Makindo Medical Notes

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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