1. ERYTHROPARVOVIRUS INFECTIONS
Primate erythroparvovirus 1, more commonly known as parvovirus B19, infects human erythroid precursor cells. It is quite widespread (by age 15 years about 50% of children have detectable IgG), and its transmission occurs through respiratory secretions and saliva, through the placenta (vertical transmission with 30–50% of pregnant women nonimmune), and through administration of blood products. The incubation period is 4–14 days. Chronic forms of the infection can occur. Bocavirus, another erythroparvovirus, is a cause of winter acute respiratory disease in children and adults.
Parvovirus B19 causes several syndromes and manifests differently in various populations.
In children, an exanthematous illness (“fifth disease,” erythema infectiosum) is characterized by a fiery red “slapped cheek” appearance, circumoral pallor, and a subsequent lacy, maculopapular, evanescent rash on the trunk and limbs. Malaise, headache, pruritus (especially on the palms and soles), and diarrhea (rarely) occur. Systemic symptoms and fever are mostly abated by the time of rash appearance. Eosinophilic cellulitis (Well syndrome) is also reported with parvovirus B19, as are microvesicular eruptions and atypical rashes. Parvovirus B19 infection is also one of the most common causes of myocarditis in childhood.
2. Immunocompromised patients
A transient aplastic crisis and pure red blood cell aplasia may occur, although symptoms and signs may be less classic among the immunocompromised populations. Bone marrow aspirates reveal absence of mature erythroid precursors and characteristic giant pronormoblasts (eFigure 32–5). The parvovirus B19 gene is detected in 16–19% of acute leukemia and chronic myeloid leukemia patients.
Erythrovirus (parvovirus) infection. (Peripheral blood, 50×.) A giant pronormoblast is shown in the middle of the field. This is a very unusual finding in peripheral blood and represents an early erythroid cell that has been transformed by infection with erythrovirus (parvovirus) B19. Whereas in normal persons erythrovirus (parvovirus) infection can cause suppression of hematopoiesis that is of very little consequence, it can also cause severe life-threatening anemia in patients with chronic hemolytic states. (Used, with permission, from L Damon.)
A limited nonerosive symmetric polyarthritis that mimics lupus erythematosus and rheumatoid arthritis, which may in some cases be a type II mixed cryoglobulinemia, can develop in middle-aged persons (especially women). Rashes, especially facial, are less common in adults.
Chloroquine and its derivatives exacerbate parvovirus B19–associated anemia and are linked with significantly lower hematocrit in hospital admissions in malaria endemic areas. Rare reported presentations include myocarditis with infarction, constrictive pericarditis, chronic dilated cardiomyopathy (although a 2016 analysis from the Netherlands dispute some cardiac findings), uveitis, encephalitis (from India), autoimmune (Hashimoto) thyroiditis, hepatitis and liver failure, pneumonitis, neutropenia, thrombocytopenia, a lupus-like syndrome, glomerulonephritis, ...