Age<unk> s acquire the virus at an early age, some as early as less than one month of age.<unk>  primary infections account for up to 20% of infant emergency room visits for fever in the United States and are associated with several more severe complications, such as encephalitis, lymphadenopathy, myocarditis and myelosuppression. The prevalence of the virus in the body increases with age (rates of infection are highest among infant between<unk>  and 12 months old) and it is hypothesized that this is due to the loss of maternal antibodies in a child that protect him or her from infections. There are inconsistencies with the correlations between age and seropositivity: According to some reports there is a decrease of seropositivity with the increase of age, while some indicate no significant decline, and others report an increased rate of seropositivity for individuals age<unk> 2 and older. After primary infection, latency is established in salivary glands, hematopoietic stem cells, and other cells, and exists for the lifetime of the host. Geographical distribution The virus is known to be widespread around the world. An<unk>  infection rate of<unk> 4–83% by age 13 months has been reported for countries including the United States, United Kingdom, Japan and Taiwan. Studies have found seroprevalence varying "from approximately 39 to 80% among ethnically diverse adult populations from Tanzania, Malaysia, Thailand, and Brazil." There are no significant differences among ethnic groups living in the same geographical location or between sexes. While<unk> B is present in almost all of the world's populations,<unk> A appears to be less frequent in Japan, North America, and Europe. Transmission Transmission is believed to occur most frequently through the shedding of viral particles into saliva. Both<unk> B and HHV-7 are found in<unk>  saliva, the former being at a lower frequency. Studies report varying rates of prevalence of<unk>  in saliva (between 3–90%), and have also described the salivary glands as an in vivo reservoir for<unk> . The virus infects the salivary glands, establishes latency, and periodically reactivates to spread infection to other hosts. Vertical transmission has also been described, and occurs in approximately 1% of births in the United States. This form is easily identifiable as the viral genome is contained within every cell of an infected individual.
Human herpesvirus 6
Human betaherpesvirus 5
Human betaherpesvirus 7
Human T-lymphotropic virus 2
Human T-lymphotropic virus 1
Trichodysplasia spinulosa polyomavirus
Molluscum contagiosum virus
Epstein–Barr virus