Oral fluid samples for the monitoring of PRRSV status and dynamics

Approximately 40 % of Danish swine herds are positive for PRRSV. PRRSV is secreted in nasal and oral fluid and can be detected in serum for weeks after infection. To control PRRSV it is critical to monitor the PRRSV status in different production stages. Information on ongoing PRRSV infection is normally obtained by test of serum which is laborious and stressful for the pigs. The aim of the study was to test if test of oral fluids can replace serum for PRRSV monitoring in Danish sow herds.

A total of 14 PRRSV positive sow herds accommodating a nursery section were included. In each herd, oral fluids (1 per pen) and blood samples (pooled from 5 pigs per pen) were collected from four pens in each of three age groups of weaner pigs. The samples were subsequently tested for PRRSV by a specific real time RT-PCR assay. The pen level agreement between the test result in the two types of sampling material (serum and oral fluid) was analysed with the Kappa statistics.

From the herds where at least one serum sample tested positive for PRRSV, one isolate of PRRS was sequenced for ORF5. The sequences were analyzed phylogenetically.

Of the 14 herds, 9 tested positive for PRRSV in both oral fluid and in serum in at least one of the pens. Similarly, in two herds, all oral fluid samples and all serum samples were negative in all pens tested. In one herd, at least one pen tested positive in oral fluids despite being negative in all serum samples and similarly, in one herd at least one pen tested positive serum in despite all oral fluids tested negative.

In total, paired samples of serum and oral fluid were available from 147 pens. Sixtyfour (64) pens were positive in serum and of those 61 were positive in oral fluid, too. Sixty-nine (69) pens tested positive in oral fluids. Seventy-five (75) pens tested negative in both serum and oral fluid. The Kappa value for agreement between the two types of sampling material was 0.85, which translates to “Almost perfect” agreement.

ORF5 sequencing of four Type 1 isolates showed that they all clustered together with other Lelystad-like Type 1 viruses from Denmark. Sequencing of the Type 2 viruses is ongoing.

The results showed that oral fluid is as sensitive as serum samples for the monitoring of PRRSV status and dynamics in Danish sow herds.

Disclosure of Interest: None Declared.