Can the processing-fluid toolbox expand beyond PRRS?

Piglet processing fluids have been shown to be a practical, time-efficient and affordable diagnostic tool for porcine reproductive and respiratory syndrome (PRRS), and some indications suggest that porcine circovirus type 2 (PCV2) offers promise as well. That has prompted veterinarians to question whether processing-fluid testing could be expanded further to monitor other common viruses.
calendar icon 18 September 2020
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“Processing fluids represent 50% to 70% of the submissions tested for PRRS virus from samples collected from suckling piglets,” Giovani Trevisan, DVM, graduate research assistant at Iowa State University, told Pig Health Today. “So, could we maximize the collection of one sample to test for other agents?”

Trevisan set up a two-part study to look deeper into processing-fluid testing for PCV2, as well as investigate the prospect for porcine epidemic diarrhea virus (PEDV) and porcine delta coronavirus (PDCoV).1

A two-study design

The PCV2 study involved four sow farms — two PRRS-negative (ELISA naïve) and two PRRS-positive. Trevisan’s team collected processing-fluid samples by room and pooled them for PCV2 testing by polymerase chain reaction (PCR) according to placement groups in wean-to-finish barns. Pig groups were placed into those barns as PCV2-positive or PCV2-negative based on PCR results. All pigs were vaccinated for PCV2 at weaning.

Trevisan followed the pigs downstream and collected data on culls, mortality, average daily gain (ADG), feed efficiency (FE) and average days to market (ADM).

For the PEDV and PDCoV portion of the study, processing-fluid samples were collected daily and tested using reverse transcription polymerase chain reaction (RT-qPCR), following two outbreaks of PEDV and one outbreak of PDCoV. The processing-fluid samples were pooled by room, day and week of collection and tested for 2 weeks prior to and for 4 weeks after the outbreaks.

The results

Trevisan noted that an intermittent pattern of PCV2 detection was observed in the sow farms, with only one farm recording PCV2-negative results for more than 5 weeks. As for the pigs, the PCV2-negative groups had 2% higher total losses (mortality and culls) than the PCV2-positive pig groups.

“We were not expecting that,” Trevisan said. “We always suspect the positive groups are going to have higher morality and higher impact on the downstream performance.” He added that more study is needed to determine why this occurred and whether it is a consistent outcome.

Notably, there were no differences in ADG, FE or ADM between the positive or negative PCV2 groups. Additionally, there were no differences between wean-to-finish groups coming from PRRS-negative or PRRS-positive sow farms that recorded PRRS-negative RT-qPCR tests using processing fluids.

“For PEDV, we could not find it using processing fluids,” Trevisan said. “So, we are not able to use processing fluids to detect PEDV before the outbreak.”

On the other hand, the study showed that PDCoV could be detected in processing fluids 6 days before a clinical outbreak on the sow farm, and positive tests continued for 17 days thereafter.

Take-home messages

In the end, Trevisan concluded that fecal and intestine-tissue samples continue to be the optimal choice for PEDV testing.

Processing fluids are a useful tool in monitoring PCV2 status in piglets and can be used to classify positive or negative pig groups at placement into weaning. Processing fluids also can be used for PDCoV monitoring. “But in any case, you always need to have a plan to use those results and take action to minimize the impact of those agents and improve animal health,” he said.

1 Trevisan G, et al.
Increasing the functionality of your processing fluid toolbox beyond PRRS monitoring: PCV2, PEDV and PDCoV.. 51st Am Assoc Swine Vet Annual Meeting. 2020;27.

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