The age of individuals is not considered in our model, even though it may affect their behavior and, thus, their risk of becoming infected [3, 8, 13] . Moreover, due to long FIV infection duration, an accumulation of infected cases develops in older age cohorts. To represent the effects of age in a simplified way, we assume that the mean age of cats in the population may act as a risk factor for FIV transmission. This is justified since, here, we mainly focus on the global prevalence of FIV within populations without reference to the age-distribution of infections.