PANLEUKOPENIA-LIKE SYNDROME OF FELV CAUSED BY COINFECTION WITH FELV AND FELINE PANLEUKOPENIA VIRUS

To study the effect of interferon on feline leukemia virus (FeLV) infe ction, 30 specific pathogen free (SPF) cats were infected with the apa thogenic FeLV A Glasgow. Unexpectedly, between 5 and 8 weeks after FeL V infection, all 19 cats with persistent FeLV infection but not the Fe LV-negative cats died from a panleukopenia-like syndrome. No feline pa nleukopenia virus (FPLV) antigen was found in feces by latex agglutina tion, enzyme-linked immunosorbent assay (ELISA) or immunoelectron micr oscopy. No enteropathogenic bacteria were found. Histopathology reveal ed changes resembling those of FPLV infection such as destruction of c rypts and pancytopenia of bone marrow. Neither clinical signs nor sero conversion to FPLV could be induced by transmitting intestinal extract s to two SPF cats. However, FPLV antigen was demonstrated by immunoflu orescence assay in intestinal cryostat sections of diseased animals. F PLV could also be demonstrated in intestinal extracts by immunoelectro n microscopy, by latex agglutination and ELISA after anti-FPLV antibod ies were removed from immune-complexed FPLV by ultracentrifugation ove r a CsCl gradient at pH 2.0. From these experiments it was concluded t hat the panleukopenia-like syndrome of FeLV may not be caused by FeLV alone but at least in some cases by co-infection with FeLV and FPLV. I n addition, some form of 'cooperation' between FeLV and FPLV must be p ostulated because neither virus alone induced symptoms.