1. A negatively stained preparation of parvovirus seen by transmission electron microscope.

2. Properties of Parvoviruses
Structure
Icosahedral
18-26 nm diameter
Single-stranded DNA, 5.6 kb
Two proteins
Nonenveloped

3. Human parvoviruses B19 Bocavirus Adeno-associated viruses (AAVs)
can cause acute respiratory disease, which may become severe in young children
Adeno-associated viruses (AAVs)
infect humans
replicate with a second “helper” virus, usually an adenovirus

4. B19
Replication in human cells restricted to erythroid progenitor cells
Adult bone marrow
Fetal liver
Transmission by close contact
Airborne droplets
50% of a household may become infected
10-60% of students in school outbreaks

5. Virologic, immunologic, and clinical course following B19 infection.
Virologic, immunologic, and clinical course following B19 infection. Data from references 8 and 254.
Heegaard E D , and Brown K E Clin. Microbiol. Rev. 2002;15:

6. Parvovirus B-19 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)
Fifth Disease (parvovirus B19)

7. Fifth Disease
Six separate childhood exanthems were defined from what was once called the “measles” (Early 20th Century)
1st Measles (rubeola) Morbillivirus
2nd Scarlet fever (Streptococcus pyogenes )
3rd Rubella (German measles)
4th Atypical scarlet fever Duke Filatow's disease staph
5th Erythema infectiosum
6th Roseola herpesviruses (HHV-6 and HHV-7)
Exanthem = rash
Fifth disease is the only one still called by this name

8. Symptoms – Fifth Disease
Incubation 7-10 days
Lasts 5-7 days
Three Phases
First phase –peak level of virus and RBC destruction
Fever
Malaise
Chills
Bright red, raised “slap cheek” rash

9. Symptoms – Fifth Disease
Second phase – rash and arthralgia
Virus has disappeared – no longer infectious
Caused by immune complexes in the capillaries of the skin
Appears at presence of parvovirus IgM
Erythematous maculopapular rash on arms and trunk
Fades into a lace-like reticular pattern
Third phase
Frequent clearing and recurrences for weeks
Due to stimuli such as exercise, irritation, or overheating of skin from bathing or sunlight.

10. Erythema infectiosum
“Slap cheek” rash on the face, lacy rash on the extremities.

11. Parvovirus Infections in Humans
Transient aplastic crisis (TAC)
B19 infection of those with other hemolytic anemias
Sickle cell disease
Thalassemias
Can complicate crises
Sometimes fatal

12. Symptoms – Aplastic Crisis
Anemic patients
Pallor, fatigue, drop in hemoglobin >1g/dL
Destroys infected red blood cells
No reticulocytes to replace aging or damaged erythrocytes
This normally happens in disease but is symptomatic in anemic patients
Thrombocytopenic patients
Bruising
Typical giant proerythroblast (arrow) seen in parvovirus B19-associated pure red cell aplasia with highly uncondensed chromatin and pale purple intranuclear inclusions. Bone marrow aspirate.

13. Parvovirus Infections in Humans
Pure Red Cell Anemia (PRCA)
Can cause persistent infection in bone marrow
Suppress red cell maturation
Leads to anemia
Hydrops Fetalis: Infection during pregnancy
Can cause fetal anemia
Usually not fatal to fetus

15. 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