Infectious Disease · Viral Exanthems
The facts most likely to be tested
Erythema infectiosum is caused by Parvovirus B19, a single-stranded DNA virus that targets erythroid progenitor cells.
The classic clinical presentation begins with a slapped-cheek rash on the face followed by a reticular, lacy, maculopapular rash on the trunk and extremities.
Infection with Parvovirus B19 in patients with chronic hemolytic anemias (e.g., sickle cell disease, hereditary spherocytosis) triggers a transient aplastic crisis due to temporary cessation of erythropoiesis.
Adults, particularly women, frequently present with acute, symmetric polyarthropathy involving the small joints of the hands, which can mimic rheumatoid arthritis.
Maternal infection during pregnancy can lead to fetal hydrops (hydrops fetalis) due to severe fetal anemia and high-output heart failure.
Diagnosis is typically clinical, but in high-risk patients, it is confirmed by detecting Parvovirus B19-specific IgM antibodies.
Patients are most infectious during the prodromal phase before the onset of the characteristic rash, and they are generally no longer contagious once the rash appears.
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A 7-year-old boy is brought to the clinic by his mother due to a rash that appeared two days ago. The mother notes he had a mild fever and runny nose last week, which have since resolved. Physical examination reveals a bright red, slapped-cheek rash on both cheeks and a faint, reticular, lacy rash on his arms and torso. The child is currently afebrile and appears well. His medical history is significant for sickle cell disease.
Given the patient's underlying condition, what is the most significant potential complication of this infection?
Transient aplastic crisis
The patient has classic signs of Fifth Disease (Parvovirus B19), which causes a temporary arrest of erythropoiesis; in patients with chronic hemolytic anemia, this leads to a life-threatening transient aplastic crisis.
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Etiology / Epidemiology
Caused by Parvovirus B19; primarily affects school-aged children via respiratory droplets.
Clinical Manifestations
Presents with slapped-cheek rash followed by a reticular, lacy rash on the trunk/extremities.
Diagnosis
Clinical diagnosis; Parvovirus B19 IgM antibodies confirm in uncertain cases.
Treatment
Management is supportive; avoid pregnant women due to risk of fetal hydrops.
Prognosis
Self-limiting in healthy hosts; aplastic crisis in patients with chronic hemolytic anemias.
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Epidemiology & Etiology
Erythema infectiosum is a common viral exanthem caused by Parvovirus B19, a single-stranded DNA virus. It spreads via respiratory droplets and has a high secondary attack rate in household contacts. Peak incidence occurs in late winter and spring among school-aged children.
Pertinent Anatomy
The virus exhibits tropism for erythroid progenitor cells in the bone marrow. This affinity explains the transient suppression of erythropoiesis that characterizes the disease course.
Pathophysiology
The virus binds to the P antigen on erythroid precursors, leading to cell lysis and a temporary cessation of red blood cell production. In healthy individuals, this is clinically silent. However, in patients with chronic hemolytic anemias (e.g., sickle cell), this leads to a transient aplastic crisis.
Clinical Manifestations
The illness begins with a nonspecific prodrome of fever and malaise. This is followed by the pathognomonic slapped-cheek facial erythema, which spares the perioral region. A reticular, lacy rash subsequently develops on the trunk and extremities. Red flag: Infection in pregnant women can cause fetal hydrops and intrauterine fetal demise.
Diagnosis
Diagnosis is typically clinical based on the classic rash pattern. In immunocompromised patients or those with suspected hematologic complications, Parvovirus B19 IgM antibodies are the diagnostic test of choice. PCR testing for viral DNA is reserved for patients with chronic anemia or immunodeficiency.
Treatment
Treatment is supportive with antipyretics and hydration. No specific antiviral therapy exists. Contraindications: Pregnant patients should be counseled on the risk of vertical transmission. Patients with aplastic crisis require blood transfusions and hospital admission.
Prognosis
The condition is self-limiting in immunocompetent children. Aplastic crisis is the most significant complication, requiring monitoring of hemoglobin levels. Patients are generally no longer infectious once the rash appears, allowing for school attendance.
Differential Diagnosis
Rubella: associated with posterior cervical lymphadenopathy
Measles: presents with the three C's (cough, coryza, conjunctivitis) and Koplik spots
Roseola: high fever that resolves abruptly before the rash appears
Scarlet Fever: sandpaper-like rash with circumoral pallor and strawberry tongue
Kawasaki Disease: prolonged fever >5 days with conjunctivitis and mucosal changes