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Parvoviruses
Properties of Parvoviruses
• Structure
• Icosahedral
• 18-26 nm diameter
• Single-stranded DNA, 5.6 kb
• Two proteins
• Nonenveloped
• Classification
• Parvoviridae (vertebrates)
• Parvovirus
• Erythrovirus
• Dependovirus (requires helper virus, such as an adenovirus)
• Densovirinae (insects)
• Replication
• Attachment and entry
• Translocation of viral DNA into nucleus
• Transcription and translation of viral nonstructural protein and nucleocapsid
• DNA replication
• Virus assembly (nucleus)
• Release from the cell through lysis
Properties of Parvoviruses
Parvovirus Infections in Humans
• Diseases
• Fifth disease (cutaneous rash)
• Transient aplastic crisis (severe acute anemia)
• Pure red cell aplasia (chronic anemia)
• Hydrops fetalis (fatal fetal anemia)
• B19 virus most common
• Fifth Disease
• Targets red blood cell progenitors
• Pain in joints
• Results in lysis of cells, thus depleting source of mature red cells
• Anemia ensues
• Rarely fatal and without complications
Fifth Disease (parvovirus B19)
• Transient aplastic crisis
• B19 infection of those with other hemolytic anemias
• Sickle cell disease
• Thalassemias
• Can complicate crises
• Sometimes fatal
• Infection of immunodeficient patients
• Can cause persistent infection in bone marrow
• Suppress red cell maturation
• Leads to anemia
• Infection during pregnancy
• Can cause fetal anemia
• Usually not fatal to fetus
Parvovirus Infections in Humans
Structure
Capsid proteins: VP1-3. These three proteins protect the genetic
information and help with entry into the host cell.
Non-Capsid protein: NS-1. This protein is necessary for viral DNA
replication and ATP binding.
Parvovirus forms an icosahedral structure that is resistant to pH,
solvents and temperature up to 50°C
Laboratory Diagnosis
• PCR is most sensitive
• Most useful during viremia
• Otherwise, requires tissue biopsy or bone marrow tap
• Serological testing for IgM
• Determines recent infection
• IgG testing is not informative
Mode of infection
• Parvovirus B19 spreads through respiratory means (when an infected person coughs or sneezes) and touching exposed surfaces (doorknobs, sinks, light switches, etc...)
• -The B19 virus can also spread through blood. If a woman infected with Parvovirus B19 is pregnant, she can pass the virus to her baby.
• -Palindromic sequences of about 120-250 nucleotides are found at the 5’ and 3’ ends of this genome. These form hairpins and are essential for viral genome replication. Basically, Parvovirus is a vector.
• -When Parvovirus enters an organism, it triggers apoptosis, or cell death. It then continues to attack muscle and bone marrow cells.
• -A person is most contagious before they get the rash or joint pain, when it seems like they have "just a cold". After the rash appears, they are probably not contagious.
Epidemiology• B19 virus is common and widespread
• Most adults have been infected
• Most infections are subclinical
• IgG is detectable in most healthy people
• Sporadic outbreaks, usually among children, occur each year
• Transmission from patient to health care staff is not uncommon
• Role in nosocomial transmission to other patients
• Treatment
• Address symptoms
• Transfusions for serious anemic crises
• Commercially-available neutralizing IgG (passive immunization)
• Prevention and control
• No vaccine available for human parvoviruses
• Good hygienic practices mitigate transmission
Canine Parvovirus
• Canine parvovirus (CPV-2) appears to be a mutant strain of feline parvovirus
• Some breeds are more sensitive to CPV infection
• The virus is considered ubiquitous in the environment
• It is a hardy virus
• Can survive for extended periods on fomites
• Transmitted through oral-fecal route
• Symptoms: dehydration, vomiting, bloody diarrhea
• Vaccine is available