Human parvovirus B19 is the primary cause of erythema infectiosum (EI, or fifth disease). It also causes aplastic anemia in patients with increased RBC turnover (e.g., sickle cell anemia), chronic anemia in immunodeficient individuals, and arthritis and arthralgias in normal hosts. There is also the potential for intrauterine infection after maternal parvovirus B19 infection.

• System(s) affected: Skin/Exocrine, Musculoskeletal, Hemic/Lymphatic/Immunologic
• Genetics: Erythrocyte P antigen-negative individuals are resistant to infection
• Incidence/Prevalence in USA: Extremely common; 50% of adults have evidence of prior infection. Most common as community epidemics in winter and spring in non-tropical regions.
• Predominant age:
  • Infection is common in childhood; approximately 2–11% of children under 11 years of age are parvovirus B19 seropositive
  • Peak age for EI is 4–12 years
• Predominant sex: Male = Female

• Erythema infectiosum (EI)
  • Incubation period 4–14 days
  • No preclinical symptoms most commonly. Fever is absent or low grade.
  • Onset of rash noted first on the face (“slapped cheek appearance”) with diffuse erythema of the face followed 1–4 days later by a second stage of a lacy reticular rash on the trunk and limbs
  • A third stage of the rash is characterized by marked evanescence and recrudescence, sometimes associated with bathing, exercise, or sun exposure
  • Pruritus and mild arthralgia may occur
  • Headache, pharyngitis, coryza, myalgia, arthralgias, arthritis, and GI disturbances are more frequent and severe in adults
• Joint disease
  • In adults, 80% of patients may manifest arthritis and/or arthralgia
  • In children, joint symptoms are less common
  • Knees, hands, and ankles (frequently symmetrical) are most commonly involved
  • Joint symptoms usually subside in weeks but may persist for months. Joint destruction generally not seen.
• Transient aplastic crisis
  • Seen in patients with chronic hemolysis, such as sickle cell anemia, spherocytosis, thalassemia, and pyruvate kinase deficiency
  • Aplastic event is self-limited with reticulocytes reappearing in 7–10 days and full recovery in 2–3 weeks
• Chronic anemia
  • Seen in immunodeficient individuals
  • No manifestations of fever, rash, or joint symptoms usually
• Fetal/neonatal infection
  • Risk of transplacental spread of virus approximately 33% in infected mothers
  • Clinical manifestations range from asymptomatic seroconversion (most commonly), no seroconversion, second trimester fetal death, or stillbirth secondary to severe anemia and the development of fetal hydrops
  • The principal organ involved in the fetus is the bone marrow: RBC survival is shortened and profound anemia can result from B19-induced erythroid bone marrow aplasia
  • Risk of fetal loss in pregnancy is highest in first trimester B19 infection (9%)
  • Anemia is the most common manifestation of later infection
  • In one study, 84% of B19-infected pregnant women who carried to term delivered normal infants
  • No known long-term developmental problems in infant survivors
• Glove-sock syndrome: severe petechial and ecchymotic rash in hand-foot distribution with associated febrile tonsillopharyngitis

• Small (20–25 nm), nonenveloped, single-stranded DNA virus
• In erythema infectiosum (EI), the period of viral shedding precedes the development of the rash, suggesting the pathogenesis of the rash is immune related
• In fetal infection, maternal viremia with transplacental passage is the source of infection. Respiratory secretions and, rarely, blood products are sources of human spread of the virus.

• Aplastic crisis – increased RBC turnover (e.g., sickle cell anemia)
• Chronic anemia – immunodeficient individuals
• Intrauterine infection – pregnant, nonimmune woman