The potential transmission of JCV through the environment has been analyzed by studying the JC viruses present in raw sewage of urban populations from widely divergent geographical areas. High numbers of JCV were found. JCV was detected in 98% (51/52) of sewage samples from different geographical areas in Europe, Africa, and USA by applying a Nested-PCR procedure. The mean estimated concentration of JCV in sewage was of 10(2)-10(3) viral particles/ml. Sequence analysis shows that JCV found in environmental samples present an archetypal structure in the regulatory region as it has been described in urine samples. Cerebrospinal fluid samples (CSF) of PML (progressive multifocal leucoencephalopathy) patients were also analyzed as control samples in this study presenting tandem repeats and rearrangements at the regulatory region (RR). Sequence analysis of the intergenic region (IGR) allowed the typification and phylogenetic analysis of the JCV sequences detected in sewage. JC viral particles were also found to be stable in sewage samples at 20 degrees C for more than 70 days. This data suggest the idea that the intake of water or food contaminated with JCV could constitute a portal of entry for the virus or the viral DNA to the human organism.