INFECTION STRATEGIES OF RETROVIRUSES AND SOCIAL GROUPING OF DOMESTIC CATS

It is thought that parasites may exert selective pressure on the socia l structure of host populations. We compared the impact of feline immu nodeficiency virus (FIV) and feline leukemia virus (FeLV), two retrovi ruses commonly found in domestic cats (Felis catus). Because of low tr ansmissibility and virulence. both infections have a worldwide distrib ution and low prevalence. Transmission modes differ: FIV is transmitte d only through biting, while FeLV transmission occurs by biting, licki ng, grooming, and sharing food and from mother to fetus. FeLV is also more pathogenic than FIV. We compared FIV and FeLV prevalence and risk factors within five populations of cats. FIV infection occurred almos t exclusively among adult male cats fighting to acquire and maintain d ominant status. Classes at risk for FeLV infection included sexually i ntact cats allowed to roam freely. The impact of FeLV on host populati on growth was greater than that of FIV but varied among populations. O ur results show that FIV is favoured by individual aggressiveness and a hierarchical social system, while FeLV is more prevalent among socia lly active cats. FeLV may constitute a source of selective pressure ag ainst numerous amicable contacts, particularly in urban cat population s, where aggression among individuals is reduced.