HHV-6 has been associated with various clinical complications, including roseola, chronic fatigue syndrome, multiple sclerosis, encephalitis, and drug hypersensitivity. Although nearly everyone is infected with HHV-6 in childhood, only a small percentage experience reactivation of HHV-6 later in life. Moreover, many of these reactivation events never cause symptoms. However, evidence has shown that HHV-6 reactivation can occur occasionally, especially during times of stress, other illnesses, in response to acute allergic reactions or during immunosuppression. Some individuals with an undiagnosed immune deficiency may reactivate with HHV-6. We encourage you to explore the resources at right to learn more about testing, treating, and identifying HHV-6 primary infection and reactivation.

Frequently Asked Questions

Dr. Jose Montoya, an infectious disease specialist at Stanford University, uses IgG antibody tests done by IFA to determine whether patients qualify for antiviral treatment since PCR DNA tests are insensitive. (This virus is found mostly in the tissues and not in the blood, so it is more productive to look for indirect evidence of HHV-6 in the form of unusually elevated antibody levels). Montoya uses the HHV-6 IgG test at Focus Diagnostics Laboratory. Other labs that offer the IFA test (which is reported as a titer such as 1:160 instead of a single number) include Specialty Laboratories and Medical Diagnostics Laboratory. Quest Diagnostics owns Focus Diagnostics so you may be able to get the Focus test through Quest. (Ask your local Quest office if they send their HHV-6 testing to Focus.) For more information about testing options, please refer to the Testing page on our website.
Almost 100% of the population has latent virus and HHV-6 antibodies. The important question is: are your antibody levels abnormally elevated? If you have a titer of 1:640 or above at Focus Diagnostics, then this raises the level of suspicion. It doesn’t tell you for certain that you have active replication. Unfortunately, these antibody tests vary by laboratory. So a lower titer of 1:160 or 1:320 might be very significant at another laboratory. If your test is NOT from Focus you need to ask your doctor to find out from the laboratory director how your value compares to the median of a normal population. The laboratory director should have these statistics from studies done to license the test. If you find out the answer, please send the Foundation an email, as we would like to start collecting this information. If your result is in the top 20% of a normal population, then this could be a clue that your HHV-6 is “active” instead of latent. Currently, there is no standard threshold to evaluate which values are “elevated”.
ELISA tests results are reported as a single number (e.g. 2.1 or 5.5) and for complicated reasons they are not as reliable as IFA tests for determining whether you have highly elevated antibodies. This assay was designed as a qualitative test (yes/no answer) and is not recommended for monitoring your HHV-6 antibody levels over time or during treatment. If the ELISA result states that you have >1 and are “positive” this usually just means that you have been EXPOSED to the virus, not that you have an active viral infection. This is a meaningless result since everyone over the age of two has been exposed to HHV-6. A high number (above 4 or 5) MAY be significant, but again, this all depends on the laboratory and the kit they use. You can ask your doctor to find out from the lab how your ELISA result compares to that of normal controls in order to interpret your value. If your value is at the high end, then consider getting the IFA test mentioned above to confirm possible reactivation.
Since the HHV-6 virus tends to hibernate in the tissues rather than circulate in the blood, it is very difficult to find viral DNA in the blood. Unlike viruses such as herpes simplex where it is very easy to detect viral DNA in the blood, HHV-6 is considered a “low copy number” virus. Therefore, unless the infection is acute, (as in post-transplant encephalitis) it will not show up in most laboratory tests because the copy number will fall below the level of detection. Also, an HHV-6 infection may reside entirely in the brain tissue, insulated from the blood stream by the blood brain barrier. Researchers at the NIH National Institute of Neurological Diseases and Health have found that even in cases of HHV-6 encephalitis, where millions of DNA copies can be found in the brain, only a tiny amount of HHV-6 DNA can be found in the blood or spinal fluid. So, if you have a negative result on an HHV-6 PCR DNA test, you could still have an active infection in the brain or other tissue.

A positive PCR result in a serum test is generally considered a sign of active infection because the virus has left the cells (either because of cell death or active replication). A positive result on whole blood, however, does NOT necessarily mean an active infection because most of us have tiny amounts of latent virus circulating in the blood (10-20 copies per ml). Usually, latent virus in a healthy person can only be picked up by the more sensitive “nested” PCR on whole blood (such as the one used by Redlabs USA). Positive-nested PCR tests for HHV-6, HHV-7 and CMV (as done at Redlabs) should not be interpreted to mean that you have an active infection as many normals have low levels of DNA from these viruses in their bloodstream. Tests on whole blood (as opposed to serum/plasma) are only meaningful if they are quantitative tests that can be compared to a normal population. We hope that physicians will be able to establish a threshold for what can be considered “active” infection. See Testing page for more details.

A small percentage of the population (approximately .8% of Caucasians and .2% of Japanese) have a condition called “Chromosomally integrated HHV-6” (ciHHV-6) which means that the virus is actually integrated into your chromosomes and passed from parent to child. If you have ever had a positive PCR test, it is possible that this is due merely to your ciHHV-6 status. (See ciHHV-6 paragraph below).

Depending on your test results, you might be a candidate for antiviral treatment. Please refer to the website’s Treatment page for more information. The most common antiviral drug in use is Valcyte, an oral drug given to patients who have compromised immune systems to prevent reactivation of CMV or HHV-5. Although there are no drugs that are FDA approved specifically for HHV-6, physicians routinely use Valcyte or IV drugs foscarnet or cidofovir. Valtrex may help prevent an HHV-6 reactivation but is not effective against an HHV-6 infection that is already active.
The HHV-6 Foundation cannot recommend a doctor. HHV-6 antiviral therapy is still considered experimental for CFS. Typically, only infectious disease specialists prescribe Valcyte, although several CFS doctors have started prescribing it for patients who have elevated antibodies to HHV-6 and EBV.
Certainly most of those with ciHHV-6 have no evidence of active infection. However, since you were born with the virus, you may have reduced immunity to community acquired HHV-6 virus. The question of whether this ciHHV-6 virus can actually replicate is currently being studied. Although preliminary reports suggest that it does not replicate, researchers at the University of Rochester recently found that 8% of infants born with ciHHV-6 had active replication and investigators from Stanford recently reported at the June HHV-6 conference that they have successfully treated several symptomatic ciHHV-6 patients with antivirals. Viracor has a quantitative ciHHV-6 test that can tell you if you have ciHHV-6. If your viral load is over 400,000 copies at Viracor, you can assume you have ciHHV-6. CiHHV-6 testing should be done on whole blood or spinal fluid (CSF) by Q PCR. In one case report, a ciHHV-6 patient had 12 million copies per ml when symptomatic and dropped to 103,000 copies after three weeks of antiviral therapy. Values above 1 copy per white blood cell, or above 4-6 million copies per ml at Viracor MAY suggest active replication. DNA copy loads can vary dramatically by laboratory. Contact the HHV-6 Foundation to learn about several ongoing studies on ciHHV-6.
The HHV-6 Foundation PATIENT FORUM contains a number of discussion topics regarding testing, treatments and related conditions.