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UDC 616.831-002:616.927-036.22
PREVENTIVE ACTIVITIES CONCERNING TICK-BORNE VIRAL ENCEPHALITIS AMONG THE ADULT POPULATION OF THE SIBERIAN FEDERAL DISTRICT
Altai State Medical University, Barnaul S.V. Shirokostup, N.V. Lukyanenko
The article presents the results of the analysis of the effectiveness of specific and non-specific prophylaxis measures against tick-borne viral encephalitis among adults in the regions of the Siberian Federal District. As a result of the factor analysis, the leading factors determining the formation of a trend in the incidence of tick-borne encephalitis in adults in the regions of the Siberian Federal District have been identified, including: mite viral resistance (r = 0.44; p <0.001); acaricidal area (r = -0,33; p <0.001) and the adult immunodeficiency index (r = -0.41, p <0.001). Based on the results of the analysis, the authors developed recommendations for optimizing the package of preventive measures for this infection in the Siberian regions. Key words: tick-borne encephalitis, prophylaxis, vaccination, immunization.
Introduction
The epidemic process of tick-borne viral encephalitis in the regions of the Siberian Federal District (SFD) is characterized by the presence of pronounced natural and anthropogenic risk factors for the development of the disease. The high proportion of the rural population (30-50%), characteristic of the Siberian regions, provides an intensive frequency of contacts of the population with foci of infection and, consequently, cases of the disease in risk groups. In the overall morbidity structure, the majority of cases occur in the adult population of the SFO regions due to occupational risks and the nature of household activities. The possibility of the development of the chronic form of the disease, the severe course of the disease, the disability of the sick persons can cause the disability of the adult working population. The combination of the causes and consequences of the disease necessitates the development and practical implementation of regional immunization schedules that take into account the specific features of the tick-borne encephalitis epidemic process in each individual region and are based on the definition of risk groups for developing the disease.
The purpose of the study was to determine the characteristics of the epidemic process of TVE in the cohort of the adult population of the Siberian Federal District, as well as to analyze the effectiveness of specific and nonspecific prevention measures carried out in the regions.
Materials and methods
The study was based on a retrospective analysis of the data on the incidence of the adult cohort in the regions of the Siberian Federal District. The materials of the study included data from regional health services, the Federal State Statistics Service, the Federal Service for Supervision of Con-
sumer Rights Protection and Human Welfare from 2000 to 2017. Forms of State statistical recording No. 5 "Data on preventive vaccinations" and No. 5 "Data on infectious and parasitic diseases" were used. Processing and analysis of the data was carried out in the program "Statistica 13.0".
Results and discussion
The study period of 2000-2017 was characterized by a pronounced trend aimed at reducing the incidence of TVE among the population of the Russian Federation. There was registered a decrease of 3.1 times from 4.1 ± 0.03 0/0000 to 1.3 ± 0.03 0/0000, respectively (p <0.001). Against the background of this trend, cases of lethal outcomes of the disease and the presence of its severe forms were recorded annually. During 2017, 1.9 thousand cases of KVE were detected in the Russian regions. The annual rate of decline in the study period was 3.7%, or 67.5% from 2000 to 2017. The prevailing features of the epidemic process were due to the increase in the volume of preventive measures, as well as the natural long-term cyclical nature of the disease.
The territory of Western Siberia, where the Siberian Federal District is located, is traditionally endemic in relation to endemic tick-borne infections, making the main contribution to the formation of the level of the annual incidence of TVE in Russia. In 2000-2017, in the regions of the Siberian Federal District, there was a downward trend with a decline of 62.3% or 3.9% per year. The average long-term incidence rate was 10.1 ± 0.23 0/0000. The largest share of cases of the disease was registered in Tomsk Oblast - 14.21 ± 0.19%, Novosibirsk Oblast - 9.88 ± 0.17%, Irkutsk Oblast - 8.45 ± 0.16%, Kemerovo Oblast - 10.38 ± 0.17% and Krasnoyarsk Krai - 33.64 ± 0.26%. The territories of these regions have favorable climatic conditions that are necessary for maintaining the active existence of natu-
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Figure 1 - Long-term dynamics of the incidence of tick-borne viral encephalitis in the Russian Federation (per 100 thousand population) in 2000-2017 with a polynomial trend line.
ral TVE foci. Within the boundaries of settlements in the regions of the Siberian Federal District, there are many anthropurgic foci, whose activity is manifested during the epidemic season and contributes to the occurrence of cases of illness among urban residents.
The main contribution to the formation of the overall TVE morbidity structure of the population of the SFD regions was made by a contingent of the population of 18 years and older, reaching 85.5%. The average long-term incidence rate in this age group during the study period from 2000 to 2017 constituted 8.7 ± 0.82 0/0000, which is 39.7% higher than the same indicator in the cohort of children and adolescents under the age of 17 years
- 6.2 ± 1.39 0/0000, p <0.001. Adult morbidity rates exceeding the average long-term levels in the Siberian Federal District were observed in the Republic of Tyva, the Republic of Khakassia, the Republic of Altai, Tomsk Oblast and the Krasnoyarsk Krai. The data are presented in Figure 2.
An average of 1,321 cases of TVE among the adult population is observed annually in the regions of the Siberian Federal District. The number of average cases of the disease among children and adolescents is 5.9 times less. During 20002017, as part of the overall incidence of TVE in the SFD, the number of cases in 5 regions accounted for 77.8% of the total number of TVE cases among adults. Thus, in Kemerovo Oblast, an average of 165 cases were reported annually, in Irkutsk Oblast - 96 cases, in Novosibirsk Oblast - 140 cases, in Krasnoyarsk Krai - 442 cases, in Tomsk Oblast
- 185 cases. In the territory of individual regions of the Siberian Federal District, in the overall structure of the average long-term incidence of TVE, from 52.9% to 94.1% accounted for the cohort of the adult population. The largest share of cas-
es of TVE among adults in the regional structure of the incidence of TVE accounted for Omsk Oblast - 93.1%, Zabaykalsky Krai - 94.1%, Tomsk Oblast -90.2%.
To analyze the territorial distribution of TVE incidence across the regions of the Siberian Federal District, cartograms were built using GIS-technologies of the ArcGIS software package. The results of data processing allowed us to estimate which areas are characterized with the highest risk of infection with TVE for the adult population. All subjects of the Siberian Federal District were ranked in three groups according to the level of the average long-term incidence rate of the population in 2000-2017: with a high potential risk of infection from 12.9 or more 0/0000, average - from 6.7 to 12.8 0/0000, low - from 0.0 to 6.6 0/0000. In the regions of the Siberian Federal District with high and medium potential risk of infection of the adult population with TVE, there was a high viral infectivity of tick-carriers of the TVE virus, as well as forest, piedmont and mountain landscapes characterized by suitable conditions for the existence and development of activity of natural foci of infection. For example, the Republic of Buryatia, which belongs to the group of regions with the share of rural residents in the general structure of the population of 80%, was attributed to subjects with a low potential danger of infection with TVE. At the same time, despite the fact that the share of citizens in the structure of the population of Krasnoyarsk Krai is 70.3%, the region was included in the group of subjects of the Siberian Federal District which have a high potential danger of infection with TVE. The data are presented in Figure 3.
The set of factors that influence the formation of the dynamics direction of TVE epidemic process is individual for each region of the Siberian
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Figure 2 - Average long-term incidence of TVE of the adult population (18 years and older) in the regions of the Siberian Federal District and the average multi-year incidence of TVE in the Siberian Federal District (dotted line) in 2000-2017,
per 100 thousand population.
of Western Siberia determines the varying severity of risk factors within the boundaries of one subject, which determines the regional characteristics of the epidemiology of TVE. In this regard, by epidemiological prediction of the incidence of certain groups of the population, it is necessary to take into account the multifactorial cumulative effect of the components of the natural and anthropogenic environment on the epidemic process of tick-borne infections. The analysis of multifactor influence will allow the sanitary-epidemiological service to make scientifically-based management
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tive measures in the areas of TVE endemic regions.
The multivariate analysis conducted in the course of this study allowed us to identify the leading components that have the most significant influence on the formation of trends in the TVE epidemic process. Such factors include the area of acaricidal treatments of the territory, the virus-pattern of tick-carriers of TVE virus, the indicator of the immune layer among the adult population of the regions of the Siberian Federal District. The tick-borne virophore index increases with advancing to the north and in the northern regions
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Figure 3 - A ranking cartogram of subjects of the Siberian Federal District according to the value of the average long-term incidence of TVE among people aged 18 and over in 2000-2017. (0/0000).
of the Siberian Federal District, reaches maximum values for Western Siberia. This factor is leading in the formation of morbidity rates due to the presence of the revealed direct correlation of the average power with the incidence rates in 2000-2017 (r = 0.44; p <0.001). The effect on the virus-infec-tivity index of TVE tick-carriers is not possible, because of the constantly high frequency of contacts of the adult population with natural and anthro-purgic foci of infection, each year causes high rates of people affected by ticks.
Acaricidal treatments are used as a measure for the non-specific prophylaxis of TVE in the endemic areas of Western Siberia, which make it possible to regulate the number of ticks in the areas under treatment. As a result of the factor analysis, an inverse correlation average force was found between this factor and the incidence of TVE in the adult population (r = -0.33; p <0.001). Acaricidal treatments in the regions of the Siberian Federal District were conducted, as a rule, within the boundaries of settlements, including places of mass visits of people. This allowed reducing the number of ticks in the an-thropurgic foci of infection.
Vaccination is a measure of specific prophylaxis that has a direct impact on the dynamics of the incidence of TVE in the endemic regions of Western Siberia. This factor is leading in the formation of the incidence rate of TVE, ensuring its reduction and the presence in the population of the immune layer. Despite the high frequency of public contact with natural and anthropurgic foci of TVE, vaccination prevents infection with the virus and, consequently, the development of the disease. The significant contribution of the factor to the formation of the average long-term levels of morbidity in the adult population of the Siberian Federal District is confirmed by the presence of an inverse correlation link of average strength (r = -0.41; p <0.001).
Conclusion
The incidence of the adult population of the regions of the Siberian Federal District is characterized by an average long-term rate of 8.7 ± 0.82 0/0000 and is 39.7% higher than that of children under 17 years of age (6.2 ± 1.39 0/0000, p <0.001). The contribution of the adult population to the formation of the overall TVE incidence in the SFD is 85.5%, which is determined by the presence of occupational risk groups, as well as the features of the household activity, suggesting a high probability of contact with natural and anthropurgic foci of infection. These circumstances form the annual incidence in all regions of Western Siberia.
The factor analysis allowed us to determine the leading factors causing the formation of trends in the incidence of TVE in the adult population cohort. The group of such factors includes the indicator of the immune layer of the adult population
(r = -0.41; p <0.001), the area of acaricidal treatment of the territory (r = -0.33; p <0.001), the viral infec-tivity of TVE tick-carriers (r = 0 44; p <0.001). Ep-idemiological prediction of the incidence of TVE in the endemic areas of the Siberian Federal District should include consideration and analysis of these leading factors, which will ensure timely adjustment of the likelihood of developing the disease in risk groups and, consequently, optimizing the volume of preventive measures.
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Contacts
Corresponding author: Shirokostup Sergey Vasi-lyevich, Candidate of Medical Sciences, Associate Professor of the Department of Epidemiology, Microbiology and Virology of the Altai State Medical University, Barnaul. 656038, Barnaul, Lenina Prospekt, 40. Tel.: (3852) 566869. Email: [email protected]
Author information
Lukyanenko Natalia Valentinovna, Doctor od Medical Sciences, Professor of the Department of Epidemiology, Microbiology and Virology of the Altai State Medical University, Barnaul. 656031, Barnaul, ul. Papanintsev, 126. Tel.: (3852) 566924. Email: [email protected]
