Description

• Human parvovirus B19 is the primary cause of erythema infectiosum (EI, or fifth disease).
• Complications in susceptible individuals include transient aplastic crisis (TAC) in patients with increased RBC turnover (e.g., sickle-cell anemia), chronic anemia in immunodeficient individuals, and arthritis and arthralgias in normal hosts:
  • Pregnant women who are not immune are at risk of intrauterine infection, with potentially significant consequences to the fetus.
• System(s) affected: Mainly Hemic/Lymphatic/Immunologic; Musculoskeletal; Skin/Exocrine; possibly Central Nervous System (CNS); Cardiac; Renal

Pregnancy Considerations
Documentation of acute infection during pregnancy should prompt referral to a maternal–fetal medicine specialist. Maternal B19 infection between 9 and 20 weeks' gestation may be associated with a significant risk for developing fetal anemia.

Epidemiology

• Infection is common in childhood.
• Predominant age: Peak age for EI is 4–12 years.
• Of children 15 years of age, 50% are parvovirus B19-seropositive.
• Predominant sex: Male = Female
• Epidemics occur in late spring every 2–4 years.

• Extremely common in the US; >50% of adults have evidence of prior infection. Most common as community epidemics in winter and spring in nontropical regions
• Antibody IgG prevalence:
  • 1–5 years: 2–15%
  • 6–9 years: 20–40%
  • 11–19 years: 35–60%
  • >50 years: >75%

Risk Factors

• School-related epidemic and nonimmune household contacts have a secondary attack rate of 50%.
• Highest secondary attack rates are for daycare providers and school personnel in contact with affected children.
• Those with increased cell turnover (e.g., sickle cell [SS] anemia, thalassemia) are at risk for aplastic crisis.
• Immunodeficiency (e.g., HIV infection) may increase risk of chronic anemia.
• Of pregnant women, 40% are not immune, with 1.5% seroconversion/year.

Genetics
Erythrocyte P antigen-negative individuals are resistant to infection.

General Prevention

• Standard hygienic practices include frequent handwashing and wearing barrier protection, such as surgical masks, when treating patients with possible respiratory viral infections.
• Because EI is so common, it is impossible to avoid exposure completely. Also, period of contagion is before clinical illness (rash) appears.
• Pregnant health care workers should avoid caring for patients with transient aplastic crises.
• No significant risk of infection based on occupational exposure. Thus, exclusion from the workplace is not recommended.
• Currently, no vaccine available to prevent the disease, although a parvovirus B19 virus-like particle (VLP) has previously been studied.

Pathophysiology

• Natural host of B19 is human erythroid progenitor.
• Infection of proerythroblasts causes cessation of RBC production.

Etiology

• Small (20–25 mm), nonenveloped, single-stranded DNA virus:
  • Only known parvovirus to infect humans; it belongs to the family Parvoviridae.
• Respiratory secretions and, rarely, blood products are sources of human spread of virus.
• Maternal viremia with transplacental passage is the source of fetal infection.
• In EI, the rash is thought to be autoimmune due to IgM complexes.