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.

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