Erythrocyte precursors beware. Its the infection of...
Parvovirus
Erythroid precursor cells infected with human parvovirus B19.
From Internet Pathology Laboratory for Medical Education.
http://www-medlib.med.utah.edu/WebPath/PEDHTML/PED042.html
Introduction
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.
Genome
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).
Replication
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!
Viral Profiles
New findings from 1999
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