Parvovirus B19
Parvovirus B19 causes exanthem and other clinical syndromes. Some 50% of children and 60-90% of adults are seropositive. Most infections are spread by the respiratory route, although spread via contaminated blood is also possible. The virus has accurate tropism for red cell precursors.
Clinical features
Many infections are subclinical. Clinical manifestations result after an incubation period of 14-21 days. The classic exanthem (erythema infectiosum) is anteceded by a prodromal fever and coryzal symptoms. A ‘slapped cheek’ rash is characteristic but the rash is very variable.
In adults, polyarthropathy is common. Infected individuals have a transient block in erythropoiesis for a few days, which is off on clinical consequence, except in individuals with increased red cell turnover due to haemoglobinopathy or haemolytic anaemia. These individuals develop an acute anaemia that may be severe (transient aplastic crisis). Erythropoiesis usually recovers spontaneously after 10-14 days.
Immunocompromised individuals, including those with congenital immunodeficiency or AIDS, can develop a more sustained block in erythropoiesis in response to the chronic viraemia that results from their inability to clear the infection. Infection during the first two trimesters of pregnancy can result in intrauterine infection and impact on fetal bone marrow; it causes 10-15% of non-immune (non-Rhesus-related) hydrops fetalis, a rare complication of pregnancy.
Diagnosis
IgM to parvovirus B19 advice recent infection but may persist for months and false positives occur. Seroconversion to IgG positivity confirms infection but in isolation, a positive IgG is of little diagnostic utility. Detection of parvovirus B19 DNA in blood is particularly useful in immunocompromised patients. Giant pronormoblasts or haemophagocytosis may be demonstrable in the bone marrow.
Management
Infection is usually self-limiting. Symptomatic relief for arthritic symptoms may be required. Severe anaemia requires transfusion.
Fifth disease (erythema infectiosum)
Small children
Three clinical stages: a ‘slapped cheek appearance. followed by a maculopapular rash progressing to a reticulate eruption on the body and limbs, then a final stage of resolution. Often the child is quite well throughout
Gloves and socks syndrome
Young adults
Fever and an acral purpuric eruption with a clear margin at the wrists and ankles. Mucosal involvement also occurs
Arthropathies
Adults and occasionally children
Symmetrical small-joint polyarthropathy. In children, it tends to involve the larger joints in an asymmetrical distribution
Impaired erythropoiesis
Adults, those with the haematological disease, the immunosuppressed
Mild anaemia; in an individual with an underlying haematological abnormality it can precipitate a transient aplastic crisis, or in the immunocompromised a more sustained but often milder pure red cell aplasia
Hydrops fetalis
Transplacental fetal infection
Asymptomatic or symptomatic maternal infection that can cause fetal anaemia with an aplastic crisis, leading to non-immune hydrops fetalis and spontaneous abortion
Persistent viraemia in immunocompromised hosts may require immunoglobulin therapy to clear the virus. Pregnant women should avoid contact with cases of parvovirus B19 infection; if they are exposed, serology should be performed
to establish whether they are non-immune. Passive prophylaxis with normal immunoglobulin has been suggested for non-immune pregnant women exposed to infection but there are limited data to support this recommendation.
The pregnancy should be closely monitored by ultrasound scanning so that hydrops fetalis can be treated by fetal
transfusion.
