Indirect assessment of porcine reproductive and respiratory syndrome virus status in pigs prior to weaning by sampling sows and the environment.

There is a need to develop cost effective approaches to sample large populations in particular to determine the disease status of pigs prior to weaning. In this study we assessed the presence of the porcine reproductive and respiratory syndrome virus (PRRSV) in the environment (surfaces and air) of farrowing rooms, and udder skin of lactating sows as an indirect measure of piglet PRRSV status. Samples were collected at processing and weaning every three weeks for 23 weeks after a PRRSV outbreak was diagnosed in a swine breeding herd. PRRSV was detected at processing in udder skin wipes, environmental wipes and airborne deposited particle samples up to 14 weeks post outbreak and at weaning in udder skin wipes up to 17 weeks post outbreak. Similar sensitivities were observed for udder skin wipes (43% [95% CI: 23%-66%]) and surface wipes (57% [95% CI: 34%-77%]) when compared to serum at the litter level from piglets at processing. PRRSV was detected in the environment and the udder skin of lactating sows, which indicates that aggregate samples of the environment or lactating sows may be used to evaluate the PRRSV status of the herd in pigs prior to weaning. However, the use of environmental samples to detect PRRSV by RT-PCR should not be used as the single method to assess the PRRSV status at the litter level. Furthermore, our findings also highlight potential sources of PRRSV infection for piglets in breeding herds.

Effect of litter aggregation and pooling on detection of porcine reproductive and respiratory virus in piglet processing fluids.

A sampling technique has been validated to monitor porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) using the serosanguinous exudate known as processing fluids (PFs) that accumulate from tissues obtained during tail docking and castration. PFs are an aggregate sample of large numbers of piglets and litters. However, little is known about the effect of litter aggregation on the ability of PCR to correctly classify an aggregated PF sample as positive. We evaluated both the effect of litter aggregation and of PF pooling on PCR detection. We estimated that aggregation of at least 50 litters was possible when a pig with a Ct value of ~22 was present in the sample, and aggregation of up to 40 litters was possible when there was a sample with a Ct value of ~33. Pooling did not affect PCR detection when initial Ct values of 20 and 25 were assessed. However, in litters with initial Ct values of ≥30, the amount of pooling should be reduced. Our results provide producers and practitioners with a general framework to interpret more accurately the results of their PRRSV-2 surveillance programs using PF.

Use of processing fluids and serum samples to characterize porcine reproductive and respiratory syndrome virus dynamics in 3 day-old pigs.

Collection of serum samples of pigs at weaning to monitor for porcine reproductive and respiratory syndrome virus (PRRSV) has become a common practice to determine PRRSV herd infection status. Diagnostic sensitivity of this practice is low in herds undergoing PRRSV elimination once prevalence of infection is near zero. Thus, the goal of this study was to characterize the dynamics of PRRSV infection in 3 day-old pigs overtime using serum and serosanguineous fluids obtained as part of castration and tail docking practices (processing fluids (PF)). Secondary goal was to estimate sensitivity and specificity of PF in the 3 day old population. A 6000 breed-to-wean sow herd was monitored every three weeks for 23 weeks after a PRRSV outbreak by collecting both PF and individual serum samples from all pigs in the selected litters. Out of the 77 litters tested, 23 (29.8%) were identified as positive using the PF and the serum samples, with a Cohen's kappa statistic of 0.81 (95% CI: 0.59-1) between the results obtained in each sample type. The sensitivity and specificity of the PF relative to the results in serum was 87% (95% CI: 66%-97%) and 94% (95% CI: 85%-99%) respectively. The percentage of PRRSV positive litters decreased over time and litters from gilts were more likely to test positive than those from older sows. Overall, the study demonstrates that PF can be a convenient and reliable specimen to monitor PRRSV infection in breeding herds.