There has been a noticeable increase in the use of processing fluid as a means of PRRSV surveillance. Because these samples are easily collected by farm staff they provide the ability to test a broader cross section of the piglet population on a more frequent basis. These US researchers wanted to determine the relationship between the actual number of viremic piglets and the detection rate of PRRSV RNA in processing fluid samples. In two PRRSV-positive breeding herds, processing fluids (n = 77) and individual piglet serum samples (n = 834) were collected from 77 litters in three sampling events and tested for PRRSV RNA.
The researchers found the following:
- 55 of the 77 litters (71.4%) contained no viremic piglets and processing fluids tested negative for PRRSV RNA.
- 22 of the 77 litters (28.6%) had ≥1 viremic piglets
- 10 litters contained a single viremic piglet and within this group with a single viremic piglet there were 5 of the 10 processing fluids that tested positive for PRRSV RNA.
- When the within-litter prevalence, however, was ≥39%, the probability of detecting PRRSV RNA in processing fluids was ≥95%.
- The results suggest that pooling processing fluids from several litters increases the probability of PRRSV RNA detection because of the greater likelihood of including multiple litters each with ≥1 viremic piglets.
- The diagnostic costs when using processing fluids such that 100% of the processing-age piglet population is covered can be estimated at €0.077 ($0.086 USD) per pig weaned.
- The diagnostic costs required to achieve an equivalent testing coverage with the use of individual piglet serum samples, would be €4.48 ($5.00 USD) per pig weaned.
Take Home Message:
- The use of processing fluid for PRRSV surveillance is practical, reliable and cost effective.
Ref: López WA, Zimmerman JJ, Gauger PC, Harmon KM, Bradner L, Zhang M, Giménez-Lirola 2, Ramirez A, Cano JP, Linhares DCL. Practical aspects of PRRSV RNA detection in processing fluids collected in commercial swine farms. Prev Vet Med. 2020 May 4;180:105021. doi: 10.1016/j.prevetmed.2020.105021. [Epub ahead of print]