This pilot study evaluated the impact of sharing ropes for sample collection between an infected pen and an uninfected pen. Further, it evaluated how the detection of a pathogen changed as the prevalence increased. Three pens of 24 to 27 pigs that were 12 weeks old and approximately 35 pounds at the beginning of the project were used. Pens #1 and #3 were infected pens, and the middle pen (Pen #2) was a control. Hard siding was placed between the pens to prevent direct contact of the pigs. To mimic infection, we used a modified live (MLV) porcine reproductive and respiratory syndrome virus (PRRSV) vaccine (Ingelvac) given intramuscularly in the neck muscle behind the ear. One pig in pen #1 and #3 were vaccinated on day 0. Individual serum and nasal swab samples were collected over a 21-day period along with pen-level oral fluid samples. Pen #1 had a single dedicated rope and a shared rope with Pen #2. Pen #3 had two dedicated ropes and one shared rope with Pen #2. Pen #2 had a dedicated rope as well. This study was done in duplicate. One set of pens successfully transmitted the vaccine strain of the virus showing a linearly increasing prevalence based on serum samples. Nasal swabs were consistently positive, but they did not show a reliably increasing prevalence. The dedicated oral fluid rope sample in Pen #1 had the most consistent and reliable detection, starting at day 6 post vaccination and remaining positive through the study. The shared rope from Pen #1 and #2 was positive on day 6, 15, and 21, but negative on day 9, 12, and 18. Pen #2 and #3 had a similar result, although Pen #3 tested positive later despite having a similar prevalence to Pen #1; it was also negative on day 18 so it had a lesser consistency. The shared rope was positive in only 66.7% of the time points that at least one of the two dedicated oral fluid rope samples from Pen #3 was positive. The other set of pens did not spread the vaccine variant as efficiently. The only difference between the sets of pens was that the side that spread the variant also had a draft form the ventilation exhaust fans, which may have added enough environmental stress to lead to shedding and direct contact transmission. Both control pens remained negative reducing consideration of air born transmission. Shared rope samples likely limit detection of pathogens in low prevalence setting and this may extend to sample pooling as well. Further studies should be done to confirm these results.

Key Findings:

  • Oral fluid samples collected by sharing a rope across an infected an uninfected pen did not lead to the detection of a pathogen as readily as pen dedicated ropes.
  • Using multiple dedicated ropes (2) in a pen delayed detection compared to the pen with a single dedicated rope.
  • PRRSV MLV vaccine can be used to mimic infections in a pen with a mild additional stressor.