Parvovirus B19 is a virus that causes a common childhood illness, also called "fifth disease" or "erythema infectiosum." The virus is found in respiratory droplets during an infection and is easily transmitted to others through close physical contact. Parvovirus can also be passed from a pregnant woman to her fetus and transmitted through exposure to blood and blood products.
<span lang="EN" font-size:12.0pt;="" line-height:115%;="" mso-fareast-font-family:calibri"="">For most people, parvovirus B19 infection is indistinguishable from other mild illnesses that develop and go away within a short time period. Many who are infected have no symptoms or have mild flu-like symptoms such as fatigue, a slight fever, headache, or an upset stomach, and many may not know that they have had parvovirus B19 infection. The majority of people do not experience any significant symptoms or health problems and once the initial infection resolves, the person becomes immune and will not get the infection again.
When To Get Tested?
Parvovirus B19 testing is usually not required when a child has the characteristic "slapped cheek" and lacy rashes. The distinctive rashes are sufficient evidence for the health practitioner to be able to diagnose the infection. In general, most people who have or have had parvovirus B19 do not require laboratory testing because illness does not typically last more than 5-7 days and symptoms are usually mild.
Parvovirus B19 IgG and IgM antibody tests may be ordered when a pregnant female has flu-like symptoms and/or has been exposed to someone with parvovirus B19 infection to determine if she has an active infection, had a recent infection, or has been exposed in the past. DNA testing may be performed on fetal samples in some cases.
Antibody testing and/or DNA testing may be ordered when someone has acute or persistent anemia or joint pain that the health practitioner suspects may be due to parvovirus B19 infection. Parvovirus B19 DNA testing is usually ordered when the affected person is immune-compromised.
One or more parvovirus B19 tests may be repeated if they are initially negative but the health practitioner still suspects that a parvovirus infection is present, or to evaluate changes in concentrations of antibody over time
What does the test result mean?
Antibody testing
If both parvovirus B19 IgG and IgM are present, then it is likely that the person tested has an active, or had a recent, parvovirus infection. This can be confirmed by measuring IgG levels again 2 or 3 weeks later. A high level of IgG is not as important as an increasing concentration of antibody. If there is a 4-fold increase in IgG between the first and second sample, then the person has an active, or had a recent, infection.
If only IgM is present, then the person may have very recently been infected, within the previous 2-4 months. If only parvovirus B19 IgG is present, then the person had a parvovirus infection at some time in the past and has protection against the virus.
If antibody tests are negative, then the person tested has not had the infection and is not immune. If a pregnant woman is not immune and has been exposed to someone with the disease, she will typically be closely monitored by her doctor.
If someone is symptomatic but has low or undetectable levels of IgG and/or IgM, it may mean that the person either has a condition other than parvovirus B19 or that their immune system is not responding normally. i.e., not producing an adequate amount of antibody even if parvovirus is present. This may be true for people with weakened immune systems (immunocompromised) and DNA testing may need to be done.
Viral detection
If a parvovirus B19 DNA test is positive, then the person is currently infected with parvovirus B19. A negative result does not rule out the infection. The virus may not be present in sufficient amount in the sample to be detected.
Fetal infection of parvovirus B19 is often detected through testing of viral DNA in maternal samples as well as samples from the baby.
The PCR assay is used to detect viral DNA and is the optimal method for detecting chronic infection in immunocompromised patients as the antibody levels are variable.
