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

Postmortem Sampling in Piglet Populations: Unveiling Specimens Accuracy for Porcine Reproductive and Respiratory Syndrome Detection

Specimens collected from dead pigs are a welfare-friendly and cost-effective active surveillance. This study aimed to evaluate the accuracy of different postmortem specimens from dead piglets for disease detection, using PRRSV as an example. Three farrow-to-wean farms undergoing PRRSV elimination were conveniently selected. Samples were collected at approximately 8- and 20-weeks post-outbreak. Postmortem specimens included nasal (NS), oral (OS), and rectal (RS) swabs, tongue-tip fluids (TTF), superficial inguinal lymph nodes (SIL), and intracardiac blood. These were tested individually for PRRSV by RT-PCR. Sensitivity, specificity, negative and positive predictive values, and agreement of postmortem specimens were calculated using intracardiac sera as the gold standard. OS and SIL had the best overall performance, with sensitivities of 94.6-100%, specificities of 83.9-85.1%, and negative predictive values of 97.3-100%. TTF had high sensitivity (92.2%) but low specificity (53.9%) and positive predictive value (48.3%). While challenges in meeting sampling targets due to variable pre-weaning mortality were noted, PRRS was detected in all postmortem specimens. OS and NS showed promising results for disease monitoring, though TTF, despite their sensitivity, had lower specificity, making them less suitable for individual infection assessment but useful for assessing environmental contamination.

Detection of PRRSV-1 in tongue fluids under experimental and field conditions and comparison of different sampling material for PRRSV sow herd monitoring

BACKGROUND

Infection with porcine reproductive and respiratory syndrome virus (PRRSV) leads to significant economic losses worldwide. One of the initial measures following an outbreak is to stabilise the herd and to prevent vertical transmission of PRRSV. The objective of this study was to detect PRRSV in different sampling material, both in an experimental model and on a commercial piglet producing farm, with a focus on evaluating the suitability of tongue fluid samples.

RESULTS

In the experimental model, PRRSV negative pregnant gilts were infected with PRRSV-1 AUT15-33 on gestation day 85 and necropsy of gilts and foetuses was performed three weeks later. 38.3% of individual foetal serum and 39.4% of individual foetal thymus samples were considered PRRSV RT-qPCR positive. Tongue fluids from individual foetuses showed a 33.0% positivity rate. PRRSV RNA was detected in all but one sample of litter-wise pooled processing fluids and tongue fluids. In the field study, the investigated farm remained PRRSV positive and unstable for five consecutive farrowing groups after the start of the sampling process. Tongue fluid samples pooled by litter in the first investigated farrowing group had a 54.5% positivity rate, with the overall highest viral load obtained in the field study. In this farrowing group, 33.3% of investigated litter-wise pooled processing fluid samples and all investigated serum samples (pools of 4-6 individuals, two piglets per litter) were considered positive. Across all investigated farrowing groups, tongue fluid samples consistently showed the highest viral load. Moreover, tongue fluid samples contained the virus in moderate amounts for the longest time compared to the other investigated sampling material.

CONCLUSION

It can be concluded that the viral load in individual foetuses is higher in serum or thymus compared to tongue fluid samples. However, litter-wise pooled tongue fluid samples are well-suited for detecting vertical transmission within the herd, even when the suspected prevalence of vertical transmission events is low.

Selection of viral variants with enhanced transmission and reduced neutralization susceptibility alongside lateral introductions may explain the persistence of porcine reproductive and respiratory syndrome virus in vaccinated breeding herds

This study investigates the long-term evolutionary dynamics of porcine reproductive and respiratory syndrome virus (PRRSV-1) in an endemically infected and vaccinated pig herd. Over a one year and a half period, piglets from seven farrowing batches in a 300-sow PRRSV-vaccinated farm were monitored from birth to nine weeks of age by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Eighty-five PRRSV-positive samples were subjected to whole genome sequencing (Illumina Miseq), and 251 samples to open reading frame 5 (ORF5) sequencing. Farm-specific PRRSV variants' impact on anti-PRRSV antibodies was evaluated using enzyme-linked immunosorbent and neutralizing antibody assays. The replication kinetics and cytokine inhibition capabilities (IFN-α and TNF-α) of these variants were assessed in porcine alveolar macrophages. The study revealed fluctuating PRRSV-1 incidences in farrowing units and nurseries, attributed to two key evolutionary events: an escape variant emergence and a lateral introduction of a new strain. Initially, strain 1 variant α was swiftly replaced within weeks by variant 1β (99.5 per cent genomic similarity), with twenty-five amino acid mutations, primarily in nsp1α, GP2, GP3, and GP5, including an additional glycosylation site and a deletion downstream the neutralization epitope of GP5. This shift to 1β correlated with increased incidence in nurseries and higher viral loads, with sera from 1α-exposed animals showing reduced neutralization against 1β. Consistently for in vitro assays, variant 1β demonstrated enhanced replication in porcine alveolar macrophages but no difference regarding IFN-α or TNF-α responses. Later, a new strain (strain 2, 83.3 per cent similarity to strain 1) emerged and led to incidence resurgence because of the low cross reactivity with the previous antibodies. The study highlights PRRSV's rapid adaptability and challenges in controlling its spread, underscoring the necessity for more effective vaccines and eradication approaches.

Alternative Samples for Porcine Reproductive and Respiratory Syndrome Surveillance in an Endemic PRRSV-1-Infected Breeding Herd: A Descriptive Study

Knowing porcine reproductive and respiratory syndrome (PRRS) status is essential for designing herd management protocols. For this, weaning-age pigs are a key subpopulation. Recently, different alternatives to blood sampling have been introduced because they are easier, welfare-friendly and cost-saving tools. Moreover, most of them allow the testing of more animals and seem to be more sensitive in low-prevalence scenarios. However, these studies were implemented mainly in PRRSV-2-infected herds. The first objective of our study was to compare the rate of detection of PRRSV-1 by RT-qPCR in individual serum samples, family oral fluid samples (FOF) and udder wipes (UW) collected the day before weaning. The second objective was to evaluate the suitability of pooling. The study was performed on a 210-sow farrow-to-finish farm which was PRRSV-1 infected and unstable. A total of 119 litters were sampled. The rate of detection of PRRSV-1 in blood samples, FOF and UW was 10.9%, 7.6% and 0.8%, respectively. The agreement between sera and FOF was almost perfect even if the detection capacity of sera was numerically superior to FOF. The Ct values of positive sera were statistically lower than those of FOF. Two modalities of pooling (1:3 and 1:5) were tested for sera and FOF. For sera, both modalities did not impact the PRRSV-1 status either at the litter level or at the batch one. On the other hand, whatever the modality (pooled by 3 or 5), most of the pools of FOF gave negative results, misclassifying many litters and batches.

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

The control of porcine reproductive and respiratory syndrome virus (PRRSV) hinges on monitoring and surveillance. The objective of this study was to assess PRRSV RNA detection by RT-PCR in tongue tips from dead suckling piglets compared to serum samples, processing fluids, and family oral fluids. Tongue tips and serum samples were collected from three PRRSV-positive breeding herd farms (farms A, B, and C) of three different age groups: newborns (<24 h), processing (2 to 7 days of age), and weaning (18 to 22 days of age). Additionally, processing fluids and family oral fluids were collected from 2–7 days of age and weaning age, respectively. In farms A and B, PRRSV RNA was detected in tongue tips from all age groups (100 and 95%, respectively). In addition, PRRSV RNA was detected in pooled serum samples (42 and 27%), processing fluids (100 and 50%), and family oral fluids (11 and 22%). Interestingly, the average Ct value from tongue tips was numerically lower than the average Ct value from serum samples in the newborn age. In farm C, PRRSV RNA was only detected in serum samples (60%) and family oral fluids (43%), both from the weaning age. Further, no PRRSV RNA was detected in tongue tips when pooled serum samples from the same age group tested PRRSV RNA-negative. Taken together, these results demonstrate the potential value of tongue tips for PRRSV monitoring and surveillance.