Parvovirus B19

A negatively stained preparation of parvovirus seen by transmission electron microscope. www.wadsworth.org

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

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

Environmental Habitat

• Wide distribution among warm-blooded animals

• B19 is only known HUMAN parvovirus

Pathogenicity

• Fifth disease– Erythema infectiosum

• Aplastic crisis– Patients with hemoglobinopathies

– Immunosuppressed, immunodeficient, immunocompromised

• Congenital parvovirus– Hydrops fetalis

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

Fifth Disease

Six separate childhood exanthems were defined from what was once called the “measles” (Early 20th Century)1st Measles (rubeola) Morbillivirus2nd Scarlet fever (Streptococcus pyogenes )3rd Rubella (German measles)4th Atypical scarlet fever Duke Filatow's disease staph5th Erythema infectiosum6th Roseola herpesviruses (HHV-6 and HHV-7)

Exanthem = rash Fifth disease is the only one still called by this name

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

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.

Erythema infectiosum

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

Symptoms – Aplastic Crisis

Anemic patientsPallor, fatigue, drop in

hemoglobin >1g/dL Destroys infected red blood

cellsNo reticulocytes to replace

aging or damaged erythrocytes

This normally happens in disease but is symptomatic in anemic patients

Thrombocytopenic patientsBruising

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.

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

Hydrops Fetalis

The fetus weighing 1,010 g shows features of hydrops fetalis. Mild maceration is observed

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.

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

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

Henoch-Schönlein purpura (HSP)

This picture is for Natalie