IDENTIFICATION OF 3 FELINE IMMUNODEFICIENCY VIRUS (FIV) ENV GENE SUBTYPES AND COMPARISON OF THE FIV AND HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1EVOLUTIONARY PATTERNS

Feline immunodeficiency virus (FIV) is a lentivirus associated with AI DS-like illnesses in cats. As such, FIV appears to be a feline analog of human immunodeficiency virus (HIV). A hallmark of HIV infection is the large degree of viral genetic diversity that can develop within an infected individual and the even greater and continually increasing l evel of diversity among virus isolates from different individuals. Our goal in this study was to determine patterns of FN genetic diversity by focusing on a 684-nucleotide region encompassing variable regions V 3, V4, and V5 of the FIV env gene in order to establish parallels and distinctions between FIV and HIV type 1 (HIV-1). Our data demonstrate that, like HIV-1, FIV can be separated into distinct envelope sequence subtypes (three are described here). Similar to that found for HIV-1, the pairwise sequence divergence within an FIV subtype ranged from 2. 5 to 15.0%, whereas that between subtypes ranged from 17.8 to 26.2%. H owever, the high number of synonymous nucleotide changes among FIV V3 to V5 env sequences may also include a significant number of back muta tions and suggests that the evolutionary distances among FIV subtypes are underestimated. Although only a few subtype B viruses were availab le for examination, the pattern of diversity between the FIV A and B s ubtypes was found to be significantly distinct; subtype B sequences ha d proportionally fewer mutations that changed amino acids, compared wi th silent changes, suggesting a more advanced state of adaptation to t he host. No similar distinction was evident for HIV-1 subtypes. The di versity of FIV genomes within individual infected cats was found to be as high as 3.7% yet twofold lower than that within HIV-1-infected peo ple over a comparable region of the env gene. Despite these difference s, significant parallels between patterns of FIV evolution and HIV-1 e volution exist, indicating that a wide array of potentially divergent virus challenges need to be considered in FIV vaccine and pathogenesis studies.