PARAMETERS OF DISEASE PROGRESSION IN LONG-TERM EXPERIMENTAL FELINE RETROVIRUS (FELINE IMMUNODEFICIENCY VIRUS AND FELINE LEUKEMIA-VIRUS) INFECTIONS - HEMATOLOGY, CLINICAL-CHEMISTRY, AND LYMPHOCYTE SUBSETS

After several years of latency, feline immunodeficiency virus (FIV) an d feline leukemia virus (FeLV) cause fatal disease in the cat. The aim of this study was to determine laboratory parameters characteristic o f disease progression which would allow a better description of the as ymptomatic phase and a better understanding of the pathogenesis of the two infections. Therefore, experimentally infected cats (FIV and/or F eLV positive) and control animals were observed over a period of 6.5 y ears under identical conditions. Blood samples were analyzed for the f ollowing: complete hematology, clinical chemistry, serum protein elect rophoresis, and determination of CD4(+) and CD8(+) lymphocyte subsets. The following hematological and clinical chemistry parameters were ma rkedly changed in the FIV-infected animals from month 9 onwards: gluco se, serum protein, gamma globulins, sodium, urea, phosphorus, lipase, cholesterol, and triglyceride. In FeLV infection, the markedly changed parameters were mean corpuscular volume, mean corpuscular hemoglobin, aspartate aminotransferase, and urea. In contrast to reports of field studies, neither FIV-positive nor FeLV-positive animals developed per sistent leukopenia, lymphopenia, or neutropenia. A significant decreas e was found in the CD4(+)/CD8(+) ratio in FIV-positive and FIV-FeLV-po sitive animals mainly due to loss of CD4(+) lymphocytes. In FeLV-posit ive cats, both CD4(+) and, to a lesser degree, CD8(+) lymphocytes were decreased in long-term infection. The changes in FIV infection may re flect subclinical kidney dysfunction, changes in energy and lipid meta bolism, and transient activation of the humoral immune response as des cribed for human immunodeficiency virus (HIV) infections. The changes in FeLV infection may also reflect subclinical kidney dysfunction and, in addition, changes in erythrocyte and immune function of the animal s. No severe clinical signs were observed in the FIV-positive cats, wh ile FeLV had a severe influence on the life expectancy of persistently positive cats. In conclusion, several parameters of clinical chemistr y and hematology were changed in FIV and FeLV infection. Monitoring of these parameters may prove useful for the evaluation of candidate FIV vaccines and antiretroviral drugs in cats. The many parallels between laboratory parameters in FIV and HIV infection further support the im portance of FIV as a model for HIV.