Cervical and postocciptal lymphadenopathy can also be seen, but this generally presents 2–4 days after the onset of the febrile phase.In rare cases, HHV-6 can become active in an adult previously infected during childhood and can show signs of mononucleosis. Cause
There are nine known human herpesviruses. Of these, roseola has been linked to two: human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7), which are sometimes referred to collectively as Roseolovirus. These viruses are of the Herpesviridae family and the Betaherpesvirinae subfamily, underwhich Cytomegalovirus is also classified. HHV-6 has been further classified into HHV-6A and HHV-6B, two distinct viruses which share 88% of the same DNA makeup, with HHV-6B the most common cause of roseola.After infection, these viruses enter a latent phase. Roseola caused by HHV-7 has been linked to the ability of HHV-7 infection to reactivate latent HHV-6. Spread
After exposure to roseola, the causative virus becomes latent in its host but is still present in saliva, skin, and lungs. HHV-6 is thought to be transmitted from previously exposed or infected adults to young children by the shedding of virus through saliva. Even so, most cases of roseola are transmitted without known exposure. Diagnosis
The diagnosis of roseola is made clinically based on the presence of the two phases: fever and rash. Laboratory testing is seldom used as the results do not alter management of the disease.
Signs and symptoms
Fever
Symptoms begin with a three to six day febrile illness. During this time, temperatures can peak above 40 °C and children can experience increased irritability with general malaise. However, many children in the febrile phase feel well, engaged, and alert. For these patients, fever is usually diagnosed incidentally.The most common complication (10-15% of children between 6 and 18 months) and most common cause of hospitalization in children with primary infection of HHV-6B is febrile seizures which can precipitate status epilepticus due to the sudden rise in body temperature. Rash
Once the febrile phase subsides, a rash develops. In some cases, the rash can present after one or two days after the fever resolves. The rash is classically described as an erythematous morbilliform exanthem and presents as a distribution of soft pink, discrete, and slightly raised lesions each with a 2-5mm diameter. It classically begins on the trunk (torso) and spreads outward to the neck, extremities, and face. This pattern is referred to as a centrifugal spread. Usually, peeling and itching are not characteristic of this rash. This phase can last anywhere from several hours to 2 days. Other symptoms
A small percentage of children acquire HHV-6 with few signs or symptoms of the disease. Children with HHV-6 infection can also present with myringitis (inflammation of the tympanic membranes), upper respiratory symptoms, diarrhea, and a bulging fontanelle. In addition, children can experience pharyngitis with lymphoid hyperplasia seen on the soft palate and swelling of the eyelids. These symptoms usually present during the febrile phase of roseola.