Human herpesvirus 6 (HHV-6)
Human herpesvirus 7 (HHV-7) Exanthem subitum (meaning sudden rash), also referred to as roseola infantum, sixth disease and (confusingly) baby measles, is a benign disease of children, generally under two years old, whose manifestations are usually limited to a transient rash ("exanthum") that occurs following a fever of about three day's duration.

Until recently, its cause was unknown: it is now known to be caused by two human herpesviruses, HHV-6 and HHV-7, also called Roseolovirus.

Despite the fact that it is occasionally called baby measles, it is caused by a different virus than that which causes measles, which is a more severe disease.

The name sixth disease stems from the fact that when diseases causing childhood rashes were enumerated, it was the sixth listed. The list of such diseases is:

1. measles, rubeola, 14-day measles
2. scarlet fever, scarlatina
3. rubella, German measles, 3-day measles
4. Duke's disease (caused by various viruses including coxsackievirus, enterovirus, or echovirus)
5. fifth disease (erythema infectiosum, slapped cheek syndrome), caused by Parvovirus B19
6. sixth disease (exanthem subitum, roseola infantum, rose rash of infants, baby measles)

Clinical Features of Exanthem subitum

Typically the disease affects a child between 6 months and 3 years of age, and begins with a sudden high fever of 39-40 degrees celsius. This can cause, in some cases, febrile convulsions (also known as febrile seizures or fever fits) - due to the suddenness of the rise in body temperature. 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 in a matter of hours to a day or so.

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

Vaccines and Treatment

There is no specific vaccine against or treatment for, Exanthem subitum, and most children with the disease are not seriously unwell. The child with fever should be given plenty of fluids to drink, and acetaminophen or ibuprofen to reduce the temperature. He or she should also be kept more lightly clothed than normal if he or she is very hot. The rash is not particularly itchy and needs no special lotions or creams.

It is likely that many children catch Exanthem subitum "subclinically", in other words they show no outward sign of the disease. Others may be unwell enough that a doctor's opinion is required to confirm the diagnosis, and particularly to rule out other more serious infections, such as meningitis or measles. In case of febrile seizures, medical advice is essential.