Chicken infectious anemia (CIA), caused by chicken anemia virus (CAV), is an immunosuppressive disease characterized by growth retardation, aplastic anemia, lymphoid depletion, and immunodepression in young chickens. In this study, 33 CAV strains were isolated from broilers in Shandong Province during 2020–2021. Phylogenetic analysis of full-length genome sequences showed that most CAV strains isolated in this study were scattered across different branches, but mainly clustered in two genotypes, indicating a certain regional characteristic. Analysis of VP1 protein identified several amino acid substitutions which were relevant with the virulence and virus spread efficiency. Interestingly, four putative DNA recombination events were detected in the genomes of novel isolated CAV strains. In summary, this study demonstrated a genomic diversity of CAV in broilers isolated in Shandong Province during 2020–2021, and provided information for the further study of CAV molecular epidemiology and viral evolution.

Chicken infectious anemia (CIA) is an immunosuppressive disease caused by chicken infectious anemia virus (CIAV) that poses a great threat to the poultry industry worldwide. At present, vaccination is an important way to prevent and control CIA. Apart from a CIAV-attenuated vaccine used in clinical practice, the research and development of a genetically engineered vaccine has good prospects. However, it is difficult to induce a strong protective effect with a single subunit vaccine or DNA vaccine. Therefore, the goal of this study is to develop and evaluate a DNA prime/protein boost vaccine strategy for defense against CIAV infection and spread. In this study, the recombinant proteins of CIAV VP1 and VP2 were prepared using an Escherichia coli (E. coli) expression system, and the eukaryotic expression plasmid pBud-VP1-VP2 was constructed. Subsequently, the effects of the DNA prime/protein boost strategy on antibody production and cellular immunity response were measured. The results showed that combined vaccination could induce a higher antibody titer than those of a DNA vaccine or subunit vaccine alone. In addition, spleen lymphocyte index (SI) and IL-2, IL-4, and IFN-γ levels were also significant in chickens the received the combined vaccination. To further investigate the protective effect of DNA prime/protein boost vaccination, a CIAV challenge experiment was carried out. The results showed that infection with CIAV reduced the hematocrit value (Hct) and thymus index, while vaccination recovered this reduction, and the combined immunization group was the least affected by CIAV infection. Furthermore, the CIAV viral load in the combined immunization group was the lowest, indicating that the combined immunization could provide a better protective efficacy. In conclusion, the DNA prime and recombinant protein boost vaccination can be used as an important anti-CIAV strategy, which can induce both enhanced cellular and humoral immunity responses in chickens and provide a new avenue for CIAV prevention and control.

A cluster of vultures, artificially bred in a zoo in Shandong Province, China, displayed signs of emaciation and some even died, which raised the suspicion of an immunosuppressive pathogen. Upon conducting nucleic acid testing on the clinical samples, it was found that the CIAV was present in the tissue of dead vulture. In this study, samples of dead vulture tissue were used to isolate a chicken infectious anemia virus (CIAV) via the MDCC-MSB1 cell line, which was designated the SDTY2021-TJ strain. The full-length genomic sequence of SDTY2021-TJ was determined and analyzed in detail. The full genomic DNA of SDTY2021-TJ was found to be 2298 bp, with no omissions or additions in the coding region. The homology between the full-length genomic sequence of SDTY2021-TJ and the reference strain ranged from 95.5% (Del-Ros) to 98.7% (YN04). In comparison with the reference strain, the VP1 protein of SDTY2021-TJ contained a number of mutations. To assess the virulence of SDTY2021-TJ, one-day-old SPF chickens were inoculated with both high and low doses of the pathogen. The results demonstrated that SDTY2021-TJ had a considerable pathogenicity to SPF chickens, as the high-dose group caused a 50% mortality rate, and even the low-dose group caused a 30% mortality rate. The chickens infected with the disease exhibited paleness in the cockscomb and stunted growth, as well as a compromised response to NDV and AIV-H9 inactivated vaccine. Furthermore, histological observation revealed an atrophy and degeneration of the thymus. To the best of our knowledge, this is the first instance of CIAV being isolated from artificially bred Aegypius monachus, implying that wild birds may be involved in the transmission and spread of CIAV.