Abstract
Infection of poultry with chicken anemia virus (CAV) is implicated in several field problems in broiler flocks due to the immunosuppression generated and, consequently, the increased susceptibility to secondary infections. Recently, we have reported an increased occurrence of clinical cases caused by CAV strains distantly related to those commonly used for vaccination. In order to understand the behavior of two Argentinean CAV strains (CAV-10 and CAV-18) in two-week-old chickens, an immune and histopathological study was performed. Neither mortality nor clinical signs were observed in the infected or control groups. Thymus lobes from chickens infected with both CAV viruses were smaller compared to the negative control group. At 14 days post-infection (dpi), only chickens inoculated with CAV-10 show a severe depletion of lymphocytes in the thymus cortex and in follicles from the bursa of Fabricius. Also thymopoiesis disorders, such as reduction in the percentage of total DP (CD4 + CD8α+) thymocytes and alteration in the percentages of DP subpopulations, were more important in animals inoculated with the CAV-10 than the CAV-18 strain. In addition, only animals infected with CAV-10 show a decrease in CD8αβ splenocytes. Altogether our results show that, although both Argentinean CAV strains produce subclinical infections in chickens causing immunosuppression at 14 dpi, they might differ in their in vivo pathogenicity.
Highlights
Chicken anemia virus (CAV) is a closed circular negative single-stranded DNA virus [1] from the Circoviridae family that belongs to the Gyrovirus genus [2]
In addition to the deletion, genome sequencing of CAV-10 and CAV-18 confirmed that both viruses present mutations in the hypervariable region of VP1 that are associated with a reduced spread in an avian lymphoblastoid cell line (MDCC-MSB1) compared with Cux-1 [26]
Despite the eleven nucleotide differences observed along VP1, only two deduced amino acid substitutions were seen in CAV-10 with respect to the CAV-18 virus
Summary
Chicken anemia virus (CAV) is a closed circular negative single-stranded DNA virus [1] from the Circoviridae family that belongs to the Gyrovirus genus [2]. Markowsky-Grimsrud and Schat [13] have demonstrated that experimental infection with CAV impairs the generation of pathogen-specific cytotoxic T lymphocytes (CTL) that may have important implications for adaptive cell-mediated immunity to several secondary pathogens. This was observed by other authors that reported secondary infections with other viruses, bacteria, parasites and/or fungi [1,14,15,16]
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