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VIRUSES OF MINOR MEDICAL IMPORTANCE

These viruses are presented in alphabetical order. They are listed in Table 46–1 in terms of their nucleic acid and presence of an envelope.

TABLE 46–1Minor Viral Pathogens

ASTROVIRUSES

Astroviruses are nonenveloped RNA viruses similar in size to polioviruses. They have a characteristic five- or six-pointed morphology. These viruses cause watery diarrhea, especially in children. Most adults have antibodies against astroviruses, suggesting that infection occurs commonly. No antiviral drugs or preventive measures are available.

BK VIRUS

BK virus is a member of the polyomavirus family. Polyomaviruses are nonenveloped viruses with a circular, double-stranded DNA genome. BK virus and JC virus (see Chapter 44) are the two polyomaviruses that infect humans.

BK virus infection is widespread as determined by the presence of antibody and is typically acquired in childhood, and infection is not associated with any disease at that time. It does, however, cause nephropathy and graft loss in immunosuppressed renal transplant patients. Asymptomatic shedding of BK virus in the urine of immunocompromised patients and pregnant women in the third trimester occurs. There is no antiviral therapy effective against BK virus.

BORNA VIRUS

Borna virus is an enveloped virus with a nonsegmented, single-strand, negative-polarity RNA genome. It has the smallest genome of any virus with this type of RNA and is the only virus of this type to replicate in the nucleus of the infected cell. DNA sequences homologous to the Borna virus genome are integrated into human cellular DNA. It is a neurotropic virus known to infect regions of the brain such as the hippocampus.

Borna is the name of a town in Germany where the virus caused a disease in horses in 1885. It is primarily a zoonotic virus causing disease in domestic animals, such as cattle, sheep, dogs, and cats. In humans, Borna virus causes an often fatal encephalitis. In addition, there is evidence that it is associated with human psychiatric diseases characterized by abnormal behavior, such as bipolar disorder.

CACHE VALLEY VIRUS

This virus was first isolated in Utah in 1956 but is found throughout the western hemisphere. It is a bunyavirus transmitted by Aedes, Anopheles, or Culiseta mosquitoes from domestic livestock ...

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