Oral-fluid samples for surveillance of commercial growing pigs for porcine reproductive and respiratory syndrome virus and porcine circovirus type 2 infections

Objectives: To validate the use of oral fluids to detect infections with porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) in three commercial swine herds. Materials and methods: Oral-fluid and serum samples were collected from one barn on each of three PRRSV-infected finishing sites. Six pens per barn (20 to 30 pigs per pen) were sampled repeatedly, beginning when the pigs entered the facilities (3 weeks of age), and then at 5, 8, 12, and 16 weeks of age. Serum samples were tested using a commercial PRRS ELISA. Both serum and oral-fluid samples were tested for PRRSV by quantitative reverse-transcriptase polymerase chain reaction (PCR), and oral fluids were tested for PCV2 by quantitative PCR. Results: Site One pigs seroconverted to PRRS at 8 to 12 weeks of age, and Site Two and Three pigs at 5 to 8 weeks of age. At all sites, individual serum samples tested PCR-negative for PRRSV in pigs 3 and 5 weeks old, while > 1 sample tested positive in pigs 8, 12, and 16 weeks old. Overall, there was 77% agreement between oral-fluid and serum pen-level results. At all sites, PCV2 was repeatedly detected in oral fluids. Implications: Oral-fluid samples may be used to monitor PRRSV and PCV2 infections in commercial production systems. PRRS virus is detectable in oral fluids for 3 to 8 weeks, and PCV2 may be detectable for > 8 weeks. Sampling at 2- to 4-week intervals is recommended for surveillance of PRRSV and PCV2.