Today, we are sharing a recent publication from the MSHMP team comparing different piglet postmortem samples to detect PRRS. The article is available in open access on the Journal’s website.

Methods

• Three farrow-to-wean farms in the U.S. undergoing PRRSV elimination after an outbreak were selected for sampling.
• 30 and 60 samples were collected at 8 and 20 weeks after PRRSV outbreak detection, respectively.
• Postmortem samples included: nasal swabs (NS), oral swabs (OS), rectal swabs (RS), tongue-tip fluids (TTF), superficial inguinal lymph nodes (SIL), and intracardiac blood.
• Blood samples from piglets in the same room as the ones used for post-mortem specimens were used to establish PRRS prevalence within the farm.
• All samples were tested for PRRSV using RT-PCR.
• Intracardiac sera served as the gold standard for calculating the sensitivity, specificity, and predictive values of other post-mortem specimens.

Results

• PRRSV was detected in all specimen types and at all sampling points, except for Farm 2 Visit 2 and Farm 3 Visit 2, where swabs (oral, nasal, rectal) and intracardiac sera did not detect the virus, respectively.
• Oral swabs and lymph nodes showed the best overall diagnostic performance:
  • Sensitivity ranged from 94.6% to 100%.
  • Specificity ranged from 83.9% to 85.1%.
  • Negative predictive values were 97.3% to 100%.
• Tongue-tip fluids had high sensitivity (92.2%) but low specificity (53.9%), indicating a potential for environmental contamination affecting results.
• Nasal swabs and rectal swabs had moderate sensitivity and specificity, indicating some diagnostic utility but less accuracy compared to oral swabs and lymph nodes.
• The agreement between postmortem specimens and intracardiac sera was highest for SIL (88.89%), followed by OS (87.10%) and NS (85.48%).
• ORF5 sequencing was successful in 29 out of the 31 tongue-tip samples.

Abstract

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.