Role of Latent Feline Leukemia Virus Infection in Nonregenerative Cytopenias of Cats

Background Nonregenerative cytopenias such as nonregenerative anemia, neutropenia, and thrombocytopenia in cats with feline leukemia virus (FeLV) antigen are assumed to be caused by the underlying FeLV infection. In addition, cats with negative FeLV antigen-test results that have cytopenias of unknown etiology often are suspected to suffer from latent FeLV infection that is responsible for the nonregenerative cytopenias. Objective The purpose of this study was to assess the role of latent FeLV infection by polymerase chain reaction (PCR) in bone marrow of cats with nonregenerative cytopenias that had negative FeLV antigen test results in blood. Animals Thirty-seven cats were included in the patient group. Inclusion criteria were (1) nonregenerative cytopenia of unknown origin and (2) negative FeLV antigen test result. Antigenemia was determined by detection of free FeLV p27 antigen by ELISA in serum. Furthermore, 7 cats with positive antigen test results with nonregenerative cytopenia were included as control group I, and 30 cats with negative antigen test results without nonregenerative cytopenia were included as control group II. Methods Whole blood and bone marrow samples were tested by 2 different PCR assays detecting sequences of the envelope or long terminal repeat genes. FeLV immunohistochemistry was performed in bone marrow samples. Results Two of the 37 cats (5.4%) in the patient group were positive on the bone marrow PCR results and thus were latently infected with FeLV. Conclusions and Clinical Importance The findings of this study suggest that FeLV latency is rare in cats with nonregenerative cytopenias.