You may need a test to look for the varicella zoster virus (VZV) if your doctor suspects that you have, or have recently had, chickenpox or shingles and needs to confirm the diagnosis. You may be tested for antibodies to VZV to check immunity to the varicella zoster virus after exposure to the virus or before receiving immunosuppressive drugs
Chickenpox and Shingles Tests
Tests for VZV virus are carried out when the doctor wants to distinguish between an active VZV infection and another cause, for example if a person has unusual (atypical) and/or severe symptoms. Tests for VZV antibodies are commonly performed to check for immunity to VZV before a person starts immunosuppressive treatments, or when a pregnant woman, immune-compromised person, or very young baby has been exposed to someone with active VZV infection
No test preparation is needed.
Tests for chicken pox and shingles are done to diagnose either a current or past infection with the virus (VZV) that causes these conditions. Formal tests are often unnecessary when there is an active infection, because a diagnosis can be made by the doctor just from examining the clinical signs and symptoms, but a diagnostic test helps to confirm the infection in patients with unusual or severe symptoms,. In people who are at higher risk from VZV infection, (such as organ transplant recipients or pregnant women), tests for VZV antibody may be useful to determine whether a person is immune.
Varicella zoster virus is a member of the herpes virus family. It is very common and the primary infection (chickenpox) is highly contagious, passing from person to person directly from the blisters, or through exhaled droplets and coughs. VZV causes chickenpox in children and adults who have not been previously exposed. Usually, about two weeks after exposure to the virus, an itchy rash occurs, followed by the pimple-like spots that become small, fluid-filled blisters (vesicles). The blisters break, form a crust and then heal. Typically, this process occurs in two or three waves or “crops” of several hundred blisters over a few days.
Once the first infection has got better, the virus becomes hidden (latent) in sensory nerve cells near the spinal cord. The person develops antibodies during the infection that usually prevent them from getting chickenpox again if exposed to the virus. However, later in life and in those with immune systems that are not working properly, VZV can reactivate, moving down the nerve cells to the skin and causing shingles (also known as herpes zoster). Symptoms of shingles include a mild to intense burning or itching pain occurring in a band of skin. It is usually limited to one place on one side of the body, often on the trunk or the face, but can also occur in several places. Several days after the pain, itching, or tingling begins, a rash forms in the same place. The rash may, or may not, develop into blisters. People with active shingles can spread VZV infection to others who have never had the infection, causing chickenpox. In most people, the rash and pain of shingles reduces within a few weeks and the virus again becomes hidden (latent). A few people may have pain that lingers for several months (known as post-herpetic neuralgia).
Most cases of chickenpox and shingles get better without complications. Occasionally the broken blisters can become infected with bacteria. Rarely, the virus can spread to the lungs or the brain, to cause life-threatening infection. In people with compromised immune systems, or who are pregnant, VZV infections can be more severe and long-lasting.
The possible effects of VZV on a growing baby or newborn depend on when exposure occurs and on whether or not the mother has been previously infected. During the first 20 weeks of pregnancy, a primary VZV infection in the mother may, rarely, cause congenital abnormalities in her growing baby. Babies infected in utero are also more likely to develop shingles in infancy. If the mother’s infection occurs one to three weeks before delivery, the baby may develop chickenpox just before or after birth, although antibodies passed from the mother may start to give some protection. If a newborn is exposed to VZV near to birth and does not have maternal antibody protection, then the VZV infection can be severe or even fatal.
How is the sample collected for testing?
The sample required depends on the patient’s symptoms (if any) and whether testing is being done to determine the presence of antibodies or to detect the DNA of the virus itself. Antibody testing requires a blood sample collected from a vein in the arm. Varicella zoster virus DNA may be detected from a variety of samples, including a swab from the rash or throat, blood and cerebrospinal fluid.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
Active cases of chickenpox and shingles, which are caused by the varicella zoster virus (VZV), are usually diagnosed from the person’s symptoms and clinical presentation. Most adults in the UK have been infected with VZV, therefore general population screening is not done. However, testing for VZV or for the antibodies produced in response to VZV infection may be needed in certain cases. For example, tests may sometimes be performed for pregnant women, newborns, patients who are about to start taking immunosuppressive drugs and those who are already immunocompromised. The reasons for testing may include:
- to determine if someone has had VZV infection or vaccination in the past and has developed immunity to the disease
- to show if someone has had a recent VZV infection
- to determine whether someone with severe or unusual (atypical) symptoms has an active VZV infection or has another condition with similar symptoms
There are several methods of testing for VZV:
When you are exposed to VZV, your immune system responds by producing antibodies to the virus. Two types of VZV antibodies (immunoglobulins) may be found in the blood: IgM and IgG. IgM antibodies are the first to be produced and are present in most individuals within a week or two after the initial exposure. This delay, following onset of infection, makes the antibody tests less helpful for diagnosing a current or active infection. The level of IgM antibody rises for a short time period after infection and then declines, eventually falling below detectable levels. IgM can sometimes be detected again if the hidden (latent) VZV is reactivated.
IgG antibodies are produced by the body several weeks after the initial VZV infection or vaccination to provide long-term protection (immunity). Levels of IgG rise during the active infection, then stabilise as the VZV infection resolves and the virus becomes inactive. Once a person has been exposed to VZV, they will usually have some measurable amount of VZV IgG antibody in their blood for the rest of their life. VZV IgG antibody testing is most commonly used to help confirm a previous infection and/or immunity to VZV infection.
Viral detection involves finding VZV in a skin or throat swab, blood, or other fluid sample such as cerebrospinal fluid. Viral detection is the most usual way of diagnosing a current infection and is normally done by detecting the virus’s genetic material (VZV DNA). VZV DNA testing is performed to detect VZV genetic material in a patient sample. This method is very sensitive and specific. It can identify and measure the amount of the virus.
The choice of tests and samples collected depends on the patient, their symptoms, and on the doctor’s clinical findings.
When is it requested?
VZV antibody tests may be requested to check immune status when a person at higher risk has been exposed to infection, or prior to vaccination. VZV DNA tests may be requested when person is ill with unusual (atypical) and/or severe symptoms of either primary (chickenpox) or reactivated (shingles) infection.
What does the test result mean?
Care must be taken when interpreting the results of VZV testing. The doctor evaluates the results in conjunction with clinical findings and the medical history of the person being tested.
If only IgG is detected, this normally indicates that the person has had VZV infection or vaccination in the past and is immune. The amount of IgG in a patient’s blood can be measured (quantified) by some antibody tests, to show the level of immunity present in that person. Occasionally, IgG can be detected in someone who has not had previous infection or vaccination: most commonly when the antibody passes across the placenta from a mother to her unborn baby; or when a person has had a recent transfusion of blood or similar.
If both VZV IgG and IgM are present in a person who has symptoms, then it is likely that either they have been recently exposed to VZV for the first time and have had chickenpox or that the previous VZV infection has been reactivated and they have had shingles. IgM and IgG cannot be detected until several days after the onset of symptoms. If a newborn has IgM antibodies, they may have had VZV infection in utero. If a symptomatic person has low or undetectable levels of IgG and/or IgM, it may be because: it is too early in the course of illness for antibodies to be present at detectable levels; they have a disease other than VZV; their immune system is not working normally to produce a measurable level of the antibodies.
If a test for VZV DNA is positive, then VZV is present. High levels of viral DNA tend to indicate an active infection. Low levels indicate a VZV infection but may not indicate a symptomatic condition. Negative results do not rule out VZV infection – the virus may be present in very low numbers or may not be present in the body sample tested.
Is there anything else I should know?
There is now a vaccine available for older adults that is intended to decrease the risk of having a re-activation of VZV (shingles) and decreases the severity of the disease if it does occur. It is currently offered to patients in the UK who are aged 70-80 years old, but is unsuitable for most immunocompromised people.
Is shingles contagious?
Yes, but not as contagious as chickenpox. The rash is the main source of infectious virus during shingles, although there may also be virus in the respiratory secretions if the infection is severe or the infected person is immunocompromised. Any pregnant woman or immunocompromised person should regard contact with a case of shingles as a risk of infection to themselves and seek rapid medical advice.
Can you get shingles by being exposed to someone who has active symptoms of shingles?
Does chickenpox leave scars?
Do chickenpox and shingles occur throughout the world?