Human herpes virus 6 (HHV-6) is the virus that most commonly causes the childhood disease, roseola. Studies show that HHV-6 infects approximately 90% of children by age 2 years. Human Herpesvirus 6 (HHV-6) is a set of two closely related herpes viruses known as HHV-6A and HHV-6B that infect nearly all human beings, typically before the age of two. A is rare and is acquired in adulthood. B is relatively common, is usually acquired in childhood, and is associated with roseola. The acquisition of HHV-6 in infancy is often symptomatic, resulting in childhood fever, diarrhea, and exanthem subitum rash (commonly known as roseola). Although rare, this initial infection can also cause febrile seizures, encephalitis or intractable seizures.
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. It is also possible 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 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.
HHV-6 establishes life-long latency and can become reactivated later in life. Reactivation can occur in locations throughout the body, including the brain, lungs, heart, kidney and gastrointestinal tract. In some cases, HHV-6 reactivation in the brain tissue can cause cognitive dysfunction, permanent disability and death. A growing number of studies also suggest that HHV-6 may play a role in a subset of patients with chronic neurological conditions such as multiple sclerosis, mesial temporal lobe epilepsy, status epilepticus and chronic fatigue syndrome.
HHV-6B is commonly found in the saliva after primary infection, and is passed to infants from family members and caregivers. Little is known about the transmission of HHV-6A since it is generally not found in the saliva. It is known that children do acquire HHV-6A from family members in Africa. One potential route of transmission could be through the nose. Several studies have suggested that HHV-6A could also be transmitted sexually. HHV-6B causes 97 – 100% of primary HHV-6 infections in the USA and Japan and is responsible for a 97% of reactivation in transplant patients.
It is only possible to differentiate HHV-6A from HHV-6B using a PCR DNA test, and due to the extremely low levels of latent virus in the blood, typing is difficult except when the virus is actively replicating during an acute illness.
Test options
CMV/HHV6/EBV panel: Differentiation between these three Herpes family of Virus’s
Learn more about HHV6
http://hhv-6foundation.org/what-is-hhv-6
http://emedicine.medscape.com/article/219019-overview
http://wwwnc.cdc.gov/eid/article/5/3/99-0306_article
http://www.medicinenet.com/script/main/art.asp?articlekey=11501
