Molecular characterization of chicken anemia virus and evaluation of maternally derived antibodies defense against commercially available vaccines

Background

Chicken infectious anemia is a young chicken’s infection caused by a single-strand DNA gyrovirus and marked by aplastic anemia, lymphoid organs atrophy, and immunosuppression, causing severe financial losses to the poultry production. The prevalence of chicken anemia virus (CAV) in 25% of Egyptian governorates (Dakahlia, Gharbia, Monufia, Ismailia, Sinai, Damietta, Al sharqiya) from 2021 to 2023 was investigated. The protective efficacy of maternally derived antibodies was assessed in one-day-old chicks against three CAV vaccines via different exposure routes (intramuscular, drinking water, or contact) to mimic field strains.

Results

Out of 98 flocks examined from 2021 to 2023, 32.65% tested positive for chicken anemia. The infection rate was 25.92% in broiler and 40.91% in unvaccinated breeder flocks. VP1 and VP3 genes sequencing and phylogenetic analysis of four chicken anemia isolates revealed that three strains (EGY-1, EGY-9, and EGY-10) closely resemble most Egyptian field strains and vaccinal strains. In contrast, one strain (EGY-5) showed lineage with some Asian and Egyptian strains. VP1 and VP3 genes amino acid substitutions, including M70I in (EGY-5, EGY-9, and EGY-10) and N78T in (EGY-1 and EGY-10), have been recorded, marking the first recorded alterations in these genes compared to vaccinal strains and other Egyptian isolates. In an experiment simulating the effects of field strains, three vaccinal strains (Cux-1, Del-Ros, and 26P4) were administered either intramuscularly or via drinking water to 120 one-day-old commercial chicks with maternally derived antibodies (4882 mean antibody titers). However, these vaccines did not provide complete protection against infection with chicken anemia vaccine viruses, resulting in histopathological alterations, body weights, and chicken viability.

Conclusion

This research enhances the understanding of chicken anemia molecular characterization in Egypt and its implications for future genetic evolution studies. Further studies are necessary to determine the maternal antibody levels required for complete protection against CAV.