Erythema infectiosum, also known as fifth disease, is an acute infection caused by parvovirus B19, mostly in children, mainly in spring. Mild systemic symptoms may be present. Spots or maculopapular rashes occur initially on the cheeks and gradually spread to the extremities.


Causes

PVB19 is the only parvovirus known to cause human diseases, and transmission mode includes exposure to nasopharyngeal secretions of patients, mother-to-child transmission, and transfusion of blood products. Patients have lifelong immunity after infection.

In patients with only eruption, contagiousness is the strongest before eruption, and may be absent after eruption. In patients with aplastic crisis, contagiousness persists for 1 week after onset, and the infectiousness of chronically infected immunosuppressed patients and severely anemic patients can last from several months to several years.


Signs and Symptoms

Erythema infectiosum occurs mainly in 2 - 10 years old children. The incubation period is 5 - 15 days. Sudden onset is often present. Viremia occurs 6 – 10 days after infection. Systemic symptoms are generally absent, or only mild fever is present. Sometimes, patients present with sore throat, vomiting, and conjunctival and pharyngeal mild congestion. Rosy red papules occur on the cheeks, rapidly fusing into butterfly, sharply demarcated, edematous erythema, without scales, with local increased temperature, resembling slapped cheek, occasionally with mild pruritus and burning sensation. Sharply demarcated, symmetrical, lacelike or reticular maculopapular rash occurs on the trunk, buttocks, and extremities 2 – 4 days after onset. Palms and soles can also be invaded. Hemorrhagic lesions may be present in the extremities, occasionally with blisters or pustules. Dark red spots can also occur on the cheeks and genital mucosa. Skin lesions are obvious or subtle, generally subtle in the cold morning and obvious in the afternoon or after winds or sports.

Skin lesions gradually subside 6 – 10 days after onset, often from the center, forming a small red ring, merging with each other, forming rings or circles. The order of skin lesion regression is the same as its order of occurrence, leaving no trace. Some patients may present with tonsil enlargement. If erythema infectiosum occurs in adults, especially in females, pruritus and migratory arthritis can occur and may persist for 2 months. It has been reported that vesiculopustular rash, anemia, aplastic crisis, and chronic myelogenous failure may occur. Patients may also be accompanied by systemic vasculitis, such as nodular polyarteritis, Wegener granulomatosis, arterial embolism, urticaria, angioedema, and papular purpuric gloves and socks syndrome.


Histopathology

Epidermal cell edema, focal basal cell liquefaction degeneration, dermal papillary vasodilation, endothelial cell swelling, and histiocyte infiltration around blood vessels, hair follicles, and sweat glands can be seen. These are chronic inflammation changes, without diagnostic value.


Diagnosis

On the basis of specific skin lesions, a diagnosis can be provided. Positive results of PVB19 IgM antibodies in serum can help diagnose. PCR can assist in the diagnosis.


Treatment

Symptomatic treatment is appropriate. For patients with chronic pure red blood cell aplasia, intravenous immunoglobulin can be used to shorten the duration and promote the production of red blood cells.