Etiology and Pathogen Characteristics
Erythema infectiosum, also known as fifth disease or slapped cheek syndrome, is caused by parvovirus B19. It is a DNA virus of the family Parvoviridae, genus Erythroparvovirus. The genus name reflects a key biological feature: the virus replicates in bone marrow erythroid progenitor cells, which determines its spectrum of clinical manifestations. Three genotypes of the pathogen are distinguished, though they show virtually no clinical differences.
The term "fifth disease" historically originates from the classification of childhood exanthems—diseases presenting with fever and rash. In this numbering, erythema infectiosum occupies the fifth place, alongside measles, scarlet fever, rubella, and other exanthematous infections.
Epidemiology
Parvovirus infection is a strict anthroponosis: humans serve as the sole reservoir and source. Main routes of transmission:
- Airborne droplet route—the primary mechanism via coughing and sneezing;
- Vertical route—from mother to fetus in the fetal form;
- Bloodstream route (hematogenous)—via transfusion of blood and its components.
The contagious period primarily occurs during the week before the rash appears. From the onset of typical skin manifestations, the child is generally no longer contagious. About 50% of the adult population lacks immunity to B19, which determines the epidemiological significance of the infection, especially for pregnant women.
Clinical Forms
Parvovirus B19 is characterized by a wide spectrum of clinical variants, depending on the patient's immune and hematological status:
- Erythema infectiosum—the typical form in immunocompetent children;
- Arthropathy and arthralgia—more common in adults, especially women, frequently polyarticular in nature;
- Transient aplastic crisis—in patients with hemolytic anemias (e.g., sickle cell disease);
- Chronic red cell aplasia—in individuals with immunodeficiency states, manifested by aplastic anemia;
- Fetal infection—infection of a pregnant woman before 20 weeks of gestation can lead to fetal hydrops, miscarriage, premature birth, and antenatal death;
- "Glove and sock" syndrome—papular-purpuric rash on the hands and feet in adolescents and young adults.
Clinical Presentation of Erythema Infectiosum
The incubation period averages 4–14 days. The disease begins with a prodromal period resembling acute respiratory viral infection (ARVI): fever (febrile or low-grade), lethargy, decreased appetite, and catarrhal symptoms.
After a few days, a pathognomonic symptom develops—bright facial erythema, giving the impression of a slap. 1–4 days later, a second wave of eruptions appears:
- The rash is maculopapular, symmetrical, localized primarily on the extremities, less commonly on the torso;
- The elements coalesce, forming a characteristic "lacy" or reticular pattern;
- The center of the lesions shows pallor, while the periphery presents a palpable elevation;
- Itching is minimal or absent.
A distinct feature is the ability of the rash to recur for weeks and months after recovery under the influence of sun exposure, overheating, hypothermia, physical exertion, or stress. Following the infection, IgG antibodies are produced, providing lifelong immunity.
Diagnostics
The diagnosis in an immunocompetent child is established clinically based on the combination of characteristic symptoms. Laboratory testing is indicated in specific situations:
- Complete blood count (CBC)—to evaluate the erythroid lineage in patients with anemia risk factors;
- PCR for parvovirus B19 DNA—in severe and atypical forms, and in immunocompromised patients;
- Serological testing (IgM, IgG)—mandatory for pregnant women who have been in contact with an infected person to determine immunity status and recent infection;
- Fetal ultrasound—in confirmed or suspected infection in a pregnant woman to rule out fetal hydrops.
Treatment and management tactics
In immunocompetent children, the infection is self-limiting; no specific antiviral therapy has been developed. Treatment is symptomatic:
- Antihistamines if itching is present;
- Antipyretic medications for significant fever;
- Supportive care and limiting sun exposure during periods of recurrent rash.
In severe cases—such as aplastic crisis or marked anemia in immunocompromised patients—packed red blood cell transfusion and intravenous immunoglobulin administration may be required. Pregnant women showing signs of fetal infection are managed jointly with an obstetrician-gynecologist; if fetal hydrops develops, intrauterine blood transfusion is considered.
Key points
- The causative agent of erythema infectiosum is a DNA parvovirus B19, which replicates in erythroid cells.
- The disease is also referred to as fifth disease and slapped cheek syndrome due to the characteristic facial erythema.
- Transmission is primarily airborne; the patient is contagious before the rash appears.
- Typical triad: ARVI-like prodrome → bright red cheeks → symmetrical lacy maculopapular rash on the extremities.
- Dangerous forms: aplastic crisis in hemolytic anemias, aplasia in immunodeficient individuals, and fetal infection before 20 weeks of gestation.
- Adolescents may develop the "glove and sock" form, while adults may experience arthropathies.
- Diagnosis is clinical; PCR and serology are used for risk groups and pregnant women.
- Treatment for healthy children is symptomatic; immunity following infection is lifelong.