Comparative Pathogenicity of PCV2, PCV3, and PCV4 in Piglets: Insights Into Clinical, Pathological, and Immunological Features.

Porcine circoviruses (PCVs) have been a significant concern in swine health, with PCV2 being a well-established pathogen. However, the newly discovered PCV3 and PCV4 have emerged, and their impact on piglets remains less understood. Understanding their pathogenicity is crucial for effective porcine health management. In this study, 3-week-old piglets were inoculated with PCV2, PCV3, and PCV4. PCV2 led to expected growth inhibition and severe clinical signs like anorexia. PCV3, though showing milder symptoms, exhibited unique tissue tropism, with detectable virus in the heart, lungs, and brain tissues. PCV4 caused distinct tissue damage, including cardiac fibrosis and renal changes. In terms of immune responses, each virus triggered different cytokine profiles. PCV3 and PCV4 also demonstrated replication capabilities in vitro and in vivo. PCV3 and PCV4 clearly have pathogenic patterns that differ from those of PCV2. These findings provide essential insights for veterinarians and swine producers. Understanding these viruses' behavior aids in developing targeted prevention and control strategies, such as improved diagnostic tools and potential new vaccines, to enhance porcine health management and safeguard the swine industry from the threats posed by these emerging PCVs.