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