Cause:Parvovirus B19
Pathophys:P antigen on rbc is prime cellular receptor for the virus; hence the rare pt who is pp (homozygously P antigen-negative) is immune from infection (Nejm 1994;330:1192). Anemias and CHF occur because infection of erythroid progenitor cells results in their lysis acutely, and these conditions then develop if there is already chronic hemolysis for some other reason, or if no antibodies are formed at all, as in AIDS (Ann IM 1990;113:926)
Endemic and epidemic; spread primarily by respiratory secretions esp in infected young children (Jama 1999;281:1099). Nosocomial epidemics in nursing staffs caring for children in aplastic crisis (Nejm 1989;321:485). 2-yr-olds are 75% seropositive (Nejm 2005;352:768). In adults, 50+% are seropositive indicating past infection
Sx:7- to 10-d incubation period. 20% of adults and children may be asymptomatic. In children it presents as a rash; in adults it presents as a polyarthritis and malaise
Si:In children, "slapped cheek" may then develop into a diffuse exanthematous, pruritic rash lasting 5-7 d (picture—Nejm 1994;331:1062). In adults, an acute arthritis; and a lacy rash on neck, extremities, trunk but not face
Arthritis is usually self-limited although it can be chronic and recurrent; rash may recur over weeks or months
r/o other childhood exanthems: chickenpox, rubeola, scarlet fever, rubella, and roseola; in adults, Lyme and collagen vascular diseases
Aplastic crisis in patients with underlying chronic hemolysis and occasionally chronic marrow failure (Nejm 1987;317:287)
In pregnant women, spontaneous abortion in 1-3% exposed in 1st 20 weeks of pregnancy (Nejm 1986;315:77); other fetal anomalies (Nejm 1987;316:183; 1985;313:74) including hydrops fetalis from anemia and CHF (Ann IM 1990;113:926)
Lab:
Hem:Marrow has giant pronormoblasts and/or multiple nucleoli in pronormoblasts
Serol:IgM, IgG antibody titers by ELISA (Jama 1999;281:1099); or, in immunosuppressed, by DNA dot-blot hybridization studies of serum (Ann IM 1990;113:926)