A.I. Kovalenko, G.E. Bondarenko, L.M. Kotovich
Directorate of the Federal Service for Surveillance on Consumer Rights Protection and Human Well-Being in the Republic of Karelia, Petrozavodsk, Russia
Citation: Kovalenko AI, Bondarenko GE, Kotovich LM. Epidemiological Situation for Tick-Borne Encephalitis and Lyme Disease in the Republic of Karelia, Russia, in 2002-2011. EpiNorth 2012;13:105-111.
Epidemiological surveillance of tick-borne infections in the Republic of Karelia is conducted by monitoring registered cases of infections and observing the circulation of causative agents among vectors by collecting ticks and performing laboratory analyses. In addition, the number of persons seeking care at health care facilities for tick bites are also analyzed.
Tick-borne encephalitis (TBE) is an acute viral infection primarily involving the central nervous system. The infection may cause permanent disability or even death. Surveillance over the epidemiological situation for TBE in the region is of great importance because 11 administrative areas of the Republic of Karelia are endemic for the infection. Several dozen cases of TBE are registered annually.
The aim of this article is to analyze and estimate the dynamics of the epidemiological situation for tick-borne infections in the Republic of Karelia over the last decade.
Materials and Methods
Data obtained from the forms for statistical registration of infectious and parasitic diseases and the results of laboratory analyses performed at the virological laboratory of the Federal Budgetary Health Care Institution “Hygiene and Epidemiology Center in the Republic of Karelia” were analyzed. Information about the number of tick-bitten patients seeking care at health care facilities was also considered.
Since 2009, all ticks collected in their natural habitat and ticks removed from people are analyzed for tick-borne encephalitis and Lyme disease by the polymerase chain reaction (PCR) diagnostic method. Each tick was also checked for infection of granulocytic anaplasmosis and monocytic erlichiosis.
The Republic of Karelia is located in the north-western part of the Russian Federation. It borders 4 regions of the North-Western Federal okrug: Leningrad and Vologda oblasts in the south, Murmansk oblast in the north and Archangelsk oblast in the east. The border with Finland is 723 km long. The Republic of Karelia consists of 18 administrative areas with a total population of 684,000. Eleven areas of the republic (from the south to 63º northern latitude) are endemic for TBE and Lyme disease (LD): Kondopoga area, Lahdenpohja area, Medvezhyegorsk area, Olonets area, Pitkyaranta area, Prionezhsky area, Pryazha area, Pudoga area and Suoyarvi area as well as the suburbs of Petrozavodsk and Sortavala. The residents of these areas are at risk for acquisition of tick-borne infections.
Annually, approximately 4.5 thousand people bitten by ticks visit health care facilities in the republic. The epidemic season lasts for 6 months from April until October. The incidence dynamics for TBE and LD is similar to the dynamics of the number of tick-bitten patients seeking care at health care facilities (Fig. 1).
In 2011, 36 cases of TBE were registered in the republic including 1 case among children and teenagers (in 2010 there were 46 and 5 TBE cases registered, respectively) and 58 cases of LD including 1 case among children and teenagers (in 2010 there were 29 and 6 LD cases registered, respectively). From 2002 to 2011 there were 2 lethal outcomes of TBE (in 2002 and 2003, respectively) among adults who were not immunized against TBE.
The dynamics of TBE incidence among children under the age of 14 is similar to the dynamics observed among adults. In general, the incidence rate among children is lower than among adults (Fig. 2).
The dynamics of LD incidence among children under the age of 14 is similar to the dynamics of LD incidence among adults with the exception of the last 2 years when there has been registered an increase among adults and a decrease among children (Fig. 2).
The incidence of TBE remains high; 6.7 and 5.3 per 100,000 population in 2010 and 2011, respectively. In recent years the TBE incidence has decreased slowly. However, the epidemiological situation for the disease remains challenging with the annual TBE incidence in the republic being two to three time higher than the incidence for the country as a whole (Fig. 3).
In 2011 the incidence of LD increased twofold (8.5 and 4.2 per 100,000 population in 2011 and 2010, respectively). From 2002 to 2011 the incidence of LD increased by 2.6 times (3.3 per 100,000 population in 2002) (Fig. 4).
In recent years, the habitat of ticks, which are major vectors of TBE and LD, has spread to the north from 63º northern latitude. People and animals are now bitten by ticks in areas located to the north of 63º northern latitude (Fig. 5).
The highest TBE incidence was registered in Pudoga and Pitkyaranta areas (20.3 and 13.7 per 100,000 population, respectively). The most endemic areas for LD are Medvezhyegorsk, Kondopoga, Pryazha, and Onega areas (43.9, 26.3, 17.8, and 12.9 per 100,000 population, respectively).
One quarter of TBE patients had a febrile form of the disease. In 93.3% cases the TBE diagnosis was laboratory confirmed. Approximately half (45.1%) of LD cases were laboratory confirmed.
During the last decade the greatest number of TBE and LD patients were adults over 60 years of age (32% and 44%, respectively) (Fig. 6 and 7). This age group was followed by people of 40-49 years of age (17% and 15%, respectively).
Only 26 of all TBE patients (4.3%) were vaccinated against the infection. Sixty eight patients (11.1%) had received immunoglobulin for preventive purposes. Among those, eight were diagnosed with a meningoencephalitic form of the disease (including 2 patients who had recently been vaccinated against TBE and 6 patients who received only immunoglobulin). The remaining patients had mild form of the disease.
Twenty percent of the republic’s population are vaccinated. Among persons working in the nature environment and considered to be at risk, 98.7% are immunized against tick-borne infections. Vaccination coverage has no considerable influence on the epidemiological situation.
No cases of tick bites among children and attending personnel were registered at summer recreational institutions.
Every year in the Republic of Karelia the number of small mammals (hosts and carriers of ticks) is estimated. Entomological surveys are conducted at the long-term monitoring stations; ticks are checked for viruses and borreliae, and from 2011 immunity among non-vaccinated population has been analyzed. In 2011, 5% of ticks removed from people and 1.5% of ticks taken from the nature were infected with the virus. Borreliae were found in 30.6% of ticks removed from people and in 51.8% of ticks taken from the nature. In addition, 5% of ticks removed from people and 4% of ticks taken from the nature were infected with erlichiosis in 2011.
In 2011, immunity against TBE was determined in 286 non-vaccinated people from 13 areas of the republic. TBE antibodies were detected among 14% of individuals, including residents from non-endemic areas. This may indicate that the population of the Republic of Karelia are naturally boostered against TBE infection.
Since the natural habitat of ticks has expanded the endemic areas in the republic must be re-defined. For this purpose it is necessary to continue:
- entomological surveys of tick populations in the republic;
- laboratory monitoring over pathogens in ticks;
- active examination of patients with fever and in meningeal condition, with symptoms of focal damage of the brain and spinal marrow of unknown etiology;
- check of immunity against TBE among the non-vaccinated population of the republic.