Relationship between weekly porcine reproductive and respiratory syndrome virus exposure in breeding herds and subsequent viral shedding and mortality in the nursery

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2020-09-01
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Trevisan, Giovani
Robbins, Rebecca
Angulo, Jose
Dufresne, Luc
Lopez, Will
Macedo, Nubia
Linhares, Daniel
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Linhares, Daniel
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Veterinary Diagnostic and Production Animal Medicine
The mission of VDPAM is to educate current and future food animal veterinarians, population medicine scientists and stakeholders by increasing our understanding of issues that impact the health, productivity and well-being of food and fiber producing animals; developing innovative solutions for animal health and food safety; and providing the highest quality, most comprehensive clinical practice and diagnostic services. Our department is made up of highly trained specialists who span a wide range of veterinary disciplines and species interests. We have faculty of all ranks with expertise in diagnostics, medicine, surgery, pathology, microbiology, epidemiology, public health, and production medicine. Most have earned certification from specialty boards. Dozens of additional scientists and laboratory technicians support the research and service components of our department.
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Abstract

Objective: Describe the relationship of weekly breeding herd status based on processing fluid (PF) testing for porcine reproductive and respiratory syndrome virus (PRRSV) RNA by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) on subsequent viral shedding and cumulative mortality during the nursery phase.

Materials and methods: Weekly cohorts (n = 121) of newborn piglets were classified into PRRSV exposure groups according to PRRSV detection in PF: low (quantification cycles [Cq] ≤ 27), medium (27 < Cq ≤ 34), high (34 < Cq ≤ 37), and negative (Cq > 37). At 6 weeks of age, oral fluids (OF) were collected from a subset of 41 cohorts, tested by qRT-PCR, and results used to classify the nursery shedding status into the same aforementioned categories. Cumulative nursery mortality was recorded for all 121 cohorts and compared between the different PRRSV exposure groups. Test agreement was assessed between PF and OF results of 41 cohorts. Moreover, the effect of 4:1 OF pooling on the probability of testing qRT-PCR-positive was evaluated.

Results: The nursery mortality for low Cq cohorts was 3.40 percentage points (range, 3.28-3.99) higher than other exposure groups. Overall, Cq values were higher in PF than in OF samples, and fair agreement (κ = 0.2398) between PF and OF was encountered. Compared to individual samples, 4:1 OF pooling resulted in 100% specificity and 76.92% sensitivity.

Implications: Weekly PF testing for PRRSV allowed for exposure group classification for each pig batch produced, which was a good predictor of subsequent cumulative nursery mortality.

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This article is published as Trevisan, Giovani, Rebecca C. Robbins, Jose Angulo, Luc Dufresne, Will A. Lopez, Nubia Macedo, and Daniel C.L. Linhares. "Relationship between weekly porcine reproductive and respiratory syndrome virus exposure in breeding herds and subsequent viral shedding and mortality in the nursery." Journal of Swine Health and Production 28, no. 5 (2020): 244-253. Posted with permission.

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Wed Jan 01 00:00:00 UTC 2020
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