Evaluating whether post-mortem specimens such as tongue tip fluids (TTF) can serve as a viable tool for disease surveillance during the post-weaning stages of pork production is needed. To help fill this knowledge gap, the Swine Health Information Center funded a study to determine if TTF can aid in detection of key pathogens affecting swine during the grow-finish phase, including PRRSV, porcine circovirus, porcine parvovirus, Lawsonia intracellularis, and influenza A virus. Led by Drs. Cesar Corzo and Marcello Melini at the University of Minnesota, the objectives of the study were to 1) assess the sensitivity and specificity of PRRSV detection in TTF compared to other specimens including intracardiac blood, oral/nasal swabs, rectal swabs, and superficial inguinal lymph nodes and 2) characterize the detection of PCV2, PCV3, PPV1, PPV2, Lawsonia intracellularis, and IAV across all sample types. Overall, most pathogens were detected in TTF indicating that this specimen can provide valuable post-mortem information during a diagnostic investigation.
Find the study summary on this page.
In the US, most postweaning swine health monitoring sampling relies on oral fluid collection. As labor constraints are a concern, assessing whether easy-to-collect post-mortem samples can provide value for diagnosis in these production phases is needed. Furthermore, finding practical and time-efficient methodologies to monitor health during the post-weaning stages provides value to swine health and production. With these potential advantages, industry adoption of TTF collection can help improve understanding of disease occurrence and dynamics.
Understanding whether TTF can effectively screen pathogens commonly found in postweaning pigs provides valuable insights for producers, offering potential solutions to rapidly respond and improve herd health management when conventional sampling methods are unavailable or impractical. By comparing the diagnostic performance of alternative specimens to traditional serum sampling for PRRSV and other pathogens through PCR, this research seeks to offer producers practical, cost-effective options for post-weaning disease surveillance.
To complete this study, samples were collected from two growing pig farms in Minnesota. The first farm, a 2,400-head wean-to-finish farm undergoing a PRRSV outbreak, was visited when pigs were five and 11 weeks of age. The second farm was a 3,300-head finishing site undergoing a similar health challenge as farm 1; this site was visited when pigs were 15 weeks of age. During each farm visit, a total of 30 dead pigs were sampled, resulting in a total sample size of 90 pigs. From each pig, TTF, intracardiac blood (IC), oral/nasal swabs (ONS), rectal swabs (RS), and superficial inguinal lymph node (SILN) samples were collected. Samples were tested for specific pathogens against a gold standard sample and then compared with TTF results.
All TTF samples were tested individually by PCR for all pathogens listed above. All specimens were tested individually for PRRSV. Additionally, ONS were individually tested for IAV; RS were individually tested for PPV1, PPV2, and Lawsonia intracellularis; and SILN were individually tested for PRRSV, PCV2 and PCV3. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for PRRSV TTF and IC serum as the gold standard. The proportion of PCR positive results from specimens tested for other pathogens was compared by descriptive statistics. Most pathogens were detected at least once in TTF with Ct values ranging from 11.6 to 39.8.
For other pathogens, PCV2 was detected in 43% of TTF and 11% of SILN samples whereas PCV3 was not detected in any sample. PPV1 was detected in 1% of TTF and 0% of RS whereas PPV2 was detected in 97% of TTF and 61% of the RS samples. Lawsonia intracellularis was detected in 6% of TTF and 0% of the RS samples. IAV was detected in 38% of TTF and 38% of the ONS samples.
Study data demonstrated that most pathogens were detected on TTF samples during the three different ages, indicating that this specimen can provide valuable post-mortem information during a diagnostic investigation. Detection of pathogens in TTF could be the result of shedding or environmental contamination which should be considered when practitioners are interpreting results. Further investigation is required to best report the diagnostic performance of the other alternative specimens utilized in this study. While a complete and exhaustive collection of multiple clinical specimens from different body systems remains the standard in diagnostic investigations, TTF provide an easy-to-collect sample type with low labor requirements and valuable diagnostic test results.
The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Megan Niederwerder at mniederwerder@swinehealth.org or Dr. Lisa Becton at lbecton@swinehealth.org.