Volgograd region is considered to be endemic West Nile fever (WNF) area due to the established circulation of the West Nile virus (WNV) therein. Some previous independent studies examining samples collected on the territory of the Volgograd region revealed markers related to the California serogroup (CSG), Sindbis and Ukuniemi viruses. WNF, CSG, Sindbis and Ukuniemi fever mainly being asymptomatic posing thereby a threat of virus spread due to transfusiological manipulations along with vector-borne transmission are manifested by diverse clinical signs. The study was aimed at detection of antibodies specific to West Nile, tick-borne encephalitis, California serogroup (Tyaginya, Inko), Sidbis, and Ukuniemi viruses in blood donors from the Volgograd region. For this, 404 blood sera samples collected from blood donors residing in the Volgograd as well as the Volgograd region were examined by ELISA. It was found that percentage of blood serum samples positive for arbovirus-specific antibodies was 18.32%. Among the, 67 out of 404 (16.58%) samples contained anti-WNV antibodies, 3 out of 279 (1.08%) samples — to tick-borne encephalitis virus, 1 out of 92 (1.09%) — to California serogroup fever and Ukuniemi viruses, and 2 out of 92 (2.17%) — to Sindbis fever virus. Importantly, the peak number of IgG and IgM WNV-positive samples was found among residents of Volgograd (29 out of 110, 26%) and Oktyabrsky district (7 out of 25, 28%). In addition, anti-Sindbis, Ukuniemi and CSG virus antibodies were detected in blood serum samples from blood donors residing in the Kalachevsky region and the city of Volgograd. Analyzing age-related distribution and percentage of seropositive subjects in each age group showed as follows: the lowest percentage (14.5%) was positive for anti-WNV, Sindbis, Ukuniemi and CSG virus antibodies in blood donors aged 32–41 years, whereas the peak percentage (25%) — in the subjects aged 52–61 years. Thus, virus specific antibodies detected in healthy individuals in the aforementioned region evidence about potential recovery after asymptomatic infections. In this regard, further research is required to determine a role of the such arboviruses in the structure of regional infectious diseases. The data obtained suggest a need to continue serological arbovirus monitoring in the Volgograd region.

The paper presents an analysis of West Nile Fever incidence in the Russian Federation in 2020, summarizes the results and identifies problematic issues of the pathogen monitoring. Manifestations of West Nile Fever in 2020 were characterized by a low incidence rate (10 times lower than the average long-term value) with sporadic cases registration in the endemic areas of the Southern (9 cases) and Central (1 case) Federal Districts. A discrepancy between the morbidity structure (distribution by age, sex, social status) and the trends that have developed in Russia in recent years is shown. The analysis of officially recorded cases doesn’t characterize the epidemic process of West Nile fever in Russia during 2020-season as a whole. The generalized results of monitoring of the West Nile virus circulation in environmental objects in 2020 indicate a decrease in the effectiveness of its implementation and a low detectability of pathogen markers. A decrease in the volume of diagnostic studies for the active detection of patients with West Nile fever in the epidemic season (5.7 times lower compared to 2019), as well as serological screening of healthy population samples (1.6 times) has been established. The results of a molecular-genetic study of the pathogen showed that lineage 2 of the pathogen was circulating in the European part of Russia. The circulation of the lineage 4 of the virus in the enzootic cycle in the Republic of Kalmykia was found out. The genome sequences of 11 West Nile virus isolates allocated in 2019 and 2020 were obtained. Phylogenetic analysis revealed that all isolates allocated in the Volgograd Region and isolates from the Rostov and Astrakhan regions belong to the Volgograd clade of the lineage 2 of the West Nile virus. Based on the assessment of abiotic and biotic factors, possible local increases in the incidence of West Nile fever in 2021 in the regions of the Southern and North Caucasian Federal Districts and in the south of Western Siberia have been substantiated.

Relevance. Natural and climatic conditions, a variety of species composition of arthropods and vertebrates determine the possibility of circulation of arboviruses in the Volgograd region. The existence of natural foci of some arbovirus infections and the possibility of the formation of others suggests the need for annual monitoring of the causative agents of arbovirus diseases. Аim. Evaluation of the results of monitoring of arbovirus infections in the Volgograd region in 2019.Materials and methods: 806 blood serum samples from donors, 44 blood serum samples from febrile sick people, 300 blood serum samples from horses and 94 pools of blood-sucking mosquitoes were examined by immunofernal analysis. Result of the study of serum samples from donors in the Volgograd region, in 140 (17.4%) of 806 were found to have antibodies to the pathogen of West Nile fever (in 35 (4.3%) – IgM, in 105 (13.0%) – IgG), in 7 (2.2%) of 319 – to the Crimean hemorrhagic fever virus (in 4 (1.3%) – IgM, in 3 (0.9%) –IgG), and in 7 (2.9%) of 240 – IgG to the viruses of the California serogroup. Specific antibodies against viruses of Sindbis, Batai and Uukuniemi in the samples was not detected. The largest number of positive samples with the presence of IgG and IgM to the West Nile virus was found among residents of Volgograd (61 out of 240, 25.4%) and Volzhsky (25 out of 100, 25, 0%). Among 44 blood serums of febrile patients, 1 sample (2.3%) was found to contain an antigen of the Sindbis virus, and 2 samples (4.5%) – antigens California serogroup viruses. Specific immunoglobulins against West Nile virus were detected in 84 (28%) of 300 blood serums of farm animals (horses). In the study of 94 samples of field material (blood-sucking mosquitoes), West Nile virus antigen was detected in 14 (14.9%), Sindbis virus – in one sample (1.0%), Batai virus – in four samples (4.2%). Conclusions: the obtained results, along with the circulation of West Nile virus and Crimean hemorrhagic fever virus virus in the Volgograd region, indicate the presence of Sindbis, Batai and California serogroup viruses and necessitate further study of their role in the infectious pathology of the population.