Drs. Mariana Kikuti, Jeff Kurt, and Cesar Corzo describe the timeline of a PRRS introduction in a breeding herd in this week’s science page.
Key Findings
- By tracing the introduction event with high certainty, this report provides valuable insights into the onset of production parameter changes following PRRSV introduction.
- The virus was introduced approximately 4 to 5 weeks before a noticeable impact on production parameters.
- The peak productivity impact occurred between 7 to 10 weeks after introduction.
Background
This peer-reviewed case reported details a porcine reproductive and respiratory syndrome virus (PRRSV-2, variant 1C.5) introduction into a 5,000 breed-to-wean sow farm in Minnesota. The breeding herd had historically been PRRSV negative (category IV for at least 4 years. The farm raised their own replacement gilts by weaning them into an off-site nursery-finisher site located approximately 80 miles away. The gilt grow-out site was constantly monitored via monthly serology testing from 30 gilts. Three days after multiple movements between the breeding and grow-out sites, gilts recently delivered to the sow herd isolation unit presented clinical signs and later tested PRRSV positive using RT-PCR. These animals were removed from the multiplier immediately after and the sow herd began to be monitored. Although no clinical signs were observed in the farrowing room next to the isolation room loadout, 2 out of 35 pools of piglets’ blood tested positive six days after positive gilts were removed from the loadout, confirming introduction. It is highly likely that the PRRSV was introduced into the case herd through an incursion from the isolation room by the loadout. The observation of water/moisture present in the farrowing room after the hallway and loadout were washed suggests that PRRSV contaminated water could have been the source of the virus into the farrowing room population.
Timeline of disease progression within the herd
Weekly production performance records were obtained from the case herd. All the parameters assessed deviated from the expected baseline after the PRRSV introduction, which is inferred to have occurred on the days positive gilts were moved to the loadout (Figure 1). Production parameters began deviating from their baseline between weeks 4 and 7. The total weaned per litter started declining during week 4, reaching its trough at week 11. Percent stillborn, total number of abortions, total number of sows dead and euthanized, and preweaning mortality rate started increasing during week 4 and peaked at weeks 7, 8, 6, and 10, respectively. Although total live born per litter, percent mummies, and total born per litter started deviating from baseline at weeks 6 or 7, no clear peaks or troughs were observed.
Discussion
The exact introduction date from the loadout to the farrowing room is also unknown but believed to be between when the gilts were housed at the case herd isolation-loadout room up to the first PRRSV detection in the sow herd. To be conservative, the estimated time to clinical detection should be interpreted considering this 12-day margin. This suggests that if PRRS diagnosis had relied solely on practitioners identifying clinical signs within the herd, without awareness of a significant epidemiological risk such as the movement of PRRS-positive gilts, the virus might have gone undetected for 4 to 5 weeks after its introduction if there was close routine monitoring of production data. Most production parameters did not decline substantially until 6 to 8 weeks post introduction.
Find out more
This case was presented by Dr. Kurt at the 2026 Leman Conference at “Managing contemporary PRRSV variants”. The case report was also published at the Journal of Swine Health and Production and is available ahead of print.