Reported Cases of TBE
The number of TBE infections in those European countries, in which the disease poses a major problem to public health and/or such figures have been known for a long time. In many of those countries, morbidity has been continually increasing for years. In highly endemic areas in which the majority of the population is vaccinated against TBE, as is the case for Austria and Bavaria, the number of reported cases of TBE doesn’t give enough information about the actual risk of infection.
TBE is a notifiable disease in many European countries, such as Austria, Czech Republic, Finland, Germany, Hungary, Latvia, Lithuania, Poland, Slovenia, Slovakia, Sweden and Switzerland.
The TBE epidemiology is very complex. There are low-risk areas, for example, in Finland, Sweden, Norway, and Switzerland with a growing trend towards spread and incidence. The emergence of new foci in Sweden and Norway has been reported, too. The example of Denmark (Bornholm) shows that risk areas can be forgotten and later rediscovered. TBE cases in Europe
Information on TBE in Europe is collected by the International Scientific Working Group on Tick-Borne-Encephalitis (ISW-TBE) and can be found at tbe-info.com.
• Albania: Natural foci are found in the whole of Albania. Older publications show a prevalence of TBE virus in the Albanian population of 22%. Alimentary cases of TBE have been reported. Before 1990, 25 new cases were registered annually. No further data are available after that time.
• Austria: In the pre-vaccination era, Austria had the highest recorded morbidity of TBE in Europe with up to 700 hospitalized cases per year. The increasing vaccination coverage (>80%) led to a steady decline of TBE. In the period of 2000 to 2004 the 5 year average was 62 annual cases, an incidence rate of 0.8 per 100,000. The regions most affected by TBE are Styria, Carinthia, as well as Upper Austria, the south of Vienna, and parts of Burgenland. In 2003 new endemic areas have been described around Mattsee, Wallersee and Thalgau, north of the city of Salzburg.
For an unvaccinated tourist staying in a highly endemic province of southern Austria (e.g. Styria), the risk of acquiring TBE was described to be 1/10,000 man-months of exposure. Based on total numbers of tourist overnight stays in Austria during the summer season, about 60 travel-associated cases of clinical TBE could be expected to occur among holidaymakers after their stay in Austria.
• Belarus: About 20 to 80 cases of TBE occur annually in Belarus with a peak of 97 cases in 1996. There is not enough information available about clinical cases in Belarus, which is believed to be a country with high risk areas and a high prevalence of TBEV in ticks. In 2003, 25 clinical cases were reported in the area of Minsk.
• Bosnia: In the northern parts of the country there may be some cases. There is not enough information available about the number of cases.
• China: Data on TBE morbidity is scarce. Natural foci are the Hunchun area, Jilin province and in the subtropical region of western Yunnan near the Burmese border.
• Croatia: Only one natural focus in the northern part of the country is described, between the rivers Sava and Drava. During the past ten years, the number of annual cases ranged from 23 to 87.
• Czech Republic: TBE exists in all parts of the country. In the period 2000 to 2004 an average of 577 cases of TBE occurred annualy. Thus the Czech Republic has one of the highest numbers of diseases due to TBE in Europe - second only to Russia. The incidence is higher in regions south of Prague near the city of Ceske Budejovice. There has been constantly high incidence near the town of Pilsen in the western part of the Czech Republic. Recently, TBE foci have been identified in the northern part of the province of Bohemia. In the east of the country there has been a high incidence near Olomouc. Clinical cases of TBE are notified from April until November every year with one peak in July.
• Denmark: The island of Bornholm has long been known for TBE cases. In total, 14 cases of TBE were found in the seven year period 1994 to 2000, giving an incidence of 3.81 per 100,000 inhabitants. Four cases were notified in the year 2003. The minimum level of prevalence of TBEV in ticks on Bornholm is similar to what has been found in other European countries where TBEV is endemic. The tick Ixodes ricinus was also found to carry the flavivirus Louping ill virus. The coexistence of TBEV and Louping ill virus in Denmark should be taken into account.
• Estonia: TBE morbidity in Estonia has been 199 annual cases (15/100,000).106) The highest TBE distribution rate is in West Estonia (Pärnumaa, Läänemaa), East Estonia (Ida-Virumaa), Saaremaa (island in west) and Southeast Estonia (Polvamaa, Tartumaa).
• Finland: In the period of 2000 to 2004 an average of 32 annual cases was reported with a record number of 41 cases in 2000. The known endemic areas are situated mainly in Åland (66% of 125 cases 1987 to 1997, 80/100,000/year in 2000), Archipelago of Turku (10%), Kokkola region (6%) and Lappeenranta region (5%). According to antibody analyses, approximately every one in five Ålanders is infected during his or her lifetime. Recently, nine cases have been identified altogether from an island close to the city of Helsinki.
• France: There are some cases reported from the Alsace region and single cases of infections are documented from the region Nancy/Lothringen. New cases were recently reported from Faverges and Grenoble.
• Germany: A map of TBE risk areas is updated periodically by the Robert Koch Institute. In Germany, 100 to 300 autochthonous clinical TBE cases have been recorded annually. There are high-risk areas in Bavaria and Baden-Wuerttemberg and ongoing low-risk areas in Hessen, Thuringia, and the Rhineland-Palatinate and single cases in Saxony. The TBE incidence in Bavaria and Baden Wuerttemberg has been stable on a high level for years; outside these areas increasing incidences were reported (Odenwald, Thuringia). In 2004, 274 cases of TBE were notified in Germany (2002: 239; 2001: 256). These occurred mainly in southern Germany in the federal states of Baden-Wuerttemberg (42%) and Bavaria (38%).
Seventy nine of Germany’s 440 counties are currently classified as TBE risk areas and nine as high risk areas. They are located in Baden-Wuerttemberg (30), Bavaria (47), Hessen (4), Thuringia (3) and Rhineland-Palatinate (1). A further five counties in Baden-Wuerttemberg are classified as endemic for TBE based on seroprevalence studies.93) 3 cases have been reported from areas previously not defined as risk areas: Brandenburg (2003), Mecklenburg-Vorpommern (2004), and Saxony Anhalt.
• Greece: Single cases were reported in the north of the country ( Thessaloniki).
• Hungary: The average yearly incidence between 1977 and 1996 was 2.5 per 100,000 population (range 1.3 to 3.8), with the highest incidences between 1981 and 1990. From 1997 to 2000, a significant decrease in the number of registered/diagnosed TBE cases was observed, with an incidence of 0.5 per 100,000 in 2000. Since 2001, the incidence has been increasing again. In the period of 2000 to 2003 an average of 79 cases was reported annually. Extended areas of high-risk are in western Hungary and along the danube region: the counties of Zala, Somogy, Vas (western Hungary), Nógrád (northern Hungary), and around the lake Balaton.
• Italy: A few clinical cases have been recorded in Northern Italy in the area of Florence, Trento and Belluno. Antibodies for TBE virus were found in about 1% of persons at potential risk (foresters, hunters, woodcutters, gamekeepers). Since the early 1990s 2 to 19 cases have been reported annually.
• Japan: TBE virus is endemic in Japan, where TBE virus was isolated from the blood samples of sentinel dogs, tick pools, and rodent spleens since 1995. In 1993, a case of TBE was reported in the southern part of Hokkaido. A seroepidemiological survey was performed among humans and animals, and it was concluded that the TBE virus may be endemic in Japan, at least on the island of Hokkaido. The main principal vector on Hokkaido was identified as I. ovatus and genomic sequence and phylogenetic analyses of a virus isolate revealed a close relationship with the Far-Eastern subtype of the TBE virus.
• Kazakhstan: Cases of TBE are supposed to have occurred but there is not enough information available.
• Latvia: Latvia is considered the TBE endemic country with the highest incidence rates in the world. Even in and around the city park of Riga TBE cases have been reported. Ticks in Lativa carry a higher number of TBE viruses than ticks in other risk countries. In 1993, annual incidence quadrupled from the mean level of the previous two decades (nearly eight cases per 100,000 population), reaching the highest levels in 1994 and 1995 at 53 cases per 100,000. Since 1999 the incidence has been significantly lower, down to 6.5 cases in 2002, but back up to 15.7 per 100,000 in 2003. Food-borne outbreaks (caused by dairy products, mainly goat milk) amounted up to 5% of total annual cases.
• Liechtenstein, Switzerland: In the period of 2000 to 2004 the 5 year average was 101 cases. In 2004 138 cases were reported. There are mainly two high-risk regions, one big one covering the midland, with the exception of the far-western part, a second smaller one being located in the upper Rhine valley, including the principality of Liechtenstein. A focus of TBE-virus-infected ticks is located on a much-used forest path near Vaduz, the capital of the principality. The canton Zürich became the most dangerous region for TBE in Switzerland, followed by Thurgau, St. Gallen, Aargau, and Bern.
• Lithuania: TBE is present in all districts of Lithuania. In 2004 a total number of 425 hospitalized cases was reported. In 2003, the epidemiology of TBE in Lithuania was very unusual. The incidence rate (763 cases, 22 per 100,000 population) was double the average incidence over the last ten years, and was the highest annual rate recorded since notification began at the end of the 1960s. This rate was also the highest of all the Baltic countries in 2003. Four lethal cases of TBE were notified in 2003. TBE is normally transmitted by a tick bite but, in 2003, 22 cases of TBE (four clusters) were acquired by consuming unpasteurised goat’s milk – a well-recognized transmission route. The highest incidences of TBE, about 80% of all notified cases, are recorded every year in the northern and central part of the country – mainly in three counties: Kaunas, Panevezys and Siauliai. In 2003, the incidence rate in these areas was the same, but incidence rates were much higher in many other counties. Eight districts out of 44 reported a two to five times higher incidence rate than the average incidence in Lithuania. The highest incidence rate was in Panevezys, at about 100 per 100,000 population.
• Moldavia: Although reliable data is missing it is assumed that TBE is present.
• Mongolia: In 2004 some endemic areas were described next to the Russian border in the north of the country (provinces of Selenga and Bulgan) and around the capital city Ulan-Bataar.
• Norway: In 1997 TBE was reported in the coastal area of Southern Norway for the first time. All cases were acquired within a limited area on the southern coast, and four were diagnosed in the municipality of Tromøy, three of them in tourists. A study done among regular patients attending a health center in Tromøy: showed a seroprevalence of 2.4% with TBEV antibodies. In previous studies, IgG antibodies to TBE virus were found in 0.3 to 0.4% of persons from different parts of Agder counties, a region where TBE has previously not been seen.
• Poland: Since 1993, the number of reported cases at country level ranged from 100 to 350 cases per year. In 2003 the number of reported cases was 339 (incidence 0.89 per 100,000). In Poland, the north-east of the country (around Bialystok) is the main area of endemicity.76) 80% of cases occurred in two northeastern provinces adjacent to Lithuania and Belarus. Another important focus of the disease is in the southwestern part of Poland, in districts adjacent to the Czech Republic.
• Romania: Risk of tick-borne encephalitis is reported for the Tulcea district and in Transylvania at the base of the Carpathian Mountains and Transylvanian Alps, but the information was never published, neither were details about annual numbers of TBE cases.
w Slovakia: The number of reported cases at country level has ranged from 54 to 101 cases per year in the last ten years. In 2002 the number of reported cases was 62 (incidence 1.15 per 100,000), and in 2003 the number of reported cases was 74 (incidence 1.38 per 100,000). Some of the reported cases were caused by drinking raw goat and sheep milk (home production). New foci have been identified in areas of eastern Slovakia traditionally thought to be free of the virus.
• Russia: TBE is endemic from Kaliningrad to Wladiwostok. The TBE morbidity rate in Russia recently increased dramatically from 6,000 to 10,000 persons per year. The highest morbidity rate is registered in the Ural, Perm, Sverdlovsk regions: 13.4/100,000 of population; Udmurt Republic: 53.5/100,000; West Siberia, Tomsk region: 72.5/100,000; East Siberia, Krasnoyarsky Krai: 37.0/100,000.113) The most dangerous foci of TBE were found to be located in the southern Okhotsk region, were dark coniferous forests grow and in the Sikhote-Alin Mountain range (near Vladivostok). In the Primorye region (far-eastern part of Russia, on the coast of the Sea of Japan) 126 people were hospitalized between January and August 2004 with a diagnosis of TBE, 17 of whom were children.
A total of 8 people among those contracting TBE have died. The total number of TBE patients in the Lake Baikal region between 1996 and 1999 ranged from 460 to 780 cases per year and shows a tendency to increase. The relative index per 100,000 population varied between 2.6 and 18.1.
The Sverdlovsk Region has long been known as the natural nidus of tick-borne encephalitis. The majority of people are attacked in Yekaterinburg and in 2003 the number of tick attacks has increased, as compared to 2002. Other foci are in Nizhni Tagil, Kamensk-Uralsky, in Verkhnyaya Pyshma, Nizhnyaya Tura, Nevyansk, and Sukhoy Lo.
Ixodes persulcatus is the main vector of TBEV in the asian and European parts of Russia. Lethal TBE outcomes were registered in Siberia (Irkutsk region and Krasnoyarsk territory) and in Russia’s European part (Yaroslavl region).
• Serbia: A few cases have been reported in the area near Belgrade, including food-borne outbreaks near the coastal regions of the Adria, but there is not enough information available.
• Slovenia: Endemic foci of TBE are spred all over the country. In the period of 2001 to 2003 the 3 year average was 265 cases. The highest number of TBE cases was reported in the year 1994 with 530 cases.
• Sweden: Since the end of the 1990s, around 100 cases have been reported annually. In the period of 2000 to 2004 the five year average was 127 annual cases. In the year 2004 the high number of 160 cases was reported. Most of the infections were acquired in the counties of Stockholm (62%), Södermanland (13%) and Uppsala (8%). In the county of Västra Götaland (to the south of Lake Vänern), five to ten cases are notified annually. Sporadic cases occur in the rest of Sweden every year.
• Switzerland, Liechtenstein: In the period of 2000 to 2004 the 5 year average was 101 cases. In 2004 138 cases were reported. There are mainly two high-risk regions, one big one covering the midland, with the exception of the far-western part, a second smaller one being located in the upper Rhine valley, including the principality of Liechtenstein. A focus of TBE-virus-infected ticks is located on a much-used forest path near Vaduz, the capital of the principality. The canton Zürich became the most dangerous region for TBE in Switzerland, followed by Thurgau, St. Gallen, Aargau, and Bern.
• Ukraine: The foci of TBE were found throughout the whole of the mountain forest zone of the Crimea and coincided with the habitat area of lxodes ricinus, the main vector of TBE. About a hundred patients with TBE were recorded over the decade 1980 to 1990 in the Crimea, where co-infections with TBE and Crimean-Congo hemorrhagic fever can be found.