Fifth Disease

Erythema infectiosum, commonly known as fifth disease or slapped cheek syndrome, is an infectious condition caused by human parvovirus B19. It is particularly prevalent among children and is characterised by a distinctive red rash on the cheeks. While the disease is generally mild, certain populations, such as pregnant women, immunocompromised individuals, and those with chronic hemolytic anaemia, may experience severe complications.

Introduction

Fifth disease typically begins with non-specific symptoms such as low-grade fever, headache, and cold-like symptoms, including a runny or stuffy nose. These initial symptoms subside, and a few days later, a bright red rash appears on the face, particularly the cheeks, giving the appearance of a "slapped cheek." Occasionally, the rash extends over the bridge of the nose or around the mouth. Additionally, children may develop a red, lacy rash on the upper arms, torso, and legs, which can last for several days to weeks and may itch.

In teenagers and adults, fifth disease may present with a self-limited arthritis, causing painful swelling in joints such as wrists, knees, ankles, fingers, and shoulders. While the disease is typically mild, it can lead to serious consequences in specific populations, including pregnant women, individuals with sickle cell disease, and immunocompromised patients.

Causes

Fifth disease is caused by parvovirus B19, a small, single-stranded, non-enveloped DNA virus. The virus primarily targets erythroid lineage cells in the bone marrow, leading to various cellular effects such as DNA damage, cell cycle disruption, and apoptosis. Parvovirus B19 infection triggers the production of specific IgM antibodies around 10-12 days post-infection, followed by the production of IgG antibodies that provide lifelong immunity.

Diagnosis

The characteristic "slapped cheek" rash can be indicative of fifth disease, but blood tests are required for a definitive diagnosis. The preferred method is an anti-parvovirus B19 IgM antibody serum assay, which can detect previous infections approximately one week after initial infection. PCR and direct hybridisation methods can also confirm the presence of viral DNA, with PCR being more sensitive.

Transmission

Fifth disease is primarily transmitted through respiratory secretions but can also spread via contact with infected blood. The incubation period ranges from 4 to 21 days, and individuals are most infectious before symptoms appear. While symptomatic individuals do not need to be isolated due to the low risk of transmission, vertical transmission from mother to foetus can occur, potentially leading to serious complications such as hydrops fetalis.

Treatment

Treatment for fifth disease is mainly supportive, as the infection is generally self-limiting. Common interventions include antipyretics to reduce fever and non-steroidal anti-inflammatory drugs (NSAIDs) to alleviate joint pain. The rash itself is not contagious and usually resolves within 5 to 10 days. However, certain triggers like stress, hot temperatures, and sunlight exposure can cause recurrence. Patients with severe complications such as anaemia may require specialist referral and blood transfusions.

Epidemiology

Fifth disease is a common viral illness, particularly affecting children aged 5 to 15 years. The virus is most prevalent during the spring and winter, with outbreaks frequently occurring in daycares and schools. Adults have lower infection rates but can experience more severe symptoms. Occupations involving close contact with infected individuals, such as healthcare workers and teachers, increase the risk of acquiring the virus.

Vulnerable Populations and Complications

Certain populations are at higher risk for complications from fifth disease. Pregnant women, especially in the first trimester, may experience miscarriage or hydrops fetalis. Individuals with sickle cell disease or other blood disorders are at risk for an aplastic crisis. Immunocompromised individuals, including those with HIV, may have difficulty controlling the infection, leading to severe anaemia.

Research has shown that daycare workers are at an increased risk of infection due to close contact with young children. Additionally, persons with pre-existing blood disorders are more susceptible to complications. Parvovirus B19 infection has also been linked to neurological complications and cardiac inflammation, although the pathophysiology of these associations remains under study.

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Self-assessment MCQs (single best answer)

What virus causes fifth disease?

Which of the following is a characteristic feature of fifth disease in children?

In which population is fifth disease likely to cause severe complications?

Which diagnostic method is preferred for confirming a current infection of parvovirus B19?

Which of the following is NOT a common symptom of fifth disease in its initial stages?

What is the primary mode of transmission for fifth disease?

Which season is fifth disease most commonly seen in?

What is the primary target cell type for parvovirus B19 in the human body?

Which of the following treatments is typically NOT recommended for fifth disease?

What serious complication can fifth disease cause in pregnant women?