#18-161

Complete

Date Full Report Received

12/20/2019

Date Abstract Report Received

12/20/2019

Investigation

Institution:
Primary Investigator:

It is clear that PRRS virus (PRRSv) has the ability to sustain infection in breeding herds at a very low prevalence. This makes it difficult to detect the virus towards the end of PRRSv-elimination programs. In other words, it is challenging to know when it is safe to bring in PRRSv-negative gilts without risk of “re-break” with the same virus. There are a couple alternatives to detect virus at low prevalence: 1) collect blood samples from a high number (150+) of pigs at weekly intervals, or 2) take advantage of ‘population-based’ sample types such as processing fluids (PF) where ‘hundreds’ of piglets are sampled at once.

The objective of this study was to characterize the patterns of PRRSV detection by PCR in processing fluids, collected at 3-5 days of age, and subsequently in family oral fluids (FOF), collected just prior to weaning (litters of 18-20 days). PF consist of serosanguineous samples derived from the process of castrating and tail docking piglets. FOF is the liquid obtained from cotton ropes exposed to lactating sow and respective due-to-wean piglets.

We followed 7 breeding herds that went through a PRRSv outbreak and were in the process of virus elimination targeting producing PRRSv-negative pigs at weaning. Those farms were monitored over time with PF and FOF. Samples were all tested for PRRSV RNA by PCR at the Iowa State University Veterinary Diagnostic Laboratory.

One of the main findings of this study was the nature of the PRRSv detection within and between weeks and rooms of a given herd. Among all farms there was intermittent weekly detection of PRRSv using PF in 15 occasions, and using FOF in 7 occasions. Within the same week, intermittent results were observed 22 times with PF and 12 times with FOF between rooms. This clearly demonstrates the crucial importance of continuously monitoring on a weekly basis, and also sampling as many rooms as possible in an attempt to minimize misclassification of farm based on the test results of a single room.

Another important finding was the need to keep sampling farms repeatedly over time to gain confidence that PRRSv is no longer circulating. There was one farm that achieved 11 weeks of consecutive negative results with PF, and that tested PCR-positive on FOF twice. PF is a great specimen to ‘screening’ farrowing rooms for PRRSv. When there is failure to detect virus in PF for a few weeks, there is the need to ‘double-check’ the status of due-to-wean litters. FOF is a great tool in that stage.

Results provide insights for the design of improved diagnostic monitoring programs for farms attempting PRRSv elimination by suggesting a combination of PF and FOF for an increased chance to detect the virus in the suckling pig population. Also provides evidence of the intermittent nature of detection in different weeks and by room within the same week with PF and FOF. This also provides evidence that a period of more than 11 weeks of consecutive negative results with PF and FOF is necessary to establish a herd as stable for PRRSv.