Epidemiology of tick-borne encephalitis in Sweden 1956-1989: a study of 1116 cases

Seroprevalence of tick-borne encephalitis virus and vaccination coverage of tick-borne encephalitis, Sweden, 2018 to 2019

BackgroundIn Sweden, information on seroprevalence of tick-borne encephalitis virus (TBEV) in the population, including vaccination coverage and infection, is scattered. This is largely due to the absence of a national tick-borne encephalitis (TBE) vaccination registry, scarcity of previous serological studies and use of serological methods not distinguishing between antibodies induced by vaccination and infection. Furthermore, the number of notified TBE cases in Sweden has continued to increase in recent years despite increased vaccination.AimThe aim was to estimate the TBEV seroprevalence in Sweden.MethodsIn 2018 and 2019, 2,700 serum samples from blood donors in nine Swedish regions were analysed using a serological method that can distinguish antibodies induced by vaccination from antibodies elicited by infection. The regions were chosen to reflect differences in notified TBE incidence.ResultsThe overall seroprevalence varied from 9.7% (95% confidence interval (CI): 6.6-13.6%) to 64.0% (95% CI: 58.3-69.4%) between regions. The proportion of vaccinated individuals ranged from 8.7% (95% CI: 5.8-12.6) to 57.0% (95% CI: 51.2-62.6) and of infected from 1.0% (95% CI: 0.2-3.0) to 7.0% (95% CI: 4.5-10.7). Thus, more than 160,000 and 1,600,000 individuals could have been infected by TBEV and vaccinated against TBE, respectively. The mean manifestation index was 3.1%.ConclusionA difference was observed between low- and high-incidence TBE regions, on the overall TBEV seroprevalence and when separated into vaccinated and infected individuals. The estimated incidence and manifestation index argue that a large proportion of TBEV infections are not diagnosed.

Potential drivers of human tick-borne encephalitis in the Örebro region of Sweden, 2010-2021

Incidence of tick-borne encephalitis (TBE) has increased during the last years in Scandinavia, but the underlying mechanism is not understood. TBE human case data reported between 2010 and 2021 were aggregated into postal codes within Örebro County, south-central Sweden, along with tick abundance and environmental data to analyse spatial patterns and identify drivers of TBE. We identified a substantial and continuing increase of TBE incidence in Örebro County during the study period. Spatial cluster analyses showed significant hotspots (higher number of cases than expected) in the southern and northern parts of Örebro County, whereas a cold spot (lower number of cases than expected) was found in the central part comprising Örebro municipality. Generalised linear models showed that the risk of acquiring TBE increased by 12.5% and 72.3% for every percent increase in relative humidity and proportion of wetland forest, respectively, whereas the risk decreased by 52.8% for every degree Celsius increase in annual temperature range. However, models had relatively low goodness of fit (R² < 0.27). Results suggest that TBE in Örebro County is spatially clustered, however variables used in this study, i.e., climatic variables, forest cover, water, tick abundance, sheep as indicator species, alone do not explain this pattern.

Tick-borne encephalitis in pediatrics: An often overlooked diagnosis

Tick-borne encephalitis (TBE) is a vector-borne disease caused by a flavivirus, the tick-borne encephalitis virus (TBEV), and transmitted by the bite of infected Ixodes ricinus ticks. The European subtype (TBEV-Eu) is endemic in 27 European countries. During the last decade, increased TBE incidence was observed in many countries, including some of those believed to be of low endemicity/devoid of TBEV circulation. However, data dealing with TBE in children are far less profuse than with adults. Historically, children are known to have mild TBEV infection with favorable outcomes. That said, recent case reports and observational studies on pediatric cohorts have challenged this point of view. Like adults, children may present severe forms and fail to completely recover following TBE infection, at times leading to long-term cognitive impairment. In this review, we comprehensively describe the incidence, exposure factors, and transmission routes of TBEV in children, as well as the clinical and biological manifestations of TBE and imaging findings in this population. We also harness new data on long-term outcomes and sequelae in pediatric cohorts. Finally, we provide an overview of vaccination recommendations for children in European countries.

Surveillance of tick-borne encephalitis in emerging risk areas in southern Sweden: a retrospective case finding study

Tick-borne encephalitis (TBE) is an emerging infection causing CNS infection of various severity. Good knowledge of the incidence in the population and defined risk areas is important in risk communication and vaccination recommendations. The aim of this study was to investigate potential underreporting by retrospectively diagnose TBE among patients with viral CNS infections of unknown etiology in a region with emerging risk areas for TBE, and define variables associated with performed TBE serology at the time of infection. Epidemiological data and microbiological diagnostics of cases with viral CNS infection of unknown etiology treated at departments of infectious diseases and pediatrics in Skåne County during 2000-2012 were investigated. Analyses to evaluate variables associated with performed TBE serology at the time of infection were performed. Retrospective TBE serology was performed on stored blood samples when available. TBE serology was already performed at the time of CNS infection in 193 out of 761 cases. Department, type of clinical manifestation, time period of illness, and whether Borrelia serology had been performed were independent variables associated with having had TBE serology performed or not at the time of illness. Only one of 137 cases, where samples could be retrospectively analyzed for TBE, turned out positive. This study shows a low frequency of TBE sampling among patients with meningoencephalitis in a region with emerging risk for TBE. A higher awareness of TBE as differential diagnosis could contribute to earlier detection of new risk areas and adequate preventive advice to the public.

Burden of Tick-Borne Encephalitis, Sweden

In recent decades, the incidence of tick-borne encephalitis (TBE) in Sweden has increased. To calculate the burden of disease over a 17-year period, we analyzed data from the Swedish National Health Data Register for TBE cases diagnosed during 1998–2014. We compared healthcare use and sick leave associated with 2,429 persons with TBE with a referent cohort of 7,287 persons without TBE. Patients with TBE were hospitalized for significantly more days during the first year after disease onset (11.5 vs. 1.1 days), logged more specialist outpatient visits (3.6 vs. 1.2 visits), and logged more sick leave days (66 vs. 10.7 days). These differences generally increased over time. The case-fatality rate for TBE was 1.1%. Our calculated cost of TBE to society provides a baseline for decisions on immunization programs. Analyzing register data, our study adds to clinical studies of smaller cohorts and model-based studies that calculate disease burden.

Clinical Characteristics of Patients with Tick-Borne Encephalitis (TBE): A European Multicentre Study from 2010 to 2017

Tick-borne encephalitis (TBE) virus is a major cause of central nervous system infections in endemic countries. Here, we present clinical and laboratory characteristics of a large international cohort of patients with confirmed TBE using a uniform clinical protocol. Patients were recruited in eight centers from six European countries between 2010 and 2017. A detailed description of clinical signs and symptoms was recorded. The obtained information enabled a reliable classification in 553 of 555 patients: 207 (37.3%) had meningitis, 273 (49.2%) meningoencephalitis, 15 (2.7%) meningomyelitis, and 58 (10.5%) meningoencephalomyelitis; 41 (7.4%) patients had a peripheral paresis of extremities, 13 (2.3%) a central paresis of extremities, and 25 (4.5%) had single or multiple cranial nerve palsies. Five (0.9%) patients died during acute illness. Outcome at discharge was recorded in 298 patients. Of 176 (59.1%) patients with incomplete recovery, 80 (27%) displayed persisting symptoms or signs without recovery expectation. This study provides further evidence that TBE is a severe disease with a large proportion of patients with incomplete recovery. We suggest monitoring TBE in endemic European countries using a uniform protocol to record the full clinical spectrum of the disease.

Mushroom hunting and consumption in twenty-first century post-industrial Sweden

BACKGROUND

The pre-industrial diet of the Swedish peasantry did not include mushrooms. In the 1830s, some academic mycologists started information campaigns to teach people about edible mushrooms. This propaganda met with sturdy resistance from rural people. Even at the beginning of the last century, mushrooms were still only being occasionally eaten, and mostly by the gentry. During the twentieth century, the Swedish urban middle class accepted mushrooms as food and were closely followed by the working-class people. A few individuals became connoisseurs, but most people limited themselves to one or two taxa. The chanterelle, Cantharellus cibarius Fr., was (and still is) the most popular species. It was easy to recognize, and if it was a good mushroom season and the mushroomer was industrious, considerable amounts could be harvested and preserved or, from the late 1950s, put in the freezer. The aim of this study is to review the historical background of the changes in attitude towards edible mushrooms and to record today's thriving interest in mushrooming in Sweden.

METHODS

A questionnaire was sent in October and November 2017 to record contemporary interest in and consumption of mushrooms in Sweden. In total, 100 questionnaires were returned. The qualitative analysis includes data extracted from participant and non-participant observations, including observations on activities related to mushroom foraging posted on social media platforms, revealed through open-ended interviews and in written sources. With the help of historical sources, including earlier studies and ethnographical data collections, a diachronic analysis is given to describe the changes over time.

RESULTS AND DISCUSSION

During the last 100 to 140 years, Sweden has changed from a mycophobic to a mycophilic society with a passionate interest in the utilization of wild mushrooms. In the late twentieth century, various social institutions connected with mushroom hunting evolved. Evening classes, study circles, clubs, exhibitions, consultants, and a wide array of handbooks promoted this interest. In the early twenty-first century, mushrooming has become widely accepted, especially among the middle class, but also among Swedes in general. The so-called hipster-generation, born in the 1990s, harvests mushrooms due to their interest in producing their own food. This group often uses social media to identify edible species. Most people who go mushrooming gather only a few species. There are, however, some dedicated individuals who have become hobby specialists and who know a wide diversity of taxa. A few study participants reported that they were afraid of not being able to distinguish between poisonous fungi species and edible ones and therefore refrain from picking any wild mushrooms at all. However, they still consume cultivated mushrooms, such as Agaricus bisporus (J.E. Lange) Imbach, bought in grocery stores or served in cafes and restaurants.

CONCLUSION

Swedish society has changed rapidly during the last decades and so has the interest in mushrooming among its members. Throughout the second part of the twentieth century, the flow of information about mushrooms has continued through lecturers, courses, media, exhibitions, and even associations. Walking in forestland is also an important leisure activity for many urban Swedes, and in the early twenty-first century, mushrooming has also become a thriving pastime among people with an urban lifestyle.

The importance of wildlife in the ecology and epidemiology of the TBE virus in Sweden: incidence of human TBE correlates with abundance of deer and hares

Background

Tick-borne encephalitis (TBE) is one tick-transmitted disease where the human incidence has increased in some European regions during the last two decades. We aim to find the most important factors causing the increasing incidence of human TBE in Sweden. Based on a review of published data we presume that certain temperature-related variables and the population densities of transmission hosts, i.e. small mammals, and of primary tick maintenance hosts, i.e. cervids and lagomorphs, of the TBE virus vector Ixodes ricinus, are among the potentially most important factors affecting the TBE incidence. Therefore, we compare hunting data of the major tick maintenance hosts and two of their important predators, and four climatic variables with the annual numbers of human cases of neuroinvasive TBE. Data for six Swedish regions where human TBE incidence is high or has recently increased are examined by a time-series analysis. Results from the six regions are combined using a meta-analytical method.

Results

With a one-year time lag, the roe deer (Capreolus capreolus), red deer (Cervus elaphus), mountain hare (Lepus timidus) and European hare (Lepus europaeus) showed positive covariance; the Eurasian elk (moose, Alces alces) and fallow deer (Dama dama) negative covariance; whereas the wild boar (Sus scrofa), lynx (Lynx lynx), red fox (Vulpes vulpes) and the four climate parameters showed no significant covariance with TBE incidence. All game species combined showed positive covariance.

Conclusions

The epidemiology of TBE varies with time and geography and depends on numerous factors, i.a. climate, virus genotypes, and densities of vectors, tick maintenance hosts and transmission hosts. This study suggests that the increased availability of deer to I. ricinus over large areas of potential tick habitats in southern Sweden increased the density and range of I. ricinus and created new TBEV foci, which resulted in increased incidence of human TBE. New foci may be established by TBE virus-infected birds, or by birds or migrating mammals infested with TBEV-infected ticks. Generally, persistence of TBE virus foci appears to require presence of transmission-competent small mammals, especially mice (Apodemus spp.) or bank voles (Myodes glareolus).

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3057-4) contains supplementary material, which is available to authorized users.

Diagnosing tick-borne encephalitis: a re-evaluation of notified cases

We set out to investigate the serological response of TBE virus (TBEV)-specific IgM and IgG antibodies in stored serum and cerebrospinal fluid (CSF) in notified TBE patients, in order to confirm or reject the diagnosis. We applied the ELISA methods used in clinical practice, Enzygnost and Immunozym, and assessed RT-PCR as a diagnostic tool. A total of 173 TBE cases were notified to the Public Health Agency. Samples from 129 patients were eligible for the study. Stored serum samples were found for 111 patients and CSF samples for 88 patients. All serum samples were analyzed with both Enzygnost and Immunozym, as well as an additional 140 control samples. CSF samples, including samples from ten controls, were analyzed with Immunozym. RT-PCR for TBEV was performed on 126 serum, two whole blood, 96 CSF, two feces and four nasopharynx samples. Only two of 111 notified patients lacked detectable TBEV IgM in serum, from whom one sample was RT-PCR positive. According to the ECDC definition, 117/129 (90.7%) of the reported TBE cases were confirmed. Positive RT-PCR results were obtained in eight patients, one from whole blood and eight from serum samples. Four out of eight of the RT-PCR positive patients were TBEV-IgM positive and none had detectable TBEV-specific IgG. All of the tested CSF, feces and nasopharynx samples were RT-PCR-negative. TBEV-specific IgG was detected in 88.4% and IgM in 31.6% of the CSF samples. RT-PCR on serum samples and CSF IgG antibodies can be used as complementary methods in TBE diagnostics, not least early in the disease course.

Tick-Borne Encephalitis sequelae at long-term follow-up: a self-reported case-control study

BACKGROUND

Tick-borne encephalitis (TBE), caused by the TBE virus (TBEV), is a major neurotropic infection throughout Europe and Asia, with a considerable risk of neurological sequelae. Our aim was to study the symptoms in patients with TBE in Western Gotaland between 1997 and 2012 in the acute phase and at follow-up after 2-15 years (median: 5.5 years).

METHODS

The medical records of 96 patients with TBE were studied. Phone-based interviews were held with 92 patients and 58 controls, matched by age, gender and residential area. The Encephalitis Support Group Questionnaire (ESGQ) 2000 was used, further developed with dimensions and scoring 1-4, where a high score is related to better outcome. Patients and controls also answered a written survey regarding functional outcome of sleep (FOSQ).

RESULTS

Of the patients, 35% had a mild disease, 56% moderate and 7.3% severe disease. At the follow-up, patients scored significantly lower than controls in the dimensions of memory/learning, executive functions, vigilance and physical impairments. In addition, the answers concerning tiredness/fatigue, poor concentration/attention, reduced initiative/motivation, balance disturbances, coordination problems, difficulties with short- and long-term memory, learning difficulties and problems with fine motor skills resulted in significantly lower scores in the patients compared with the controls. The patients scored lower than the controls in the FOSQ dimension social outcome.

CONCLUSIONS

At the long-term follow-up, the patients scored significantly lower in a diversity of neurocognitive and motor symptoms, in comparison with controls. These sequelae and their pathogenesis should be further explored and specific neurocognitive assessment tests are needed.

Single-Stranded RNA Viruses

In this chapter, we describe 73 zoonotic viruses that were isolated in Northern Eurasia and that belong to the different families of viruses with a single-stranded RNA (ssRNA) genome. The family includes viruses with a segmented negative-sense ssRNA genome (families Bunyaviridae and Orthomyxoviridae) and viruses with a positive-sense ssRNA genome (families Togaviridae and Flaviviridae). Among them are viruses associated with sporadic cases or outbreaks of human disease, such as hemorrhagic fever with renal syndrome (viruses of the genus Hantavirus), Crimean–Congo hemorrhagic fever (CCHFV, Nairovirus), California encephalitis (INKV, TAHV, and KHATV; Orthobunyavirus), sandfly fever (SFCV and SFNV, Phlebovirus), Tick-borne encephalitis (TBEV, Flavivirus), Omsk hemorrhagic fever (OHFV, Flavivirus), West Nile fever (WNV, Flavivirus), Sindbis fever (SINV, Alphavirus) Chikungunya fever (CHIKV, Alphavirus) and others. Other viruses described in the chapter can cause epizootics in wild or domestic animals: Geta virus (GETV, Alphavirus), Influenza A virus (Influenzavirus A), Bhanja virus (BHAV, Phlebovirus) and more. The chapter also discusses both ecological peculiarities that promote the circulation of these viruses in natural foci and factors influencing the occurrence of epidemic and epizootic outbreaks

Tick-borne encephalitis virus sequenced directly from questing and blood-feeding ticks reveals quasispecies variance

The increased distribution of the tick-borne encephalitis virus (TBEV) in Scandinavia highlights the importance of characterizing novel sequences within the natural foci. In this study, two TBEV strains: the Norwegian Mandal 2009 (questing nymphs pool) and the Swedish Saringe 2009 (blood-fed nymph) were sequenced and phylogenetically characterized. Interestingly, the sequence of Mandal 2009 revealed the shorter form of the TBEV genome, similar to the highly virulent Hypr strain, within the 3′ non-coding region (3′NCR). A different genomic structure was found in the 3′NCR of Saringe 2009, as in-depth analysis demonstrated TBEV variants with different lengths within the poly(A) tract. This shows that TBEV quasispecies exists in nature and indicates a putative shift in the quasispecies pool when the virus switches between invertebrate and vertebrate environments. This prompted us to further sequence and analyze the 3′NCRs of additional Scandinavian TBEV strains and control strains, Hypr and Neudoerfl. Toro 2003 and Habo 2011 contained mainly a short (A)3C(A)6 poly(A) tract. A similar pattern was observed for the human TBEV isolates 1993/783 and 1991/4944; however, one clone of 1991/4944 contained an (A)3C(A)11 poly(A) sequence, demonstrating that quasispecies with longer poly(A) could be present in human isolates. Neudoerfl has previously been reported to contain a poly(A) region, but to our surprise the re-sequenced genome contained two major quasispecies variants, both lacking the poly(A) tract. We speculate that the observed differences are important factors for the understanding of virulence, spread, and control of the TBEV.

Prevalence of tick-borne encephalitis virus in Ixodes ricinus ticks in northern Europe with particular reference to Southern Sweden

Background

In northern Europe, the tick-borne encephalitis virus (TBEV) of the European subtype is usually transmitted to humans by the common tick Ixodes ricinus. The aims of the present study are (i) to obtain up-to-date information on the TBEV prevalence in host-seeking I. ricinus in southern and central Sweden; (ii) to compile and review all relevant published records on the prevalence of TBEV in ticks in northern Europe; and (iii) to analyse and try to explain how the TBE virus can be maintained in natural foci despite an apparently low TBEV infection prevalence in the vector population.

Methods

To estimate the mean minimum infection rate (MIR) of TBEV in I. ricinus in northern Europe (i.e. Denmark, Norway, Sweden and Finland) we reviewed all published TBEV prevalence data for host-seeking I. ricinus collected during 1958–2011. Moreover, we collected 2,074 nymphs and 906 adults of I. ricinus from 29 localities in Sweden during 2008. These ticks were screened for TBEV by RT-PCR.

Results

The MIR for TBEV in nymphal and adult I. ricinus was 0.28% for northern Europe and 0.23% for southern Sweden. The infection prevalence of TBEV was significantly lower in nymphs (0.10%) than in adult ticks (0.55%). At a well-known TBEV-endemic locality, Torö island south-east of Stockholm, the TBEV prevalence (MIR) was 0.51% in nymphs and 4.48% in adults of I. ricinus.

Conclusions

If the ratio of nymphs to adult ticks in the TBEV-analysed sample differs from that in the I. ricinus population in the field, the MIR obtained will not necessarily reflect the TBEV prevalence in the field. The relatively low TBEV prevalence in the potential vector population recorded in most studies may partly be due to: (i) inclusion of uninfected ticks from the ‘uninfected areas’ surrounding the TBEV endemic foci; (ii) inclusion of an unrepresentative, too large proportion of immature ticks, compared to adult ticks, in the analysed tick pools; and (iii) shortcomings in the laboratory techniques used to detect the virus that may be present in a very low concentration or undetectable state in ticks which have not recently fed.

Tick-borne encephalitis in children and adolescents in the Czech Republic between 1960 and 2007

BACKGROUND

The Czech Republic ranks among the countries with the highest prevalence of tick-borne encephalitis worldwide. The region of West Bohemia has the second highest morbidity within the Czech Republic.

METHODS

Between 1960 and 2007, laboratories confirmed 410 cases of tick-borne encephalitis in children and adolescents of West Bohemia. Available epidemiological data were analyzed.

RESULTS

The highest incidence (per 100 000 population) was found in the group of 15-19 years for both genders (males: 6.2; females: 4.3). Data on the consumption of non-pasteurized milk were found in 5.4% of patients. The preschool age group showed its highest incidence in June and September, and the risk of infection for older children was in July and August.

CONCLUSIONS

The current low coverage of vaccination leads to an insignificant improvement to the overall frequency of this disease.

Why is tick-borne encephalitis increasing? A review of the key factors causing the increasing incidence of human TBE in Sweden

The highest annual incidence of human tick-borne encephalitis (TBE) in Sweden ever recorded by the Swedish Institute for Communicable Disease Control (SMI) occurred last year, 2011. The number of TBE cases recorded during 2012 up to 6th August 2012 indicates that the incidence for 2012 could exceed that of 2011. In this review of the ecology and epidemiology of TBE in Sweden our main aim is to analyse the possible reasons behind the gradually increasing incidence of human TBE during the last 20 years. The main TBE virus (TBEV) vector to humans in Sweden is the nymphal stage of the common tick Ixodes ricinus. The main mode of transmission and maintenance of TBEV in the tick population is considered to be when infective nymphs co-feed with uninfected but infectible larvae on rodents. In most locations the roe deer, Capreolus capreolus is the main host for the reproducing adult I. ricinus ticks. The high number of roe deer for more than three decades has resulted in a very large tick population. Deer numbers have, however, gradually declined from the early 1990s to the present. This decline in roe deer numbers most likely made the populations of small rodents, which are reservoir-competent for TBEV, gradually more important as hosts for the immature ticks. Consequently, the abundance of TBEV-infected ticks has increased. Two harsh winters in 2009-2011 caused a more abrupt decline in roe deer numbers. This likely forced a substantial proportion of the "host-seeking" ticks to feed on bank voles (Myodes glareolus), which at that time suddenly had become very numerous, rather than on roe deer. Thus, the bank vole population peak in 2010 most likely caused many tick larvae to feed on reservoir-competent rodents. This presumably resulted in increased transmission of TBEV among ticks and therefore increased the density of infected ticks the following year. The unusually warm, humid weather and the prolonged vegetation period in 2011 permitted nymphs and adult ticks to quest for hosts nearly all days of that year. These weather conditions stimulated many people to spend time outdoors in areas where they were at risk of being attacked by infective nymphs. This resulted in at least 284 human cases of overt TBE. The tick season of 2012 also started early with an exceptionally warm March. The abundance of TBEV-infective "hungry" ticks was presumably still relatively high. Precipitation during June and July was rich and will lead to a "good mushroom season". These factors together are likely to result in a TBE incidence of 2012 similar to or higher than that of 2011.

Tick-borne viruses in Europe

The aim of this review is to present briefly background information on 27 tick-borne viruses ("tiboviruses") that have been detected in Europe, viz flaviviruses tick-borne encephalitis (TBEV), louping-ill (LIV), Tyuleniy (TYUV), and Meaban (MEAV); orthobunyaviruses Bahig (BAHV) and Matruh (MTRV); phleboviruses Grand Arbaud (GAV), Ponteves (PTVV), Uukuniemi (UUKV), Zaliv Terpeniya (ZTV), and St. Abb's Head (SAHV); nairoviruses Soldado (SOLV), Puffin Island (PIV), Avalon (AVAV), Clo Mor (CMV), Crimean-Congo hemorrhagic fever (CCHFV); bunyavirus Bhanja (BHAV); coltivirus Eyach (EYAV); orbiviruses Tribec (TRBV), Okhotskiy (OKHV), Cape Wrath (CWV), Mykines (MYKV), Tindholmur (TDMV), and Bauline (BAUV); two thogotoviruses (Thogoto THOV, Dhori DHOV); and one asfivirus (African swine fever virus ASFV). Emphasis is laid on the taxonomic status of these viruses, range of their ixodid or argasid vectors and vertebrate hosts, pathogenicity for vertebrates including humans, and relevance to public health. In general, three groups of tibovirus diseases can be recognized according to main clinical symptoms produced: (i) febrile illness-usually with a rapid onset, fever, sweating, headache, nausea, weakness, myalgia, arthralgia, sometimes polyarthritis and rash; (ii) the CNS affection-meningitis, meningoencephalitis or encephalomyelitis with pareses, paralysis and other sequelae; (iii) hemorrhagic disease. Several "European" tiboviruses cause very serious human (TBEV, CCHFV) or animal (LIV, ASFV) diseases. Other arboviruses play definite role in human or animal pathology though the disease is usually either less serious or infrequently reported (TYUV, BHAV, AVAV, EYAV, TRBV, DHOV, THOV). The other European arboviruses are "orphans" without a proven medical or veterinary significance (BAHV, MTRV, MEAV, GAV, PTVV, ZTV, SAHV, UUKV, SOLV, PIV, AVAV, CMV, OKHV, CWV, MYKV, TDMV, BAUV). However, certain arbovirus diseases of free-living vertebrates (but also those of domestic animals and even man) may often pass unnoticed or misdiagnosed and eventually, they might potentially appear as emerging diseases. Active search for new tiboviruses or for new, pathogenic variants of the known tiboviruses in Europe should therefore continue.

Protection against tick-borne encephalitis (TBE) for people living in and travelling to TBE-endemic areas

Once considered a local health issue confined to certain regions in Russia and Central and Eastern Europe, tick-borne encephalitis (TBE) is now considered an international health concern, and the most important and widespread viral disease transmitted by ticks in Europe. The number of reported TBE cases continues to increase in many endemic regions, and new foci have been identified. Increases in travel, access to high-risk areas, and the pursuit of leisure activities within TBE-endemic areas are placing more people at risk of TBE. Travellers from non-endemic regions are often unaware of the risk of acquiring TBE and therefore many travellers are not protected against TBE. Active immunization is the most effective way to avoid TBE and its potentially life-threatening sequelae. After a tick bite, no post-exposure treatment including active/passive vaccination is available or recommended in the immunologically naive patient. Available vaccines have undergone a series of modifications and improvement in both composition (with special formulations for children) and schedules to further enhance the safety of immunization and to meet the needs of vaccinees. Efforts to develop internationally recognized recommendations for TBE vaccination for travellers are underway.

Tick-borne encephalitis

We review the epidemiological and clinical characteristics of tick-borne encephalitis, and summarise biological and virological aspects that are important for understanding the life-cycle and transmission of the virus. Tick-borne encephalitis virus is a flavivirus that is transmitted by Ixodes spp ticks in a vast area from western Europe to the eastern coast of Japan. Tick-borne encephalitis causes acute meningoencephalitis with or without myelitis. Morbidity is age dependent, and is highest in adults of whom half develop encephalitis. A third of patients have longlasting sequelae, frequently with cognitive dysfunction and substantial impairment in quality of life. The disease arises in patchy endemic foci in Europe, with climatic and ecological conditions suitable for circulation of the virus. Climate change and leisure habits expose more people to tick-bites and have contributed to the increase in number of cases despite availability of effective vaccines. The serological diagnosis is usually straightforward. No specific treatment for the disease exists, and immunisation is the main preventive measure.

Tick-borne encephalitis in Slovenia from 2000 to 2004: comparison of the course in adult and elderly patients

OBJECTIVE

To present epidemiological data and clinical characteristics of tick-borne encephalitis (TBE) in adult patients, and to compare findings in the subgroup over the age of 60 years with those aged 60 or under.

METHODS

The information for this retrospective study was obtained by review of medical documentation. All patients over 15 years of age hospitalized at the Department of Infectious Diseases, University Medical Center Ljubljana, Slovenia, between 2000 and 2004 with pleocytosis (cerebrospinal fluid leukocyte count >5 x 10(6) cells/l) and the presence of serum IgM antibodies against TBE virus qualified for inclusion in this report. Patients were divided into two groups according to their age (patients over the age of 60 were classified as seniors and those aged 60 or under as adults); the findings in the two groups were compared.

RESULTS

Of 448 patients with TBE, 318 were in the adult group and 130 in the senior group. Males predominated in both groups. A biphasic course of the illness was reported by 56% of patients. There were no significant differences in the majority of clinical parameters in the initial phase of TBE but several distinctions between adults and seniors were found in the second phase of the illness. Adults more often presented with fever, headache, stiff neck and photophobia, whereas seniors more frequently reported fatigue, altered consciousness and decreased muscle strength, these differences indicating a more classic course of TBE in the younger group and a somehow different and more severe acute disease in the older group. More severe acute disease and less favorable outcome in seniors was further corroborated by the occurrence of urine retention (18/318, 5.7% versus 27/130, 20.8%; P < 0.001), frequency of pareses (10/318, 3.1% versus 7/130, 5.4%; P = 0.002) and the need for antiedematous treatment (103/318, 32.4% versus 61/130, 46.9%; P = 0.005), as well as by the duration of treatment, duration of hospital stay and the death rate (0/318 versus 3/130, 2.3%; P = 0.024). Several distinctions were present also in laboratory findings, including higher cerebrospinal fluid leukocyte count in the adults than in the seniors (107 x 10(6) cells/l versus 47 x 10(6) cells/l; P < 0.001).

CONCLUSION

Direct comparison of the course and outcome of TBE revealed several distinctions between patients over 60 years of age and those aged 60 or under and corroborates previous assumptions that TBE is a more serious illness in the elderly population.

Study of the serological response after vaccination against tick-borne encephalitis in Sweden

The antibody response to vaccination against tick-borne encephalitis (TBE) with FSME-Immun Inject (Immuno AG/Baxter) was studied in 535 persons, mainly adults, attending a vaccination centre in Stockholm, Sweden. Emphasis was laid on long-term follow-up. Antibody activity was measured by three different serological test systems: a commercial ELISA kit, a hemagglutination inhibition (HI) test and a neutralization test (RFFIT). The neutralization test proved to be the most sensitive assay for the detection of the vaccine response, which was demonstrable in the majority of vaccinees (>90% after three and >98% after four and five vaccinations, respectively). ELISA and HI were less sensitive for antibody measurement during primary immunization. Neutralizing antibody activity persisted prior to the third dose in 77% of the vaccinees and prior to the fourth to sixth doses in 89-95% of the vaccinees. ELISA activity, but no neutralizing activity, was found in some individuals. Based on our data and previous experience of vaccine failures after two doses, a more condensed three-dose vaccination schedule may be advantageous and ought to be tested. The persistence of neutralizing antibodies justifies further studies of the antibody responses after the fourth dose for periods beyond the recommended 3-year booster intervals.

Severe tick-borne encephalitis in Slovenia in the years 2001–2005: Time for a mass vaccination campaign?

The aim of this retrospective study was to assess some clinical, epidemiological and laboratory parameters of severe tick-borne encephalitis in Slovenia in the last five years, to compare them with published data, and to estimate need for providing a policy of active immunization. Thirty-three adult patients with a severe course of the disease, admitted to the intensive care unit of the Department of Infectious Diseases, University Medical Centre Ljubljana, Slovenia during a five year period, participated. All the patients had specific serum IgM antibodies against tick-borne encephalitis virus at admissions and IgG antibodies were present in 29 out of 33 patients. Twenty-two patients were admitted because of severe consciousness disturbances, nine suffered from spinal nerve paralysis, in two patients cranial nerve paralysis was observed, and one suffered from generalized tonic-clonic seizures. Ten patients were mechanically ventilated and three died. Leukocytosis in peripheral veins was found in twenty-one patients and nine had a C-reactive protein serum concentration over 50 mg/l. Nineteen patients had a cerebrospinal fluid leukocyte count exceeding 100 x 10(6)/l and a cerebrospinal fluid protein concentration was over the cut-off value of 0.45 g/l in majority. The findings of the present study confirmed some previous reports about clinical, epidemiological and laboratory characteristics of patients with severe tick-borne encephalitis. We have found that tick-borne encephalitis in Slovenia has a relatively low fatality rate. However, the severe course with long-lasting sequelae of the disease justifies vaccination of a risk population in endemic areas.

Tick-borne encephalopathies : epidemiology, diagnosis, treatment and prevention

Tick-borne encephalopathies constitute a broad range of infectious diseases affecting the brain and other parts of the CNS. The causative agents are both viral and bacterial. This review focuses on the current most important tick-borne human diseases: tick-borne encephalitis (TBE; including Powassan encephalitis) and Lyme borreliosis. Rocky Mountain spotted fever (RMSF) and Colorado tick fever (CTF), less common tick-borne diseases associated with encephalopathy, are also discussed. TBE is the most important flaviviral infection of the CNS in Europe and Russia, with 10 000-12 000 people diagnosed annually. The lethality of TBE in Europe is 0.5% and a post-encephalitic syndrome is seen in over 40% of affected patients, often producing a pronounced impairment in quality of life. There is no specific treatment for TBE. Two vaccines are available to prevent infection. Although these have a good protection rate and good efficacy, there are few data on long-term immunity. Lyme borreliosis is the most prevalent tick-borne disease in Europe and North America, with >50 000 cases annually. Localised early disease can be treated with oral phenoxymethylpenicillin (penicillin V), doxycycline or amoxicillin. The later manifestations of meningitis, arthritis or acrodermatitis can be treated with oral doxycycline, oral amoxicillin or intravenous ceftriaxone; intravenous benzylpenicillin (penicillin G) or cefotaxime can be used as alternatives. The current use of vaccines against Lyme borreliosis in North America is under discussion, as the LYMErix vaccine has been withdrawn from the market because of possible adverse effects, for example, arthritis. RMSF and CTF appear only in North America. RMSF is an important rickettsial disease and is effectively treated with doxycycline. There is no treatment or preventative measure available for CTF.

Characterisation of human tick-borne encephalitis virus from Sweden

Viruses of the tick-borne encephalitis (TBE) antigenic complex, within the family Flaviviridae, cause a variety of diseases including uncomplicated febrile illness, meningo-encephalitis and haemorrhagic fever. Different wildlife species act as reservoir hosts with ixodid tick species as vectors. TBE virus (TBEV) causes 40-130 cases confirmed serologically in Sweden each year. Characteristics of TBEV strains circulating in Sweden have not been investigated previously and no viral sequence data has been reported. In the present study, virus strains were isolated from serum of patients with clinical symptoms consistent with acute TBEV infection. Serologic characterisation, using a panel of E-specific monoclonal antibodies and cross-neutralisation tests, indicated that the Swedish strains of TBEV, isolated 1958-1994, all belonged to the Western TBEV subtype, which includes the Austrian vaccine strain Neudoerfl. Genetic analysis of a partial E-sequence confirmed this close relationship: all Swedish TBEV strains belonged to the European lineage of the Western TBEV subtype, which includes the previously characterised strains Neudoerfl, Hypr, and Kumlinge. Further, three Swedish strains showed partial E-sequences identical to that of the Finnish Kumlinge strain, ten Swedish strains formed a well-supported separate cluster, whereas four others did not show any real clustering. No apparent correlation was observed in comparison of clinical parameters with genetic data or geographic origin of the strains.

Tick-borne encephalitis--pathogenesis, clinical course and long-term follow-up

The prospective studies available today confirm the experience gained from several retrospective studies that TBE is a disease with a severe acute clinical course and considerable long-term morbidity. A defined post-encephalitic TBE syndrome exists, causing long-lasting morbidity that often affects the quality of life and sometimes also forces the individual to a change in life-style. The sequelae render high costs for individual patients and the society. Three clinical courses may be identified: one with complete recovery within 2 months, occurring in approximately one fourth of patients, one with protracted, mainly cognitive dysfunction, and one with persisting spinal nerve paralysis with or without other post-encephalitic symptoms. Up to 46% of patients are left with permanent sequelae at long-time follow-up, the most commonly reported residuals being various cognitive or neuropsychiatric complaints, balance disorders, headache, dysphasia, hearing defects, and spinal paralysis. This knowledge enhances the need for continued local epidemiological surveillance of TBE to form a basis for vaccination policies. Even though knowledge of the clinical course of TBE has improved in recent years, there are still several aspects of this disease that warrant further studies. These comprise the clinical picture and prognosis in children, an evaluation of different rehabilitation strategies, and an improved understanding of pathogenic mechanisms to permit the development of antiviral or, maybe more probable, immune modulatory treatment strategies.

Epidemiology and ecology of TBE relevant to the production of effective vaccines

This review focuses on the epidemiology and ecology of the tick-borne encephalitis (TBE) virus including all the factors influencing the ecology of the TBE virus, environmental and climatic conditions, the vectors and reservoir hosts and their interactions. Consequently, the structure and the conditions of natural foci of TBE are described, as well. Special emphasis is given on data regarding the virus prevalence in ticks in the field. In the second part of this review all the epidemiological and surveillance data of TBE in the 27 European countries and in the Far East with risk areas of TBE and in China and Japan are summarised. Therefore the review is a basis for travellers and inhabitants to get background information for their personal risk assessment.

Report of the Meningitis Program of the International Scientific Working Group on TBE. Serological screening of patients with viral CNS-infection of unknown etiology in search of undiagnosed TBE cases

The endemicity of tick-borne encephalitis (TBE) in Europe is changing. Potential undetected or emerging TBEV foci and the risk of underdiagnosis due to a low awareness among the medical community form the background of this retrospective multicenter follow-up study. We investigated the possibility of undiagnosed TBE cases among patients with presumed viral central nervous system (CNS)-infection of unknown etiology. Eight centers in four European countries provided sera and/or cerebrospinal fluid (CSF) samples from 233 individuals. The samples were screened with a commercial TBEV ELISA test system (IgM and IgG). Positive or borderline samples were re-evaluated at the Institute of Virology in Vienna by an in-house ELISA test and a neutralization test (NT). Two previously undiagnosed Swedish TBE patients were verified. Three additional individuals from Swedish centers were IgG ELISA and NT positive. No NT positive individuals were found from France, Belgium or The Netherlands. Nineteen individuals were found IgG TBE ELISA positive, but negative in NT, indicating unspecific reactivity. At least four of those patients were vaccinated against yellow fever. The probable reason for the reactivity seen in these individuals is the well-known cross-reactivity existing among flaviviruses.

Occurrence of TBE in areas previously considered being non-endemic: Scandinavian data generate an international study by the International Scientific Working Group for TBE (ISW-TBE)

Tick-borne encephalitis virus (TBEV) has been endemic in many countries in central, northern and eastern Europe. More than 3000 human cases are reported annually, the Baltic states included. TBEV causes CNS infections presented as meningitis or meningoencephalitis with or without myelitis. The case fatality rate in Europe is approximately 0.5%, and up to 40% of the patients are left with long-lasting sequelae. The endemicity of TBE in Sweden has been stable over the years but during the last decade several new foci have been discovered. In Norway the first verified cases of TBE have now been found. The reason for this changing epidemiology of TBE is discussed.

Survival strategy of tick-borne encephalitis virus: cellular basis and environmental determinants

Although TBE virus can be transmitted in the laboratory by a wide variety of ixodid tick species to a wide variety of vertebrate host species, nevertheless in nature endemic cycles of TBE virus depend principally on just two tick species, Ixodes ricinus in the western and I. persulcatus in the eastern Palaearctic. A complete transmission cycle, from tick to tick via vertebrates, occurs most efficiently between co-feeding ticks in the absence of a systemic viraemia. This non-systemic route depends on TBE virus replication within particular immunocompetent cells in the skin, and only certain vertebrate species, notably Apodemus mice, are susceptible to this. Amongst the potential tick vectors in Europe, only I. ricinus has the correct host relationships and appropriate natural life cycle to support such non-systemic transmission cycles. Within the wide European distribution of this tick-host relationship, only in certain places do larval and nymphal ticks feed together on the same hosts with sufficient coincidence to ensure TBE virus survival. The environmental factors that determine this seasonal coincidence are being identified with the help of remotely-sensed meteorological satellite imagery to create predictive risk maps of TBE foci.

Intrathecal IgM, IgA and IgG antibody response in tick-borne encephalitis. Long-term follow-up related to clinical course and outcome

BACKGROUND

Tick-borne encephalitis (TBE) of western subtype causes long-term morbidity and is considered a health problem in Scandinavia, eastern and central parts of Europe and Russia. The pathophysiology is not fully elucidated. As TBE RNA is rarely demonstrable in cerebrospinal fluid (CSF) the kinetics of the CSF antibody response to the disease has attracted attention.

OBJECTIVES

To investigate the intrathecal TBE-specific antibody response and to correlate its intensity and persistence to the clinical course. To compare indirect, commercially-based ELISA methods indexed against albumin ratio or IgG ratio with the capture ELISA method for the establishment of CSF response.

STUDY DESIGN

The specific IgM, IgG and IgA antibody responses in serum and CSF were analysed in 69 Swedish patients included in a prospective study of TBE from the acute phase up to 11-13 months after onset.

RESULTS

Antibody response by all three classes was demonstrable in serum and CSF. All methods were useful, but capture technique was the most sensitive and results were easiest to interpret. Peak IgM activity was seen early during the disease and persisted after 6 weeks. Maximum IgG levels were encountered in late convalescent samples (median 6 weeks). Intrathecal antibody production was demonstrable in nearly all patients: in 41% days 0-6, in 97% days 7-19, in 98% days 21-61 and-at lower levels-in 84% of the patients after 1 year (50/52 of CSF-serum sampled in the interval 11-61 days). Day 9 after onset, patients with dominating encephalitic symptoms showed significantly lower intrathecal IgM activity. The persistence of serum and CSF antibodies did not correlate to severity of disease.

CONCLUSIONS

Capture IgM and IgG assays were superior to indirect ELISA. Low early CSF IgM response correlated to encephalitic symptoms, otherwise the intensity and duration of intrathecal antibody response were of limited value for the prediction of clinical course and long-term outcome.

Tick-bone encephalitis in Sweden in relation to aseptic meningo-encephalitis of other etiology: a prospective study of clinical course and outcome

A total of 149 patients with clinical symptoms of acute viral meningo-encephalitis were enrolled in this study from June 1991 to December 1993. Tick-borne encephalitis (TBE) was diagnosed in 85 of the 149 patients (males 54%, median age 42 years (range 15-78)). The initial clinical appearance of TBE was classified as mild (mainly meningeal; (n = 47), moderate (n = 31) or severe (n = 7), more or less encephalitic. The most common acute symptoms of encephalitis were ataxia (26%), altered consciousness (20%), decreased concentration or memory (9%), irritable response to light and sound (28%), tremor (9%) and dysphasia (9%). Spinal nerve paralysis (11%) occurred in all three clinical stages and did not correlate with the severity or duration of encephalitis. The duration of hospitalisation, the time on the sick-list and the time to recovery were significantly longer in TBE patients. All patients survived, but many patients with TBE suffered an extended period of neurological dysfunction. Of patients with TBE 80% (68/85) showed persisting symptoms of CNS dysfunction on follow-up at week 6, compared with 55% (35/64) of the patients with aseptic meningitis of other aetiology. The corresponding figures after 1 year were 40% (33/83) and 20% (13/64). One year after TBE 13 (28%) patients with initially mild, meningeal symptoms had decreased memory and decreased concentration capacity, dysphasia or ataxia. Spinal nerve paralysis persisted after 1 year in 5 of 9 patients with TBE. In conclusion, TBE in Sweden is associated with a significant morbidity and a post-TBE syndrome existed after 1 year in more than one third of the patients.

Clinical features and serology of 14 dogs affected by granulocytic ehrlichiosis in Sweden

The clinical features and the titres to Ehrlichia equi, E canis, E risticii, Rickettsia rickettsii and Borrelia afzelii in 14 Swedish dogs, in which ehrlichiosis was diagnosed on the basis of the presence of inclusions in granulocytes, are reported. Most of the dogs were moderately ill but made a rapid recovery after treatment with doxycycline. The dogs with inclusions were thrombocytopenic. Analysis of the antibody titres indicates that serology to E equi will remain the most appropriate serological test for granulocytic ehrlichiosis in Swedish dogs, until a specific test is developed for detecting the recently identified subspecies of Ehrlichia.

Flow cytometric analysis of lymphocytes in cerebrospinal fluid in patients with tick-borne encephalitis

INTRODUCTION

Cerebrospinal fluid (CSF) lymphocyte subsets were examined by flow cytometry in 33 patients with tick-borne encephalitis (TBE) in order to determine their values.

PATIENTS AND METHODS

Lymphocytes were isolated from CSF and lymphocyte subsets were determined: lymphocytes T (CD3+), lymphocytes B (CD19+), NK cells (CD3-CD56+), helper T cells (CD3+CD4+) and cytotoxic T cells (CD3+CD8+). The expression of IL-2 receptors (CD25+) and transferrin receptors (CD71+) on T cells and HLA-DR molecules on T cell subsets was examined. Furthermore, possible relationships among different TBE patient population variables (gender, age, severity of disease, duration of meningitis) were considered.

RESULTS

The analyses of the CSF lymphocyte population subsets are presented. Lymphocytes T (CD3+) were significantly higher in the CSF than in the peripheral blood as was the case with the T cells that expressed transferrin receptors (CD71). Lymphocytes B (CD19+) and NK cells (CD3-CD56+) prevailed in the peripheral blood. In the early course of the disease, a higher expression of HLA-DR molecules on T lymphocytes was observed, while later a higher expression of IL-2 receptors (CD25+) was observed.

DISCUSSION

Significant differences in lymphocyte subsets between the CSF and the peripheral blood were found. Significant time-dependent changes of CSF lymphocyte subsets during course of infection were observed. The results of the present study give us deeper insight into CNS cellular immunopathogenic mechanisms in patients with TBE.

Severe tick borne encephalomyelitis after tick bite and passive immunisation

Images

Geographic correlation of multiple sclerosis with tick-borne diseases

An arboviral theory of multiple sclerosis (MS) is presented. Although high MS rates correlate with the distribution of certain population, high rates also correlate with the distribution of Ixodes genus tick viruses. These ticks and viruses are globally distributed by polar-migrating seabirds which are important food sources for island and coastal communities with high MS. Investigation of tick-borne viruses, especially those found in seabirds, in MS is warranted.

A 10-year follow-up study of tick-borne encephalitis in the Stockholm area and a review of the literature: need for a vaccination strategy

143 people treated for tick-borne encephalitis (TBE) were included in a retrospective follow-up study. Sequelae and epidemiological characteristics in 114 individuals were analysed. The case fatality rate and the prevalence of residual paresis were low, 1.4 and 2.7%, respectively. However, 40 (35.7%) individuals were found to have a postencephalitic syndrome after a median follow-up time of 47 months, and a majority (77.5%) of these were classified as moderate to severe. Various mental disorders, balance and co-ordination disorders and headache were the most frequently reported symptoms. Increasing age was correlated to a longer duration of hospital stay, longer convalescence and increased risk of permanent sequelae. Results from a neuropsychiatric questionnaire showed marked differences between the subjects with sequelae compared to controls. 57% had noticed a tick bite before admission, and 48% were aware of at least one person in their environment who previously had contracted TBE. 79% were permanent residents or visited endemic areas often and regularly. In conclusion, we have found that TBE in the Stockholm area has a low case fatality rate, but gives rise to a considerable number of different neurological and mental sequelae, which justifies vaccination of a defined risk population in endemic areas.

Vector-borne viral diseases in Sweden--a short review

Ockelbo disease, caused by a Sindbis-related virus transmitted to man by mosquitoes, was first described in the central part of Sweden in the 1960s as clusters of patients with fever, arthralgia and rash. An average annual rate of 30 cases was recorded in the 1980s but no cases have been diagnosed during the last few years. Nephropathia epidemica (NE) characterized by fever, abdominal pain and renal dysfunction has been known to cause considerable morbidity in Sweden during the last 60 years but the etiologic agent (Puumala virus) was not isolated until 1983. This virus's main reservoir is the bank vole (Clethrionomys glareolus). NE is endemic in the northern two thirds of Sweden where more than a hundred cases are diagnosed each year. Tick-borne encephalitis transmitted by Ixodes ricinus ticks is restricted to the archipelago and Lake M-alaren on the east coast close to Stockholm. Between 30 and 110 cases are diagnosed every year. Inkoo virus, a California encephalitis group virus, has been isolated from mosquitoes in Sweden. The antibody prevalence to Inkoo virus is very high in a normal population, but no disease has as yet been associated with this virus in Sweden. Among the vector-borne virus diseases imported to Sweden, dengue is the most important, with approximately 50 cases recorded every year.

Intrathecal production of neopterin and beta 2 microglobulin in tick-borne encephalitis (TBE) compared to meningoencephalitis of other etiology

To study the pathophysiology of tick-borne encephalitis (TBE), the kinetics of neopterin and beta 2 microglobulin (beta 2M) production were measured in sequential, cerebrospinal fluid (CSF) and serum samples in 133 patients with aseptic meningoencephalitis (TBE, n = 72; non-TBE, n = 61). Intrathecal production of neopterin was demonstrable in all patients. Neopterin levels in CSF were elevated already at day 2: geometric mean value in TBE 36 nmol/l (range 1-253), in the non-TBE group 29 nmol/l (0.2-96). At day 9 and week 6 the neopterin level was significantly higher in TBE (86 (19-725) and 17 (4-122) nmol/l) than in non-TBE (28 (5-109) and 3 (0.2-58) nmol/l) (p < 0.001). After 1 year CSF levels were within the normal range. The beta 2M response in CSF followed the pattern of neopterin. The intensity and duration of neopterin and beta 2M was not correlated to the clinical course. Neopterin seems to be a more sensitive indicator of intrathecal T-cell response and inflammatory reaction than beta 2M. The results indicate that a long-lasting strong inflammatory reaction is of pathophysiological significance in TBE.

Risk of infections transmitted by arthropods and rodents in forestry workers

One hundred and fifty-one forestry workers and 151 matched office clerks were compared as to the presence of antibodies against Borelia burgdorferi, tick-borne encephalitis virus, Puumalavirus and lymphocytic choriomeningitis virus. Their occupational risks of being infected by Borrelia was fourfold and significant, by Puumalavirus and lymphocytic choriomeningitis virus was increased but not significant. No seropositivity has been established against tick-borne encephalitis virus.