Does porcine circovirus type 3 (PCV3) interfere with porcine circovirus type 2 (PCV2) vaccine efficacy?

PCV2 is globally spread pathogen involved in a number of diseases (PCVD). Commonly used vaccines against PCV2 are proved to be highly efficacious. The role of recently discovered PCV3 for pig health and interference with PCV2 remains unknown. The study performed on serum samples from seven farms vaccinated against PCV2 and four non-vaccinated showed very low prevalence of PCV2 viremia in the former (3 out of 106 positive serum pools) and high prevalence of PCV2 viremia in the latter (35 out of 60 positive pools). Mean log₁₀ PCV2 genome equivalents were lower in vaccinated farms (4.8 ± 0.6 log₁₀  copies/ml) than in non-vaccinated farms (6.3 ± 1.3 log₁₀  copies/ml). PCV3 was detected in 31 out of 106 and 12 out of 60 serum pools from vaccinated and non-vaccinated farms, respectively. Mean log₁₀ PCV3 genome equivalents were significantly (p < 0.05) lower in vaccinated farms (3.9 ± 0.8 log₁₀  copies/ml) than in non-vaccinated farms (4.4 ± 0.6 log₁₀  copies/ml). Concurrent PCV2 and PCV3 infection was rare and found only in 1 out of 529 and 4 out of 292 individual serum samples from vaccinated and non-vaccinated farms, respectively. Our results showed lack of impact of PCV3 circulation on PCV2 vaccine efficacy. On the other hand, intensive PCV2 circulation and high viremia detected in non-vaccinated farms did not seem to increase the level of PCV3 infection.