Polyomaviruses

Subjects: virology, microbiology · Systems: virology, microbiology · Tags: virology, microbiology, polyomavirus

Polyomaviruses: JC and BK

Structure and General Features

• Small, non-enveloped, double-stranded DNA viruses with icosahedral symmetry.
• Similar structure to papillomaviruses, but not associated with squamous lesions.
• Establish latent infection in kidneys, lymphoid tissues, and sometimes CNS.
• Polyoma = “many tumors” (oncogenic in animals, not in humans).
• Disease occurs mostly in immunocompromised patients.

JC Virus

Epidemiology & Pathogenesis

• Acquired in childhood, latent in kidneys/lymphoid tissue.
• Reactivates in immunosuppressed hosts, especially AIDS patients.
• Infects oligodendrocytes, causing demyelination.

Clinical Syndrome: Progressive Multifocal Leukoencephalopathy (PML)

• Subacute neurological decline: weakness, visual changes, cognitive dysfunction.
• Progresses over weeks–months to severe disability or death.
• MRI: multifocal, non-enhancing white matter lesions (no mass effect).

Diagnosis

• PCR detection of JC virus DNA in CSF.
• Brain biopsy rarely needed.

Treatment

• No specific antiviral therapy.
• Management = restore immune function:
  • ART for HIV patients.
  • Reduce immunosuppression in transplant patients.

BK Virus

Epidemiology & Pathogenesis

• Acquired in childhood, latent in urinary tract/kidneys.
• Reactivates with immunosuppression.
• Renal transplant patients: nephropathy → graft dysfunction.
• Bone marrow transplant patients: hemorrhagic cystitis.

Diagnosis

• PCR detection of viral DNA in blood or urine.
• Histology: “decoy cells” = epithelial cells with enlarged basophilic intranuclear inclusions.

Treatment

• No proven antiviral.
• Main strategy = reduce immunosuppression to allow immune system to clear virus.

High-Yield Exam Summary

• JC virus → PML (oligodendrocytes, AIDS patients).
• BK virus → hemorrhagic cystitis + nephropathy in transplant patients.
• Both establish latent infections and reactivate in immunosuppression.
• Treatment = immune restoration, not antivirals.

Disclaimer: For education only. Not medical advice; always follow your institution's guidance.