Virus

REVIEW ARTICLE

Polyoma BK virus: an emerging opportunistic infectious agent of the human central nervous system

Authors Rodrigo Lopes da Silva1
1

ABSTRACT BK virus, a double-stranded DNA virus, is a member of the Polyomaviridae family which is known to infect humans. Clinical evidence of disease is mostly encountered in immunosuppressed individuals such as AIDS patients or those whoundergo renal or bone marrow transplantation where complications associated with BKV infection manifest commonly as a polyomavirus nephropathy or hemorrhagic cystitis, respectively. Recent evidence suggests that in addition to the JC virus (the other member of the same family known to be strongly neurotropic and responsible for the progressive multifocal leukoencephalopathy), BK virus can infect andcause clinically relevant disease in the human central nervous system. In this mini-review, an analysis of the literature is made. A special focus is given to alert clinicians to the possibility of this association during the differential diagnosis of infections of the central nervous system in the immunocompromised host. Keywords: BK virus; bone marrow transplantation; AIDS-related opportunisticinfections.
[Braz J Infect Dis 2011;15(3):276-284]©Elsevier Editora Ltda.

MD, Hospital Santo António dos Capuchos CHLC, Lisbon, Portugal

INTRODUCTION BK virus (BKV), also known as Polyomavirus hominis 1, was first isolated in 1971 from the urine of a renal transplant patient, initials B.K. BKV is a non-enveloped encapsulated circular double-stranded DNA virus that belongs to thePolyomaviridae family which includes other polyomaviruses that have been found to infect humans namely JC virus (JVC), simian virus 40, KI virus, WU virus and Merkel cell polyomavirus (MCV). BKV is widely distributed in the human population. Primary asymptomatic infection usually occurs during childhood via the respiratory tract. Then, latent infection is established in renal epithelial cells and possiblyother tissues (including brain, since BKV-DNA has been detected in the brain tissues from normal subjects) with most individuals having antibodies to BKV. Reactivation may subsequently occur in immunocompromised and healthy individuals, but may be more likely if there is an impairment of the immune function (patients with T-cell deficiencies). Clinical evidence of disease is rare and mostlyencountered in patients in

Submitted on: 12/20/2010 Approved on: 01/15/2011 Correspondence to: Rodrigo Lopes da Silva Hospital Santo António dos Capuchos – CHLC Alameda Santo António dos Capuchos , 1169-050 Lisbon, Portugal. ronolosi@gmail.com I declare no conflict of interest.

states of relative or absolute immunodeficiency, such as patients with AIDS or transplant recipients where BKV reactivationis associated with diverse entities such as polyomavirus nephropathy (PVN), a form of acute interstitial nephritis and the most frequent BKV-associated disease after renal transplantation, or the hemorrhagic cystitis, a serious BKV-associated complication characterized by dysuria and varying degrees of hematuria that affects up to 10% of the bone marrow tran plant (BMT) patients.1-4 JCV, one ofthe other member of the Polyomaviridae family that causes human infection, is strongly associated with progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the central nervous system (CNS). Until now, JCV was the only human polyomavirus known to have the ability to infect the CNS. Recently, however, an increasing body of evidence favors the possible neurotropism of BKV,since BKV DNA has been detected in the brain tissue and cerebrospinal fluid (CSF) of both immunocompetent and immunocompromised individuals (mostly adults) with or without neurological symptoms.5

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Lopes da Silva

BKV related CNS infection may often be overlooked and under-diagnosed in immunocompromised patients. Only a few cases of neurological disease associated with a possible or...