April

• 30 minutes
• Top publications | April
• Heather L. Walker, BS; Andrew S. Bowman, DVM, PhD, DACVPM; Juliana B. Ferreira, DVM, MSc, DVSc; Sarah W. Nelson, MS; Monique Pairis-Garcia, DVM, PhD; Andreia G. Arruda, DVM, PhD

Objective: The main objective of this study was to describe the use and limitations of tonsil scrapings (TS), oral fluids (OF), nasal swabs (NS), and environmental swabs (ES) to detect porcine reproductive and respiratory syndrome virus (PRRSV).

Materials and methods: Two PRRSV-positive growing pig farms using different PRRSV control strategies were enrolled in this study. Sampling began approximately 52- and 21-days post PRRSV exposure for farms 1 and 2, respectively, and occurred once a month for four months using fixed spatial sampling. Samples for OF and ES were collected at the pen level and TS and NS samples were collected at the individual level. All samples were tested using reverse transcriptase-polymerase chain reaction (RT-PCR).

Results: A total of 192 samples were collected over the study period: 48 TS, 48 OF, 48 NS, and 48 ES. Overall, 20 TS (41.6%), 0 OF (0.0%), 6 NS (12.5%), and 1 ES (2.1%) tested RT-PCR positive for PRRSV throughout this study.

Implications: Tonsil scraping samples yielded more positive PRRSV RT-PCR results for longer time periods when compared to OF, NS, and ES for PRRSV detection in growing pigs. Tonsil scraping samples tested RT-PCR positive for PRRSV up to 168 days post exposure. Oral fluids, NS, and ES sampling methods for PRRSV detection in growing pig populations, particularly months after the initial infection or vaccination, should be used with caution given low RT-PCR positive samples found in this study.

• 10 minutes
• Top publications | April
• Dylan John Melmer, Terri L. O’Sullivan, Amy Greer, Lori Moser, Davor Ojkic, Robert Friendship, Dinko Novosel, Zvonimir Poljak

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.