Ashley Laird and Yana Greenstein

Humans and Viruses
Human Biology 115A
Winter, 2000
Robert Siegel, instructor

Erythrocyte precursors beware.  Its the infection of...


Erythroid precursor cells infected with human parvovirus B19.
From Internet Pathology Laboratory for Medical Education.


General Properties
   The Parvoviridae family contains the smallest of all human viruses, with each virion measuring only 20-25 nm in diameter.  The virus has an naked, icosahedral capsid morphology, which encapsidates an infectious single stranded DNA genome of only 5 kilobases.  Its small genome size allows it very limited coding potential, and prohibits it from inducing replication in host cells.  In effect, they are only able to replicate in dividing cells such as marrow, gut and the developing fetus cells.
    The Parvoviridae may be small, but they are mighty.  The virus itself is very stable, surviving temperatures of up to 60 degrees Celsius at a pH ranging from 3-9!  They also have the ability to cause serious diseases in their hosts.  Animal parvoviruses cause congenital malformation in rats, and panleukopenia in cats, dogs, and mink.  The human parvovirus B19 is associated with not only very common exanthemous disease of children, but also with hydrops fetalis  and aplastic crises in patients with chronic hemolytic anemia.  Enteric parvoviruses, are also associated with gastroenteritis.

    The genome is linear ssDNA, with the proportion of positive strands varying from 1-50% depending upon particular virus species and other conditions.  The genome has two open reading frames (ORF).  A right handed ORF encodes the two capsid proteins, VP1 and VP 2, which are transcribed from alternatively spliced mRNA. The left-handed ORF encodes at least one of the nonstructural proteins (NS1).

    The parvoviruses have also evolved a unique mechanism of DNA replication.  All genomes of currently sequenced parvoviruses display long terminal palindromic sequences, which enable each end of the molecule to fold back on itself to form a hairpin structure that is useful during replication.  The palindromic sequence serves as a self-primer for initiation of synthesis of plus sense DNA.  The current model for the mechanism of viral replication postulates that the growing strand replicates back on itself, producing a tetramic form from which two plus strands and two minus strands are generated by endonuclease cleavage. All replication takes place in the nucleus and occurs only in dividing cells, with the use of cellular enzymes.

The Family
    There are three mammalian genera in the Parvoviridae family:
    - Parvovirus
    - Erythrovirus
    - Dependovirus
    Dependovirus includes the Adeno-associated viruses, while Erythrovirus includes pathogens such as B19.  The genus Parvovirus contains several animal viruses, such as canine parvovirus, as well as some viruses suspected of causing gastroenteritis in humans.

Please refer to the Viral Profiles for more information on individual viruses. Enjoy!

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Viral Profiles

New findings from 1999

Useful web links

Updated reference link

Pathogen Cards

Drug Profiles
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Created: February 1, 1998
Modified: February 8, 2000
Last modified: April 7, 2007