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The article is dedicated to the review of some hazardous and extremely hazardous emergent viral infections of the beginning of the XXI century – severe acute respiratory syndrome (SARS), Middle­East respiratory syndrome (MERS), Lujo hemorrhagic fever (LHF) and severe fever with thrombocytopenia syndrome (SFTS). Special attention is paid to the time of reveal and identification of infectious agents, their taxonomic belonging, genome organization, possible ways of the appearance of strains, virulent for human beings, to endemic regions, probable ways of infection, reservoirs and transmitters of infection, morbidity and mortality. These infections should be of particular concern because of the severity of illnesses, caused by the above mentioned viruses, the absence of characteristic clinical signs that makes diagnostics more difficult, especially in non­endemic areas, the absence of means of specific prophylaxis and treatment and the difficulties in their identification. The analyze of this emergent viral infections reveals their potential threat for the Armed Forces and population of the Russian Federation in case of accidental or intentional delivery of causative agents of these diseases to the Russian territory.

For many years, arbovirus infections have been a global health problem and one of the urgent threats to the sanitary and epidemiological well-being of the population. Climatic conditions, species diversity and abundance of vectors, epidemiological and demographic factors are of fundamental importance for the emergence and persistence of natural foci of arbovirus infections. In the Socialist Republic of Vietnam (SRV) and other countries of the Asia-Pacific region, the most complex epidemiological situation is observed in regard to a number of arboviral infectious diseases transmitted by mosquitoes, inter alia to dengue fever. In this review we analyzed the literature data to identify the features of the circulation of some arboviruses in Vietnam, such as dengue virus, Zika, Chikungunya, Japanese encephalitis virus, Dabie virus, and the routes of their transmission and spread. It is shown that the climatic, ecological, epidemiological and demographic conditions existing on the territory of Vietnam contribute to the spread of pathogens of many arboviruses. Areas of more active circulation and ways of spreading pathogens of arbovirus infections have been identified. Based on the data obtained, it is necessary to conduct annual epidemiological and epizootiological survey of the territory of the SRV in order to identify markers of pathogens and determine the boundaries of natural foci of arbovirus infectious diseases which will enhance and increase the effectiveness of preventive and anti-epidemic measures.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a new virus (SFTS virus) reported to be endemic to central and northeastern parts of China. SFTS virus, which is classified into the genus Phlebovirus (the Bunyaviridae family), is suspected to be a tick-borne virus owing to evidence in two species of ticks: Haemaphysalis longicornis and Rhipicephalus microplus. SFTS virus is detected among many species of domestic animals in China. The clinical symptoms of SFTS include fever, thrombocytopenia, leucocytopenia, gastrointestinal symptoms, neural symptoms, bleeding tendency. The fatality rate of SFTS is 6-30%. Person-to-person transmission of SFTS virus is possible through blood contact. Clinical and epidemiological studies of SFTS, the cases of SFTS outside China, person-to-person transmission of SFTS virus, evolutionary and molecular analysis of the emergent SFTS virus, and risk assessment of human infection with a novel phlebovirus are considered in this review.

In 2009, a novel virus, named severe fever with thrombocytopenia syndrome (SFTS) virus, was isolated from a patient in China. The illness caused by this novel virus is characterized by a sudden onset of fever and respiratory or gastrointestinal disorders, followed by progressive thrombocytopenia and leucocytopenia, the case-fatality rate amounting to 6–30 %. Genomic sequencing of the isolated agent indicated that the SFTS virus constituted a new (third) group of Phlebovirus genus, Bunyaviridae family. Presently, different means for specific diagnostics of SFTS (real-time reverse transcription polymerase chain reaction, indirect fluorescent antibodies method, enzyme-linked immune-sorbent assay) are developed. Constructing of diagnostic kits, basic characteristics of methods for determination of causative agent of infection or specific antibodies against it are considered in this review.

Since the Dabie bandavirus (DBV; former SFTS virus, SFTSV) was identified, the epidemics of severe fever with thrombocytopenic syndrome (SFTS) caused by this virus have occurred in several countries in East Asia. The rapid increase in incidence indicates that this infectious agent has a pandemic potential and poses an imminent global public health threat.The analysis of molecular evolution of SFTS agent that includes its variants isolated in China, Japan and South Korea was performed in this review. The evolution rate of DBV and the estimated dates of existence of the common ancestor were ascertained, and the possibility of reassortation was demonstrated.The evolutionary rates of DBV genome segments were estimated to be 2.28 × 10-4 nucleotides/site/year for S-segment, 2.42 × 10-4 for M-segment, and 1.19 × 10-4 for L-segment. The positions of positive selection were detected in the viral genome.Phylogenetic analyses showed that virus may be divided into two clades, containing six different genotypes. The structures of phylogenetic trees for S-, M- and L-segments showed that all genotypes originate from the common ancestor.Data of sequence analysis suggest that DBV use several mechanisms to maintain the high level of its genetic diversity. Understanding the phylogenetic factors that determine the virus transmission is important for assessing the epidemiological characteristics of the disease and predicting its possible outbreaks.