Epidemiological Character of Tick-Borne Viral Encephalitis Extension in the Arkhangelsk Region

Abstract

The regional characteristics of the epidemic process and the incidence rates of tick-borne encephalitis (TBE) in the Arkhangelsk region have been examined in the paper. In the period 2005 -2015 the annual TBE incidence rates per 100 thousand population were from 2,0 to 5,4 times higher as compared to the corresponding averages reported for the whole population of the Russian Federation. The most possible causes of the increased incidence rates of tick-borne viral encephalitis in the Arkhangelsk region and temporal trends in its changes as well as potential risk factors of TBE extension have been stated. The vectors of viral encephalitis in the Arkhangelsk region are represented by two types of ixodic ticks: Ixodes persulcatus (the "taiga" tick) and Ixodes ricinus ("forest" tick), the Ixodes persulcatus constitutes over 99 % of their total number. Spring-summer season is typical for TBE cases occurrence which is associated with higher tick activity in this area. The average tick infection rate for the period was 7.8 %. The cases of TBE are reported to occur mainly in urban citizens; and lethality rate due to TBE reached 4.3%. Since 2010 decrease in the TBE morbidity has being observed in the Arkhangelsk region. Reducing morbidity can be connected to the increase in the proportion of vaccinated persons, which reached 6.3 % of the total population of the Arkhangelsk region. The main indices of the acaricide treatment volume which increased since 2005 nearly 6 times, from 128.2 to 740.0 hectares have been stated. Considering the fact that the area of acaricide treatment in the region increases every year, and the number of persons seeking medical advice concerning tick bites remains high it is necessary to control the effectiveness of acaricide treatment regularly. Core measures to decrease the tick-borne viral encephalitis conducted by the Regional Office of Federal Service for Consumers' Rights Protection and Human Wellbeing as well as ways for further research have been introduced.

Permafrost as a potential pathogen reservoir

“…Although speculative, there is still a risk that an unknown pathogen could arise from 'wild' permafrost where it has survived over a long period of time in a dormant or quiescent state. A more immediate concern is expansion of modern infectious diseases via vectors (e.g., ticks and mosquitoes) in areas where permafrost has thawed and the soil becomes wetter, or collapses into thermokarst bogs, as the climate warms [91][92][93] . Increased temperature and precipitation can further expand the geographical distribution of animal vectors 94 .…”

Aanalyzing risks of incidence of tick-borne encephalitis in areas with different climatic and geographical conditions

“…In the 4 th decade in the observation period people were bitten by these blood-sucking arthropods in almost all districts in the region including the northern zone. Very few cases when people applied for medical aid due to tick bites were registered __________________________ 4 Severodvinsk, cities located in the northern zone, were probably to a great extent due to intense migration of people who lived in these cities to other districts in the AR and even beyond the region. However, a considerable growth in a number of bitten people 10 was registered in the Primorskiy district where these two cities were located.…”

“…Thus, a number of vaccinated people in the AR grew by 3.6 times from 6,699 in 2005 to 23,933 in 2015; in 2015 almost 30 % of bitten people were provided with emergency seroprevention with immunoglobulin [4]. Growing natural immunization among population may be another reason for this decrease in TBE incidence.…”

“…There were substantial differences between these three zones regarding ecological and epidemiological situation associated with this infection. Overall area covered with forests didn't change significantly over the analyzed period in the AR and amounted to 23 million hectares in 2019 4 . Ixodes persulсatus prevails in the AR (more than 99 %) and this species is a major source of TBE virus spread among people [4].…”

“…Overall area covered with forests didn't change significantly over the analyzed period in the AR and amounted to 23 million hectares in 2019 4 . Ixodes persulсatus prevails in the AR (more than 99 %) and this species is a major source of TBE virus spread among people [4].…”