The work presented here supports this last hypothesis: random fluctuations in the transmission process lead to much greater variation in disease prevalence than with a simple Binomial distribution, underlying classical risk factor analyses. So the simplest model describes well the data and explains the large variability observed in disease prevalence between cat populations without invoking any risk factor. Finally, we determine confidence intervals for the model parameters. The model is very simple, explains the data well, and hence constitutes an interesting tool for further understanding and control of the spread of FIV in these cat populations. The approach developed here can easily extend to many host-parasite interactions.