SHIC-Funded Study Examines Piglet Postmortem Sampling for PRRS Detection

With a goal to provide welfare-friendly and cost-effective methods for active PRRSV surveillance, Drs. Cesar Corzo, Mariana Kikuti and colleagues from the University of Minnesota led a study to evaluate the accuracy of different postmortem specimens collected from piglets in breeding herds for disease detection. Funded by the Swine Health Information Center, the study focused on the sensitivity of PRRSV detection by PCR across six sample types, including nasal, oral, and rectal swabs, tongue-tip fluids, superficial inguinal lymph nodes, and intracardiac blood. Overall, investigators concluded that oral swabs and lymph nodes showed the best diagnostic performance. Tongue-tip fluids had high sensitivity (92.2%) but low specificity (53.9%) due to likely environmental contamination and may be a less suitable sample type for individual pig diagnosis.

Published by mdpi.com, you can find the entire piglet postmortem sampling study here, including citations for content included in this summary.

In the US, PRRS continues to be the primary health challenge faced by swine herds. PRRS outbreaks afflict a significant portion of US breeding and growing herds, causing a major economic impact and production losses across the industry. The estimated weekly PRRS virus prevalence was 20%–40% between 2019 and 2023 in US breeding herds, according to the SHIC-funded Morrison Swine Health Monitoring Project.

Traditionally, PRRS surveillance efforts in breeding herds have heavily relied upon live animal sampling methods, including individual pig-level serum, oropharyngeal and nasal swabs, along with group-level oral fluids and environmental samples. Live animal specimens collected directly from individual pigs tend to have higher analytical sensitivity, the ability to detect a true positive sample, when compared to the group or environmental specimens. However, individual pig sampling poses labor and logistical challenges including concerns for staff safety and animal welfare.

Monitoring the dead piglet population through sampling tongue-tips for PRRS diagnosis has been proposed by European researchers (Baliellas et al., 2021) as an alternative to processing-fluids surveillance for PRRS and was quickly adopted in the US as a complementary specimen when monitoring breeding herds. In the study described herein, the aim was to determine the sensitivity of PRRSV detection across six postmortem sample types collected from dead piglets in US breeding herds.

Three Midwestern US farrow-to-wean farms undergoing PRRS elimination after an outbreak were utilized as the study population. Farms that utilized PRRS-modified live virus vaccination protocols for sows or piglets were excluded. Farm size ranged from 2500 to 5000 sows and all farms were representative of modern pig production and have year-round negative-pressure air-filtration systems.

For each farm, 30 and 60 samples were collected at eight and 20 weeks, respectively, after the PRRS outbreak. Postmortem samples included nasal swabs, oral swabs, rectal swabs, tongue-tip fluids, superficial inguinal lymph nodes, and intracardiac blood. All samples were tested for PRRSV RNA using RT-PCR. Intracardiac serum served as the gold standard for calculating the sensitivity, specificity, and predictive values of other post-mortem specimens.