In the context of HIV infection, it has been described that the detection of BKPyV and JCPyV DNA in urine increases concomitantly with a decrease in CD4+ cell counts [63,64]; although, the importance of other factors during JCPyV reactivation, when the viruria does not correlate with the degree of immunosuppression, has also been reported [65]. Here, CD4 is linked to HIV infectious disease.