Reverse transcription real-time PCR; Vaccine-like; reference screening PCR.

This article is protected by copyright. All rights reserved.

 

Review

 

. 2021 Feb 22;9(2):185.

 doi: 10.3390/vaccines9020185.

Commercial PRRS Modified-Live Virus Vaccines

Chanhee Chae 1

Affiliations 

• PMID: 33671826
 
• PMCID: PMC7926738
 
• DOI: 10.3390/vaccines9020185

Free PMC article

Abstract

Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) presents one of the challenging viral pathogens in the global pork industry. PRRS is characterized by two distinct clinical presentations; reproductive failure in breeding animals (gilts, sows, and boars), and respiratory disease in growing pigs. PRRSV is further divided into two species: PRRSV-1 (formerly known as the European genotype 1) and PRRSV-2 (formerly known as the North American genotype 2). A PRRSV-2 modified-live virus (MLV) vaccine was first introduced in North America in 1994, and, six years later, a PRRSV-1 MLV vaccine was also introduced in Europe. Since then, MLV vaccination is the principal strategy used to control PRRSV infection. Despite the fact that MLV vaccines have shown some efficacy, they were problematic as the efficacy of vaccine was often unpredictable and depended highly on the field virus. This paper focused on the efficacy of commercially available MLV vaccines at a global level based on respiratory disease in growing pigs, and maternal and paternal reproductive failure in breeding animals.

Keywords: modified-live virus vaccine; porcine reproductive; respiratory syndrome virus.

Conflict of interest statement

The authors declare no conflict of interest.

The impact of PRRSV genotypes, established on the basis of ORF-5 sequences, on three production parameters in Ontario sow farms

 Prev Vet Med

. 2021 Feb 23;189:105312.

 doi: 10.1016/j.prevetmed.2021.105312.Online ahead of print.

The impact of porcine reproductive and respiratory syndrome virus (PRRSV) genotypes, established on the basis of ORF-5 nucleotide sequences, on three production parameters in Ontario sow farms

Dylan John Melmer 1, Terri L O'Sullivan 2, Amy Greer 2, Lori Moser 3, Davor Ojkic 4, Robert Friendship 2, Dinko Novosel 5, Zvonimir Poljak 2

Affiliations 

• PMID: 33676324
 
• DOI: 10.1016/j.prevetmed.2021.105312

Abstract

The porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus, with high mutation rates and genetic variability; which is evident by the large number of discrete strains that co-circulate in swine populations. Veterinary practitioners frequently identify certain discrete PRRSV strains as having a higher clinical impact on production. However, with exception of a few strains, production impact is not well characterized for the majority of PRRSV variants. Predictive analytics, coupled with routine diagnostic sequencing of PRRSV, provide opportunities to study the clinical impact of discrete PRRSV strains on production. Thus, the primary objective of this research was to evaluate clinical impact of discrete PRRSV clades observed in Ontario sow farms. PRRS viruses were classified into discrete clades using Bayesian analysis of the nucleotide sequences of the ORF-5 region of the genome. Production data were gathered through veterinary clinics from herds participating in the ongoing PRRSV surveillance system. Data about pre-weaning mortality, sow mortality, and abortion rates were measured up to 8 weeks post initial PRRSV outbreak. Through conventional regression analysis, results support that clinical impact of the viruses varied among clades over time for abortion rate (p = 0.05) and pre-weaning mortality (p < 0.01). Using predictive modelling approaches based on grouped K-fold cross-validation, it was identified that PRRSV clade designations and other measured factors showed low predictive performance for abortion (R2 = 0.07), pre-weaning mortality (R2 = 0.09), and sow mortality (R2 = 0.04). Clade designation consistently showed moderate importance for abortion and pre-weaning mortality, with clade 2 viruses being identified, on average, as having higher impact. These results demonstrate that the prediction of clinical impact, through production parameters, based on phylogenetic classification of PRRS viruses is possible. However, very high impact outbreaks were difficult to predict across production parameters. More surveillance-derived data are required to continue to improve predictive performance of the models.

Keywords: BEAST; Bayesian; Ontario; PRRSV; Phylogenetics; Porcine reproductive and respiratory syndrome; Predictive modeling; Random forest; Swine.

Copyright © 2021 Elsevier B.V. All rights reserved.