Can swabs replace serum for PRRSV surveillance at weaning?

Problem: PRRSV surveillance in piglets at weaning is challenging when viral prevalence is low, and few alternative sample types to serum had been characterized in this population.

Methods: In three PRRSV-positive herds, 666 piglets from 55 litters were sampled using serum, ear-vein blood swabs, nasal swabs, oral swabs and family oral fluids; samples were tested by RT-qPCR individually and, for swabs, in litter pools.

Takeaway 1: PRRSV was detected in serum from 96 piglets, compared with 80 ear-vein blood swabs, 80 oral swabs and 72 nasal swabs.

Takeaway 2: The probability of PRRSV detection in pooled swabs reached ≥95% when ≥23% of ear-vein blood swabs, ≥27% of oral swabs or ≥26% of nasal swabs were positive.

Takeaway 3: To detect at least one infected piglet with 95% confidence at prevalence ≥10%, estimated sample sizes were 30 for serum, 36 for ear-vein blood swabs, 36 for oral swabs and 40 for nasal swabs.