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CHAPTER 11
Parvovirus
Definitions of the virus:

Parvoviruses are the causative
agents of several important animal
diseases.

They require cells that are passing
through mitotic S phase to replicate
their DNA.

Parvovirus infections are most
severe in fetuses and neonates.
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Definitions of the virus:

This requirement for mitotic active
cells reflected in the tropism of
parvoviruses for rapidly dividing
hemopoietic precursors and
lymphocytes, and progenitor cells
of the intestinal mucosal lining.
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Definitions of the virus:

The family Parvoviridae comprises
two subfamilies: Paroviridae
(vertebrates).

The genus Parvovirus includes
feline panleukopenia virus and
closely related canine parvovirus,
porcine and chicken parvoviruses.
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Definitions of the virus:

The genus Erythrovirus includes
human parvovirus B19 and related
viruses of non-human primates,
bovine parvovirus type 3 and
chipmunk parvovirus.

The genus Dependovirus includes
adeno-associated viruses that are
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Definitions of the virus:
unable to replicate except in the
presence of a helper virus, an
adenovirus; goose and duck
parvoviruses; bovine parvovirus 2.

The genus Amadovirus includes
Aleutian mink disease virus; The
genus Bocavirus includes bovine
parvovirus and canine minute virus.
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INTRODUCTION

Parvovirus virions are nonenveloped, 25 nm in diameter, and
have icosahedral symmetry.

The capsid displays a hollow
cylinder at each fivefold axis of
symmetry that is surrounded by a
circular depression, prominent
protrusions around the threefold
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axis of symmetry and a depression
at each twofold axis of symmetry.

The capsid is composed of VP2 (90%)
and approximately 10% being the
overlapping but larger VP1 protein.

VP1 and VP2 are formed by
alternative splicing of the same
mRNA.
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
The genome consists of a linear singlestranded DNA (4.5-5.5 kbp).

Individual virions of these viruses contain
single-stranded DNA of either polarity.

The genome contains two ORFs: an ORF in
the 3’ half of the genome that encodes the
non-structural proteins for DNA
transcription and replication; another ORF
towards 5’ half encodes the structural
proteins (CAP, VP, or S) of the capsid.
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
The entire sequence of VP2 is
encoded within the VP1 gene.

A third structural protein, VP3, is
formed by cleavage of a peptide
from the amino terminus of VP2.

Parvoviruses are extremely stable to
environmental conditions such as
heat, pH, and disinfectant.
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INTRODUCTION

The genome has terminal palindromic
sequences, enabling each end to form
hairpin or other complex base-paired
structures.

Transferrin receptor is the receptor for
canine parvovirus and feline panleukopenia
virus, and it directs the virus into the
clathrin-mediated uptake pathway.

Utilization of the transferrin receptor
facilitates replication of these viruses which
is upregulated on proliferating cells.
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INTRODUCTION

Parvovirus replication occurs only in cells
that pass through mitotic S phase.

Parvovirus binds to sialic acid residues,
consistent with their ability to
hemagglutinate erythrocytes of other
species.

Virions traffic through the endosomal
pathways within the early and late
endosomes.

The VP1 protein contains a phospholipase
A2 enzymes in its N-terminal region.
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INTRODUCTION

The non-structural protein (NS1) that is
encoded in the 3’ portion of the genome
serves (1) attached to the 5’ end of the viral
DNA during replication; (2) serves as a
helicase during replication and DNA
packaging; (3) serves as a site-specific
nickase; (4) mediates arrest of the cell in the
G1 phase.

A rolling-hairpin replication: the 3’-terminal
hairpin on the negative-sense DNA genome
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serves as a rolling-hairpin replication.

A rolling-hairpin replication: the 3’-terminal
hairpin on the negative-sense DNA genome
serves as a self-primer for the initiation of
synthesis of a double-stranded DNA
replicative intermediate.

The detection of a dimeric form of the
replicative intermediate, a head-to-head
concatemer of two covalently linked doublestranded forms- has led to a model in which
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the growing DNA strand replicates back on
itself to produce a tetrameric form.

The detection of a dimeric form of the
replicative intermediate, a head-to-head
concatemer of two covalently linked doublestranded forms- has led to a model in which
the growing DNA strand replicates back on
itself to produce a tetrameric form from
which two complete positive or negative
strands are generated.
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INTRODUCTION

Parvovirus infections of the fetus or
newborn at critical stages of organogenesis
when there is considerable cell divisions
may result in developmental defects.

Replication of parvovirus is restricted in
hemopoietic precursors, lymphocytes, and
progenitor cells of intestinal mucosa of
older animals.
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INTRODUCTION

Parvovirus infections of the fetus or
newborn at critical stages of organogenesis
when there is considerable cell divisions
may result in developmental defects.

Replication of parvovirus is restricted in
hemopoietic precursors, lymphocytes, and
progenitor cells of intestinal mucosa of
older animals.
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INTRODUCTION

Many parvoviruses cause acute infections
that last only a few days, others persist for
long periods in the faeces of apparently
robust host immune responses.

Disease develops in persistently infected
mink as a result of the high levels of
circulating antigen-antibody complexes that
deposit in tissues and initiate a type III
hypersensitivity reaction that results in
tissue injury and destruction.
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Circovirus
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DEFINITION

The family Circoviridae includes
viruses with circular single-stranded
DNA genomes, and which share
common physicochemical and
genomic properties.

The family contains two genera
(Circovirus and Gyrovirus).

Circovirus uses an ambisense genome
strategy, with viral genes in different
orientations.
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DEFINITION

The genus Circovirus includes beak
and feather disease virus, canary
circovirus, goose circovirus, pigeon
circovirus, and porcine circoviruses 1
and 2.

Chicken anemia virus is the type
member of the genus Gyrovirus, in
which the viral genes are all in the
same orientation.
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INTRODUCTION

They are small (approximately 20-25
nm in diameter), non-enveloped,
spherical in outline, with T=1
icosahedral symmetry.

Virions are made up of 60 capsid
subunits that package the viral circular
single-stranded DNA.

Chicken anemia virus has 12 trumpetlike structures that are less obvious in
the other circoviruses.
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
Mature virions appear in diagnostic
specimens and in linear “strings of
pearls” in cell-free diagnostic
specimens.

Beak and feather disease virus,
porcine circovirus 1 and 2, and the
other members of the genus Circovirus
utilize an ambisense transcription
strategy-some genes are encoded in
the viral sense DNA and others in the
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
Mature virions appear in diagnostic
specimens and in linear “strings of
pearls” in cell-free diagnostic
specimens.

Beak and feather disease virus,
porcine circovirus 1 and 2, and the
other members of the genus Circovirus
utilize an ambisense transcription
strategy-some genes are encoded in
the viral sense DNA and others in the
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complementary strand.

Beak and feather disease virus has
three ORFs and porcine circovirus has
four; in each case there is one major
capsid protein.

The genes of chicken anemia virus are
all encoded in the complementary
positive-sense DNA strand that is
transcribed to give a single
polycistronic transcript.
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
Chicken anemia virus has three ORFs;
one encodes the VP1 (present in
virions); another virus-encoded VP3,
apoptin, induces apoptosis of T
lymphocytes.

These viruses are stable ; not
inactivation by heating.

CAV hemagglutinate RBC and binds to
sialic acid on the cell surface.
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
Viral DNA replication occurs in the
nucleus and requires cellular proteins
and other components produced
during the S phase.

Replication of the genome occurs via a
rolling circle that originates at a stemloop structure.

The viral replication is maximized in
actively dividing cells in young animals.
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
Viral DNA replication occurs in the
nucleus and requires cellular proteins
and other components produced
during the S phase.

Replication of the genome occurs via a
rolling circle that originates at a stemloop structure.

The viral replication is maximized in
actively dividing cells in young animals.
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INTRODUCTION

Replication of porcine circovirus is
enhanced during periods of immune
stimulation that result in proliferation
of lymphocytes in which virus can
replicate.

CAV replication in the oviduct may be
regulated by estrogen, particularly
during egg laying, to allow more
efficient vertical transmission.
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INTRODUCTION

Replication of porcine circovirus is
enhanced during periods of immune
stimulation that result in proliferation
of lymphocytes in which virus can
replicate.

CAV replication in the oviduct may be
regulated by estrogen, particularly
during egg laying, to allow more
efficient vertical transmission.
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INTRODUCTION

The apoptin causes destruction of
infected lymphocytes and promotes a
relative immune suppression that
favors virus persistence.
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