JC VirusPolyomavirus InfectionsPolyomavirusLeukoencephalopathy, Progressive MultifocalTumor Virus InfectionsAntigens, Polyomavirus TransformingDNA, ViralAntigens, Viral, TumorBK VirusViral Regulatory and Accessory ProteinsMerkel cell polyomavirusCapsid ProteinsVirus ReplicationNeurogliaGene Expression Regulation, ViralSimian virus 40Molecular Sequence DataCarcinoma, Merkel CellBase SequenceCell LineRNA VirusesPolyomaviridaeReceptors, VirusVaccinia virusGenes, ViralVirus Shedding