Abstract
Samples were obtained on four occasions from three closed pig farms for the purposes of polymerase chain reaction (PCR) tests to detect the Porcine reproductive and respiratory syndrome virus (PRRSV) and Porcine circovirus 2 (PCV-2). No clinical signs of the disease were observed on those farms. Sera for PRRSV detection and whole blood, nasal swabs, and feces for PCV-2 detection were collected from 313 pigs in 5 age groups: nursery pigs; pigs aged from 1 to 2 months, from 3 to 4 months, and from 5 to 6 months; and sows. Breakdown detection by month is as follows: in August, PRRSV in 1 and PCV-2 in 24 of 72 head; in November, PRRSV in 20 and PCV-2 in 60 of 120 head; in March, PRRSV in 0 and PCV-2 in 9 of 67 head; in June, PRRSV in 3 and PCV-2 in 27 of 72 head. Total percentages: PRRSV 24 head (7.7%) and PCV-2 120 head (38.3%). Frequency of PRRSV and PCV-2-positive pigs increased after the nursery stage. PRRSV frequency peaked among pigs aged from 1 to 2 months. PCV-2 frequency peaked among pigs aged from 3 to 4 months. After those stages, frequencies of pigs positive for PRRS and PCV-2 decreased to reach low levels in grown sows. These results suggest that the frequency of pigs positive to PRRSV and PCV-2 varies seasonally and that, on the farms studied, these infections develop rapidly after weaning.
