Parameters of disease progression in long-term experimental feline retrovirus (feline immunodeficiency virus and feline leukemia virus) infections: hematology, clinical chemistry, and lymphocyte subsets

Abstract

After several years of latency, feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) cause fatal disease in the cat. The aim of this study was to determine laboratory parameters characteristic of disease progression which would allow a better description of the asymptomatic phase and a better understanding of the pathogenesis of the two infections. Therefore, experimentally infected cats (FIV and/or FeLV positive) and control animals were observed over a period of 6.5 years under identical conditions. Blood samples were analyzed for the following: complete hematology, clinical chemistry, serum protein electrophoresis, and determination of CD4 ؉ and CD8 ؉ lymphocyte subsets. The following hematological and clinical chemistry parameters were markedly changed in the FIV-infected animals from month 9 onwards: glucose, 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 persistent leukopenia, lymphopenia, or neutropenia. A significant decrease was found in the CD4 ؉ /CD8 ؉ ratio in FIV-positive and FIV-FeLV-positive animals mainly due to loss of CD4 ؉ lymphocytes. In FeLV-positive cats, both CD4 ؉ and, to a lesser degree, CD8 ؉ lymphocytes were decreased in long-term infection. The changes in FIV infection may reflect subclinical kidney dysfunction, changes in energy and lipid metabolism, and transient activation of the humoral immune response as described 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 animals. No severe clinical signs were observed in the FIV-positive cats, while FeLV had a severe influence on the life expectancy of persistently positive cats. In conclusion, several parameters of clinical chemistry 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 importance of FIV as a model for HIV.

Feline immunodeficiency virus (FIV) infection leads to increased incidence of feline odontoclastic resorptive lesions (FORL)

“…Furthermore, FIV infection leads to an impaired humoral and cellular immune response and finally to an AIDS-like syndrome in infected cats (Pedersen et al, 1987;Ishida and Tomoda, 1990;Pedersen and Barlough, 1991). CD4 T lymphocytes progressively decline in FIV-infected cats Torten et al, 1991), but also elevated serum globulin fractions were demonstrated in such animals (Shelton et al, 1995;Hofmann-Lehmann et al, 1997). The FIV-infected cats of the present study had significantly lowered CD4 blood lymphocyte counts (Fig.…”

“…They were all negative for FeLV p27 antigen by ELISA, and for antibodies to FHV (<1:20), FCV (<1:20), FPV (<1:25), FCoV (<1:25) and FeSFV (<1:25). Cats of group 1 from which FIV had been re-isolated numerous times (Hofmann- Lehmann et al, 1997), were positive for antibodies to TM measured by ELISA, while cats of group 2 were ELISA-negative (Table 1). Cats of group 1 had significantly lower absolute CD4 lymphocyte counts (p0.0025, Fig.…”

“…They were intraperitoneally infected with FIV Z2 (Morikawa et al, 1991) at the age of 17 weeks (Lehmann et al, 1991). By the time of the study, these cats had been FIV-positive for 6 years and 9 months, but were still clinically healthy (Hofmann-Lehmann et al, 1997). Nine cats were kept under identical conditions as age-matched FIV-negative controls (group 2).…”

“…Samples taken before vaccination yielded titers of less than 25, while samples collected 3 weeks after the second vaccination produced titers up to 1600. Lymphocyte subsets were determined by flow cytometry in platelet-free whole blood as described (Hofmann-Lehmann et al, 1997). The cats were fed canned and dry cat food (Whiskas and Brekkies, Effems AG, Zug, Switzerland).…”

FIV vaccine development and its importance to veterinary and human medicine: a review

“…These secondary infections frequently become resistant to antimicrobial therapy and eventually result in death (Yamamoto et al, 1989). Long-term survivors have been reported for FIV-infected cats similar to the long-term nonprogressors reported for HIV-positive individuals (Bendinelli et al, 1995;Hofmann-Lehmann et al, 1997). The long-term survivors appear to make up a sizable population of naturally infected pet cats which can survive for many years with minimal clinical disease.…”