Frequency evaluation and molecular characterization of HHV-6 and HHV-7 among children under 5 years with fever and skin rash.

Skin rash is one of the most common complications during childhood. Viral agents play an essential role in the development of such symptoms. Present study aims to determine the prevalence and genetic variability of Human Herpesvirus 6 and 7 (HHV-6 and HHV-7) infections and their subtypes in children under 5 years of age with skin rash and negative for rubella and measles. We used serum and throat swap samples from 196 children with skin rash and fever. ELISA and IFA tests were performed to detect antibodies against HHV6/7. Sequencing was performed using Sanger sequencing, and BioEdit and MEGA10 software were used for sequence analysis. According to the results, 66% and 40% of cases were positive for HHV-6 IgM and HHV-7 IgM, respectively. According to the molecular analysis, HHV-6 Nested-PCR was positive in 18% of cases, however, HHV-7 Nested-PCR was positive in 7.7% of cases. On the other hand, HHV-6 IgG and HHV-7 IgG were positive in 91% and 55% of study cases, respectively. For HHV-6, we found some genetic variabilities resulting in antigenic changes compared to reference strains. HHV-7 isolates showed no genetic differentiation and had a stable gene sequence. Based on the results, the detection of some cases of HHV6/7 primary infection and the presence of specific symptoms of roseola in the study population needs continuous evaluation of HHV6/7 frequency and distribution, also genetic variabilities of HHV6. This can pave the way for investigating HHV6 immune evasion and vaccine research and studying the relationship between viral genetic variations and other factors like disease severity. Furthermore, it is necessary to determine the relation between HHV6 genetic changes and latent infection to be considered in possible future vaccines and antiviral drug development.