[Ixodes tick-borne borreliosis and tick-borne encephalitis in the Udmurt republic: retrospective analysis of their spread]

The primary clinical-anamnestic and laboratory data on 1,062 cases, registered in Udmurtia in 1965-1968 and caused by the bites of taiga ticks (ixodes persulcatus), were retrospectively analyzed. The study revealed that not less than 27% of these cases could be regarded as cases of Ixodes tick-borne borreliosis (ITBB); formerly they were classified with tick-born encephalitis (TBE) or diseases of unclear etiology. The spread of ITBB on the territory of the Udmurt Republic was shown to be similar to that of TBE.

[Interrelations between Ixodes persulcatus ticks and the tick-borne encephalitis virus of the red vole (Clethrionomys rutilis) in western Siberia]

We present the data of 12-year survey (1989-2001) of the red vole population in southeastern West Siberia, including estimation of host relative numbers, abundance of immature taiga ticks, and percentage of animals with antigemagglutitnins against tick-borne encephalitis (TBE) virus. We discuss the role of demographic groups of voles as tick's hosts and their participation in the maintenance of TBE causative agent population. The estimation of spontaneous TBE infection rate in summer as well as in winter and early spring seasons, which have been made using a set of molecular-biological, serological and virological methods, demonstrates that a high proportion of red voles maintain non-pathogenic TBE causative agent over a long time, presumably, in the form of persistent infection.

Dynamics of infection in tick vectors and at the tick–host interface

Tick-borne flaviviruses are common, widespread, and successfully adapted to their mode of transmission. Most tick vectors of flaviviruses are ixodid species. These ticks are characterized by a comparatively long life cycle, lasting several years, during which the infecting virus may be maintained from one developmental stage of the tick to the next. Hence ticks act as highly efficient reservoirs of flaviviruses. Many tick-borne flaviviruses are transmitted vertically, from adult to offspring, although the frequency is too low to maintain the viruses solely in the tick population. Instead, the survival of tick-borne flaviviruses is dependent on horizontal transmission, both from an infected tick to a susceptible vertebrate host and from an infected vertebrate to uninfected ticks feeding on the animal. The dynamics of transmission and infection have traditionally been considered in isolation: in the tick, following virus uptake in the infected blood meal, infection of the midgut, passage through the hemocoel to the salivary glands, and transmission via the saliva; and in the vertebrate host, virus delivery into the skin at the site of tick feeding, infection of the draining lymph nodes, and dissemination to target organs. However, there is now compelling evidence of a complex interaction between the tick vector and its vertebrate host that affects virus transmission profoundly. The feeding site in the skin is a battleground in which the hemostatic, inflammatory, and immune responses of the host are countered by antihemostatic, anti-inflammatory, and immunomodulatory molecules (mostly proteins and peptides) secreted in tick saliva. Here we speculate that exploitation of the tick pharmacopeia, rather than development of viremia, is the key step in successful tick-borne flavivirus transmission.

[Half century of the TBE in Poland]

The article presented short information about history of TBE in Poland. Data connected to epidemiology, clinic and prevention of TBE are presented.

[Studies on the importance of tick-borne encephalitis in Rhineland-Pfalz]

Within the scope of a prospective clinical study during 2001 in Rhineland-Palatinate specimen from sera and cerebrospinal fluids of 163 patients with suspected meningitis were controlled in an enzyme immunoassay concerning a TBE infection. Questionable results were checked via a neutralisation test. In no case such an infection was confirmed. No virus specific nucleic acids could be detected in 998 nymphs and adults of Ixodes ricinus in an additional investigation in 2000. Therefore Rhineland-Palatinate has to be considered as a region with low virus prevalence. A general recommendation for vaccination is not necessary.

[Comparative characterization of a risk for infection with tick-borne encephalitis in the foci with different regional confinement]

A comparative study of the foci of tick-borne encephalitis (TBE) has revealed that the infectivity of vectors taiga ticks (Ixodes persulcatus) plays the leading role in the formation of foci with the highest epidemic activity (including forest steppe ones). The morbidity rates in each regional focus are directly related to the number of tick-bitten persons and to the quantity of the vector.

[Tick-borne neurological diseases]

Some microorganisms transmitted to man via tick bite are responsible for infections, which can be associated with neuro-meningeal complications. TBE virus is the most frequent virus associated with potentially severe neurological lesions. No treatment is available so far. The most frequent bacterial diseases in which neurological complications may appear are Lyme borreliosis, Q fever and some rickettsial infections. More recently ehrlichiosis have emerged as new infections that may be associated with neuro-meningeal complications. Appropriate antibiotic therapy may be used for the treatment of these bacterial infections, but no vaccine is available so far.

[New molecular biology detection methods for tick-borne infectious agents]

Tick-borne zoonotic pathogens are well known in many areas all over the world. Among the tick-borne transmitted diseases in Switzerland, Lyme disease caused by Borrelia burgdorferi, ehrlichiosis caused by various species of Ehrlichia and tick-borne encephalitis caused by the tick-borne encephalitis virus (TBEV) are the most important zoonotic diseases. Early diagnosis and treatment is necessary to prevent fatal infections and chronic damage to various tissues. Due to the variety of uncharacteristic clinical signs, tick-borne diseases are not easily recognized. Diagnosis is based on clinical findings, a record of tick exposure, and direct or indirect detection of the pathogen. Here we discuss briefly the most important tick-borne infections and their diagnosis with emphasis on a new molecular diagnostic tool--the real-time TaqMan PCR--and its importance for the diagnosis of tick-borne pathogens.

Diagnostics of tick-borne diseases in the endemic region of Russia

A clinical-laboratory survey of 1952 patients with acute feverish diseases developing after tick bite was carried out in the Pre-Ural region of Russia, which is endemic for tick-borne encephalitis and ixodid tick-borne borreliosis, in 1999-2001. Enzyme-linked immunosorbent assay and indirect immunofluorescence assay were used for the detection of tick-borne encephalitis, ixodid tick-borne borreliosis and ehrlichiosis specific antibodies. Tick-borne encephalitis was diagnosed in 22.8% of patients, ixodid tick-borne borreliosis in 50.5%, ehrlichiosis in 4.5% and mixed infections in 2.9%. For the first time in Russia, a new transmitted disease that appeared to be human monocytic ehrlichiosis was identified and its clinical manifestations were described. The common feature of these infections is the acute course and the marked general infectious syndrome at the early period of the disease. Disorders of the nervous system predominate in tick-borne encephalitis. In ixodid tick-borne borreliosis the development of erythema migrans and organic pathology (disorders of the cardio-vascular system and liver) associated with the involvement of the nervous and locomotor system are pathognomonically significant. The specific characteristics of human monocytic ehrlichiosis include nervous impairments, hepatic lesions, the frequent development of a two-wave course and hemogram changes.

Tick-borne encephalitis virus foci in Slovakia

Tick-borne encephalitis (TBE) virus as a typical arbovirus relies on two types of hosts for its survival: ticks act both as virus vectors and reservoir hosts, and vertebrates amplify the virus infection by acting as a source of infection for feeding ticks. Longitudinal monitoring of TBE virus in ticks and vertebrate hosts including humans over a period of 40 years resulted in the identification of the areas of Slovakia where TBE virus is endemic. These are concentrated to the western, southern, and eastern parts of the country. Even with recently identified foci there is no evidence that the size and location of the natural TBE foci have changed significantly during the last decades. Numbers of diagnosed hospitalised cases of TBE in Slovakia vary from less than 20 to almost 100 cases annually with 54-89 cases in recent years. A part of these cases (33 cases during the last 5 years) are alimentary infections after drinking of raw goat and sheep milk.

[Multistage mechanism of reproductive sympatric isolation of the closely-related species, Ixodes persulcatus and I. Pavloskyi (Ixodidae)]

The closely related species Ixodes persulcatus and I. pavlovskyi are vectors of agents tick-born encephalitis and Lyme disease. These species have two great disjunctive sympatric distribution areas (fig. 1), where both species inhabit the same biotopes, and during the same season. In these conditions there are prerequisites of contacts of opposite sexes of the different species during ambushing the hosts on vegetation. Sequence of "switching on" of the morphological, physiological, and hostparasite factors of reproductive isolation has been established. The features and the range of manifestation of these factors at different combinations of sexes and species of the partners have been revealed. The studied factors, such as precopulative and postcopulative components of the mechanism of reproductive isolation of I. persulcatus and I. pavlovskyi were considered. A hypothesis for sympatric origin of the species as a result of specialization the adults of I. persulcatus to mammals, and I. pavlovskyi to birds is proposed.

[Involvement of the common shrew, Sorex araneus (Insectivora, Soricidae), in circulation of the tick-borne encephalitis virus in south-western Siberia]

We presented the data on the abundance of immature instars of the taiga tick Ixodes persulcatus Schuize on the common shrews Sorex araneus L. in natural foci of tick-borne encephalitis in the south of Western Siberia. Basing on the results of virological and serological studies we demonstrated a low effectiveness of this host species as a donor of disease agent strains, which are predominant in the territory under study, for ticks feeding on shrews. The analysis of samples taken from the young shrews in winter and spring using reverse RNA transcription with polymerase chain reaction and ELISA revealed occurRence of subvirion components of the tick-borne encephalitis (RNA and capsid protein E) ether in brain, liver or spleen in 90 percent of shrews (n = 42). Neither hemagglutination antigen nor infectious virus have been detected. We discussed a possible epizootic role of the maintenance of non-infectious tick-borne encephalitis virus in overwintering animals.

Tick-borne encephalitis in Sweden and climate change

BACKGROUND

The incidence of tick-borne encephalitis (TBE) in Sweden has substantially increased since the mid-1980s. During the same period the climate has become milder and ticks have become more abundant. We investigated whether there is a link between the change in climate and the increase in incidence of TBE.

METHODS

Since the late 1950s all cases of encephalitis admitted in Stockholm County have been serologically tested for TBE. We analysed the period 1960-98 with multiple regressions. The number of days per season with temperatures of known importance for tick prevalence and pathogen transmission were studied. 2 years of temperature data were related to each TBE incidence rate to account for the tick's long life-span.

FINDINGS

Increases in disease incidence was significantly related (R(2)=0.58; p<0.0001) to a combination of two consecutive mild winters, temperatures favouring spring development (8-10 degrees C) and extended autumn activity (5-8 degrees C) in the year prior to the incidence year, and temperatures allowing tick activity (5-8 degrees C) early in the incidence year.

INTERPRETATIONS

The findings indicate that the increase in TBE incidence since the mid-1980s is related to the period's change towards milder winters and early arrival of spring. Other factors may have influenced TBE incidence such as more people in endemic locations, and increases in host animal populations; factors which are partly climate related. Access to TBE vaccination since 1986 and increased awareness of ticks might have caused an underestimation of the links found. Our findings also suggest that the incidence of other tick-borne zoonoses might have been affected by the milder climate.

[Borreliae as possible antagonists of tick-borne encephalitis virus: parasitologic and clinical aspects]

An attempt was made to compare the Borrelia-TBE-virus interface in Ixodes ticks and in patients. The authors suppose that Borrelia might suppress viral replication in ticks and in TBE-susceptible individuals. Whether antibiotics (particularly representatives of the tetracycline group) may be essential in treating tick-borne diseases is also discussed. Examples of antibiotic suppression of Borrelia that made the clinic presentation of encephalitis more severe as a consequence are analyzed and discussed. The calculated risk for borreliosis or tick-borne encephalitis and the actual morbidity rates were compared. Possible reasons for disagreement in the results are also discussed.

Enzootic transmission of deer tick virus in New England and Wisconsin sites

To determine whether rodents that are intensely exposed to the deer tick-transmitted agents of Lyme disease, human granulocytic ehrlichiosis, and human babesiosis are also exposed to deer tick virus (DTV), we assayed serum samples from white-footed mice (Peromyscus leucopus) and meadow voles (Microtus pennsylvanicus) in sites densely infested by deer ticks. To conduct serosurveys, we developed an enzyme-linked immunosorbent assay (ELISA) and Western blot assay by cloning, expressing, and purifying a portion of the DTV envelope glycoprotein (DTV rE) for use as test antigen. Sera from mice and voles trapped in Massachusetts, Rhode Island, and Wisconsin were screened by ELISA for IgG reactive to DTV rE. Samples that were positive or borderline by ELISA were subsequently analyzed by immunoblotting. Samples reactive in both assays were considered to be positive. Three percent of 264 mouse samples collected from sites in Rhode Island, 3.8% of 52 samples from mice trapped in Wisconsin, and 3.9% of 282 samples collected from mice trapped on Nantucket Island, MA were positive. No samples from either Great Island, MA, or voles from any study site were reactive. A reverse transcriptase-polymerase chain reaction yielded molecular evidence of DTV infecting questing adult deer ticks in sites where seroreactive mice were trapped, but not from ticks collected where serologic evidence of virus perpetuation was absent. White-footed mice appear to be exposed to DTV in certain sites where other deer tick-borne agents perpetuate. This virus may be maintained in the same enzootic cycle.

[Tick-borne encephalitis in Norway]

BACKGROUND

Tick-borne encephalitis is caused by a virus that is transmitted to man by tick-bite. The virus is found in central and eastern parts of Europe and also in Sweden.

MATERIAL AND METHODS

We report the first two cases of tick-borne encephalitis resulting from transmission of virus in Norway.

RESULTS

Both patients had been to the island of Tromøy on the south coast of Norway. The course of the disease was very different in the two patients. One patient had significant neurological dysfunction. The other patient had intense headache, but no motor dysfunction. Both patients had reduced general health and fever, and leukocytosis and increased protein was found in the spinal fluid. The incubation period is most often 1 to 2 weeks. The disease may have a bi-phasic course with initial fever, headache and muscle pain. One week later symptoms of encephalitis follow. Subclinical infection is common, especially in children. One third of patients get permanent sequelae after encephalitis. Diagnosis is made by demonstration of antibodies in serum. Treatment is symptomatic.

INTERPRETATION

These two patients indicate that there may be a reservoir of TBE virus in Norway.

[Results of the 20-year study of tick-borne encephalitis in Crimea]

The history of tick-borne encephalitis (TBE) study in the Crimea was retraced and the possibility of introduction of TBE virus to the Crimea in the process of the acclimatization of vertebrates from areas enzootic for TBE is discussed. 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. Such ticks as Dermacentor reticulatus, D. marginatus and Hyalomma marginatum were also found to take part in the circulation of the virus. Among the residents of the mountain forest zone, 13.9% were found to have immunity to TBE, testifying to the wide contact of the population with the pathogen. TBE morbidity had pronounced seasonal character and the morbidity rate was low with the prevalence of mild clinical forms. The characteristic feature of the virus population was polymorphism: strains identical to the Far-Eastern strains Sofyin (about 60-70%) and strains differing in their antigenic structure circulated here.

Fragile transmission cycles of tick-borne encephalitis virus may be disrupted by predicted climate change

Repeated predictions that vector-borne disease prevalence will increase with global warming are usually based on univariate models. To accommodate the full range of constraints, the present-day distribution of tick-borne encephalitis virus (TBEv) was matched statistically to current climatic variables, to provide a multivariate description of present-day areas of disease risk. This was then applied to outputs of a general circulation model that predicts how climatic variables may change in the future, and future distributions of TBEv were predicted for them. The expected summer rise in temperature and decrease in moisture appears to drive the distribution of TBEv into higher-latitude and higher-altitude regions progressively through the 2020s, 2050s and 2080s. The final toe-hold in the 2080s may be confined to a small part of Scandinavia, including new foci in southern Finland. The reason for this apparent contraction of the range of TBEv is that its transmission cycles depend on a particular pattern of tick seasonal dynamics, which may be disrupted by climate change. The observed marked increase in incidence of tick-borne encephalitis in most parts of Europe since 1993 may be due to non-biological causes, such as political and sociological changes.

[A medico-geographical assessment of the land area of the Maritime Territory relative to tick-borne encephalitis with some remarks on the structural organization of the foci of said infection]

A division of the Primorskiy Kray into districts in relation to the tick-borne encephalitis was based on three criteria: long-term dynamics of infection, chorological structure of ixodid tick populations and probability of this or that clinical form of infection.