Porcine circovirus type 2 (PCV-2) continues to be one of the most important pig diseases. Since 2006 when PCV-2 vaccines first became available the control of PCV-2 has been nothing less than remarkable even as the virus has been slowly evolving over time. ( Eg PCV-2d increased prevalence.) Many in the industry have been wondering if that stellar vaccine performance will be lost if the virus changes too much. In the past veterinarians have commented about sporadic cases of clinical PCV-2 that has ultimately been determined to have been related to vaccine storage issues, vaccine administration errors, excessively fractionated dosages or changes in vaccine timing. Normally when these issues are addressed the control of PCV-2 will improve. Sow herd instability with increased numbers of PCV-2 viremic piglets at birth, increased PCV-2 shedding by sows and the subsequent increased “infectious pressure” can also set off increased clinical disease. PCV-2 viremic piglets at birth may also be less responsive to vaccination.
These Brazilian researchers wanted to investigate the PCV-2 viremic status of pre-suckling piglets and the PCV-2 status in sows. There were 18 breeding farms enrolled in this study. Participating herds needed to have more than 1,000 sows; sows were not vaccinated for PCV-2 for at least for 2 years prior to the study; farms had no history of PCV-2 clinical disease in the last 12 months; and production systems had a maximum of two sites. Blood samples were taken from the umbilical cords in sow placenta. In addition blood was collected from presuckle piglets from 30 litters on each farm and tested for PCV2 PCR. In addition, blood from 538 sows was collected for PCV-2 antibody detection.
The researchers found the following:
- 17.29% of the placental umbilical cord serum samples (PUCS) from all farms tested positive for PCV-2. Figure 1 ( Highest farm was 86.7% and lowest farm was 0%)
- 94.4% of farms had at least 1 placental umbilical cord sample testing positive for PCV-2
- 94.8% of the sows in the study were positive for PCV-2 antibodies.
- 44.4% of the farms , however, had at least 1 PCV-2 seronegative sow .
- All 18 farms enrolled in the study had at a minimum 46.9% seropositive dams.
- A higher percentage of seronegative sows was observed for farms with more than 10% of PCV-2-positive litters compared to those with ≤10% of PCV-2 positive litters (8.9 +/-1.7% vs. 1.5 +/- 0.7%, p < 0.01, respectively).
Take Home Messages:
- This study suggests that as the percent of PCV-2 seronegative sows increases the percent of PCV-2 positive litters increases. The researchers commented several times that on occasion replacement gilts that are vaccinated for PCV-2 at weaning will lose their vaccine protection by the time they are selected as breeding stock. If they have not been exposed to PCV-2 before becoming pregnant they will be at increased risk of generating PCV-2 viremic piglets at birth.
- The researchers commented that the presence of pre-suckling viremic piglets has been associated with a higher chance of horizontal transmission of PCV-2 among littermates, increasing the number of infected piglets at weaning. When pigs are infected very early in life they will go on to develop clinical signs more quickly. Even if these viremic piglets are subclinical it may only take a few extra stresses or coinfections to “tip” them into clinical disease
Reference: Ricardo T Lippke , Elisa R De Conti , Luciana F Hernig , Angélica P Teixeira , Fernando A de Quadros , Aparecida T Fiúza , Juliana B Pereira , Rafael da Rosa Ulguim , David E S N Barcellos , Karine Ludwig Takeuti Assessment of sow herd frequency of PCV-2 using placental umbilical cord serum and serology in 18 breeding farms in Brazil Front Vet Sci . 2024 Apr 8:11:1368644. doi: 10.3389/fvets.2024.1368644. eCollection 2024.
