EPIDEMIOLOGICAL FEATURES OF TICK-BORNE BORRELIOSIS IN THE VORONEZH REGION

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Relevance. A wide reservoir of sources of ixodes tick—borne borreliosis (ICB) or Lyme disease — domestic and wild animals, as well as carriers of Ixodes ticks (pasture, forest, taiga) contribute to the widespread spread of the disease worldwide and in the Russian Federation. In our country, this disease began to be studied in 1984, but official registration was introduced in 1992. Over a long period of time, among vector-borne infections, ICD is registered most often [1]. People are infected not only in natural, but also in anthropurgical foci, with pronounced seasonal increases in morbidity in May-July [2]. There is a coincidence of natural foci of infection with the distribution areas of ixodic ticks. In addition to sucking a tick in rural areas, cases of infection of people when visiting forest park areas by citizens during recreation are an urgent problem [3]. Borreliosis disease can lead to permanent disability, or even death. Specific prophylaxis against borreliosis has not been developed, which leads to repeated cases of diseases. To find out the sources of infection with ixodic tick-borne borreliosis and to determine the boundaries of various (natural, natural-anthropurgical) foci of ICB, constant epizootological monitoring is necessary [4].
The purpose of the study: to assess the epidemic situation of Lyme disease for 2012-2021 and the effectiveness of preventive measures in the Voronezh region.
Materials and methods. The materials for the study are: State reports "On the state of sanitary and epidemiological well-being of the population in the Russian Federation" for 2012-2021, reports "On sanitary and epidemiological well-being of the Voronezh Region" for 2012-2021, data from the Rosstat form No. 2 "Information on infectious and parasitic diseases" for the Voronezh region (by districts) for 2012-2021, information on the population (in the context of municipalities, urban and rural population, adults and children) according to the Territorial Body of the Federal State Statistics Service for the Voronezh Region https://voronezhstat.gks.ru /. The study was carried out on the basis of the Department of Epidemiology. The method is a retrospective epidemiological analysis. In the course of the study, the following were analyzed in the whole region and in the context of municipalities: the dynamics of the epidemic process of borreliosis over time with the calculation of average, maximum and minimum incidence rates (incidence), the age structure of the incidence of ICD and its change over time; the incidence of urban and rural populations; the dynamics of the appeal regarding bites (suction) by ticks. The long-term results of monitoring of infection in its natural foci (2014-2021) were evaluated according to the laboratory "Center of Hygiene and Epidemiology in the Voronezh Region" - the study of ticks by PCR using the test system "Ampliftbev, B. Burgdorferisl., A. Phagocytophilum, E. Chaffeensis/E. Muris-AD" for tick-borne infections. On average, 1147 samples are examined annually, during this period, during the study of material from the external environment, the RNA of the causative agent of ICB was found in 168 samples; in ticks taken from people - in 2093 samples. The volume of acaricide treatments in the region is analyzed. Statistical processing was carried out using the Microsoft Excel computer program. The incidence rates (per 100 thousand population/contingent), the average value (M), the standard deviation from the average (m) were calculated.
Results. During the studied period, cases of ICD in the region are registered annually. The maximum incidence was noted in 2019, the minimum in 2014. The average long-term indicator (SMP) (M±m) in the Voronezh region was 3.9±2.0 per 100 thousand population, and it is lower than the SMP in the Russian Federation - 4.1 ± 1.3 per 100 thousand population. There are periodic fluctuations in morbidity levels, but there is no regular interval (a year of increase, a year of fall, or two or more years of increase, two or more years of fall, etc.).
Cases of borreliosis in the districts of the Voronezh region are recorded unevenly. In Kashirsky, Petropavlovsk, Povorinsky districts, not a single case was registered during the entire period of accounting for the ICB. The maximum average for 2012-2021 levels of incidents per 100 thousand population (above the regional average) were observed in Ternovsky (9.1±10.5), Ramonsky (8.3±9.1), Anninsky (8.3±7.2), Nizhnedevitsky (5.3±3.7) districts and among residents of Voronezh (6.3±3.3).
The age structure of Lyme disease patients is dominated by adults, ranging from 83.6% to 96.6% in different years. Isolated cases are registered among children; the proportion of children ranges from 3.4% to 16.4% and averages 7.7% over a 10-year period. When calculating the incidence rates per 100 thousand of the contingent (adults-children), the most affected group with borreliosis is also adults. Indicators per 100 thousand adults ranged from 4.2 to 6.53, with an average of 5.1 ± 0.88 over 10 years. In children, the M±m index was 1.7±0.99 per 100 thousand children under 17 years of age. Thus, adults suffered from borreliosis in the period 2012-2018 1.7-4.3 times more often than children; over the past 3 years – 13.7-21.8 times.
The proportion of urban residents in the structure of all cases was 82.9%. The incidence of ICD among residents of urban settlements varied from 1.6 to 8.6 per 100 thousand population, with a tendency to increase. The incidence rates of rural residents ranged from 0.4 to 4.8 per 100 thousand population and did not have a linear trend.
Appeals about tick bites or suckling are noted annually in all territories of the region. In general, from 845 to 3488 victims of bites are registered in the region, the average turnover rate per 100 thousand population was 90.7 ± 40.5. When compared with the incidence levels of ICD, there is no correspondence between the increase in morbidity as the number of tick bites increases. In 16 of the 33 municipalities of the region, the conversion rates are 1.1-2.3 times higher than the regional average. The maximum levels were observed in the Podgorensky (212.0 per 100 thousand population), Ostrogozhsky (191.9), Ternovsky (187.5), Anninsky (175.7), Ramonsky (160.2) districts. Only in the 3rd territories, there is a correspondence between the incidence of ICD and tick bites.
Studies of the vector are carried out in order to prevent borreliosis and monitor infection in its natural foci. On average, studies of ticks removed from people gave positive results in 30.1% of cases; RNA was detected in 12.2% of samples in environmental objects. The maximum detection of positive results in ticks removed from humans was noted in 2020-2021 – respectively 41.6%-42.0% of the samples studied. Only in the Nizhnedevitsky district during this period there were no positive findings. Single pathogen RNAs were found in Anninsky, Buturlinovsky, Verkhnemamonsky, Verkhnekhavsky, Kamensky, Kantemirovsky, Olkhovatsky, Paninsky. Petropavlovsk, Podgorensky, Repyevsky, Talovsky, Ertilsky districts. The maximum finds are in the territories of Borisoglebsk, Novaya Usmani, Ostrogozhsk and Semiluk.
The volume of acaricide treatments in the region over the studied period increased, from 536.6 hectares in 2012 to 903.298 hectares in 2019. First of all, the territories of children's health institutions (DOW) and sanatoriums were processed – 197.7-306.8 hectares annually. During the period of restrictive measures for COVID-19 and non-operating DOW, volumes decreased to 652.3 hectares in 2020 (including only 146.9 hectares of DOW). In 2021, acaricidal treatments were carried out by the Center for Hygiene and Epidemiology in the Voronezh Region and private disinfection organizations on a total area of 856.09 hectares, of which 246.19 hectares in the DOW.
Discussion. Since 2017, the incidence in the Voronezh region has been leveled with those in the country, and over the past 3 years it has exceeded the indicators of the Russian Federation. The years of maximum rises and minimum indicators in the region do not coincide with the national average, which is explained by the wide variety of natural and climatic factors in the territory of the Russian Federation that affect the activity of vectors. In our study, the task was not set to analyze the seasonality of both the incidence of ICD and the number of complaints from the population about tick bites, depending on the temperature factor, this is planned to be done in the future. Moreover, with the change in climatic conditions in the region, the activation of ticks in 2021 was noted in the last decade of March, and the largest number of complaints from the population about tick bites fell on the 1st decade of June (2015-2016 - at the end of May - beginning of June; 2017 - in June; 2018 - at the end of June; 2019 G. – for the third decade of May; 2020 – for June). Hospitalizations for ICD continued in September-October [5, 6].
The fact of a higher incidence of ICD among residents of the cities of the region, who are sick more often than the rural population by an average of 2.6 times, and account for 82.9% in the structure of cases, is associated with both low alertness of citizens about tick attacks, and more frequent visits to suburban recreational areas or suburban areas. This corresponds to data from other regions of the country, when the increased mobility of the population due to the increase in the provision of people with vehicles increased the accessibility of the natural habitat of tick-borne infections for people. Most of the cases (86%) are citizens, most of them are residents of large cities [7], and the presence of forests within the city limits creates conditions for contact of the population with carriers of borreliosis, which is confirmed by data on a high number of local cases of infection (67.6%) [8].

Since the registration of tick bites in official statistics has been introduced since 2013, the increase in complaints about this during the first 5 years is obviously associated with an improvement in statistical registration. The maximum rate of appeals of victims of bites was registered in 2018, the rate of appeals per 100 thousand population was 149.5, and in 2021 – 98.5 per 100 thousand population. This is lower than the average in Russia: the number of requests for medical help regarding the suction of ticks in 2021 amounted to 309.49 per 100 thousand. the average annual indicator for the entire period of official registration of such appeals (2014-2021) is 342.34 per 100 thousand population [1].
In the Voronezh Region, in dynamics over the years, an increase in the proportion of positive findings in ticks taken from people was noted to 42.0% of the samples studied in 2021, which indicates an increase in the purposefulness of appeals about tick bites or sucking. At the same time, the detection of the pathogen RNA in ticks taken from environmental objects (on average 12.2%) is significantly lower than was revealed in the 2008-2009 study in the Voronezh Biosphere Reserve (23.9%). During that period, 18.3% infection of dogs with borrelia was also noted [9]. Obviously, the acaricidal treatments carried out, along with a decrease in the number of vectors, also affect the occurrence of borrelia in ticks. In addition, it is necessary to analyze the detection of infected ticks by periods of the year and in connection with average daily and average daily temperatures, as this affects the indicators of tick infestation [10].
Conclusion: Tick-borne borreliosis is the most common of tick-borne infections registered in the region, diseases are registered annually. There is no correspondence between the increase in the incidence of ICD with an increase in the number of people who have applied for tick bites or sucking. Cases of borreliosis in the districts of the Voronezh region are recorded unevenly. Adults predominate in the structure of cases; isolated cases are registered among children. Urban residents get sick 2.6 times more often than residents of rural settlements. In the Voronezh region, studies of ticks by PCR have been established in order to prevent borreliosis and monitor infection; ticks infected with ICB have been registered on the territory of almost all districts of the region.
As practical recommendations, in the absence of specific immunoprophylaxis of ICB, the population should be trained in proper outdoor recreation to avoid a tick bite. so that people know where to look for a tick on their body and how to remove it correctly. It is also recommended to visit polyclinics for a preventive examination for possible infection and the appointment of an emergency course of antibiotic prophylaxis. Explanatory work should also be aimed at the need for appeals to medical organizations to extract the tick, and if it is removed independently, it is advisable to take the tick for examination on borrelia to the Center for Hygiene and Epidemiology.

About the authors

Nikita Vadimovich Zakupnev

Author for correspondence.
Email: nzakupnev@yandex.ru
ORCID iD: 0000-0003-0035-0441
Russian Federation, 10 Studentskaya str., Voronezh, 394036, Russia

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