A blood sample is taken from a vein in your arm to test for the presence of parvovirus B19 antibody. To detect the virus itself a blood or rarely a bone marrow sample is required.
Parvovirus B19 is a virus that causes a common childhood illness, also called "fifth disease" or "erythema infectiosum." It is also known as “Slapped Cheek Disease” because of the typical rash that appears in some children. The virus is found in respiratory droplets during an infection and is easily transmitted to others through close physical contact (coughing or sneezing). In the United Kingdom, 60% of adults and 90% of the elderly have been infected with parvovirus B19 at some time in their lives, usually as children or young adults. The infection typically has an incubation period of several days to two to three weeks. It is often asymptomatic (no symptoms are apparent) but where symptoms occur, they are present for a short period of time.
For most people, parvovirus B19 infection is indistinguishable from other mild illnesses that develop and go away after a short period. Many who are infected have no symptoms or have mild flu-like symptoms such as tiredness, a slight fever, headache, or an upset stomach, and many may not know that they have had a parvovirus B19 infection. The majority of people do not have any significant symptoms or health problems and once the initial infection resolves, the person becomes immune to the infection and will not get it again.
Some children with the infection develop a characteristic and distinctive bright red "slapped-cheek" rash on both cheeks and a raised lacy rash on the chest and extremities. The rashes may come and go for several weeks, reappearing and/or getting worse with exposure to heat and sunlight and with stress. By the time the rash appears, the child is no longer considered infectious. Parvovirus is sometimes called fifth disease because it is the fifth of six common childhood illnesses that can cause rashes.
Less commonly, some adults become infected and may develop "gloves and socks syndrome" with painful swelling of joints and reddening of the hands and feet that typically ends abruptly at the wrists and ankles. This condition usually resolves within a few weeks.
Parvovirus can also be passed from a pregnant woman to her foetus and through blood and blood products. Sometimes, the infection can lead to more serious disease.
Parvovirus B19 can cause major health problems in three types of patients:
- People with iron deficiency anaemia or a condition that affects or shortens the life of red blood cells (RBCs), such as iron deficiency anaemia or thalassaemia, may develop severe acute anaemia during a parvovirus B19 infection. Parvovirus B19 targets cells in the bone marrow that become RBCs and disrupts the production of new RBCs, which may affect those with underlying blood disorders more severely.
- Women who are infected during pregnancy can pass the infection to their baby. Most foetuses will be fine, but a small proportion will develop severe anaemia and a few may have an inflammation and infection of the heart muscle (myocarditis). These conditions can cause heart failure in the foetus, miscarriage, hydrops fetalis - associated with fluid accumulation, and sometimes stillbirth. The greatest risk for foetal complications is during the first twenty weeks of pregnancy.
- In those with compromised immune systems, a parvovirus B19 infection may cause chronic anaemia and be challenging to resolve. This includes people with HIV/AIDS, those who have had organ or bone marrow transplants, and those undergoing chemotherapy treatment for cancer.
Parvovirus B19 testing is not typically used to screen the general population. It is usually requested to find out whether someone is, or has recently been, infected with parvovirus if they are at risk of complications. This enables the most appropriate treatment to be given to minimise the consequences of parvovirus B19 infection. It may also sometimes be necessary to find out whether someone has ever been exposed to parvovirus (for example if they are in a higher parvovirus B19 disease risk group and have recently been in contacted with a patient with parvovirus B19 symptoms). Testing involves either a measurement of parvovirus antibodies, immune proteins produced in response to parvovirus B19 exposure, or the detection of the genetic material of the virus itself (its DNA) during an active infection.
How is the sample collected for testing?
The sample required depends on whether testing is being done to look for the presence of antibody or to detect the virus itself and it also depends on the health of the patient. Antibody testing requires a blood sample, obtained by inserting a needle into a vein in the arm. Viral detection may be done on blood or more rarely on a sample of bone marrow collected through a bone marrow aspiration or biopsy.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
Parvovirus B19 testing is not generally used to test those with mild and uncomplicated infections. It is normally used to detect a current infection or check the immunity in those who are at an increased risk of complications, such as those with sickle cell anaemia. There are several methods of detecting a parvovirus B19 infection:
Two types of parvovirus B19 antibodies may be produced in response to an infection: IgM and IgG. IgM antibodies are the first to be produced by the body in response to a parvovirus infection. They are present in most individuals within a week or two after the initial exposure. IgM antibody production rises for a short time period and declines. A few weeks after infection, the level of parvovirus IgM antibody usually falls below detectable levels. IgG antibodies are produced by the body a few weeks after the initial infection to provide long-term protection. Levels of IgG rise during the active infection, then stabilise as the parvovirus B19 infection disappears. Once a person has been exposed to parvovirus B19, they will have some measurable amount of IgG antibody in their blood for the rest of their life.
Parvovirus B19 antibody testing may be done to check immunity to parvovirus in pregnant women who have been exposed to someone with parvovirus B19 or who have symptoms suggestive of parvovirus infection. It may also be requested in people who have acute or chronic anaemia or persistent joint pain that may be due to a parvovirus B19 infection. By comparing the absence or presence of both IgG and IgM in the same sample, the doctor can tell the difference between current, recent, and past infections. Antibody testing is usually not done on children who have the characteristic fifth disease rashes and, since parvovirus B19 infection is widespread and causes few problems to those with healthy immune systems, general population screening is rarely done.
Viral detection involves finding parvovirus B19 genetic material (DNA) in a blood sample or, less commonly, in a bone marrow sample. Parvovirus B19 DNA testing is performed primarily to detect active parvovirus infection in immune-compromised people who have acute or persistent anaemia. These people will frequently not produce a sufficient amount of antibodies to detect or to resolve the infection.
When is it requested?
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 doctor to be able to diagnose the infection.
Parvovirus B19 IgG and IgM antibody tests may be requested when a pregnant female has flu-like symptoms and/or has been exposed to someone with a parvovirus B19 infection to determine if she has an active infection, had a recent infection, or has been exposed in the past. Antibody testing and/or DNA testing may be requested when someone has acute or persistent anaemia or joint pain that the doctor suspects may be due to a parvovirus B19 infection. Parvovirus B19 DNA testing is usually requested when the affected person is immune-compromised .
One or more parvovirus B19 tests may be repeated if they are initially negative, but the doctor still suspects that a parvovirus infection is present, or to evaluate changes in concentrations of antibody over time.
What does the test result mean?
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 patient has an active, or had a recent, infection.
If only IgM is present, then the patient may have been infected very recently. 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. Often, a second blood sample will be tested about a month after contact with a person with the disease, even if the woman has no symptoms, because a significant proportion of adults do not have symptoms when infected with parvovirus B19.
If a person is symptomatic but has low or undetectable levels of IgG and/or IgM, it may mean that they either have a condition other than parvovirus B19 or that their immune system is not responding normally – not producing an adequate amount of antibody even if parvovirus is present. This may be true for immunocompromised . people, and DNA testing may need to be done.
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.
Is there anything else I should know?
Sometimes a reticulocyte test may be performed along with parvovirus B19 testing to evaluate red blood cell (RBC) production. This test measures new immature RBCs in the blood that still contain genetic material. Since parvovirus B19 disrupts RBC production, the number of reticulocytes will decrease during an active infection.
Parvovirus B19 infections are usually self-limiting in otherwise healthy people. Treatment may be given to relieve symptoms and, when necessary, to address anaemia.
Pregnant women who pass parvovirus B19 infection to their foetus will be closely monitored for several weeks with periodic ultrasounds. In most cases, the foetus will be healthy. When hydrops fetalis or severe anaemia develops, it can sometimes be addressed by giving the foetus a blood transfusion. The parvovirus B19 infection is not known to cause birth defects.
Is this the same parvovirus that affects dogs? Can I catch it from my dog?
Is there any way to prevent getting a parvovirus B19 infection?
There is no vaccine available for parvovirus. The virus is passed through close contact, and people may be infectious even when no symptoms are present. However, careful hygiene can help prevent transmission of the virus. Most people are infected when they are children.