Genotypic diversity and immunological implications of porcine circovirus: Inspiration from PCV1 to PCV4

Porcine circovirus (PCV) is a group of DNA viruses that cause diseases in pigs, with multiple genotypes ranging from PCV1 to PCV4. PCV1 is generally considered non-pathogenic, while PCV2 can cause severe immune system damage, especially associated with porcine multisystemic wasting syndrome (PMWS). PCV2 has a genetic homology of about 68 % but differs from PCV1 in antigenicity and phenotype. PCV3 and PCV4 have lower genetic homology with PCV1 and PCV2, with limited research available on their pathogenicity. During virus infection, the host's innate immune system detects PCVs through pattern recognition receptors (PRRs) like TLRs and NLRs. PCV disrupts immune pathways, including interferon and NF-κB pathways, aiding viral replication and causing immunosuppression. This review systematically compares the characteristics and pathogenicity of different genotypes of PCV and their interactions with the host's immune system, aiming to better understand the mechanisms of PCV infection and provide a theoretical basis for prevention and treatment.