Rare Infectious Disease News

Disease Profile

HHV-6 encephalitis

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Human Herpesvirus 6 encephalitis; Variant A or HHV-6A; Variant B or HHV-6B


HHV-6 encephalitis refers to inflammation of the brain due to an infection with human herpesvirus 6. People who have undergone allogeneic hematopoietic cell transplantation are at an increased risk for developing HHV-6 encephalitis, particularly when umbilical cord blood stem cells are used. People with immune system disorders may also be at an increased risk for developing this infection. Signs and symptoms vary, but often include confusion, anterograde amnesia (difficulty learning new information following the onset of amnesia), short-term memory loss, and seizures. Diagnosis often involves lumbar puncture, virus testing, and MRI. EEG's may also be recommended when seizures are suspected. HHV-6 encephalitis is treated with an antiviral agent with activity against HHV-6. Long term outlook (chance of full recovery) can vary considerably depending individual patient factors.[1]


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

    Learn more

    These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

    Where to Start

    • The HHV-6 Foundation provides information on HHV-6 and associated conditions on their Web site. Click HHV-6 Foundation to view the information.

      In-Depth Information

      • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
      • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
      • PubMed is a searchable database of medical literature and lists journal articles that discuss HHV-6 encephalitis. Click on the link to view a sample search on this topic.

        Selected Full-Text Journal Articles

        • Caserta MT, Mock DJ, Dewhurst S. Human herpesvirus 6. Clin Infect Dis. 2001 Sep 15;33(6):829-33. Epub 2001 Aug 10.


          1. Zerr D. Human herpesvirus 6 infection in hematopoietic cell transplant recipients. In: Basow DS. UpToDate. Waltham, MA: UpToDate; 2013;