Prevalence of hematological abnormalities and detection of infected bone marrow cells in asymptomatic cats with feline immunodeficiency virus infection.

Peripheral blood cytopenia such as anemia, leukopenia with neutropenia and thrombocytopenia is frequently observed in cats infected with feline immunodeficiency virus (FIV). Although previous studies report that cytopenia has been observed in FIV-infected symptomatic cats, yet the asymptomatic cats also present cytopenia occasionally. In the present study, hematological and virological analyses in FIV-infected asymptomatic cats were carried out to understand the prevalence and pathogenesis of peripheral blood cytopenia in FIV infection. Hematological abnormalities were detected in 24 of 50 FIV-infected asymptomatic cats (48%) in which no other cause of cytopenia than FIV infection was observed. Anemia only, neutropenia only, thrombocytopenia only, bicytopenia and pancytopenia were observed in 10%, 10%, 6%, 14% and 8%, respectively. Bone marrow (BM) examination was performed in 8 FIV-infected asymptomatic cats with peripheral blood cytopenia. Myeloid dysplasia was observed in 4 cats with neutropenia of which 2 cats with concurrent thrombocytopenia presented morphological abnormalities of megakaryocytes. FIV-infected BM cells in the 8 cats were analyzed by PCR and immunocytochemistry. Lobulated mononuclear cells in BM were infected with FIV in 5 cats with neutropenia of which 2 cats with concurrent thrombocytopenia showed FIV-infected megakaryocytes. Parts of isolated stromal cells from BM were infected with FIV in all the 8 cats. Present results suggest that FIV infection of BM cells can cause peripheral blood cytopenia and myelodysplasia even if the cat is asymptomatic. Such FIV-related hematological abnormalities are supposed to be diagnosed as FIV-myelopathy.