A novel chicken infectious anemia virus vaccine candidate: complete attenuation, strong immunogenicity, and a...

Chicken infectious anemia virus (CIAV) is a globally important immunosuppressive pathogen of poultry, causing anemia, impaired immunity, and production losses. Current live-attenuated vaccines have practical limitations: incomplete attenuation restricts safe use to older birds (e.g. ≥ 6 weeks), while over-attenuation can reduce in-vivo replication and manufacturable vaccine titers. To address these gaps, we serially passaged the virulent Korean field strain 17AD008 in MDCC-MSB1 cells for 200 generations, generating two attenuated derivatives, P45 and P100. Pathogenicity and replication were evaluated in SPF chicks, followed by a homologous immunization-challenge model. Early host responses were analyzed by thymic immune-related gene expression profiling, and a novel multiplex PCR assay targeting a unique single nucleotide polymorphism (SNP; A750G) in the overlapping VP2/VP3 coding region of P100 was developed as a molecular DIVA (Differentiating Infected from Vaccinated Animals) tool. P100 was fully attenuated yet retained replication in lymphoid tissues, unlike P45, which caused anemia and thymic atrophy. Notably, P100 induced stronger early antiviral and pro-inflammatory transcriptional responses than parental strain without associated pathology. In homologous challenge studies, P100 administered at four weeks prevented thymic lesions and anemia, substantially curtailed cloacal virus shedding, and elicited higher CIAV-specific antibody titers. The multiplex PCR assay targeting the VP2/VP3 SNP (A750G) unambiguously distinguished P100 from field isolates, with 100% sensitivity and specificity. In conclusion, these data identify P100 as a DIVA-compatible live-attenuated CIAV vaccine candidate that combines complete attenuation, robust immunogenicity and transmission-blocking potential, warranting field evaluation for cross-genotype protection and large-scale production stability.