PCV2 shedding profiles in oral fluid on clinically and sub-clinically affected farms.

Little is known about oral fluid qPCR for PCV2, viral load and threshold values associated with clinical or sub-clinical disease. The aim of this study was to evaluate the usefulness of OF-based surveillance of PCV2 shedding on farms with or without clinical or subclinical PCVD.

Shedding of PCV2 in OF was monitored at 2-weekly intervals in six wean-to-finish all-in-all-out farms. Sampling commenced at arrival (28 days old), after being PCV2 vaccinated, and ended in the 21st week of age. Six pens (16-120 pigs/pen) were sampled on each occasion in each farm with a rope:pig ratio of 1/25. Samples were transported on chill-packs to the laboratory (SAC, Penicuik, Edinburgh) where DNA was extracted (MagMax™ Pathogen RNA/DNA kit, Thermo Fisher Scientific®) and analyzed by qPCR (LSI VetMAX™ Porcine Circovirus Type 2– Quantification, Thermo Fisher Scientific®). Complementary necropsy samples of lung or lymph nodes were submitted for histological and immunohistochemical evaluation.

Farms 1, 2, 3, and 4 reported low total mortality (2.7% – 3.7%). Wean-to-finish average daily gain (ADG) from ranged from 790 to 875 g/day. Maximum levels of PCV2 in OF were < 5x103 PCV2 copies/mL and shedding was found on all farms at most timepoints in > 1 of the six sampled pens. There was no evidence of PCV2 capsid protein detected by immunohistochemistry (IHC) in post-mortem samples.

Farm 6 reported total mortality of 8%, low ADG (under 800 g/day against expected ≈830g/day) and PCV2 load exceeded 1x10⁶ copies/ml in most of pens at 11 weeks of age and ranged between 10⁴ and 10⁵ copies/mL until finishing age in all pens. In 4/14 pigs, an interstitial pneumonia associated with positive IHC labelling confirmed clinical PCVD in these animals.

Farm 5 reported low mortality (1.6%) and an ADG of 830 g/day, a lower gain than expected. PCV2 levels in OF were markedly higher in one pen compared to the other 5 pens from week 7 (10⁵ copies/mL) through to week 21 (10^7.9 copies/mL). The other 5 pens presented values < 10³ copies/mL until week 19 when they rose to 10⁴ copies/mL. A single focus of positive PCV2 labelling was found in the bronchial gland of one animal out of 2 tested.

Levels of PCV2 detection in OF differed between three farm categories, namely those with no evidence of active PCVD, a farm affected by clinical PCVD, and a farm in which subclinical PCVD was suggested.

More studies are needed to determine the sampling requirements and virus copy thresholds that could define a range of potential PCVD-associated scenarios. This study demonstrates the potential benefit of qPCR PCV2 testing in OF in commercial conditions to monitor PCV2 status in farms.

Disclosure of Interest: J. Hernandez-Garcia Conflict with: Zoetis, Conflict with: University of Cambridge, N. Robben Conflict with: Thermo Fisher Scientific, D. Magnee Conflict with: Thermo Fisher Scientific, C. Pettit: None Declared, I. Dennis: None Declared, T. Eley: None Declared, H. M. Martineau: None Declared, D. Werling: None Declared, S. M. Kayes: None Declared, J. R. Thomson: None Declared, A. W. Tucker: None Declared.