Human herpesvirus 6, also called HHV-6, is most likely in your body right now, hanging out and not doing much of anything. If you're part of a certain minority, though, it may be causing one or more illness.

As the name suggests, HHV-6 was the sixth member of the herpes virus "family" to be discovered. Other herpes viruses include the Epstein-Barr virus, cytomegalovirus, and herpes simplex 1 and 2 (both of which can cause cold sores and genital herpes).

Symptoms are most likely when you first become infected; however, it is possible for the virus to reactivate at some point down the road. In that case, it may cause health problems including any of several neurological conditions.

HHV-6 can target the nervous system, which is made up of your brain and spinal column, the immune system, and a wide variety of organs.

HHV-6 comes in two types, called A and B. Scientists originally thought they were variants of the same virus, but now they believe them to be completely separate from each other. HHV-6 A is rare and is usually found in adults, while the B type generally infects children.

All herpes-family viruses stay in your body for life, usually lying in a dormant (inactive) state. You cannot cure HHV-6, but it does not cause disease in everyone.

HHV-6 A

Research links HHV-6 A to numerous neurological conditions. Some of these links are supported by considerable evidence, while other ties are less certain. At this point, we can't say for certain that HHV-6 directly causes any of these conditions.

Diseases linked to HHV-6 reactivation are many. For most of them, though, we don't know if HHV-6 is the actual cause. These diseases include:

Autoimmune diseases, such as Hashimoto's thyroiditis, Sjogren's syndrome, lupus, multiple sclerosis, and Guillain-Barre syndrome
Bone marrow suppression
Cancer, including Hodgkin lymphoma, gliomas, and cervical cancer
Chronic fatigue syndrome
Cognitive dysfunction, including delirium and amnesia
Colitis
Drug hypersensitivity reactions, including Stevens-Johnson syndrome
Encephalitis
Endocrine (hormonal) disorders
Epilepsy
Heart disease, including myocarditis, arteriopathies, and left ventricle dysfunction
Kidney disease
Liver disease
Lung disease
Sarcoidosis

Some people with an active HHV-6 infection may develop more than one of these illnesses. However, a vast majority of people infected with this virus have no symptoms at all, and many have only mild short-term symptoms.

Anyone with HHV-6 can experience a reactivation, but it is most common in people with a compromised immune system, such as organ transplant recipients and people with HIV.

HHV-6 B

HHV-6 B is the more common form of the virus. Most of us—more than 90 percent—are infected during our first three years and therefore carry it around with us for the vast majority of our lives. For most babies, the initial infection doesn't cause any noticeable health problems.

Roseola

In about 20 percent, however, HHV-6 B infection causes a condition called roseola. Symptoms of roseola generally come in two stages. The first may include:

Sudden high fever (above 103 F) lasting three to five days
Mild sore throat
Runny nose
Cough
Swollen lymph nodes in the neck
Irritability
Mild diarrhea
Decreased appetite
Swollen eyelids

Within a day of the fever going away, the child may develop a rash that doesn't itch or cause discomfort. The rash is made up of lots of small pink spots or patches, some of which may have a white ring around them. It will usually begin on the torso and then spread to the limbs and possibly the face. It can go away in as little as a few hours or hang around for several days.

Roseola usually isn't serious. In rare cases, a child may develop a high fever that can lead to complications such as seizures. Treatment is typically focused on alleviating fever and ensuring plenty of bed rest.

Epilepsy

In addition to fever-induced seizures, HHV-6 B has been linked to epilepsy, a chronic neurological condition characterized by recurrent seizures. Symptoms of epilepsy can vary and may involve any of the processes coordinated by the brain. Epilepsy is chronic, meaning that it's a condition that requires long-term treatment and management.

Common symptoms of epilepsy include:

Uncontrollable jerking movements
Temporary confusion
Staring off into space for a short time
Fear and anxiety
A sense of deja vu
Loss of consciousness
Loss of awareness

Encephalitis

HHV-6 is also linked to encephalitis (inflammation of the brain), a condition that can be fatal. Common symptoms of encephalitis include:

Seizures
Headaches
Muscle or joint pain
Fatigue
Weakness
Fever
Confusion
Partial paralysis
Speech problems
Hearing problems
Loss of consciousness

In babies and young children, it may also cause:

Bulging in the skull's soft spots
Nausea
Vomiting
Stiffness
Irritability
Poor feeding
Sleeping through feeding times

If you suspect a child has encephalitis, it is imperative that you seek immediate medical attention.

According to research in Infectious Disease Clinics of North America, nearly all children with encephalitis in the United States require hospitalization with 40% requiring critical care in an intensive care unit.

Diagnosis

We have a few different blood tests that can detect whether you're infected with HHV-6. One of the tests comes back with a "yes" or "no" answer, though, which isn't terribly useful. Remember that most of us have probably carried this virus around since childhood.

Instead of looking at whether it's there, another test looks at the level of antibodies in your blood, since an elevated number can indicate an active infection rather than a latent one. (Antibodies are Y-shaped immune proteins that your body produces in response to infection, with each type "tailored" to the identify and tag the specific infectious microorganism.)

Complicating matters is the fact that getting a negative result from a blood test doesn't necessarily mean you don't have an active infection. That's because HHV-6 can infect a single organ, including the brain, heart, lungs, liver, and uterus. That means tissues have to be tested to determine whether you're infected.

Because blood tests are often unreliable, your doctor may diagnose HHV-6 based on symptoms alone, ruling out other likely causes such as mononucleosis, meningitis, cytomegalovirus (CMV), rubella, or sepsis.

Your doctor may also use diagnostic imaging, tissue biopsy, lumbar puncture ("spinal tap"), or bronchoscopy (to view inside your airways).

Before diagnosing roseola in a baby, doctors generally consider other possible causes of rash and fever—of which there are many. Different lab tests are used for diagnosing HHV-6 reactivation in organ transplant recipients or people with hepatitis, encephalitis, or HIV.

Treatment

At this point, we don't have a well-established treatment regimen for active HHV-6 infection. Because symptoms can vary widely from one person to another, doctors generally tailor the treatment to the individual case.

Antiviral drugs have gotten some attention for treating HHV-6, but so far, they remain unproven. Some of the more common drugs suggested for combating this virus are Cytovene (ganciclovir) and Foscavir (foscarnet).

There is no vaccine to prevent HHV-6 infection.

A Word From Verywell

If you think you may have an illness that could be related to an HHV-6 infection or reactivation, be sure to bring it up with your doctor. A proper diagnosis is the first step toward finding the treatments that help you feel better.

Many of the illnesses linked to HHV-6 are chronic, so you may have to learn to manage them. Educating yourself, working with your doctor, and exploring different treatment options are all important when it comes to finding your optimum treatment regimen.

Human Herpesvirus 6 (HHV-6) Links to Numerous Diseases