Family: Polyomaviridae

Genome: Double-stranded, circular, DNA, ~5,000 nt

• The Family includes:

  Simian vacuolating virus 40 (SV40; Type Species)
  BK virus
  JC virus
  KI polyomavirus (Allander et al, 2007)
  Another coming soon.

• 40-55nm, non-enveloped icosahedral virions (72 capsomers)
  

Infection and Replication:

• Replicate in the nucleus of the target cell
• Express caopsid proteins VP1 to VP3
• Regulatory large (T or LT) and small (t or ST) T antigens
• The virus is easily grown in cell culture

Pathology:

• Do not resemble HPV in their ability to cause human disease
  
  JC Virus
  • Named after the intials of the patient from whom virus was isolated in 1970
  • Is spread throughout the population but the route of primary infection is not well defined
  • Once a rare cause of disease in humans, is now increasingly important in immunosuppressed AIDS patients
  • Causes persistent infection in the urinary tract
  • Causes progressive multifocal leucoencephalopathy (PML), through its infection of oligodendrocytes and interaction with astrocytes, in these patients. Examintaion of brain tissue reveals demyelination and abnormal neuroglial (non-neuronal) cells. Disease is characterised by dementia, muscular weakness affecting one side of the body, speech and vision disruption and progression to death.
  • Remains latent in the kidney and B cells
  • Differences are apparent in the regulatory regions of strains from urinary or brain tissue
  • Genotypes are also geographically distinct
  BK Virus
  • Readily isolated from the urine of immunosuppressed patients
  • Is also spread throughout the population - infection occurs early in life.
  • Obvious disease is rare and PML is not related to BK virus. Reactivation can occur in immunosuppressive states (eg pregnancy).
  KI Virus
  • Result of intensively investigating two chronologically distinct pools of nasopharyngeal aspirates (NPAs) using a random PCR-cloning-sequencing approach
  • Detected in the respiratory tract (1% of nasopahryngeal aspirates, of which 83.3% included coincident detection of another virus, and in 0.5% of faeces extracts. At the time of writing KI virus had not been found in urine, serum, whole blood or purified leukocytes
  • Tentatively associated with acute respitatory tract infections in a largely paediatric population