As for the FIV-FPV pair, this study is to our knowledge the first to search for a potential association. Whether risk factors were taken into account or not, we did not find any significant association between the two viruses. Again, this could be at first surprising as both viruses are supposed to be immunosuppressive [84, 95, 96] . In experimental conditions, FPV infection is more severe in FIV-infected cats [97] . Consequently, a positive association could have been expected if infections had facilitated each other (leading to numerous co-infections) or a negative association if the co-infection had led to a strong host mortality (leading to few co-infections). However, the FPV-induced decrease in the immune response is transient and more likely to occur in young kittens, whereas FIV infection is more frequent in adult cats. The persistence of FPV-antibodies can be longer than 7 years [98] , and consequently, double seropositivity against FPV and FIV is not synonymous of co-infection. It is likely that co-infections by the two viruses are not frequent and mainly occur in adult animals which are less sensitive to FPV. As no association was evidenced for these three pairs of viruses, the FIV infection does not seem to modify the risk of infection by another virus. However, our results do not exclude the occurrence of an interaction once both parasites are in contact within the host (e.g., directly through competition or indirectly via the host immune system), as suggested by several experimental co-infection studies. In addition, the FIV seropositivity status may encompass different stages of the infection with various degrees of immunodeficiency. The results of this study do not exclude the possibility that late stage FIV infection may increase the sensitivity to the other feline viruses.