Parvovirus B19 A negatively stained preparation of parvovirus seen by transmission electron microscope.

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 20 th Century) 1 st Measles (rubeola) Morbillivirus 2 nd Scarlet fever ( Streptococcus pyogenes ) 3 rd Rubella (German measles) 4 th Atypical scarlet fever Duke Filatow's disease staph 5 th Erythema infectiosum 6 th 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 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.

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 IgGIgMRisk PositiveNegativeNo risk Positive Possible risk NegativePositiveHigher risk 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