Non-viraemic transmission of tick-borne encephalitis virus: a mechanism for arbovirus survival in nature

The vectors of arthropod-borne viruses (arboviruses) become infected by feeding on the viraemic blood of an infected animal. This theory is based on transmission studies involving artificial infection of vertebrate hosts by syringe inoculation. To reproduce natural conditions of virus transmission, infected and uninfected vectors (ticks) of tick-borne encephalitis virus, the most important arbovirus in Europe, were allowed to feed together on uninfected wild vertebrate hosts. The greatest numbers of infected ticks were obtained from susceptible host species that had undetectable or very low levels of viraemia. The results suggest that 'nonviremic transmission' is an important mechanism for the survival of certain arboviruses in nature.

Construction and characterization of chimeric tick-borne encephalitis/dengue type 4 viruses

Dengue type 4 virus (DEN4) cDNA was used as a vector to express genes of the distantly related tick-borne encephalitis virus (TBEV). Full-length chimeric TBEV/DEN4 cDNAs were constructed by substituting TBEV genes coding for proteins such as capsid (C); pre-membrane, which is the precursor of membrane (M); envelope (E); or nonstructural protein NS1 for the corresponding DEN4 sequences. RNA transcripts prepared from cDNAs were used to transfect permissive simian cells. Two viable chimeric viruses that contained TBEV CME or ME genes were recovered. Compared with DEN4, chimeric TBE(ME)/DEN4 virus [designated vTBE(ME)/DEN4] produced larger plaques and grew to higher titer in simian cells. In contrast, vTBE(ME)/DEN4 produced smaller plaques on mosquito cells and grew to lower titer than DEN4. Analysis of viral RNA and proteins produced in vTBE(ME)/DEN4- and DEN4-infected mosquito or simian cells revealed that the chimera was restricted in its ability to enter and replicate in mosquito cells. In contrast, vTBE(ME)/DEN4 entered simian cells efficiently and its RNA was replicated more rapidly in these cells than was parental DEN4 RNA. Following intracerebral inoculation, vTBE(ME)/DEN4 caused fatal encephalitis in both suckling and adult mice, while nearly all mice inoculated by the same route with DEN4 did not develop disease. Unlike wild-type TBEV, vTBE(ME)/DEN4 did not cause encephalitis when adult mice were inoculated by a peripheral route. Adult mice previously inoculated with the chimera by a peripheral route were completely resistant to subsequent intraperitoneal challenge with 10(3) times the median lethal dose of TBEV, whereas mice previously inoculated with DEN4 were not protected. These findings indicate that (i) the TBEV M and E genes of the chimeric virus are major protective antigens and induce resistance to lethal TBEV challenge and (ii) other regions of the TBEV genome are essential for the ability of this virus to spread from a peripheral site to the brain. Success in constructing a viable TBEV/DEN4 chimera that retains the protective antigens of TBEV but lacks its peripheral invasiveness provides a strategy for the development of live attenuated TBEV vaccines.

The importance of tick-borne encephalitis virus RNA detection for early differential diagnosis of tick-borne encephalitis

BACKGROUND

Tick-borne encephalitis virus (TBEV) is one of the most important causes of human viral infections of the central nervous system in Europe. Currently, the diagnosis of TBE is based on the demonstration of specific antibodies in patient's serum, which appear only several weeks after the infection.

OBJECTIVE

To determine how successfully can viral RNA be detected by RT-PCR in the samples of body fluids of patients with TBE prior to and after the appearance of antibodies.

STUDY DESIGN

Serum, whole blood and CSF samples from 34 patients with a serologically confirmed TBE were collected. Samples were tested for the presence of TBEV RNA by using RT-PCR method.

RESULTS

Viral RNA was detected in all blood and serum samples collected before the development of antibodies. After the appearance of IgM antibodies, the number of positive samples dropped by at least one third. After the development of IgG antibodies, only 3% of serum and 16% of blood samples tested positive for viral RNA. Samples of cerebrospinal fluid were shown to be inappropriate for the molecular diagnosis of TBE using this assay, since only one sample (10%) that was collected in the sero-negative phase of disease was found positive by the PCR assay.

CONCLUSIONS

RT-PCR is an efficient method for an early detection of TBEV in blood and serum samples collected prior to the appearance of antibodies. This method can be of valuable use for a differential diagnosis of TBEV infection in patients with febrile illness after a tick bite, particularly in regions where more than one tick-transmitted diseases are endemic.

The molecular biology of tick-borne encephalitis virus. Review article

Tick-borne encephalitis (TBE) virus is a member of the flavivirus genus and the family Flaviviridae. Like other flaviviruses such as yellow fever, Japanese encephalitis or the dengue viruses, it is an important human pathogen, endemic in many European countries, Russia and China. The disease can be effectively prevented by vaccination with a formalin-inactivated whole virus vaccine. In recent years major advances have been made in the understanding of the molecular biology of TBE virus, including the complete sequence analysis of the genomic RNA of the European and Far Eastern strains. As shown in these studies, the virion RNA contains a single long open reading frame that codes for the structural proteins at the 5' end and the nonstructural proteins at the 3' end. Co- and posttranslational cleavages by a viral and cellular proteases lead to the formation of individual viral proteins. The mature virion is composed of an isometric capsid surrounded by a lipid envelope with two membrane-associated proteins. One of these, protein E, is of paramount importance for several important viral functions, especially during the entry phase of the viral life cycle. Protein E is also responsible for the induction of a protective immune response. A detailed map of antigenic sites has been established and the structure of an anchor-free form of E is currently being investigated by X-ray diffraction analysis. Understanding the molecular basis of the functions of this protein together with the knowledge of its three-dimensional structure may provide clues for developing specific antiviral agents. Protein E has also been shown to be an important determinant of virulence, with single amino acid substitutions at selected sites leading to attenuation. Engineering of such mutations into cDNA clones to produce new recombinant viruses may open up new avenues for the development of live vaccines.

Evidence of Babesia microti infection in multi-infected Ixodes persulcatus ticks in Russia

To detect Babesia-infected Ixodes persulcatus Shulze in a suburb of St. Petersburg, Russia, 738 adult ticks were studied using Babesia specific primers and PCR techniques. The entire sample (more than 1,200 individuals) was screened for the presence of Borrelia spp., Ehrlichia spp. and tick-borne encephalitis virus (TBEV). All 7 ticks infected with Babesia microti, were also infected with other pathogens (all 7 among 417 infected ticks, zero amongst the remaining 321 naive ones (chi2 = 5.25, p<0.05). Babesia microti occurred twice with Borrelia afzelii, 3 times with Borrelia garinii, once with both, and once with both B. garinii and TBEV. The prevalence of infection with Borrelia spp. was 34.0%, with Ehrlichia spp. 6.2%, with TBEV 1.5%, and with Ba. microti 0.9%. Babesia microti infection was not found in combination with Ehrlichia sp. or Borrelia burgdorferi sensu stricto. The latter pathogen (prevalence 2.6%), just like Ba. microti, was not encountered as a monoinfection. The data suggest that Ba. microti infection can only survive in I. persulcatus in combination with Borrelia spp. (7 of 7 infections). The disease in humans is more severe and longer-lasting when more than one pathogen is involved. Our observations show that the well known St. Petersburg focus of tick-borne encephalitis and Lyme disease is also a focus of ehrlichiosis and babesiosis.

Classification of a new member of the TBE flavivirus subgroup by its immunological, pathogenetic and molecular characteristics: identification of subgroup-specific pentapeptides

The antigenic, pathogenic and molecular characteristics of Turkish sheep encephalitis (TSE) virus, strain TTE80, were compared with other members of the tick-borne encephalitis (TBE) virus complex. Monoclonal antibodies with defined specificity for the flavivirus envelope glycoprotein distinguished TSE virus from louping ill (LI), western or far eastern TBE, Langat and Powassan virus in indirect immunofluorescence, haemagglutination-inhibition and neutralization tests. On the other hand, TSE virus, which produces an LI-like disease in sheep, resembled LI virus in mouse neurovirulence tests. Molecular homology data of all the structural genes of TSE virus compared with other tick-borne flaviviruses demonstrated that TSE virus is a distinct member in the TBE virus subgroup. The data are consistent with the conclusion that TSE virus has evolved by a separate evolutionary pathway as compared with the close antigenic relatives, western European, far eastern TBE viruses and LI virus. By aligning the encoded amino acids in the viral envelope glycoprotein of mosquito- and tick-borne flaviviruses, we have also identified subgroup-specific pentapeptide motifs for the tick-borne encephalitis, Japanese encephalitis and dengue subgroup viruses of the genus Flavivirus. These pentapeptides have important implications for the evolution, classification and diagnosis of flaviviruses.

Infection of Macaca radiata with viruses of the tick-borne encephalitis group

Our studies confirmed the susceptibility of Macaca radiata (bonnet macaques) to Kyasanur Forest disease (KFD) and enabled us to demonstrate KFD virus-specific gastrointestinal and lymphoid lesions. Significant histopathological changes occurred in the small and large intestine, spleen and lymph nodes; and viral antigens were found in these same organs by immunohistochemistry. Viral antigen-positive cells were always associated with histological evidence of necrosis, which suggests that cell death occurred directly from viral replication or secondarily from attack by immune mechanisms. In contrast, M. radiata infected with Omsk virus did not show any signs of clinical disease, and no virus could be isolated from tissues or blood at the end of the experiment. However, M. radiata infected with Russian spring-summer encephalitis (RSSE) developed clinical signs in the central nervous system; and, in one monkey, RSSE virus was isolated from the brain, and viral antigen was localized in neurons. Our data indicate that M. radiata is an excellent model to study human disease caused by KFD virus and could serve as a model for human disease caused by other, related strains of this group of viruses.

Deep Sequencing Analysis of the Ixodes ricinus Haemocytome

BACKGROUND

Ixodes ricinus is the main tick vector of the microbes that cause Lyme disease and tick-borne encephalitis in Europe. Pathogens transmitted by ticks have to overcome innate immunity barriers present in tick tissues, including midgut, salivary glands epithelia and the hemocoel. Molecularly, invertebrate immunity is initiated when pathogen recognition molecules trigger serum or cellular signalling cascades leading to the production of antimicrobials, pathogen opsonization and phagocytosis. We presently aimed at identifying hemocyte transcripts from semi-engorged female I. ricinus ticks by mass sequencing a hemocyte cDNA library and annotating immune-related transcripts based on their hemocyte abundance as well as their ubiquitous distribution.

METHODOLOGY/PRINCIPAL FINDINGS

De novo assembly of 926,596 pyrosequence reads plus 49,328,982 Illumina reads (148 nt length) from a hemocyte library, together with over 189 million Illumina reads from salivary gland and midgut libraries, generated 15,716 extracted coding sequences (CDS); these are displayed in an annotated hyperlinked spreadsheet format. Read mapping allowed the identification and annotation of tissue-enriched transcripts. A total of 327 transcripts were found significantly over expressed in the hemocyte libraries, including those coding for scavenger receptors, antimicrobial peptides, pathogen recognition proteins, proteases and protease inhibitors. Vitellogenin and lipid metabolism transcription enrichment suggests fat body components. We additionally annotated ubiquitously distributed transcripts associated with immune function, including immune-associated signal transduction proteins and transcription factors, including the STAT transcription factor.

CONCLUSIONS/SIGNIFICANCE

This is the first systems biology approach to describe the genes expressed in the haemocytes of this neglected disease vector. A total of 2,860 coding sequences were deposited to GenBank, increasing to 27,547 the number so far deposited by our previous transcriptome studies that serves as a discovery platform for studies with I. ricinus biochemistry and physiology.

Tickborne encephalitis outbreak in Estonia linked to raw goat milk, May-June 2005

In May and June 2005, 27 cases of tickborne encephalitis (TBE) were reported to the Estonia’s Tervisekaitseinspektsioon

Purification and analysis of infectious virions and native non-structural antigens from cells infected with tick-borne encephalitis virus

By employing the techniques of column chromatography and membrane filtration, we have succeeded in purifying flavivirus particles with low particle to infectivity ratios and free from contamination with cellular proteins. Virus particles purified by this method have an average diameter of 53 nm, a particle to infectivity ratio of less than 10, and a KD (partition coefficient) consistent with a molecular weight of 2.63 x 10(7). In addition it has been possible to purify the extracellular form of non-structural protein 1 (NS1), which in its native form appears to be a hexamer. It is also apparent from these studies that the slowly sedimenting haemagglutinin particle (or SHA) is an artifact of purification methods using gradient centrifugation. This technology should not only prove useful in the laboratory for studying the detailed structure of these viruses and the proteins encoded by them, but should also prove useful in industrial vaccine manufacture where large volumes of highly pathogenic material are handled.

Nucleotide sequence of the envelope protein of a Turkish isolate of tick-borne encephalitis (TBE) virus is distinct from other viruses of the TBE virus complex

Turkish tick-borne encephalitis (TTE) virus causes an acute form of meningoencephalomyelitis in sheep in the north-western region of Turkey. The clinical syndrome resembles louping ill (LI) and the viruses responsible for both LI and TTE are members of the tick-borne encephalitis (TBE) complex of the Flaviviridae. The envelope protein gene of TTE virus was reverse-transcribed, amplified, cloned and sequenced. Alignment of the resultant sequence with those from other viruses of the TBE complex reveals that TTE virus is more closely related, at both nucleotide and amino acid levels (84.6% and 96% respectively), to the Central European (CEE) subtype of the TBE virus, usually associated with human disease. The relationship with LI virus is more distant (83% and 93.5% respectively). These studies support the assertion that the ovine encephalomyelitis found in Turkey is caused by a virus that is genetically distinct from known strains of both LI and CEE viruses and from a number of other known viruses of the TBE complex.

Experimental encephalitis in monkeys caused by the Powassan virus

We have carried out a comparative study of the experimental infection of monkeys with the P-40 strain of the Powassen virus, isolated in the Primor'e Territory of the USSR, and with the Canadian prototype LB strain. The Powassan virus was found to be pathogenic for Macaca rhesus. The clinical and pathomorphological picture of the experimental encephalitis was studied, and the full identity of the infection produced in the monkeys by the P-40 strain and the Canadian LB strain of the Powassan virus was demonstrated. On electron microscopic examination of the central nervous system the virus was detected in the neurons, glial cells, and intercellular spaces. The virions of the strains studied have identical morphological parameters, being 37-45 nm in diameter and of spherical shape. The data obtained indicated a marked neurotropism of the virus. They will contribute to the elucidation of the role of the virus in the infection pathology of humans, i.e., in the differentiation of encephalitis cases not associated etiologically with the virus of the spring-summer tickborne encephalitis.

Etiology of tick-borne febrile illnesses in adult residents of north-eastern Poland: Report from a prospective clinical study

Febrile tick-borne diseases can be caused by different pathogens. The study objective was to prospectively determine the etiology of infection among adults exposed to tick bite and to detect acute human granulocytic anaplasmosis (HGA), a recently emerging infection, in north-eastern Poland. We evaluated 68 patients (34 males and 34 females, mean age 44.2+/-15 years) who had fever within 4 weeks after a tick bite. Paired sera were tested for antibodies against tick-borne encephalitis virus, Borrelia burgdorferi and Anaplasma phagocytophilum. Microscopic examination of EDTA whole blood and nested PCR targeting A. phagocytophilum 16S rDNA gene fragment were carried out at enrolment. Tick-borne infections were diagnosed in 57 individuals (84%). Sixty-four patients were hospitalised. Tick-borne encephalitis (TBE) was revealed in 49 cases; in 39 patients as a single infection, in three patients concurrent with erythema migrans or other Lyme borreliosis symptoms, in five patients concurrent with probable or possible Lyme borreliosis, and in two patients concurrent with A. phagocytophilum infection. Diagnosis of HGA was confirmed in one patient by PCR and in another one by seroconversion. In two further individuals, A. phagocytophilum infection was confirmed by immunofluorescence (antibody titers > or = 1:128), which, however, does not fulfil the ESCAR (European Society of Clinical Microbiology and Infectious Diseases Study Group on Coxiella, Anaplasma, Rickettsia, and Bartonella) criteria for HGA case definition. Lyme borreliosis was diagnosed in 16 patients; in six of them as a single infection. Both confirmed HGA cases and seropositive individuals had A. phagocytophilum infection concurrent either with Lyme borreliosis (two cases) or with TBE (two cases). The clinical course was severe in three and moderate to mild in the remaining TBE cases, as well as in all Lyme borreliosis and HGA cases. TBE was found the most prevalent disease among adults with febrile illnesses occurring after a tick bite in north-eastern Poland. Concurrent tick-borne infections were frequent with multiple pathogens involved. Two confirmed acute HGA cases (fulfilling the European case definition criteria defined by ESCAR) were detected for the first time in a prospective manner in Poland.

Pathogenesis and immune response of vaccinated and unvaccinated rhesus monkeys to tick-borne encephalitis virus

The rhesus monkey was used as a model for diseases caused by viruses of the tick-borne encephalitis virus complex to study the efficacy and safety of a commercial killed vaccine. Animals infected intravenously developed a subclinical infection with no histopathological lesions but with transient clinical chemical changes that included elevated transaminase, dehydrogenase, and creatine kinase activities and that declined as an immune response developed. The immune response was detected as neutralizing antibody in serum and serum antibody to several viral proteins. Antibodies to viral envelope protein and two other infected cell-specific polypeptides were also detected. Intranasal infection resulted in a disease resembling that in humans, except that no pyrexia was observed. Clinical chemical changes similar to those in intravenously infected monkeys developed, but most animals died before an immune response was mounted. Using this model, we have demonstrated that a commercial vaccine protects animals against a wild-type virus isolate and that it elicits an effective immune reaction without any evidence of an immune enhancement phenomenon or adverse side effects as judged by clinical observation, clinical chemistry, and histopathology.

Powassan virus infection in snowshoe hares (Lepus americanus)

Sera from snowshoe hares (Lepus americanus) trapped near Rochester, Alberta, Canada were tested for Powassan virus antibody by the constant virus/serum dilution neutralization test. Of 1264 serum samples tested, 137 had an antibody titer of at least 1:4 for Powassan virus. Ten hares were inoculated with Powassan virus in the laboratory. Viremia lasted 4-5 days and ceased with the appearance of Powassan antibody in the serum. Neutralizing antibody reached a peak titer of 1:119 on day 15 post-inoculation and was still detectable 13 months post-inoculation.

Experimental infection of lambs with tick-borne encephalitis virus and co-infection with Anaplasma phagocytophilum

Tick-borne encephalitis virus (TBEV) is a zoonotic pathogen which may cause tick-borne encephalitis (TBE) in humans and animals. More than 10,000 cases of TBE are reported annually in Europe and Asia. However, the knowledge on TBE in animals is limited. Co-infection with Anaplasma phagocytophilum and louping ill virus (LIV), a close relative to TBEV, in sheep has been found to cause more severe disease than single LIV or A. phagocytophilum infection. The aim of this study was to investigate TBEV infection and co-infection of TBEV and A. phagocytophilum in lambs. A total of 30 lambs, aged five to six months, were used. The experiment was divided into two. In part one, pre- and post-infection of TBEV and A. phagocytophilum was investigated (group 1 to 4), while in part two, co-infection of TBEV and A. phagocytophilum was investigated (group 5 and 6). Blood samples were drawn, and rectal temperature was measured daily. Lambs inoculated with TBEV displayed no clinical symptoms, but had a short or non-detectable viremia by reverse transcription real-time PCR. All lambs inoculated with TBEV developed neutralizing TBEV antibodies. Our study is in accordance with previous studies, and indicates that TBEV rarely causes symptomatic disease in ruminants. All lambs inoculated with A. phagocytophilum developed fever and clinical symptoms of tick-borne fever, and A. phagocytophilum was present in the blood samples of all infected lambs, shown by qPCR. Significantly higher mean TBEV titer was detected in the group co-infected with TBEV and A. phagocytophilum, compared to the groups pre- or post-infected with A. phagocytophilum. These results indicate that co-infection with TBEV and A. phagocytophilum in sheep stimulates an increased TBEV antibody response.

Viraemia and antibody response of the mallard (Anas platyrhynchos) to infection with tick-borne encephalitis virus

The course and intensity of viraemia after experimental infection with a TBE virus was studied in mallards of varying age and weight. Although virus titres in the blood can range from log102.65 to log104.85, in general these titres are believed to be of sufficient magnitude to infect ticks with the virus. Neutralizing antibodies in the serum of ducks are long-lasting and of sufficient titre to prevent a second viraemia. That mallards can play a role in the epidemiology of TBE virus is likely. Although some ducklings died in unexplained circumstances, none of the infected mallards showed overt disease.

Dose-dependent viremia and the differential immunoglobulin response of hamsters to Powassan virus

Hamsters injected subcutaneously with a single "low-dose" inoculum (10 mouse LD50) of Powassan virus developed viremia titering 106.2 mouse LD50 per milliliter of blood whereas hamsters receiving a "high-dose" inoculum of 105.0 mouse LD50 of virus developed a viremia of only 104.5 mouse LD50 per milliliter.Hemagglutination-inhibiting (HI) antibodies were first detected 7 days following the "low-dose" inoculation and attained maximum titers of 160. The HI antibody response to the "high-dose" virus inoculation began on the 5th day, at a time when viremia was present, and antibody titers did not exceed 40. Sucrose-density analysis and 2-mercaptoethanol treatment of sera revealed that IgM antibodies were induced by both inocula but animals receiving a low dose of virus produced higher IgG responses than did animals receiving a high dose of virus. Neutralizing antibodies, which did not appear until 30 days post inoculation, were present at a log neutralizing index (NI) of 2.0 at 60 days in animals receiving 10 mouse LD50 of virus and at a log NI of 1.0 in those receiving 105.0 mouse LD50. The NI of IgG was equal to the index for total gamma globulin in samples that contained both IgM and IgG as demonstrated by the HI test.Animals originally exposed to a "low-dose" inoculum produced a more prolonged anamnestic response when challenged 63 days later with 105.0 mouse LD50 of virus than did animals receiving a second inoculum containing only 103.0 or 10 mouse LD50 of virus. In contrast, poor secondary antibody responses were elicited by challenge doses of 105.0, 103.0, or 10 mouse LD50 of virus in animals that originally had received a "high-dose" of virus. IgM and IgG classes of antibody were induced in all secondary responses and the log NI of each group of animals was elevated by about 1 during anamnesis.

Morphological demonstration of the virus of tick-borne encephalitis in the human brain

A case is presented in which the fourfold increase of the HI titer during the progression of the disease, and an increase in IgM content found at the beginning of the second week of the disease confirmed the diagnosis of tick-borne encephalitis. The light microscopic changes correspond to the findings accepted as characteristic to tick-borne encephalitis. Viruses, morphologically belonging to the Flavivirus genus were found by electron microscopy in the thalamus, substantia nigra, and cerebellum of the dissected brain. This paper presents the first demonstration of the virus in a case of a human tick-borne encephalitis.

Problems in the study and prophylaxis of mixed infections transmitted by ixodid ticks

The spread of mixed infections with natural focality transmitted by ixodid ticks is a normal phenomenon attributable to trends in the relationships of different pathogens in the vector organism and ecosystem as a whole. Any disease developing as a result of tick bite should be regarded as a potentially mixed infection. Clinically, tick-borne mixed infections proceed more severely than the corresponding diseases caused by a single agent. The residual course of the disease may sometimes be accounted for by the persistence of two or even several pathogens. This implies the necessity of a comprehensive approach to the study, diagnosis, treatment, management and prophylaxis of infections belonging to this group.

Tickborne encephalitis epidemiology in Estonia, 1950-2004

The first case of tickborne encephalitis (TBE) in Estonia was reported in 1950 in the south of the country. Since that time, TBE has spread and today it is endemic in Estonia.

Occurrence of antibodies to Anaplasma phagocytophilum in patients with suspected tick-borne encephalitis

INTRODUCTION AND OBJECTIVES

Human granulocytic anaplasmosis (HGA) is an emerging tick-borne infectious disease caused by Anaplasma phagocytophilum. In Europe, the first serological evidence of HGA was described in 1995 in Switzerland, and the first clinical case was confirmed in 1997 in Slovenia. Since then, many European countries, including Slovakia, have reported the occurrence of HGA. The aim of this study was to examine the occurrence of IgG antibodies against A. phagocytophilum in blood sera of humans with suspected tick-borne encephalitis.

MATERIAL AND METHODS

181 people were examined for the presence of anti-A. phagocytophilum IgG antibodies; 113 were patients with suspected TBE (65 males, 48 females), and 68 from the control group (18 males, 50 females). Respondents were aged 2-80 years (mean age: 31.39; STD: 17.1). Anti-A. phagocytophilum IgG antibodies were detected by the IFA IgG test. Relative risk (RR) and their 95% confidence intervals (95% CI) were estimated for the occurrence of IgG A. phagocytophilum antibodies.

RESULTS

Of the total number of 181 people examined, 32 (17.7%) showed positive for IgG antibodies against A. phagocytophilum, 22 of whom were patients with suspected TBE (19.5%) and 10 people from control group (14.7%). The RR of occurrence of IgG A. phagocytophilum was 1.3-times higher in the patients with suspected TBE than in the control group.

CONCLUSION

None of the examined patients with suspected TBE had the disease confirmed. Hoever, as shown by the results, the relative risk of occurrence of anaplasmosis is higher in people examined for some another vector-borne disease (in this case TBE). Therefore, the performance of screening examinations in patients suspected of having any tick-borne disease is very important.