Makindo Medical Notes

Erythrovirus B19, commonly known as Parvovirus B19, causes Fifth disease. It specifically infects erythroid progenitor cells, leading to transient erythroid hypoplasia and temporary failure of red blood cell production.

About

• Renamed to Human Erythrovirus B19, previously known as Parvovirus B19.
• It is a small, single-stranded, non-enveloped DNA virus.
• Targets cells in the erythroid lineage, particularly in the bone marrow.
• Transmission occurs primarily through airborne droplets, though vertical transmission can also occur in pregnancy.

Aetiology

• Erythrovirus B19 infects cells expressing the P antigen, found on erythroid progenitor cells.
• Individuals lacking the P antigen are naturally resistant to the infection.
• The virus replicates within erythroid colony-forming units (E-CFU) and burst-forming units (E-BFU) in the bone marrow, disrupting red cell production.
• Leads to reductions in red blood cells, white blood cells, and platelets, potentially causing aplastic crises in individuals with pre-existing haemolytic disorders.
• Severe anaemia occurs in individuals with conditions like sickle cell anaemia or other haemolytic anaemias.

Clinical Presentation

• Aplastic anaemia: Characterized by anaemia, thrombocytopenia, and lymphopenia.
• Pregnancy-related complications: Can cause fetal anaemia, spontaneous abortion, or hydrops fetalis.
• Erythema infectiosum: Also known as "slapped cheek" syndrome, presenting with a distinctive facial rash in children.
• Acute arthritis/arthralgia: More common in adults, affecting the small joints.
• Transient aplastic crisis: Particularly in individuals with haemolytic anaemias.
• Chronic anaemia: Occurs in immunocompromised patients, such as those with HIV or acute lymphoblastic leukaemia (ALL).

Complications

• Fifth Disease (Slapped Cheek Syndrome): Primarily affects young children, causing minor symptoms such as fever and the characteristic facial rash.
• Gloves and Socks Syndrome: A purpuric rash seen in adolescents, affecting the hands and feet.
• Arthritis/Arthralgia: Adults, particularly women, may develop small joint arthritis. In children, larger joint involvement is less common.
• Red Cell Aplasia: While mild in some cases, it can precipitate aplastic crises in patients with underlying haematological conditions.
• Hydrops Fetalis: A potentially fatal condition where the fetus develops severe anaemia, leading to heart failure and spontaneous abortion.

Investigations

• Blood Tests: May show reduced haemoglobin (Hb), white cell count (WCC), and platelets, with decreased reticulocyte counts.
• PCR Testing: Erythrovirus B19 can be detected in serum by PCR, which is particularly useful for diagnosing the infection.

Management

• Severe Anaemia: In patients with chronic haemolytic anaemia, a sudden drop in haemoglobin may require urgent blood transfusion.
• Supportive Care: The disease is typically self-limiting, and analgesics can be used for joint pain or arthritis.
• Pregnancy Management: Immunoglobulin therapy may be administered to non-immune pregnant women exposed to the virus.
• Fetal Management: Fetal blood transfusion may be necessary in cases of hydrops fetalis to treat severe anaemia.

References

• Erythrovirus B19 infection