Porcine Reproductive and Respiratory Syndrome Surveillance in breeding Herds and Nurseries Using Tongue Tips from Dead Animals

Abstract

The detection capacity of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) in tongues from dead animals in breeding herds (stillborns and piglets dying during the lactating period) and nursery farms (naturally dead animals) for PRRSV surveillance was evaluated. The samples were selected if pairs of serum and tongues were available from 2018 to 2020. Serum (pools of five) and exudate from tongues (one bag) were analyzed by PRRSV RT-PCR. The agreement between the serum sample procedure versus tongues exudate was assessed using a concordance test (Kappa statistic) at batch level. A total of 32 submissions, corresponding to 14 farms, had PRRSV diagnostic information for serum and tongues exudate. The overall agreement of batch classification as positive or negative, based on RT-PCR PRRSV results, between serum and tongue exudate of the 32 pairs was 76.9%. Cohen’s Kappa was 0.55. The main discrepancy came from the presence of positive samples in tongues exudate and not in serum, suggesting that tongue exudate to monitor PRRSV seems to be more sensitive than serum. These results suggest that this sample procedure could be also used for PRRSV surveillance and monitoring.

Porcine reproductive and respiratory syndrome virus RNA detection in tongue tips from dead animals

“…Interestingly, the average Ct value from tongue tips was numerically lower than the average Ct value from serum samples in newborns (<24 h). This finding agreed with Baliellas et al ( 13 ), and it might be explained by the fact that tongue tips were derived from dead animals, which were potentially more likely to harbor PRRSV. Additionally, PRRSV viremia can be detected 6 to 48 h post-infection ( 17 ), and PRRSV RNA-positive tongue tips from neonatal pigs were demonstrated in this study to be great indicators of PRRSV activity in the breeding herd and could be an alternative tool to umbilical cords ( 18 ), serum, and placenta to characterize vertical transmission in stillbirths.…”

“…Baliellas et al ( 13 ) reported that the optimum number of tongue tips per bag was 30 to 100 to obtain enough exudate for PCR testing. However, in this study, tongue tips were collected by room and pig age group, with the number of tongues per bag limited by the number of daily dead pigs.…”

“…Tongue tips were held from the dead piglets with Russian Tissue Forceps, severed with Mayo Dissecting 6.5” Straight Blunt Scissors from each age group (approximately 2 cm), and placed in a disposable plastic bag ( Figure 2 ). Following sampling, tongue tips were frozen at −20 °C, as previously described by Baliellas et al ( 13 ).…”

“…However, the current population-based sampling schemes commonly used for PRRSV monitoring do not cover all pig production phases, e.g., newborn piglets and gestating sows. In cases in which the application of individual- and population-based samplings are limited, new methods have been proposed to monitor PRRSV infection, such as the usage of “tongue tips” ( 13 ). Tongue tip sampling consists of collecting a fragment of tongue tissues from dead animals and could be used in breed-to-wean herds for PRRSV surveillance ( 13 ).…”

“…In cases in which the application of individual- and population-based samplings are limited, new methods have been proposed to monitor PRRSV infection, such as the usage of “tongue tips” ( 13 ). Tongue tip sampling consists of collecting a fragment of tongue tissues from dead animals and could be used in breed-to-wean herds for PRRSV surveillance ( 13 ). Given that approximately 36% and 40% of the piglet losses happen during the first and from the second to the seventh day of life, respectively ( 14 ), collecting tongue tips from dead pigs for monitoring and surveillance may be an effective way to sample a large number of pigs in the farrowing room.…”