Parvo viruses
lec-10
Family Parvoviridae:
The Parvoviruses are very small simplest viruses that are 18–26 nm in diameter.
Their genome contain small coding capacity in ssDNA so viral replication is
dependent on functions supplied by replicating host cells or by co infection
helper viruses . family containing three genera.. These viruses are specific for
the spectrum of tissues that can be infected. Unlike other DNA viruses, the
parvoviruses do not encode genes that induce the cell to enter lysogenic phase,
and they can only replicate in cells that are actively replicating.
Properties of Parvo viruses:
i.Structure:
o Icosahedral
o 18-26 nm diameter
o Single-stranded DNA , 5.6 kb
o Two proteins one major(VP1) & one minor(VP2)
o Non enveloped
ii.Classification
Parvoviridae (vertebrates)
1. Parvovirus
2. Erythrovirus
3. Dependovirus (requires helper virus, such as an adenovirus)
iii. Replication:
o Attachment and entry
o Translocation of viral DNA into nucleus
o Transcription and translation of viral nonstructural protein and nucleocapsid
o DNA replication
o Virus assembly (nucleus)
o Release from the cell through lysis .
iv.
Transmission:
B19 virus is transmitted by respiratory route.
Transplancental transmission.
Blood donated for transfusions.
Parvovirus Infections in Humans
There are four main diseases for parvo virus (B19):
Fifth disease
fetal anemia
Diseases
Transient aplastic
crisis
chronic anemia
Erythema infection {Fifth Disease}(cutaneous rash)
Erythema infectiosum (EI) often occurs in among school-aged children,
although it can occur in adults as well , the classic rash appears on the cheek ,
This facial rash is often followed by a reticulated rash on the trunk and
extremities .
 Targets red blood cell progenitors Results in lysis of cells.
 Pain in joints
 Anemia & Rarely fatal and without complications.
Transient aplastic crisis(severe acute anemia)
Individuals with a history of hematologic abnormalities, including increased
RBC destruction eg, Sickle cell disease & Thalassemias or decreased RBC
production (eg, iron deficiency anemia) are at increased risk of developing
transient aplastic crisis (TAC) secondary to parvovirus infection & Sometimes
fatal .
Infection of immunodeficient patients(chronic anemia)
Immunosuppressed patients are at risk of developing acute or chronic anemia
following B19 infection due to lack of protective antibodies .Can cause persistent
infection in bone marrow & Suppress red cell maturation this Leads to anemia.
Infection during pregnancy(fatal fetal anemia)
-If woman infected with B19 virus in first months of pregnancy ,virus cross
placenta and infect fetus so can cause fetal anemia and this infection associated
with fetal death.
-Whereas infection during last months of pregnancy leads to Hydrops fetalis in
which failure heart ,liver & bone marrow.