Chapter 319

Human parvovirus (HPV) B19 was first discovered in 1975 in serum specimens from healthy blood donors.1 Parvovirus B19 belongs to the genus Parvovirus, an autonomously replicating, small single-stranded DNA virus. It is the infectious agent of a number of clinical syndromes, including erythema infectiosum (formerly known as fifth disease), acute arthritis, and aplastic crises in patients with congenital hemolytic anemia.2-4 When acquired by a pregnant woman, it can lead to spontaneous abortion, intrauterine fetal hydrops, and stillbirths.5,6

The Parvoviridiae family includes two genera of vertebrate viruses and one genus of invertebrate viruses. Only HPV B19 infects humans and is known to be associated with disease.

### Epidemidology

Parvovirus infections are most commonly recognized in school-age children. Infections can be sporadic, although epidemics occasionally do occur, most commonly in late winter or spring. Approximately 70% of recognized infections occur in children between 5 and 15 years of age. Children younger than 5 years have a seroprevalence of 2% to 9%, children 5 to 18 years old have a seroprevalence of 15% to 60%, and adults have a seroprevalence of 30% to 60%.7 Secondary attack rates are approximately 50% within households and variable in school outbreaks.7Males and females are equally affected with erythema infectiosum, whereas arthritis is more common in females.8

Because the virus is present in respiratory secretions of viremic patients, transmission occurs most frequently via respiratory droplets. Patients with erythema infectiosum are infectious before, not during, the rash, whereas patients with an aplastic crisis are likely to be most infectious at the time of the acute presentation.9 Parvovirus is rarely transmitted by transfusion of blood or, more commonly, clotting factor concentrates. Vertical transmission from mother to infant also occurs.

### Pathophysiology

The virus enters cells by binding to a receptor called globoside or erythrocyte P antigen. Individuals lacking this receptor cannot be infected with HPV B19.10 Intranasal infection of HPV in human volunteers resulted in fever, malaise, and itching approximately 1 week after infection. During this period, susceptible volunteers were viremic and had respiratory shedding. During the second week of infection, IgM developed, and there was reticulocytopenia. Development of arthritis or rash during the third week of infection coincided with the development of an IgG response.11 Therefore, the pathogenesis in patients with erythema infectiosum or arthritis is believed to be secondary to immune complex disease. The pathogenesis of some of the more serious complications is related to the viral effect on erythrocyte precursors, leading to pronormoblast arrest.

### Clinical Manifestations

#### Erythema Infectiosum

Many infected individuals have no recognizable symptoms; however, when a clinical syndrome does occur, it causes erythema infectiosum (EI), also known as fifth disease, a common childhood exanthem. It is characterized by a prodromal illness, usually consisting of malaise, pharyngitis, and low-grade ...

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