SEROPREVALENCE OF HUMAN HERPESVIRUS-6 AND HERPESVIRUS-7 INFECTIONS INTHE THAI POPULATION

Seroprevalence of human herpesvirus 6 (HHV-6) and 7 (HHV-7) was estima ted in the Thai population using indirect immunofluorescence assay to determine serum antibodies to HHV-6 and HHV-7. A total of 333 serum sa mples obtained from umbilical cord blood and venous blood of healthy p ersons at Siriraj Hospital and Krabi Hospital during 1990-1993 were in vestigated. Of 73 infants aged 0-1 month, 73% and 78% were found tob a positive for HHV-6 and HHV-7 antibodies, respectively. Antibody to HH V-6 was detected in age groups 2-3 months (38%), 4-5 months (14%), 6 m onths (44%), 7-11 months (66%), 1-2 year (84%), 3-4 years (82%), 5-9 y ears (83%), 10-19 years (83%), 20-29 years (80%), 30-39 years (67%), a nd over 40 years (58%), respectively. The positive rates of HHV-7 anti body in age groups 2-3 months, 4-5 months, 6 months, 7-11 months 1-2 y ears, 3-4 years, 5-9 years, 10-19 years, 21-29 years, 30-39 years, and over 40 years were 50%, 21%, 10%, 37%, 47%, 82%, 75%, 72%, 72%, 67%, and 67% respectively. At 6 months of age as the starting time of infec tions, 34%(14/41) and 9%(3/41) of infants had presumed primary infecti ons of HHV-6 and HHV-7, respectively. In the follow-up study, 53% (20/ 38) of children were infected with HHV-6 prior to HHV-7 and only 5% vi ce versa. Eighty-four percent of children had acquired antibody to HHV -6 by 1-2 years old while 82% of children had acquired antibody to HHV -7 by 3-4 years old. These results suggest that HHV- 6 and HHV- 7 are prevalent viruses in the Thai population. The infections of both virus es begin at 6 months of age, However, infection of HHV-7 in most child ren begins later. The data also provided evidence that antigenic disti nction between HHV-6 and HHV-7 existed with a limited cross-reactivity in an anbitody test. The antibody responses to HHV-6 and HHV-7 occurr ed independently.