NAPRRS: Post-mortem sampling from growing pigs

Most post-weaning sampling relies on oral fluid samples since jugular venipuncture can be time-consuming and requires skilled personnel. Assessing whether easy to collect post-mortem samples can provide value for diagnosis and monitoring in the post-weaning stages is necessary as this methodology can be adopted by industry when resources are scarce, even though they are not the gold standard specimen.

Those samples are:

• Tongue tip fluid (TTF)
• Intracardiac blood (IC)
• Oral/nasal swabs (ONS)
• Rectal swabs (RS)
• Superficial inguinal lymph nodes (SILN)

The objectives of a study by C.M. Melini and colleagues at the University of Minnesota were:

• Assess the sensitivity and specificity of TTF, ONS, and SILN in growing pigs when compared to IC, in presence of porcine reproductive and respiratory syndrome virus (PRRSV),
• Describe detection of porcine circovirus type 2 and 3 (PCV-2, PCV-3), porcine parvovirus type 1 and 2 (PPV-1, PPV-2), Lawsonia intracellularis (Li), and Influenza A virus (IAV), through RT-PCR of collected post-mortem samples (e.g., TTF, ONS, RS, SILN). The results of the study were presented at the 2024 North American PRRS Symposium.

One wean-to-finish farm group of pigs undergoing a PRRS outbreak was sampled when animals were 5 weeks of age (WOA) and 11 WOA. A second group of growing pigs undergoing a similar health challenge was sampled at the grow-finish farm at 15 WOA at a different location. During each sampling event, 30 dead pigs were included in the study for a total sample of 90 pigs.

Besides TTF, the other collected post-mortem specimens were IC (for PRRSV), ONS (for IAV and PRRSV), RS (for PPV and Li), SILN (for PCV and PRRSV), all samples were tested individually through RT-PCR. The sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) were calculated for PRRSV. Proportion of RT-PCR positive results from sample types tested for other pathogens were compared by descriptive statistics.