RECOMBINANT FELV VACCINE - LONG-TERM PROTECTION AND EFFECT ON COURSE AND OUTCOME OF FIV INFECTION

The efficacy and the long-term protection of a recombinant feline leuk emia virus (FeLV) vaccine were determined in 30 specified pathogen fre e cats for over 3 years. At the same time, in order to specify the eff ects of feline immunodeficiency virus (FIV) on the immune system, one half of the cats (n=15) were previously infected with the Swiss isolat e FIV Zurich 2. The second half of the animals (n=15) served as non-in fected controls. Eighteen (nine FIV-negative, nine FIV-positive) vacci nated and 12 (six FIV-negative, six FIV-positive) non-vaccinated cats were intraperitoneally challenged with FeLV A. Seventeen of 18 vaccina ted cats were protected against persistent viremia, while ten of 12 no n-vaccinated controls became infected. An increase of antibodies again st FeLV SU was found in all protected cats after the challenge exposur e. No difference in vaccine efficacy was found between FIV-negative an d FIV-positive animals. The whole group of cats was observed for over 3 years. There were no further vaccinations during this period. CD4(+) and CD8(+) cell subsets, clinical outcome and time of survival of the cats were recorded. FIV-negative and FIV-positive animals were kept i n two different rooms. However, FeLV-negative and FeLV viremic cats we re housed together in both rooms in order to imitate a natural FeLV ex posure situation. Anti-recombinant FeLV SU antibodies were measured by enzyme-linked immunosorbent assay. Although a continuous decline of a ntibodies was found in FeLV vaccinated cats, they remained protected a gainst constant FeLV challenge for over 3 years. FIV infection had a s tronger effect on the depression of the CD4(+):CD8(+) ratio than FeLV infection. Within the group of FIV-positive cats, the FeLV-vaccinated animals had significantly better survival rates as well as better clin ical and laboratory parameters, FIV- and FeLV-coinfected cats showed t he lowest CD4(+):CD8(+) ratio, mainly caused by decreased CD4(+) lymph ocyte counts. CD8(+) lymphocytes with strong fluorescence (CD8(high)) disappeared and cells with weak fluorescence (CD8(low)) appeared inste ad. Prevention of coinfection by immunizing FIV-positive cats against FeLV infection improved the clinical outcome and prolonged the cat's l ife expectancy.