David Helfinstine Clinical Microbiology II July 31, Parvovirus B19

Transcription

1 David Helfinstine Clinical Microbiology II July 31, 2007 Parvovirus B19

2 Parvovirus B19 Family: Parvoviridae Latin parvus means small ~20 nm in diameter (0.02 µm) Single-stranded DNA virus Icosahedral capsid X-ray crystallographic image of parvovirus No envelope Only known human 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

4 Environmental Habitat Wide distribution among warm-blooded animals B19 is only known HUMAN parvovirus

5 Pathogenicity Fifth disease Erythema infectiosum Aplastic crisis Patients with hemoglobinopathies Immunosuppressed, immunodeficient, immunocompromised Congenital parvovirus Hydrops fetalis

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 20 th Century) 1 st Measles 2 nd Scarlet fever 3 rd Rubella (German measles) 4 th Atypical scarlet fever 5 th Erythema infectiosum 6 th Roseola 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 Myalgia 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 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 IgG IgM Risk Positive Negative No risk Positive Positive Possible risk Negative Positive Higher risk Negative Negative No infection Repeat serology tests in 3 weeks. Development of IgM indicates an acute infection. Can be fatal to the fetus

13 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

14 Henoch-Schönlein purpura (HSP) This picture is for Natalie