BACKGROUND
Human Herpesvirus Type 6 (Enveloped, double stranded DNA virus).
1. How is the virus transmitted?
Most likely, it is spread by close
personal contact or by the respiratory route.
2. What is known about the pathogenesis of
the infection? Why is this illness often a cause of emergency room visits?
HHV-6 infection is ubiquitous in young
children and results in an appreciable burden on our health care resources.
It accounted for 10% of visits to the emergency department for acute febrile
illness among children in the first 2 years of life, and for 20% of such
visits among those 6 to 12 months old. Its protean manifestations and the
lack of means of diagnosis often resulted in lengthy and costly evaluations
and hospitalizations. The actual human and financial costs, however, cannot
be estimated without a better understanding of the spectrum and consequences
of HHV-6 infection.
Most initial HHV-6 infections in normal
children are benign, although there are case reports of occasional
complications, including thrombocytopenia, granulocytopenia, hepatitis, and
disseminated infection. The most common complications are central nervous
system manifestations, as has been long suggested by reports associating
roseola with seizures, bulging of the anterior fontanelle,
meningoencephalitis, and encephalopathy. HHV-6 accounted for one third of
the febrile seizures evaluated in children two years of age or less in one
emergency department. Seizures occurred in 19.4 % of those 6 months or older
and in 36% of those 12 to 15 months of age -- significantly more often than
in age-matched children with febrile illnesses not due to HHV-6. The
mechanism by which HHV-6 cause central nervous system manifestations remains
unclear, but it may involve more than the high fevers. In several recent
Japanese reports HHV-6 DNA was detected in the
cerebrospinal fluid of infants with roseola complicated by neurologic
symptoms and in eight patients with recurrent febrile convulsions. These
finding raise the possibility of direct invasion of the central nervous
system during the viremic phase of the initial illness, with possible
subsequent latency.
3. Both case studies 2 and 3 are generally
diagnosed clinically. List the distinguishing features of these two
infections?
HHV-6 generally presents with higher fever (104o versus 101-102oF) and fever persists for a longer time (4 days versus 2 days). The rash starts when the fever resolves. The rashes are distinct, parvo = Aslapped cheek@ and lace-like rash on arms and trunk which is present at the time of the fever. HHV-6 = erythematous rash over the entire body.
4. Are there any vaccines available to
prevent this disease?
No.
5. Are there any effective anti-viral
agents that act against this virus?
No.
6. Are there any long term consequences
associated with this viral infection?
There is latent infection of T cells. HHV-6 appears to be capable of reactivation in immunosuppressed patients, but the clinical significance of reactivation is unknown.