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EPIDEMIOLOGICAL DIAGNOSTICS OF TICK-BORNE ENCEPHALITIS AMONG THE RURAL POPULATION OF THE SIBERIAN FEDERAL DISTRICT REGIONS
Altai State Medical University, Barnaul S.V. Shirokostup, N.V. Lukyanenko
This work presents the results of the epidemiological diagnosis of tick-borne viral encephalitis in rural areas of the Siberian Federal District. The authors analyzed the incidence of tick-borne encephalitis in rural regions, analyzed the impact of factors on the trends of morbidity dynamics. The article includes a cartogram of the spatial spread of the rural population incidence in the territory of the Siberian Federal District. Specific features of the influence of measures of specific and nonspecific prophylaxis of tick-borne encephalitis are described, and the effectiveness of their influence on the incidence of the infection in rural areas of Western Siberia is estimated. Key words: tick-borne encephalitis, epidemiological diagnostics, rural population, foci of tick-borne infections, prevention.
Regions of the Siberian Federal District are endemic for tick-borne viral encephalitis (TVE). Favorable natural and climatic conditions for the formation and preservation of high activity of foci of infection in combination with the intensive frequency of contacts of the rural population with the habitats of tick-borne encephalitis virus cause an annual registration of new cases of the disease. A feature of most regions of the Siberian Federal District is a high proportion of rural residents in the overall structure of the population of the subject.
This determines the set of social, professional and anthropogenic factors that influence the formation of trends in the incidence of TVE. The task of epidemiological surveillance in this case is to develop a comprehensive system for monitoring the development of morbidity factors, analyzing the contribution of each factor to the formation of trends in TVE incidence, as well as the formation of a sufficient and reliable base of analytical material for making timely and effective management decisions.
Currently, in the rural areas of the Siberian Federal District, there is noticed an active economic and domestic development of the territories. Intensive development of infrastructure projects, development of new agricultural land, construction of extensive trunk transport projects leads to an increase in the frequency of public contact with natural foci of infection. The formation of new anthropurgic foci of TVE takes place against the background of the rapid development of residential and industrial construction in areas remote from the urban environment. In the case of contact with an anthropur-gic foci of infection, a person becomes a part of the existing biological chain in the circulation of tickborne encephalitis virus in nature. As a result, new cases are reported annually in rural and suburban areas of the regions of the Siberian Federal District.
The research objective was to study the characteristics of the epidemiological process of TVE in the territory of rural areas of the Russian regions of Western Siberia.
Materials and methods
As materials for this study, there were used the data from regional departments of the Federal Service for Consumer Rights Protection and Human Welfare, regional structures for managing the health system and the Federal State Statistics Service for the period from 2000 to 2017. Data processing was carried out using the method of factor analysis in the program Statistica 12.0. The spatial distribution of incidence and the factors influencing it were studied by means of the ArcGIS software package. The work involved statistical, descriptive and evaluative research methods, elements of mathematical modeling and GIS technologies.
Results and discussion
Russian regions of the Siberian Federal District occupy a significant part of the territory of Western Siberia and are characterized as endemic for TVE and other tick-borne infections. During 2000-2017, the average long-term incidence rate of the population of the Siberian Federal District constituted 10,1±0,23 0/0000. At the same time, there was a pronounced tendency to decrease in incidence by 62%, on average - 3.9% annually. The current trend is determined by the cumulative effect of a number of climatic and anthropogenic factors, including the natural long-term cyclical nature of morbidity, the number of tick-borne encephalitis virus ticks and their infection rate, as well as such preventive measures as vaccination, immunization and area of acaricidal treatments of the territory.
In the overall structure of TVE incidence among the population of the regions of the Siberian Fed-
eral District, the largest proportion of cases of the disease falls on Novosibirsk Oblast - 9.9±0.17%, Irkutsk Oblast - 8.5±0.16%, Kemerovo Oblast -10.4±0.17%, Tomsk Oblast - 14.2±0.19%, Krasnoyarsk Krai - 33.6±0.24%. During the study period from 2000 to 2017, the average long-term incidence rate of the rural population of the regions of the Siberian Federal District was 11,3±0,57 0/0000, which is 38.7% higher than the similar indicator among residents of urban agglomerations - 8,1±0,84 0/0000 (p<0,001).
In the structure of all cases of TVE disease in the population of SFO regions, 600 cases were registered among rural residents, which is 35.7%. The current situation is explained by the presence of subjects with a high proportion of rural residents in the regional population structure in the SFD. These regions include Altai Krai - 50%, the Altai Republic - 58%, Zabaykalsky Krai - 68.3%, the Republic of Buryatia - 80.2%, the Tyva Republic - 67%, Omsk Oblast - 65.8%, the Republic of Khakassia - 40 %. SFD also includes the regions with the highest average registered number of TVE cases among all
the subjects of Russia: Irkutsk Oblast - 170 cases per year, Novosibirsk Oblast - 199 cases per year, Kemerovo Oblast - 209 cases per year, Tomsk Oblast - 286 cases per year, Krasnoyarsk Krai - 676 cases per year.
Among the regions of the Siberian Federal District, the highest average long-term incidence rate of TVE in rural areas is observed in the Republic of Khakassia and constitutes 24,3±3,85 0/0000, which is 7.4 times higher than the smallest similar indicator for the Siberian Federal District registered in Altai Krai - 3,3±0,54 0/0000 (p <0.001). Among all regions of the Siberian Federal District, in 8 subjects during 2000-2017, there was registered an increase in the average long-term incidence of TVE in rural areas. This epidemiological situation is typical for the republics of Buryatia (13,6±1,82 700J, Tyva (16,8±3,40 700J, Altai (22,2±3,85 °/00J, Khakassia (24,3±3,85 7°°J, as well as Krasnoyarsk Krai (22,9±1,83 0/0000), Tomsk (13,6±2,08 0/0000), Kemerovo (12,8±1,78 0/0000) and Irkutsk Oblasts (11,7±1,52 0/0000). The data are presented in Figure 1.
25,0 20,0 15,0 10,0 5,0 0,0
Figure 1 - Average long-term incidence of TVE in rural areas of the regions of the Siberian Federal District, taking into account the average long-term TVE incidence of rural residents in the Siberian Federal District (dotted line) in 2000-2017.
(0/
V '0(
The ranking of regions of the Siberian Federal District by the average long-term TVE incidence rate among the rural population allowed to analyze the spatial distribution of the incidence. According to the data obtained, the highest incidence rates are observed in the subjects of the Siberian Federal District, characterized by the presence of a high proportion of the rural population in the overall demographic structure of the region, as well as
mountain, foothill landscapes and forests. The data are presented in Figure 2.
The trend of the dynamics of the TVE epide-miological process in rural regions of the Siberian Federal District is subject to the cumulative influence of various climatic, anthropogenic factors and the natural long-term cyclicity of the number and infection rate of ticks-carriers of the virus. Many factors influencing the epidemic process consist of
having a direct and indirect effect on the number of cases of the disease component. Identification of the leading factors that make the most significant contribution to the formation of TVE incidence rates in rural areas of the Siberian Federal District is one of the key tasks of the epidemiological fore-
ical service. As a result of the factor analysis, it was found that the leading components involved in the formation of TVE incidence rates in the rural population of the Siberian Federal District are infection rate of tick-borne encephalitis virus ticks-carriers, acaricidal treatments and the immune layer among
1 - Altai Republic
2 - Altai Krai
3 - Republic of Buryatia
4 - Zabaikalsky Krai
5 - Irkutsk Oblast
6 - Kemerovo Oblast
7 - Krasnoyarsk Krai
8 - Novosibirsk Oblast
9 - Omsk Oblast
10 - Tomsk Oblast
11 - Republic of Tyva
12 - Republic of Khakassia
I - from 16,7 and more /,
0000)
- from 10,2 to 16,6 7,
0000> I
I-from 0,0 to 10,1 7,
0000-
Figure 2 - Ranking cartogram of subjects of the Siberian Federal District according to the value of the average long-term TVE incidence rate among the rural population in 2000-2017. (0/0000).
The most significant influence on the formation of TVE morbidity indicators in the rural population of the Siberian Federal District has the virus-carrying nature of ticks, as evidenced by the presence of a direct strong correlation (r = 0.66; p <0.001). The average long-term level of virus communication in the Siberian Federal District during 200-2017 amounted to 4.0 ± 0.15%. Among the regions of the Siberian Federal District, the excess of this indicator was typical for Kemerovo Oblast - 4.7 ± 0.16%, the Republic of Altai - 13.4 ± 0.18% and the Republic of Khakassia - 8.8 ± 0.22%.
In the course of factor analysis, the presence of a negative correlation link of the average power between the incidence of TVE in the rural population of the Siberian Federal District and the area of acaricid-al treatments was detected (r = -0.44; p <0.001). The current situation testifies to the significant role of acaricidal treatment as the only measure of non-specific TVE prophylaxis in the TVE prophylaxis on the territory of the SFD regions. The consequence of a
decrease in the number of ticks within the rural areas is a decrease in the activity of anthropurgic foci of infection. This, against the background of a constant frequency of contact of the population with these foci, makes it possible to reduce the number of people affected by tick-bites and, consequently, reduce the number of cases of TVE.
The level of the immune layer among the rural population is one of the leading factors influencing the decrease in the TVE incidence rate of the rural population, which is confirmed by the presence of an inverse correlation of an average strength (r = -0.43; p <0.001). The indicator of the immune layer is formed by taking into account vaccinated against TVE and immunized persons. In 2000-2017, the child population under the age of 14 and risk groups contingents were vaccinated as part of the implementation of regional immunization schedules that take into account the individual characteristics of the subject's territory when forming the list of risk groups. The coverage of risk groups with
preventive vaccinations against TVE in rural areas of the SFD regions amounted to 98%. The group of regions of the Siberian Federal District with the largest proportion of rural residents vaccinated against TVE included Krasnoyarsk and Altai Krai, Omsk, Kemerovo and Novosibirsk Oblasts with an indicator of 20.0% or more.
Conclusion
The regions of the Siberian Federal District, being endemic for TVE, make the main contribution to the formation of the incidence of this infection in Russia. Favorable climatic conditions contribute to the maintenance of the activity of natural foci, the intensive economic and domestic development of the territories leads to the emergence of new anthro-purgic foci. Factor analysis, as a component of the epidemiological diagnosis of TVE in the territories of endemic regions, allows identifying the leading risk factors for the development of morbidity and ways to manage them. Under current conditions, this approach allows the sanitary and epidemiolog-ical service specialists to ensure the effectiveness of epidemiological surveillance of the incidence rate and make management decisions based on the calculation of reliable scientifically based data.
As the leading factors involved in shaping the incidence of TVE in the rural population of the Siberian Federal District, there were indicated the infection rate of TVE virus ticks (r = 0.66; p <0.001), area of acaricidal treatments of the territory (r = -0.44; p < 0.001) and the immune layer of the population (r = -0.43; p <0.001). The mapping of the spatial distribution of the TVE incidence in the macro-region of Western Siberia made it possible to identify the regions of the Siberian Federal District with the highest potential risk for the development of TVE disease among the rural population. The revealed patterns of the spread of the TVE incidence and the factors determining it will allow for more rational and effective planning of preventive measures in the endemic regions of Western Siberia.
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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, 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, Altai State Medical University, Barnaul. 656031, Barnaul, ul. Papanintsev, 126. Tel.: (3852) 566924. Email: [email protected]
