Processing fluids hold promise for PCV2 testing on sow farms

Understanding the pathogen status of a sow herd helps determine the prevention, control and treatment options to protect piglets as they grow. For porcine circovirus type 2 (PCV2) there is no treatment; however, vaccination is an effective option. Key to that success is understanding the sow and litter immune status and virus-exposure timing, which relies on an accurate, reliable and easy-to-collect sample for diagnosis.

Placental umbilical cord serum (PUCS) has been used to test for PCV2 on sow farms; however, the procedure is time and labor intensive. Piglet processing fluids (PF), which are easily collected, are increasingly being studied as a possible sampling vehicle for a wide range of swine pathogens.

“The convenience of PF makes it an attractive choice and may help determine vertical transmission [of PCV2] as measured by piglet viremia,” Shelby Perkins, University of Missouri veterinary student, told Pig Health Today. Consequently, she conducted a study to compare the ability of PF and PUCS to detect PCV2 in sow farms.¹

Processing the sow farms

To begin the study, four sow farms from a single production system each contributed 32 to 35 sows and litters for the project.

PUCS was collected from as many umbilical cords as possible, but samples that did not represent ≥20% of total born alive were excluded, Perkins noted.

PF from tails and testicles were collected from pigs in those same litters at 4 to 6 days of age. It’s worth noting that cross-fostered pigs were tagged and excluded from the PF sample.

“Precautions were taken to minimize cross-contamination for both PUCS and PF collection,” Perkins said. “This included dipping tools in chlorhexidine solution and changing gloves between litters.”

All samples were sent to the Iowa State University Veterinary Diagnostic Laboratory for PCV2 polymerase chain reaction (PCR) testing.

Sorting out the results

The overall finding was that PF samples had a higher PCV2 detection rate than did PUCS. (See accompanying table.) Perkins noted that this may be due to piglets being born PCV2-negative and then being infected after birth or piglets born with PCV2 virus at undetectable levels.

“Vertical transmission is not always in utero,” she said. “It may occur from the sow to piglets via the environment.”

PCV2 PCR test agreement of PUCS and PF, and percent PCV2-positive by farm and sample

Perkins noted that Farm C had more PCV2-positive PUCS compared to PF, possibly due to placental contamination or very low virus prevalence.

Based on the matched results of 66.4%, and an agreement rate calculated at 0.143, the two sample types are determined to have very low agreement.

“PF and PUCS are not directly comparable, potentially due to age differences,” Perkins said. Another prospect could be that more pigs are represented in the PF sample (11.5) versus the PUCS sample (5.5).

More research is needed, and Perkins recommended the following considerations:

• Compare more herds.
• Standardize the number and age of piglets contributing samples within a pool.
• Determine the PCV2 environmental contamination.

¹ Perkins S, et al. Comparison of processing fluids and placental umbilical cord serum to detect porcine circovirus type 2 in sow farms. Student Research Posters, 50^th American Association of Swine Veterinarians’ Annual Meeting. 2019;263.