Human herpesvirus 6 (HHV-6) is the virus that most commonly causes the childhood disease, roseola. It was first discovered in 1986. Studies show that HHV-6 infects approximately 90% of children by age 2 years. It is usually marked by several days of high fever followed by a distinctive rash just as the fever breaks. It is probably very difficult and probably inadvisable to avoid infection. It's not whether you have HHV-6, but instead how much virus you have, and is it latent or active.
About 1 percent of all infants in the U.S. are born with asymptomatic infections. It was believed that they were infected in utero when viral particles from their pregnant mothers crossed the placental barrier. But recently a study documented a new way for HHV-6 infection in which HHV-6 integrated into parental DNA and was passed on at conception. In less than 1 percent of all adults, the virus can also slyly work its own DNA into the human genome. This makes it possible for mothers and fathers to pass HHV-6 to their children if these insertions are present in their eggs or sperm. "With chromosomal integration, all cells have the virus from the beginning," says senior study author Caroline Hall, a pediatrician at the University of Rochester. But, she adds, "it is unclear whether the presence of the virus during development affects a child's health."
Two types have been discovered: human herpesvirus 6A (HHV-6A), A is rare, and acquired in adulthood, and human herpesvirus 6B (HHV-6B), B is common, usually acquired in childhood. Both A and B can reactivate at a later date, and are believed to contribute to diseases of the bone marrow and/or central nervous system in some people. HHV-6B has been associated with a variety of viral illnesses, including exanthem subitum, roseola infantum, fatal encephalitis, focal encephalitis, mononucleosis, lymphadenopathy, myocarditis, myelosuppression, and pneumonitis.
Many cases of HHV-6 infections are silent or appear with a fever, but HHV-6 infection in infants is the most common cause of fever-induced seizures usually associated with the primary HHV-6 infection. HHV-6 infection in adults is seen usually in those having a compromised immune system, those who have undergone organ transplants or in those with HIV infection.
New research suggests that HHV-6 may play a role in several chronic neurological conditions including MS (multiple sclerosis), mesial temporal lobe epilepsy, status epilepticus, fibromyalgia, and chronic fatigue syndrome.
Children with roseola usually develop a mild upper respiratory illness, followed by a high fever (often over 103° F) which can last a week. The fast-rising fever that comes with roseola triggers febrile seizures and convulsions in about 10% to 15% of young children. Children may be crancky or irritable and may have a decreased appetite and swollen lymph nodes in the neck.
The high fever ends all of a sudden and then a pinkish-red flat or raised rash appears on the trunk and spreads over the body.
Virus detection is not practicable as a routine diagnostic procedure. PCR DNA tests can detect HHV-6 but with difficulty. Indirect evidence of the HHV-6 antibodies are easier to find than the HHV-6 virus itself. Therefore elevated IgG antibody levels may be the only indication of a reactivated chronic central nervous system (CNS) HHV-6 infection.
The virus is spread through saliva and possibly by genital secretions.
Older siblings can be a source of HHV-6 transmission.
No formal treatment or prophylaxis for HHV-6 infection presently exists. The virus lays dormant and is always in the body.