Parvovirus B19 is a small, non-enveloped, single-stranded DNA virus that causes Fifth disease or erythema infectiosum. It is transmitted through respiratory droplets and replicates in human erythroid progenitor cells. Parvovirus B19 infection presents as a characteristic "slap cheek" rash and can cause aplastic crisis in patients with blood disorders by destroying red blood cells. In pregnant women, it can cause hydrops fetalis, a severe fetal condition of fluid buildup. While Fifth disease resolves within a week, supportive care and immunoglobulins may be used to treat more severe manifestations of Parvovirus B19 infection.
1. Parvovirus B19
A negatively stained preparation of parvovirus seen by
transmission electron microscope. www.wadsworth.org
2. Parvovirus B19
• Family: Parvoviridae
– Latin parvus means small
• ~20 nm in diameter
– (0.02 µm)
• Single-stranded DNA virus
• Icosahedral capsid
• No envelope
• Only known human parvovirus
X-ray crystallographic image of parvovirus
3. Body source & Transmission
• 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
6. Pathogenicity
• Associated with:
– Encephalitis, neuropathies, myocarditis, nephritis,
systemic lupus erythematosus (SLE), Henoch-
Schönlein purpura (HSP), and rheumatoid arthritis
Henoch-Schönlein purpura (HSP)
Note: this is usually caused by the measles
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.
11. 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.
12. Symptoms – Hydrops Fetalis
• Pregnant women exposed to B19 should have IgG
and IgM serology ASAP
– Repeat serology tests in 3 weeks. Development of IgM
indicates an acute infection.
– Can be fatal to the fetus
IgG IgM Risk
Positive Negative No risk
Positive Positive Possible risk
Negative Positive Higher risk
Negative Negative No infection
13. Hydrops Fetalis
The fetus weighing 1,010 g shows features of hydrops fetalis. Mild maceration is observed
14. Hydrops Fetalis
In the internal organs, the markedly anemic (pale yellowish brown-colored) liver is quite
characteristic (gross findings). The fetus with hepatic hematopoiesis (19-29 weeks of
gestation) is susceptible to this single-stranded DNA virus.
15. Identification
• Lab studies not normally done because it resolves in
5-7 days
• Serology – IgM and IgG
– ELISA
– Radioimmunoassay (RIA)
– Immunofluorescence
– Difficult to interpret
• Polymerase Chain Reaction (PCR)
– Useful for clinical diagnosis
– Detects viral DNA in serum
• Cannot be cultured in cells
16. Treatment
Mainly supportive care
Acetaminophen or Ibuprofen for fever
Topical anesthetic or antihistamine for itching
Intravenous Immunoglobulin (IVIG) in
chronic parvovirus
Aplastic crisis may require
packed RBC transfusion
Vaccine is in trials