In Russia, of the whole variety of EBV- and HHV6-etiology diseases, only infectious mononucleosis is subject to official statistical reporting, which significantly complicates an objective assessment of their etiological structure, incidence rate, characteristics of the development of the epidemic process. Currently, information on the genetic heterogeneity of EBV, even at the level of the main types (EBV1 and EBV2), as well as HHV6A and HHV6B, their prevalence and clinical significance are limited mainly by foreign data. In Russia, there are isolated publications devoted to this issue. At the same time, the study of the circulation of genetic types (variants) and the use of this information in the implementation of epidemiological surveillance of some other infections have already become routine practice. One of the key issues is the level of development of laboratory support for molecular genetic monitoring. The purpose of this work was to improve the methodological base of differential detection of HHV6A/B and the main types of EBV. The material for the study was peripheral blood leukocytes of children aged 1-15 years with acute infectious mononucleosis (n = 50) and without clinical symptoms of this disease (n = 29). The detection and quantification of EBV DNA and HHV6 DNA was performed using real-time PCR. For differential determination of EBV1/EBV2 and HHV6A /HHV6B, an optimized one-round PCR with electrophoretic detection of amplification products in an agarose gel was used. According to the results of our own research, the frequency of detection of  EBV DNA and HHV6 DNA in acute infectious mononucleosis was 74% and 72%, and in the control group - 35% and 74%, respectively. It was found that among the examined children of the Nizhny Novgorod region, EBV1 and HHV6B prevail in the viral population, which is consistent with existing views about their geographical distribution in the adjacent territories. EBV2 was found in a single sample in the control group only. HHV6A was not detected in any of the studied groups. The methodological approach optimized in this work makes it possible to separately detect HHV6A/HHV6B and the main types of EBV according to a single laboratory protocol, and in combination with an additional stage of DNA concentration increases the diagnostic sensitivity of PCR analysis, minimizes the proportion of discordant and false negative results. Such an integrated approach can be applied for diagnostic, epidemiological and research purposes.

EpsteinBarr virus (EBV) and human herpesviruses 6A and 6B (HHV6A and HHV6B) are ubiquitous, infecting representatives of all social groups, starting from early childhood. Currently, information on the genetic heterogeneity of EBV, even at the level of the main types (EBV1 and EBV2), as well as HHV6A and HHV6B, their prevalence and clinical significance are limited mainly by foreign data. In Russia, there are not so many publications devoted to this issue. In this case, the objects of study are mainly plasma and leukocytes of peripheral blood, scrapings or swabs from the oropharynx are used much less often. Saliva is the main factor in the transmission and spread of EBV and HHV6A/B infections. Saliva testing is an affordable, inexpensive, and non-invasive method for detecting viral DNA. The purpose of this work is to improve the methodological base for differential detection of HHV6A/HHV6B and the main types of EBV in saliva. The material for the study was unstimulated mixed saliva of children aged 117 years with acute infectious mononucleosis (n = 22) and no clinical symptoms of this disease (n = 26), as well as conditionally healthy adults (n = 9). Samples were collected once and dynamically (daily for 14 days). The detection and quantification of EBV DNA and HHV6A/B DNA was performed using real-time PCR. For the differential determination of EBV1/EBV2 and HHV6A/HHV6B, an optimized one-round PCR variant with electrophoretic detection of amplification products in an agarose gel was used. Statistical data processing was carried out using the R programming language and the RStudio environment. According to the results of our own research, the frequency of detection of EBV, HHV6A/B and EBV+HHV6A/B DNA in acute infectious mononucleosis was 95, 91 and 86%, and among conventionally healthy children 69, 85 and 61.5%, respectively. It was found that among the examined children of the Nizhny Novgorod Region, EBV1 and HHV6B prevail in the viral population, which is consistent with existing ideas about their geographical distribution in the adjacent territories. EBV2 and HHV6A were not detected in any of the examined saliva samples. According to the results of 14-day dynamic monitoring of saliva virus secretion in healthy virus carriers (adults and children), it was shown that a single EBV DNA study does not allow to reliably assess the infection of individuals or the intensity of EBV secretion. In this case, HHV6A/B is characterized by a more constant and uniform release. The methodological approach optimized in this work makes it possible to separately detect EBV1/EBV2 and HHV6A/HHV6B according to a single laboratory protocol, and in combination with an additional stage of saliva sample preparation increases the diagnostic sensitivity of PCR analysis, minimizes the proportion of discordant and false negative results. Such an integrated approach can be applied for diagnostic, epidemiological and research purposes.

This review is devoted to the comparative characteristics of human herpesvirus 6A (HHV6A) and human herpesvirus 6B (HHV6B), taking into account their exogenous and endogenous (inherited chromosomally integrated) forms. The analysis of the literature data on the main interspecies differences and intraspecies features of these viruses in molecular-genetic, biological, epidemiological and clinical aspects has been consistently carried out. Modern views about HHV6A and HHV6B, including their unique inherited chromosomal-integrated form, are the basis for organizing a system of epidemiological surveillance of infections caused by these viruses, as well as developing standardized methodological approaches to differential diagnosis, treatment and specific prevention of a wide range of virus-associated diseases. The development of this direction requires a greater evidence base and intensification of joint efforts of the scientific and medical communities.

In general, the characteristic of the genetic diversity of the Epstein-Barr virus (EBV) underlies the study of pathogenesis, targeted development of laboratory diagnostic methods, vaccines, specific therapy for associated diseases, improving the system of epidemiological surveillance of EBV infection, as well as further detailing the taxonomy and virus classification. The purpose of this review is to summarize and analyze the literature data on the genetic diversity of EBV for the prospective development of the methodology of molecular research in clinical practice and epidemiological surveillance of EBV-associated diseases. The work was carried out based on an analysis of publications in the PubMed, Web of Science, Scopus, eLibrary databases. Special attention was focused on the studies in Russia. It has been shown that approaches based on the analysis of nucleotide and amino acid variability of individual EBV genes or their regions have been used for several decades. However, there is no single, unified system that takes into account the entire genetic diversity of EBV, and the strengths and weaknesses of both earlier and modern classifications. Most publications are devoted to the study of the LMP-1 oncogene. With the development of whole genome sequencing technologies, the search for genovariants and subtypes of EBV has resumed. It is demonstrated that despite the dynamic development of this area, the conclusions of researchers are still based on a relatively small number of genomes sequenced with variable quality, analyzed using different bioinformatic strategies, with an unequal sample in terms of geographical origin. Moreover, some nosological forms of EBV-associated diseases, geographical areas and ethnic groups remain uncharacterized. The development and optimization of methodological approaches based on whole genome sequencing and sequencing of a specific set of genes will contribute to the expansion of existing ideas about the genetic diversity of EBV throughout the world, its relationship with diseases and, possibly, the clinical features of their course, and the improvement of epidemiological surveillance of EBV infection.

Introduction: Today, we are witnessing the process of forming a fundamentally new epidemiological situation on infectious mononucleosis. Over the past decade, a general increase in the incidence of infectious mononucleosis, its proportion in the structure of respiratory tract infections, and economic importance was noted in Russia. Information about the epidemic process of infectious mononucleosis in different areas is limited. Our objective was to study the features of the epidemic process of infectious mononucleosis in the Nizhny Novgorod Region in 2010–2019. Methods: We conducted a retrospective epidemiological analysis of the incidence of infectious mononucleosis in the Nizhny Novgorod Region for 2010–2019 based on official statistics using standard statistical approaches. Results and discussion: The long-term incidence rate of infectious mononucleosis in the Nizhny Novgorod Region was stable (+0.6 %) with the long-term average rate of 12.6 ± 0.6 ‰оо. An autumn-winter-spring seasonality with two distinct peaks (in November–December and May) was revealed. The majority of cases were children aged 0–14 years (72.8 ± 2.2 %). The highest incidence rates were regis�tered in the age groups of 1–2 and 3-6 years. We established a reverse trend in the disease incidence among children aged 0–6 (decrease) and 7 years and older (increase). Adolescents aged 15–17 demonstrated the most pronounced growth rate (+7.5 %). The typical annual dynamics in adults was distinguished by a clear spring-summer seasonality, the absence of a characteristic growth in the autumn months, and a low rate in December. The identified features of the epidemic process in different age groups require clarification and detailing. Conclusions: We established recent patterns and features of the epidemic process of infectious mononucleosis in the Nizhny Novgorod Region. This work is an important component of epidemiological surveillance of infection and a scientific basis for improving the existing system of preventive and anti-epidemic measures.