BACKGROUND

The "slapped cheek" appearance is typical of parvovirus B19 infection. Parvovirus B19 is a single stranded DNA virus with no envelope.

In addition to asymptomatic infection, parvovirus B19 can cause erythema infectiosum. Erythema infectiosum (fifth disease) is a benign rash of childhood. Infected persons develop fever and facial erythema described as a "slapped cheek" appearance. A lacy reticular rash may occur on the trunk and extremities. Other clinical syndromes caused by parvovirus B19 are an acute symmetrical peripheral arthritis in adults, TAC (transient aplastic crises) in patients with hemoglobinopathies (e.g., sickle cell disease), chronic anemia in immunodeficient patients, and intrauterine infection and fetal death.

1. How is the virus transmitted? Is the child contagious?

Parvovirus B19 can be transmitted by the respiratory route and by transfusions. (By early adulthood, 30 to 60% of the population have acquired parvovirus B19 infection). This child is no longer infectious, but likely exposed all household contacts prior to the development of the rash.

2. What is known about the pathogenesis of the infection?

Parvovirus B19 infects and lyses erythroid precursor cells. This can lead to transient aplastic crises (TAC) in patients with hemolytic states. Bone marrow examinations in these patients characteristically show erythroid hypoplasia. The duration of TAC is usually 7 to 10 days. Fetal death appears to be caused by severe anemia. Fetal infections may not always be fatal. There is no association of parvovirus B19 with congenital anomalies. Patients with TAC have a high virus load and are very contagious. Patients with Fifth disease are experiencing an immune-mediated reaction to the virus following viremia, and are not contagious at the time of the rash.

3. This patient didn't even go to the doctor. What other parvovirus B-19 infected patients are more likely to be seen in the clinic or hospital? Are these patients contagious?

Patients are generally contagious at the initial (prodrome) phase of the illness, not when the rash is present. The clinical consequences of this effect are generally trivial, unless the patient is already compromised by a chronic hemolytic process, such as sickle cell disease or thalassemia, in which maximal erythropoiesis is continually needed to counterbalance increased destruction of circulating erythrocytes. Primary infection by parvovirus B19 in such patients often produces an acute, severe, sometimes fatal anemia manifested as a rapid fall in red blood cell counts and hemoglobin. This may present initially with no clinical symptoms other than fever, and is commonly referred to as transient aplastic crisis. These patients are highly contagious and should be placed in respiratory isolation. Immunocompromised patients, such as individuals with AIDS, sometimes have difficulty clearing the virus and develop persistent anemia with reticulocytopenia. Parvovirus B19 has also been occasionally implicated as a cause of persistent bone marrow failure and an acute hemophagocytic syndrome.

Serious complications are extremely rare; however active transplacental transmission of parvovirus B19 can occur during primary infections in pregnancy, sometimes resulting in stillbirth of fetuses that are profoundly anemic. The progress can be so severe that hypoxic damage to the heart, liver, and other tissues leads to extensive edema (hydrops fetalis). The frequency of such adverse outcomes is as yet undetermined.

4.  If you had to confirm the diagnosis, how could you do it?

The diagnosis can be made by demonstrating parvovirus B19 IgM serum antibodies in the patient with Fifth disease or by the presence of parvovirus B19 DNA or antigen in the serum in the patient with aplastic crisis. Histopathologically, eosinophilic intranuclear inclusions in infected tissues or virus particles seen by electron microscopy can lead to the diagnosis. Although parvovirus B19 can replicate in bone marrow explant cultures, no routine virus isolation methods are currently available for diagnostic purposes.

5. The patient's mother is pregnant and expresses concern about her unborn child. What do you tell her?

She should be informed that parvovirus B19 is a common illness which she likely had as a child. However, if she does experience a primary infection, her unborn child should be monitored (by ultrasound) for possible hydrops.