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Background
Chicken infectious anemia (CIA) has been considered a recent disease from the last three decades that leads to production losses in both the percentage of livability and the percentage of condemnations [1].
Chicken anemia virus (CAV) is the smallest DNA virus, measuring between 23 and 25 nm. It is a non-enveloped, icosahedral structure, a single-stranded genome and act as a member of the genus Gyrovirus, family Anelloviridae 2023 by the International Committee on Taxonomy of Viruses (ICTV) [2].
The genome is composed of three overlapping open reading frames (ORFs) that encode three viral proteins: VP1, the primary capsid protein; VP2, a dual-specificity phosphatase [3] that also likely serves as a scaffolding protein during virion assembly [4]; and VP3, also known as apoptin, which has been revealed to have apoptotic activity in transformed cell lines [5]. Phylogenetic characterization of the VP1 and VP3 genes is essential for understanding CAV evolution because these genes play significant roles in viral pathogenicity, antigenic variation, and host adaptation [6].
CAV causes erythroblastoid damage of the thymocyte cortex, subcutaneous and muscular hemorrhages, aplastic anemia, and immunosuppression [7]. VP3 triggers p53-independent apoptosis, leading to T cell depletion and bone marrow suppression. The virus replicates in the nucleus, affecting immune function by decreasing CD4 + and CD8 + T cell levels and delaying macrophage activity. Consequently, this causes thymic atrophy, anemia, and increased susceptibility to secondary infections [8].
The infections may be either subclinical or clinical [8]. The clinical infection occurs in young chicks through vertical transmission during the 1st and 2nd weeks of life. Birds older than two to three weeks of age are also susceptible to disease, but infection remains subclinical [9].
Breeder vaccination is the primary method for the protection of progeny in the first few weeks of life against vertical or horizontal CAV transmission through maternally derived antibodies [10]. Although most breeder flocks in Egypt have antibody titers to CAV either due to natural infections in the brooding period or due to vaccination, there is still a possibility of vertical transmission [11]. Horizontal transmission can also occur between different flocks during chick handling in hatcheries, during the transportation of chicks to farms, or in the first few days of rearing chicks in the farms [12].
The polymerase chain reaction (PCR)...