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Chapter 267 Polyomaviruses

The polyomaviruses are small (45-nm), nonenveloped, double-stranded circular DNA viruses with genomes of approximately 5,000 bp. JC virus and BK viruses infect humans and cause disease. Two other polyomaviruses, designated KI virus and WU virus, can be detected in respiratory samples from children; the role of these viruses as pathogens is still under investigation. A fifth polyomavirus, called Merkel cell polyomavirus, can be detected in tumor tissue from individuals with Merkel cell carcinoma, an unusual neuroectodermal tumor of the skin that occurs primarily in elderly and immunocompromised individuals. A sixth human polyomavirus has been isolated from patients with the dermatologic condition trichodysplasia granulosa. The new virus has been provisionally named Trichodysplasia spinulosa virus. Trichodysplasia granulosa is a condition of the skin that occurs in immunocompromised individuals and involves the development of follicular papules and keratin spines, usually involving the face. JC and BK viruses are closely related to each other, with about 75% genome homology. KI and WU have a similar relationship to each other but are distinct from other human and animal polyomaviruses. Merkel cell polyomavirus is also distinct from the other human polyomaviruses.

JC and BK viruses are tropic for renal epithelium; JC virus also infects brain oligodendrocytes and is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a rare and fatal demyelinating disease of immunocompromised persons, especially those with AIDS. PML has been reported in small numbers of individuals receiving the immunomodulatory agents natalizumab (Tysabri), used to treat multiple sclerosis and Crohn’s disease, and efalizumab (Raptiva), used to treat psoriasis. BK virus is the cause of transplant nephropathy in renal transplant recipients and of hemorrhagic cystitis in hematopoietic stem cell and bone marrow transplant recipients. Several million persons in the USA were exposed to simian virus 40 (SV40), an oncogenic polyomavirus of Asian macaques that shares 70% homology to human polyomaviruses, from contaminated poliovirus vaccines administered during 1955-1963. There were no recognized sequelae and no demonstrable increased risk for cancer.

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