Paired sera should be obtained wherever possible:
(a) acute sample - as early as possible in the illness, and
(b) convalescent sample 2 - 3 weeks after onset.
Tests performed every 1 - 2 weeks.
On occasions, false positive IgM results may occur in patients who are either ANA positive and/or have an EBV infection
A negative B19 IgM result does not necessarily exclude infection. A repeat sample should be tested two weeks after the initial bleed.
Human Parvovirus B19 infection is not uncommon, with at least 50% of adults being sero-positive. When patients are symptomatic (adults may not have a rash ) infection is most often recognised as erythema infectosium, which is characterised by mild systemic symptoms, fever in up to 30% of patients and frequently a distinctive rash. Preceding the rash onset (more likely to occur in children) is 7-10 days of non-specific symptoms. The facial rash is intensely red in colour with a ?slapped cheek? appearance. A symmetric maculopapular lacelike rash also occurs on the arms, moving caudally to involve the trunk, buttocks and thighs. The rash can recur and change in intensity when subjected to environmental fluctuations of light and temperature. Arthralgia is rare in children but common in adults especially women. Since human Parvovirus causes a temporary cessation in red cell production by replicating in the nuclei of erythroid precursor cells, patients with existing red cell abnormalities (e.g. sickle cell) become infected they can experience life threatening aplastic crises. In immunocompromised patients, human Parvovirus infection can become chronic resulting in persistent severe anaemia.
Transplacental transmission does occur (1/3) with effects including fetal hydrops, spontaneous abortion and stillbirth. Studies have indicated the risk of fetal death in an infected pregnancy to be 9% during the first half and less in the second half of the term.
Transmission is via respiratory secretions and blood. Secondary infections amongst susceptible household contacts are common and occur in approximately 50% of contacts. Patients presenting with erythema infectosium are likely to be infectious preceding symptom onset. This contrasts with patients suffering aplastic crises, who are contagious before symptom onset and for at least a week after onset. The incubation period ranges from 4-14 days but can be as long as 21 days.
IgM class antibodies are detectable 2-3 weeks after symptom onset, peak at 30 days and are usually undetectable after 60-90 days. IgG class antibodies may not be detected until 5 weeks after symptom onset. High titre IgG antibodies usually confer immunity. Parvoviral viremia can be established by detecting human Parvoviral DNA by PCR in serum. In general, acute infection can be serologically diagnosed by the presence of both symptoms and IgM class antibodies, whereas absence of symptoms but a reactive IgM assay may indicate recent infection.
CLINICAL MANIFESTATIONS:
Erythema Infectiosum ( fifth disease ) - this is typically a mild febrile illness of childhood affecting primarily children between the ages of 4 and 15 years. The incubation period is 4 - 7 days. There is usually a prodrome of malaise, headache, myalgias and sometimes respiratory and gastrointestinal symptoms followed after a few days by a rash, typically involving the face ("slapped cheek") but which may also involve the limbs including the palms and soles. Not all cases develop a rash, with adults being less likely to do so.
Arthralgias/arthritis - this may accompany or follow the skin eruption and is more common in adults, particularly women. Involvement is typically symmetric and polyarticular. Other connective tissue disease symptoms have been linked to parvovirus B19 but these are rare.
Haematologic manifestations - in otherwise healthy hosts, acute parvovirus infection usually results in a mild anaemia of short duration. In patients with 'stressed' erythropoiesis, a transient aplastic crisis may occur e.g. chronic haemolysis, erythrocyte membrane defects (hereditary spherocytosis), haemoglobinopathies, erythrocyte enzymopathies, etc.
Immunocompromised hosts - in patients with immunodeficiency, parvovirus infection may lead to a persisting anaemia because of inability of the immune system to mount a neutralising antibody response. As part of the immune system failure, rash and arthritis are typically absent, these symptoms being thought to be immune-complex related.
Fetal Infection - in utero infection may result in spontaneous abortion or 'hydrops fetalis'. Outcome is worse if infection occurs in the first or second trimesters. Fetal malformations are unknown. Cases of congenital anaemia have been described, but a convincing link to in-utero infection is not established.
? Full clinical details are essential. This enables the laboratory to select appropriate tests and request additional specimens where necessary to establish the diagnosis. Additional consultation may be indicated.
References
1. Biotrin package insert from the Parvovirus IgM ELISA kit.
2. Red Book (23rd Ed, 2003). Report of theFor further information contact the laboratory (contact via Lablink: 22000 or (09) 307-8995 or 0800 522 7587) ,or:
the Virology team
virology@adhb.govt.nz