Orginal Article Cent Asian J Med Sci. 2017 Nov;3(3):250-258. https://doi.org/10.24079/CAJMS.2017.11.006 Geographical Distribution of Tick-borne Encephalitis and Its Vectors in Mongolia, 2005-2016 Uyanga Baasandavga1, Burmaajav Badrakh2, Tserennorov Damdindorj1, Otgonbayar Damdin1, Purevdulam Lkhagvasuren1, Unursaikhan Ulaankhuu1, Undraa Baatar1 1Department of Professional Service, National Center for Zoonotic Diseases, Ulaanbaatar, Mongolia; 2Mongolian Academy of Medical Science, Ulaanbaatar, Mongolia Submitted: July 6, 2017 Objectives: In the last several years, the incidence and fatality rates of tick-borne encephalitis Revised: September 12, 2017 (TBE) in Mongolia have been increasing with new cases being registered in areas without Accepted: September 18, 2017 the main tick vector. Therefore, we sought to determine the geographical distribution of TBE in Mongolia. Methods: Data were analyzed on TBE virus prevalence of collected ticks and Corresponding Author seroprevalence rate of TBE and TBE incidence rate among the human population from 2005 to Burmaajav Badrakh, MD, PhD, DSc 2016. Results: During this time, TBE incidence was 0.75 per 10,000 populations in Mongolia. Mongolian Academy of Medical Among 2,182 people investigated, seroprevalence rate was 14.6±10.9% (n=312) in 10 Sciences, Ulaanbaatar 14200, Mongolia provinces and Ulaanbaatar city. The seroprevalence rate among the populations of Selenge, Tel: +976-9981-7218 Bulgan and Khuvsgul provinces, which are home to the main tick vector I.Persulcatusis, were E-mail: [email protected] 1.8 times (CI 95% 1.5-2.3, p< 0.001) higher than other provinces where the tick species D.nuttalli and D.silvarumare found. The TBE virus prevalence of I.Persulcatus was 3.18%, D.nuttalli was 0.61% and D.silvarum was 2.9% among the 10,464 ticks sampled. This is an Open Access article distributed under the terms of the Creative Commons Conclusion: Endemic areas of TBE are expanding from northern parts of the country where Attribution Non-Commercial License (http:// the main vector I. persulcatus is more common to steppe areas where the vector D. nuttalli creativecommons.org/licenses/bync/4.0/) which permits unrestricted non-commercial is abundant. use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright© 2017 Mongolian Keywords: Tick-borne Encephalitis, Incidence, Seroprevalence, Ticks, Mongolia National University of Medical Sciences Introduction emissions, human behavior, economics and regional politics [1]. Since 2005, the most commonly observed human tick-borne In recent years, increasing numbers of tick-borne diseases are diseases in Mongolia include tick-borne encephalitis, tick-borne becoming a major public health issue due to climate change, borreliosis and tick-borne rickettsiosis. shifting host communities, tick and human demographic Tick-borne encephalitis (TBE) is an important viral infectious patterns, pathogen diversity, deforestation, greenhouse gas disease involving the central nervous system and is transmitted 250 www.cajms.mn Uyanga Baasandavga et al. by a bite from an infected tick. The World Health Organisation according to the standards set forth by the publication, “Health (WHO) reports (2014) that between10,000-12,000 tick-borne care technology. Diagnosis, treatment and surveillance of Tick- encephalitis cases are reported each year around the world borne encephalitis” MNS 5348-44:2003. [2]. Tick-borne encephalitis was first described by an Austrian physician (Shneider) in 1931 and the tick-borne encephalitis 2. Sample collection virus was first isolated in 1937 by the Soviet scientist Zilber, NCZD and local Center for Zoonotic Diseases (CZD) agencies when it was understood to be transmitted by the bite of infected implemented an active surveillance program through species of Ixodes persulcatus tick [3, 4]. In Mongolia, tick-borne advertisement of TBD among at-risk populations. Teams encephalitis virus was first isolated (Kraminskii V.A) from marmot collected 2,172 specimens of human blood serum from volunteer liver in Dornod province in 1979 while the Ixodes persulcatus participants. Participant’s name, province, and the sample tick was identified in 1987 (M.Dash) [5, 6]. Ixodes persulcatus collection date were recorded with the informed consent of the is a taiga tick distributed in coniferous forests consisting mostly participants. Local CZD offices from the provinces of Arkhangai, of pines, spruces and larches [7]. Much of northern Mongolia Bayankhongor, Bayan-Ulgii, Dundgobi, Uvurkhangai, Selenge, is covered in coniferous forest and the southern edge of Uvs, Khuvsgul, Khentii, Zavkhan, Umnugobi, Khovd, Gobi-Altai the Siberian taiga is located along the Khangai and Khentii and the city of Ulaanbaatar contributed to the surveillance effort. mountains. Mongolian scientists have been conducting TBE For tick collection, a tick drag method was implemented research since the 1980s. In a 2005 study, researchers found using a 1 square-meter strip of white cloth sized 60x100 cm. Ticks Ixodes persulcatus tick counts were high in Selenge province were kept in a tube until they could be investigated. Tick species [5]. were visually identified using a tick identification guide created Tick-borne encephalitis has recently attracted much by Russian researcher Serdyukova in 1956 [8]. attention because of the increasing incidence and consequent significant harm to human health. Since 2005, prevention 3. Ethical statement measures such as vaccination, training and advocation among Ethical clearance was not required for this surveillance. the population have been administered but human cases of Surveillance has been conducted among at-risk individuals since TBE continue to increase. TBE cases are also being registered in 2005 and is considered the routine work of NCZD and local CZD areas without the main vector Ixodes persulcatus tick, thereby offices responsible for zoonotic infectious disease response and expanding the natural foci of disease. The goal of this research is prevention measures. This practice is also mentioned in “Health to define geographical distribution of tick-borne encephalitis in care technology. Diagnosis, treatment and surveillance of Tick- Mongolia. Furthering knowledge of the distribution of tick-borne borne encephalitis” MNS 5348-44:2003. encephalitis in Mongolia is urgently needed for the prevention and control of this disease, as well as for reducing the disease 4. Laboratory methods burden among the human population. From the human participants, approximately 5 ml of blood was collected where 1.5 ml of serum was separated and kept at -200 Materials and Methods C until analyzed. The IgG anti-TBEV levels were measured using an enzyme linked immunosorbent assay (ELISA) (EUROIMMUN, 1. Documentation of tick-borne encephalitis cases ELISA kit, Germany) and immunofluorescence assay (IFA) Data on TBE cases were documented by the National Center (EUROIMMUN, Antibody Kit, Germany). Neutralization titer of for Zoonotic Diseases (NCZD), acting as the National Reference ≥1.10 was considered positive. Seroprevalence rate was the Laboratory for TBE virus, confirming the diagnosis through percentage of persons in the population who had detected questionnaires on tick bites and visits to endemic areas from 2005 able IgG anti-TBEV among all tested specimens based on to 2016. All cases were confirmed by serological investigation serological investigation. It was presented as a percent of the using ELISA and IFA methods for the detection of IgM and IgG total specimens tested. In ticks, the TBE virus RNA was detected anti-TBEV. Confirmatory diagnostic methods were carried out using polymerase chain reaction (PCR). RNA was extracted from Vol.3• No.3• November 2017 www.cajms.mn 251 Tick-borne encephalitis in Mongolia ticks using kits (Machereynagel, Germany) according to the population and tick infection rate in provinces. A p-value< 0.05 manufacturer’s instructions. The cDNA synthesis was performed was considered statistically significant. A distribution of TBE using primers (Super script® in Platinium® One step RT-PCR, incidence map was made using ArcGIS 10.1 program. Invitrogen, USA) of reverse transcription polymerase chain reaction (RT-PCR). RT-PCR for detection of the TBEV E gene was Results performed with primers EncE-L and 1643-R. 1. TBE cases 5. Statistical analysis A total of 225 confirmed cases were registered in 47 soums TBE incidence was calculated per 10,000 population for each of Arkhangai, Bayankhongor, Bulgan, Darkhan-Uul, Dundgobi, province. Seroprevalence rate were calculated in the surveillance Dornod, Orkhon, Uvurkhangai, Selenge, Tuv, Uvs, Khunsgul, and data. Prevalence data were expressed as mean ±SD. Statistical Khentii provinces and among 9 districts of Ulaanbaatar city. The analysis was conducted using the MS Excel 2010 and Open incidence rate was 0.75 per 10,000 population in Mongolia Epi Info version. Chi-squere test was performed between from 2005-2016. The incidence in Selenge (11.5), Bulgan (2.7), the seroprevalence rate among the populations of different Darkhan-uul (1.6), and Orkhon (1.1) provinces were higher areas with an abundance of different tick species. Correlation than the national incidence level. In the last two years, three analysis was performed between seroprevalence rate among provinces (Uvs, Uvurkhangai and Dundgobi) were added to the Figure 1. TBE Incidence rate and tick bites in Mongolia 2005-2009. The tick symbol designates location of tick bite. 252 www.cajms.mn