Vet Microbiol

. 2021 Aug 12;261:109190.

 doi: 10.1016/j.vetmic.2021.109190.Online ahead of print.

Probability of PRRS virus detection in pooled processing fluid samples

Will A López 1, Phillip C Gauger 2, Karen M Harmon 2, Derald J Holtkamp 2, Jean Paul Cano 3, Nubia Macedo 2, Min Zhang 4, Gustavo S Silva 2, Jose Angulo 5, Jeffrey J Zimmerman 2, Daniel C L Linhares 6

Affiliations 

Affiliations

• 1Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States; PIC North America, 100 Bluegrass Commons Blvd #2200, Hendersonville, TN 37075, United States.
• 2Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States.
• 3Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States; Pipestone Veterinary Services, 1300 US-75, Pipestone, MN 56164, United States.
• 4Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA 50011, United States.
• 5Zoetis, Parsippany, NJ, United States.
• 6Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States. Electronic address: linhares@iastate.edu.

• PMID: 34411996
 
• DOI: 10.1016/j.vetmic.2021.109190

Abstract

There has been a tremendous increase in recent years of population-based diagnostic monitoring and surveillance strategies in swine populations. One example is the use of processing fluids (PF) to screen breeding herds for porcine reproductive and respiratory syndrome virus (PRRSV) activity. An important question from practitioners using such methods is on how intensively can the sample be pooled. More specifically, processing fluids of how many litters can be pooled into a single sample for diagnostic testing to preserve a high probability of PRRSV RNA detection at low prevalence situations? The objective of this study was to model the effect of pooling PF samples on the probability of PRRSV RNA detection. For this study, a PRRSV-positive PF field sample with a RT-rtPCR quantification cycle (Cq) value of 28 was selected to represent a litter of 11 pigs with a single viremic piglet. PF samples from a PRRSV-naïve herd were used to perform 6 replications of 8 two-fold serial dilutions of the PRRSV-positive sample, thus modeling the pooling effect (dilution). Each two-fold dilution represented an increase in the number of PRRS-negative pigs in the sample by a factor of 2. Samples were tested for PRRSV RNA by RT-rtPCR and the data was analyzed using linear and probit regression models. There was an average increment of 1.37 points in Ct for each two-fold dilution. The estimated probability of testing positive on RT-rtPCR was 43 %, 80 %, and 95 % when there was a single PRRSv-positive piglet among 784, 492, and 323 PRRSv-negative piglets contributing to the sample respectively. Results from this study support the practice of collecting and aggregating PF samples from multiple litters for PRRSV RNA testing.

Keywords: Monitoring; PRRS virus; Pooling; Processing fluids; Surveillance; Swine.

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

Factors associated with PRRS outbreaks in US breeding herds

 Prev Vet Med

. 2020 Oct;183:105128.

 doi: 10.1016/j.prevetmed.2020.105128. Epub 2020 Sep 1.

Spatial relative risk and factors associated with porcine reproductive and respiratory syndrome outbreaks in United States breeding herds

Juan M Sanhueza 1, Mark A Stevenson 2, Carles Vilalta 3, Mariana Kikuti 4, Cesar A Corzo 4

Affiliations 

• PMID: 32937200
 
• DOI: 10.1016/j.prevetmed.2020.105128

Abstract

Details of incident cases of porcine reproductive and respiratory syndrome (PRRS) in United States breeding herds were obtained from the Morrison's Swine Health Monitoring Project. Herds were classified as cases if they reported an outbreak in a given season of the year and non-cases if they reported it in a season other than the case season or if they did not report a PRRS outbreak in any season. The geographic distribution of cases and non-cases was compared in each season of the year. The density of farms that had a PRRS outbreak during summer was higher in Southern Minnesota and Northwest-central Iowa compared to the density of the underlying population of non-case farms. This does not mean that PRRS outbreaks are more frequent during summer in absolute terms, but that there was a geographical clustering of herds breaking during summer in this area. Similar findings were observed in autumn. In addition, the density of farms reporting spring outbreaks was higher in the Southeast of the United States compared to that of the underlying population of non-case farms. A similar geographical clustering of PRRS outbreaks was observed during winter in the Southeast of the United States. Multivariable analyses, adjusting for the effect of known confounders, showed that the incidence rate of PRRS was significantly lower during winter and autumn during the porcine epidemic diarrhea (PED) epidemic years (2013-2014), compared to PRRS incidence rates observed during the winter and autumn of PED pre-epidemic years (2009-2012). After 2014, an increase in the incidence rate of PRRS was observed during winter and spring but not during autumn or summer. Pig dense areas were associated with a higher incidence rate throughout the year. However, this association tended to be stronger during the summer. Additionally, herds with ≥2500 sows had an increased incidence rate during all seasons except spring compared to those with <2500 sows. PRRS incidence was lower in year-round air-filtered herds compared to non-filtered herds throughout the year. We showed that not only the spatial risk of PRRS varies regionally according to the season of the year, but also that the effect of swine density, herd size and air filtering on PRRS incidence may also vary according to the season of the year. Further studies should investigate regional and seasonal drivers of disease. Breeding herds should maintain high biosecurity standards throughout the year.

Keywords: Factors; Incidence; PRRS; Risk; Sow; Spatial.

 Porcine Health Manag

. 2021 Apr 12;7(1):31.

 doi: 10.1186/s40813-021-00210-5.

Longitudinal piglet sampling in commercial sow farms highlights the challenge of PRRSV detection

Marcelo Nunes de Almeida 1, Cesar A Corzo 2, Jeffrey J Zimmerman 3, Daniel Correia Lima Linhares 3

Affiliations 

Affiliations

• 1Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, 1811 Veterinary Medicine Annex, 1856 Christensen Dr. Ames, Ames, Iowa, 50011, USA. malmeida@iastate.ed.
• 2Veterinary Population Medicine Department, College of Veterinary Medicine, University of Minnesota, St. Paul, MN, USA.
• 3Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, 1811 Veterinary Medicine Annex, 1856 Christensen Dr. Ames, Ames, Iowa, 50011, USA.

• PMID: 33845917
 
• DOI: 10.1186/s40813-021-00210-5

Free article

Abstract

Background: Processing fluids (PF) and family oral fluids (FOF) are population-based surveillance samples collected from 2- to 5-day-old piglets and due-to-wean piglets, respectively. Although they are described for the surveillance of PRRSV in sows and piglet populations at processing and weaning, there is limited information on their use in commercial herds. This observational study described PRRSV RNA detection over time in PF, FOF, and piglet serum collected from farrowing groups in commercial breeding farms with the objective of achieving robust, practical, and effective PRRSV surveillance protocols. Weekly PF (an aggregate sample of all litters processed in a week from each room), and FOF (a convenience sample attempted from at least 20 individual litters in at least one farrowing room each week) samples were collected from six PRRSV-endemic commercial breeding herds for up to 38 weeks. A total of 561 PF room samples, 2400 individual litter FOF samples, and 600 serum samples (120 pools of 5 samples) were collected during the study period and tested for PRRSV RNA. Data were evaluated for patterns of PRRSV RNA detection by specimen within farms over time.

Results: In particular, the detection of PRRSV was commonly sporadic over time within farms (weeks of PRRSV RNA negative results followed by one or more weeks of positive results); was often non-uniform within farms (negative and positive farrowing rooms at a given point in time); and PF and FOF testing results agreement was 75 and 80% at week and room level, respectively, demonstrating that both sampling methods could complement each other. Non-uniformity in PRRSV detection in rooms sampled within the same week and detection after ≥11 consecutive weeks of PRRSV negative PF and FOF results underline the challenge of consistently detecting the virus.

Conclusions: These results suggest that monitoring protocols for breeding herds attempting PRRSV control or elimination can use both PF and FOF to improve PRRSV detection in suckling pig populations.

Keywords: Family oral fluids; PRRSV; Processing fluids; Serum; Surveillance; Swine.

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.