Parvovirus B-19 - MegaMicro

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Parvovirus B-19

Microbiology > Virology > DNA viruses
Structure:  The family Parvovirdiae  contain the smallest of the DNA viruses (18-26 nm in diameter).   Parvovirus B19 is included in the Erythroparvovirus genus.  Structurally, they are non-enveloped with an icosahedral capsid containing a linear, single-stranded DNA genome.

Epidemiology:
• Discovered in 1975 while screening blood for Hepatitis B virus; the sample was number 19 in panel B, thus the designation B19.  B19 is the predominant parvovirus pathogen in humans.
• Found worldwide with infections more often in winter through late spring.
• Most commonly causes Fifth’s Disease (erythema infectiosum), a mild rash illness generally affecting children (historically the 5th skin rash illness described in children).  Adults may also become infected.
• Transmission is primarily via respiratory secretions, but may also be spread by infected blood/blood products and pregnant women may pass the virus to their fetus (especially when infected in the first 20 weeks of gestation).  
• Transmission is human-to-human.  Although dogs and cats can become infected with other parvoviruses, these cannot be transmitted to humans.

Pathobiology:
• Studies with volunteers suggest that the virus first replicates in the nasopharynx or upper respiratory tract, comes viremic and spreads to the bone marrow.
• Erythroid precursor cells (EPC) in the bone marrow are the only known cell type to support full replication of the virus resulting in reduced numbers of reticulocytes, lymphocytes, neutrophils, and platelets.
• Although the pathogenesis of the rash and arthropathy is not clear, they are presumed to be at least partially immune mediated.

Laboratory diagnosis:
• Serological tests are the standard diagnostic tool to determine parvovirus  immune status.
• Acute disease is associated with elevated parvovirus specific IgM levels.
• Detection of the viral DNA by molecular techniques (such as PCR) in samples of blood, amniotic fluid, CSF, bone marrow and synovial fluid.
• Decrease in hematocrit and reticulocytes.

Disease manifestations:
• The incubation period is 4-12 days with nonspecific symptoms including fever, runny nose, malaise and headache.  
• Initial flu-like symptoms are followed by the development of a characteristic red rash  on the face (“slapped cheek” rash).  Some individuals may experience a second rash on their body that appears shortly after the face rash.  The rash varies in intensity and may resolve and reappear for a few weeks.  More commonly it resolves within 7-10 days.  
• Painful and swollen joints are another symptom of fifth disease, and may be the only symptom in adult infections.
• Aplastic crisis: The reduction in normal erythropoiesis may be dangerous for immunocompromised patients who may develop chronic infection, and patients with sickle cell disease or other chronic anemias that require hyperactive bone marrow to replace lysed RBCs.
• Infection of a pregnant, seronegative woman may be life-threatening for the fetus by leading to anemia or congestive heart failure. Congenital anomalies have not been associated with this infection.

Differential Diagnosis:
• Depends on the clinical presentation:
o fifth’s disease:  other infectious exanthemas such as rubella, roseola, measles, enterovirus and Group A streptococcus infections or drug hypersensitivity
o arthropathy:  rheumatoid arthritis, transient arthritis caused by other infectious organisms

Treatment:
  • Supportive treatment for symptomatic relief as no specific anti-viral medication is available.
  • IV immune globulin may be used for chronic infection in the immune compromised (ie. HIV/AIDS)

Prevention and Control:
• Currently, no vaccine or medication can prevent parvovirus B19 infections; however the illness is typically mild and bestows immunity.  
• Preventative measures include good hand hygiene and proper respiratory etiquette.
• If sick, stay at home.  After the rash appears, the infected individual is most likely no longer contagious and can return to normal daily activity.  

Related concepts
Aplastic crisis
Anemia

Web links:  http://www.cdc.gov/parvovirusb19
Images: from CDC.gov/parvovirusb19
“slapped cheek” rash of fifth’s disease

 
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