Determination of tissue tropism of chicken anaemia virus on chicken embryos: a molecular insight.

IMPORTANCE: Few studies have examined the interactions of the chicken anemia virus (CAV) with the immune system of embryos. OBJECTIVE: To study the pathogenicity of the CAV in chicken embryos with respect to its tissue tropism and viral load in different tissues. METHOD: The pathogenicity of the CAV was examined in about-to-hatch embryos through cytology, histopathological examinations, molecular detection, immunocytochemistry (ICC), immunofluorescent test, and immunohistochemistry techniques. RESULTS: The experimental study using a polymerase chain reaction (PCR) assay revealed the presence of CAV in the liver, bone marrow, and thymus tissues of embryos where embryos were inoculated with CAV-positive bone marrow specimens obtained from chicken anemia-suspect cases. Intracytoplasmic and intranuclear inclusion bodies were detected cytologically in the bone marrow of the embryos, whereas no inclusion body was detected in the thymus. On the other hand, both kinds of inclusion bodies were observed in bone marrow and thymus in the histopathology. In addition, various organs of PCR-positive CAV embryos revealed the depletion of lymphocytes and hematopoietic cells in the thymus and bone marrow, respectively. The CAV antigen was confirmed in the bone marrow and thymus cytological smears using ICC and immunofluorescence techniques. CONCLUSIONS AND RELEVANCE: Viral antigen exhibited more tropism towards the bone marrow of embryos than the thymus in ICC and immunofluorescence techniques. The presence of CD44, a marker for progenitor cells and an antigen in the serial sections of bone marrow, confirmed the relevance of viral tropism for the hemocytoblasts of the bone marrow as the main target cells in embryos and subsequently in chicks for viral replication.