Varicella-Zoster Virus (VZV)

A blistering or raw sore on the vulva or vagina is almost always assumed to be herpes, and most of the time it is. In a few cases out of every hundred, though, the cause is VZV (varicella-zoster virus). That's the chickenpox virus, waking up in a nerve near the base of your spine.

Which virus it is changes what you do next. Genital shingles usually comes from virus you already carry, so a partner didn't give it to you. In people with healthy immune systems it usually happens once, and it needs higher antiviral doses than herpes does. A swab of the sore is how you find out which one you have.

Where the Virus Comes From

The first time this virus infects you, it causes chickenpox. It spreads through droplets in the air or through contact with fluid from the blisters. After the rash heals, the virus travels up sensory nerves and settles in clusters of nerve cells beside the spinal cord, where it stays dormant for the rest of your life.

Your immune system keeps it in check through white blood cells called T cells. When that surveillance weakens with age, illness, or medication, the virus can reawaken and travel back down the same nerve to the skin it supplies, which is what shingles is. Some of the lowest nerves in the spine supply the vulva, vagina, cervix, groin, and the skin around the anus. When the virus reawakens in one of those, the sores show up there.

This swab looks for the virus in material taken from the genital tract. In a healthy state the virus isn't on that surface; it appears there only while it's replicating in the skin or lining. So the result is a yes or no about one moment: whether the virus is active at that spot right now. A swab can't reach the dormant virus in your nerves, so it says nothing about that.

When Shingles Looks Like Genital Herpes

Genital shingles and genital herpes produce blisters and raw sores that can look identical, and both can cause burning nerve pain. When labs test genital swabs for both viruses, the chickenpox virus turns up in a small share of positives, often when no one suspected it.

Sources: Birch et al.; Granato et al.; McIver et al.

The misdiagnosis runs both ways. In the largest study, many of the people who turned out to have the chickenpox virus had been presumed to have herpes before lab testing. In a large shingles vaccine trial, a small share of rashes that doctors called shingles tested positive for herpes simplex instead.

What this means for you: herpes simplex is still the far more common cause of a genital sore. If a sore is swabbed, though, make sure the sample is tested for both herpes simplex and the chickenpox virus. A swab tested for herpes alone will come back negative on genital shingles, and you may leave believing you had a false alarm, or a herpes infection the test somehow missed.

Why Knowing Which Virus Changes Your Plans

The two infections lead to very different conversations. Genital herpes is sexually transmitted, tends to recur, and can be shed silently between outbreaks. Genital shingles comes from virus you've carried since chickenpox, so it tells you nothing about a partner. In people with healthy immune systems shingles usually happens once, though roughly 1 in 10 people have another episode at some point.

Treatment differs too. Shingles needs higher antiviral doses than the regimens used for herpes, so a herpes-dose prescription can undertreat it. For many people the biggest change is emotional, since a shingles episode replaces what would otherwise have been a lifelong herpes label.

Pregnancy and a Weakened Immune System

Two groups face higher stakes, though for different reasons. In pregnancy the main danger comes from a first infection: chickenpox while pregnant carries a risk of a pattern of birth defects called congenital varicella syndrome, and chickenpox around delivery can cause a severe, sometimes life-threatening infection in the newborn. Shingles in pregnancy, which is what a genital episode usually is, hasn't been linked to harm to the baby, because the antibodies you already have cross the placenta. It still calls for prompt contact with your obstetrician, especially close to delivery.

If your immune system is suppressed, the virus can escape the nerve it started in and spread to internal organs, and sometimes to the brain and spinal cord. Among people admitted to intensive care with severe infection, death rates were high and depended more on how suppressed their immune systems were than on which organ was involved. These spread-out cases are often misdiagnosed at first, and survival improves when antivirals start early.

Pooled studies of shingles risk point to the same groups: older age, cancer, diabetes, immune-suppressing treatment, physical trauma, and a family history of shingles all raise the odds, and organ transplantation carries the highest risk of the conditions studied. If any of these apply to you, a genital episode deserves prompt treatment, ideally starting the day it's confirmed.

Shingles, Your Heart, and Your Brain

The findings in this section come from studies of shingles anywhere on the body, so they apply to a genital episode by extension. Large reviews pooling many studies find that a shingles episode is followed by a higher risk of stroke and heart events, with stroke the most consistent link, and the stroke link is strongest in younger people. A large population study linked shingles to more heart attacks and episodes of unstable chest pain. These are observational links, so they show the two travel together without proving the shingles caused the events.

Carrying the virus quietly looks different. Among several thousand adults in the UK Biobank, a large British health study, having antibodies to herpes-family viruses, this one included, wasn't linked to stroke, heart attack, or death.

Those two results fit together once you separate the dormant virus from an active episode. Antibodies show only that the virus lives somewhere in you, which is true for a large share of adults and doesn't track with risk. A reactivation is a distinct event, and that event is what the studies tie to vascular problems. A positive swab marks one of those events.

A 2026 review pooling the available studies also linked infection with this virus to a higher risk of Alzheimer's disease, an association that doesn't yet show cause and effect.

How Reliable the Swab Is

Labs detect this virus in several ways, and the method changes how much a negative result is worth. Check your report or ask your lab which method was used, because results from different methods can't be compared directly.

DNA-based tests are the standard. The most common one is called PCR, and it copies tiny amounts of viral DNA until there's enough to detect. On lesion swabs, these tests caught nearly every true case in validation studies with very few false positives.

Older methods miss far more, and current lab guidance no longer recommends them for diagnosis. In studies of skin and mucosal sores, growing the virus in a lab dish caught only 26% to 53% of cases, partly because it grows slowly and labs often stop watching before it shows. Staining cells with fluorescent antibodies caught 55% to 80%, and an old smear test caught 60% to 79% while being unable to tell this virus from herpes simplex at all. A newer rapid DNA method built for clinic use caught most but not all cases in children's chickenpox sores, with no false positives.

What this means for you: a negative from anything other than a standard DNA-based test doesn't rule this virus out, and if the sore still fits, it's worth swabbing again with a DNA test.

When a Result Can Mislead You

This test gives a yes-or-no answer, so there's no level to interpret. What can go wrong is a negative that should have been positive, and occasionally the reverse.

• Timing: crusted or healing sores carry much less virus than fresh blisters or open sores, so a late swab can come back negative during a real episode.
• No sore to sample: the virus reaches the genital surface only while it's active, so a swab of healthy tissue will be negative and says nothing about whether shingles is coming.
• Substances in the sample: blood from a vigorous swab, lubricant gels, or topical medicines can block the chemical reaction DNA tests depend on. Well-designed tests include a built-in check that flags this, but tests without one can report a blocked reaction as a negative.
• A recent live vaccine: the weakened virus in the live chickenpox vaccine, or the older live shingles vaccine, can occasionally show up on skin or mucosa, and its DNA is nearly identical to the wild virus, so a specialized test is needed to tell the two apart. That distinction rarely changes treatment. The current non-live shingles vaccine can't cause this.

Rarely, contamination inside the lab produces a false positive, which is why labs run blank control samples alongside patient samples.

Testing Again

This isn't a number you trend. The virus is either active at the sampled spot or it isn't, and between episodes a swab will be negative whatever your future risk happens to be.

Retesting makes sense in three situations. Swab again if a negative came from a sore that was already crusting and the picture still fits. Swab any new sore, since a second genital episode can have a different cause than the first. And because repeat episodes are uncommon in people with healthy immune systems, a second confirmed episode is worth a closer look at what might be weakening your defenses.

The thing worth tracking over time is your immunity, which a blood antibody test shows, along with your vaccination status. That matters most before pregnancy and before starting immune-suppressing treatment.

What to Do With Your Result

Read the swab alongside what you can see and feel. These are the patterns that should drive your next step.

• Positive, with a painful cluster of sores on one side: this is genital shingles. Antiviral treatment works best started early and needs a prescription, so get one promptly and make sure it's dosed for shingles, which runs higher than herpes dosing.
• Positive, and you're pregnant or immune-suppressed: contact your obstetrician or the clinician managing your treatment the same day. With a weakened immune system the virus can spread through the body, and in pregnancy your obstetrician will want to plan around it, especially near delivery.
• Positive with no known reason for weakened immunity: an unexplained episode is a reason to check for conditions that raise shingles risk. An HbA1c test is a good start, since diabetes raises the risk; it reflects your average blood sugar over the past few months. An HIV test is also worth doing, because HIV weakens the immune defenses that keep this virus dormant.
• Negative, but the sore is still there: confirm the same sample was tested for herpes simplex, get a syphilis test, and swab a fresh sore if a new one appears. A dermatologist or gynecologist can examine sores that keep coming back negative.
• Exposed to chickenpox or shingles while pregnant, with no sores: a swab can't help here. A blood antibody test shows whether you're already immune, and that decides whether you need a protective antibody injection soon after the exposure.