We obtained 7,566 peripheral blood mononuclear cell (PBMC) samples from 2,332 individuals and screened them for human herpesvirus infection. We identified five individuals who persistently harbored high copy numbers of human herpesvirus 6 (HHV-6) DNA in their PBMCs. HHV-6 DNA was also detected in other somatic tissues of these individuals. Five additional cases were identified among their family members. For two of these families, chromosomally integrated HHV-6 DNA (CIHHV-6) was detected in the PBMCs by fluorescence in situ hybridization. The prevalence of CIHHV-6 among all the subjects was 0.21%. The HHV-6 DNA was variant B in four families and variant A in one family. Antibodies to immediate early antigen and glycoprotein B were detected in 57 and 14% of individuals with CIHHV-6 and in 0 and 60% of healthy volunteers without CIHHV-6, respectively. HHV-6 could not be isolated from PBMCs with CIHHV-6. These cases shared no clinical features, and included three healthy individuals. Our data suggest that CIHHV-6 is rare but detectable in the general population and that hereditary transmission is one of the routes of HHV-6 transmission.

Fifty-nine acute flaccid myelitis cases were reported nationwide, coincident with enterovirus D68 (EV-D68) outbreak from August to December 2015. Strong temporal association was noted, and EV-D68 was detected from some cerebrospinal fluid and blood specimens. Antiganglioside antibodies were identified in some patients, and prognostic factors were analyzed.

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis and some malignancies including EBV-associated-lymphomas. A large portion of adults all over the world are infected with EBV. In children, however, there are geographic variations. Most of the children in Asia and in other developing countries are infected in their early life, before 1 year of age (>90% of 5-9-year-old children are infected), while the age of primary infection is delayed in Western countries (approx. 50% of 5-9-year-old children are infected). The purpose of the present paper was to investigate the recent time trend of the EBV seropositivity among 5-7-year-old children living in Tokyo and its neighboring prefectures. Indirect immunofluorescein study for IgG antibody to viral capsid antigen was performed on 442 archival sera. Before the early 1990s, >80% of 5-7-year-old children were found to be seropositive, while the positivity rate decreased to 59% (P < 0.001) for the years 1995-1999. These results also showed that the delay in the age of primary infection is continuing and that the rate is estimated to be <50% in 2006. This result suggests that the delay will affect the incidence of EBV-associated disorders in Japan.

The presence of human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) in throat swabs of 62 children of different age groups (group I, ages 0-5 month; group II, ages 6-11 months, group III, ages 12-23 months, group IV, age 2-8 years) and 28 adults was detected by polymerase chain reaction. The detection rate of HHV-6 DNA was the highest (87%) in children aged 1-year-old and decreased with age, whereas the detection rate of HHV-7 increased with age and reached a maximum in adults. HHV-6B was detected in almost all samples except for two children who secreted only HHV-6A. When the antibody prevalence was determined in the four groups of children, HHV-6 antibody was detected in 8/12 (66.7%), 10/12 (83.3%), 15/16 (93.8%), and 13/14 (92.9%), respectively. Antibody to HHV-7 in these groups was detected in 6/12 (50.0%), 4/12 (33.3%), 12/16 (75.0%), and 13/14 (92.9%), respectively. Detection of HHV-6 DNA in throat swabs of triplets who had the sequential onset of exanthem subitum was attempted by using samples sequentially collected from these children after the onset of the disease in the first patient. HHV-6 DNA with high copy numbers was detectable during the acute and convalescent phases of the disease in all patients, but no DNA was detected in samples collected before the onset of disease.