1.What is HHV-6?

Human Herpes Virus 6 (HHV-6) is a β-herpes virus which was first isolated in 1986 from the peripheral blood of 6 patients with a variety of lymphoproliferative disorders, some of whom had AIDS.

The virus has worldwide distribution with infection generally occuring within the first two years of life. It is the cause of childhood illnesses known as “6th Disease” or “Roseola Infantum”. The symptoms of this primary infection may begin with the child experiencing a sudden high fever (39 - 40oC). This sudden rise in temperature can in some cases lead to febrile convulsions.  After a few days, the fever subsides and a red rash appears on the child’s body. The rash disappears within twenty four hours.

It is estimated that HHV-6 is the single most common cause (10 – 40%) of children presenting to hospitals with a rash.

After the primary infection, the virus establishes a dormant latent infection in the individual for life. Re-activation of the virus can occur if the individual becomes immuno-compromised. Re-activation has been reported to be relatively common after solid organ and stem-cell transplantation.

These re-activations can cause skin rashes, hepatitis, bone marrow suppression, interstitial pneumonitis and encephalopathy. In some cases, the virus has been shown to cause allograft dysfunction.

HHV-6 is also thought to play a role in a number of diseases, including, the progression from HIV to AIDS, Multiple Sclerosis, Chronic Fatigue Syndrome and other neurologically-related disorders. Further study is required in these areas.

Two genetically distinct variants of human herpesvirus 6 have been discovered: Human Herpesvirus 6A (HHV-6A) and Human Herpesvirus 6B (HHV-6B).

HHV-6A has not been shown to cause any diseases; HHV-6B, unlike HHV-6A, has been associated with a variety of viral illnesses, including, exanthem subitum (roseola infantum), mononucleosis syndromes, focal encephalitis, and pneumonitis.

2. How prevalent is HHV-6?

HHV-6 is highly seroprevalent and studies have shown that the virus is present in almost 100% of the general population. Primary infection generally occurs within the first 2 years of life. HHV-6 has a worldwide distribution.

3. What groups are most at risk to this virus?

Almost all individuals become infected with HHV-6 before they reach 2 years of age. As a result, primary HHV-6 infections in adults is rare. After the initial infection during childhood, the virus establishes a lifelong infection whereby it enters into a latent stage. HHV-6 may reactivate if the individual becomes immuno-compromised.

These re-activations can cause skin rashes, hepatitis, bone marrow suppression, interstitial penumonitis and encephalopathy. In some cases, the virus has caused early and late solid organ rejection.

4. Who should be tested for HHV-6?

• Young children with a rash or who have suffered from a febrile convulsion
  
• Transplantation donors & recipients
  
• Research groups working on the association between HHV-6 and MS, CFS, Carcinoma, HIV and a range of other illnesses.

Biotrin are always interested to hear from research groups working in these areas. Please contact us at info@biotrin.ie with details of your work on HHV-6.

5. What is 6th disease, Exanthum Subitum and Roseola Infantum?

Exanthum Subitum (meaning sudden rash), is also referred to as roseola infantum (or rose rash of infants) and sixth disease. It is a childhood disease that affects most children by 2 years of age.

HHV-6 and HHV 7 are known to be the causative agents of this childhood disease.

Typically, Roseola affects a child between the ages of six months and three years of age. It begins with a sudden high fever of 102-104 degrees Fahrenheit (39-40 degrees Celsius). This can cause, in some cases, febrile convulsions due to the sudden rise in body temperature, but in many cases the child appears and acts normal. After a few days the fever subsides, and just as the child appears to be recovering, a red rash appears. This usually begins on the trunk, spreading to the limbs but usually not affecting the face. It disappears again after a few hours to a day.

In contrast, a child suffering from measles would usually appear more infirm, with symptoms of conjunctivitis, a cough, and their rash would affect the face and last for several days.

6. How is HHV-6 transmitted?

Transmission occurs via saliva from infected individuals, blood transfusion and organ transplantation.

7. How are HHV-6 infections treated?