MICROBIOLOGY

• JC virus (JCV) is a DNA polyomavirus discovered in 1971, isolated from patient John Cunningham.
  • Other polyomaviruses:
    • JCV is genetically closely related to BK and SV40 viruses.
    • Other members of the human polyomavirus group include:
      
      • Trichodysplasia spinulosa virus: associated with skin disease
      • Merkel cell polyomavirus: associated with a rare form of skin cancer called Merkle cell cancer
      • KI, WU, MW, human polyoma 6, 7, and 9 viruses: Found in human specimens, but no clear disease associations
  • Oncogenic potential:
    • Members of this DNA tumor virus family are well-known to cause tumors in rodents; however, except for Merkle cell cancer, oncologic potential in humans is less certain.
    • Some studies have linked the virus to human colorectal cancer, but this concept remains controversial.
  • Structure and composition: All polyomaviruses (including JCV) are non-enveloped and contain double-stranded DNA
  • 3-stage model of pathogenesis:
    • Stage 1: Nonpathogenic virus establishes latent infection (generally in the kidney and other sites such as tonsils and immune cells ): Virus may gain access to CNS at this stage.
    • Stage 2: Viral reactivation and accumulation of genetic alterations leading to the emergence of neurotropic variants: Virus may gain access to CNS at this stage.
    • Stage 3: Progressive multifocal leukoencephalopathy (PML) with rapid viral replication in oligodendrocytes with resultant demyelinating disease.