Polyomaviruses

Although relatively little is known about the human polyomaviruses (BK and JC viruses), other animal polyomaviruses e.g. the simian virus SV40 are the best characterized DNA tumor viruses.   Structure :      In comparison with the papillomaviruses, the polyomaviruses are slightly smaller (44 nm diameter).   Pathogenesis :      Polyomaviruses have a high specificity for certain hosts and particular cells within that host. In humans both JC and BK viruses probably enter through the respiratory tract, spread by viremia. In immunocompromised patients, reactivation of virus in the kidneys leads to potentially severe urinary tract infection (BKV) or viremia and central nervous system infection (JCV). Suppressed T-cell function appears to be responsible for reactivation of BK an JC viruses. Both viruses cause tumors when injected into hamsters; however, they are not consistently associated with any human tumors.   Epidemiology :      BK and JC viruses are widely distributed in human populations, as evidenced by the presence of specific antibodies in 70-80% of adults sera.   Clinical Syndromes :      Primary infection is virtually always asymptomatic, although mild respiratory symptoms might occur and cystitis has been reported.      Ureteral stenosis in renal transplant patients appears to be associated with BK virus, as does haemorrhagic cystitis in bone marrow transplant recipients.      Progressive multifocal leukoencephalopathy (PML) is a rare syndrome that occurs in immunocompromised patients, including those with AIDS, and is due to JCV. As the name implies, patients may have multiple neurologic symptoms unattributable to a single anatomic lesion. Impairment of speech, vision, and coordination occurs followed by paralysis of the arms and legs, and finally death.   Laboratory Diagnosis :      Urine cytologic tests can reveal the presence of JC or BK viruses by showing enlarged cells with dense basophilic intranuclear inclusions resembling those induced by cytomegalovirus.      Electron microscopy can be used to visualize viral particles in brain tissue in case of PML.      Culture is the definitive method for documenting active polyomavirus infection, although viral antigen and viral nucleic acid may be demonstrated in tissues or cells by immunofluorescence or immunoperoxidase assays and DNA hybridization techniques respectively.   Treatment, Prevention and Control :      No specific treatment is available, but some stabilization or improvement may occur if the immune suppression can be reduced.