A Predictive Model Has Identified Tick-Borne Encephalitis High-Risk Areas in Regions Where No Cases Were Reported Previously, Poland, 1999-2012

During 1999–2012, 77% of the cases of tick-borne encephalitis (TBE) were recorded in two out of 16 Polish provinces. However, historical data, mostly from national serosurveys, suggest that the disease could be undetected in many areas. The aim of this study was to identify which routinely-measured meteorological, environmental, and socio-economic factors are associated to TBE human risk across Poland, with a particular focus on areas reporting few cases, but where serosurveys suggest higher incidence. We fitted a zero-inflated Poisson model using data on TBE incidence recorded in 108 NUTS-5 administrative units in high-risk areas over the period 1999–2012. Subsequently we applied the best fitting model to all Polish municipalities. Keeping the remaining variables constant, the predicted rate increased with the increase of air temperature over the previous 10–20 days, precipitation over the previous 20–30 days, in forestation, forest edge density, forest road density, and unemployment. The predicted rate decreased with increasing distance from forests. The map of predicted rates was consistent with the established risk areas. It predicted, however, high rates in provinces considered TBE-free. We recommend raising awareness among physicians working in the predicted high-risk areas and considering routine use of household animal surveys for risk mapping.

Psychiatric aspects of herpes simplex encephalitis, tick-borne encephalitis and herpes zoster encephalitis among immunocompetent patients

The psychopathological symptoms occurring in the course of diseases associated with infections are often initially isolated and non-characteristic, and may cause diagnostic difficulties. Moreover, such disorders tend to be less responsive to psychiatric management. Among possible causes such as trauma, neoplasm and vascular changes, inflammatory changes of the brain as a result of a viral infection should also be considered. There were 452 registered cases of viral encephalitis in Poland in 2010, and although not very prevalent they remain a severe and life-threatening condition. What is more, the frequently occurring neurological and psychiatric complications of viral encephalitis often result in permanent disabilities, causing a significant decrease in the quality of life. This article presents the three types of encephalitis that are most prevalent among immunocompetent patients in Poland, i.e. herpes simplex encephalitis (HSE), tick-borne encephalitis (TBE) and herpes zoster encephalitis (HZE). The psychopathology of the acute phase of the infection, the residual symptoms, features apparent in imaging studies and some neuropathological aspects are also presented. The paper also focuses on psychiatric aspects of the diagnostics and treatment of the described conditions. The clinical pictures of these infections are quite specific, although they cover a wide range of symptoms, and these characteristic features are described. The aim of this review is also to show the significance of thorough diagnostics and a multidisciplinary approach to patients with viral CNS infections.

Epilepsia partialis continua in tick-borne Russian spring-summer encephalitis

OBJECTIVES

Epilepsia partialis continua (EPC) is characterized by localized continuous jerks, from time to time with spreading Jacksonian seizures and, more rarely, secondarily generalized tonic-clonic seizures. EPC has numerous possible etiologies. In this paper we describe EPC in the tick-borne Russian spring-summer encephalitis (TBRSSE) and compare it with Rasmussen syndrome.

METHODS AND METHODS

We included patients with EPC in TBRSSE (between 2003 and 2010). The diagnosis was verified by immunology (antibodies against TBRSSE virus). The patients were followed 1-7 (mean 3.4) years.

RESULTS

We studied 10 patients (eight males, age 10-21 years) with MRI and video-EEG. Nine developed EPC after acute TBRSSE (meningoencephalitic form), and one had a tick bite without clinical symptoms of encephalitis, but with subsequent EPC. All patients came from Ural and Siberia. The onset was at age 4-14 (mean 8.6 years). The interval from onset of TBRSSE or the tick bite to seizure onset was 1 day-4 years. We identified three phases of clinical course EPC in TBRSSE: (i) acute (meningoencephalitic/encephalitic); (ii) development of EPC; and (iii) chronic EPC. The effect of antiepileptic drugs differed according to seizure types.

CONCLUSION

EPC caused by TBRSSE is relatively frequent in the Eastern parts of the Russian Federation but not west of the Ural. Unlike Rasmussen encephalitis, EPC with TBRSSE does not progress even in the long term. It appears as disabling but not fatal condition with a time course where three phases can be distinguished.

Update on Powassan virus: emergence of a North American tick-borne flavivirus

Powassan virus (POW) (Flaviviridae: Flavivirus) is the cause of rare but severe neuroinvasive disease in North America and Russia. The virus is transmitted among small- and medium-sized mammals by ixodid ticks. Human infections occur via spillover from the main transmission cycle(s). Since the late 1990s, the incidence of human disease seems to be increasing. In addition, POW constitutes a genetically diverse group of virus genotypes, including Deer tick virus, that are maintained in distinct enzootic transmission cycles. This review highlights recent research into POW, focusing on virus genetics and ecology and human disease. Important directions for future research are also discussed.

Early detection of tick-borne encephalitis virus spatial distribution and activity in the province of Trento, northern Italy

New human cases of tick-borne encephalitis (TBE) have recently been recorded outside the recognised foci of this disease, i.e. in the province of Trento in northern Italy. In order to predict the highest risk areas for increased TBE virus activity, we have combined cross-sectional serological data, obtained from 459 domestic goats, with analysis of the autumnal cooling rate based on Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data. A significant relationship between finding antibodies against the virus in serum (seroprevalence) in goats and the autumnal cooling rate was detected, indicating that the transmission intensity of the virus does not only vary spatially, but also in relation to climatic factors. Virus seroprevalence in goats was correlated with the occurrence of TBE in humans and also with the average number of forestry workers' tick bites, demonstrating that serological screening of domestic animals, combined with an analysis of the autumnal cooling rate, can be used as early-warning predictors of TBE risk in humans.

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.

Tick-borne encephalitis virus in northern Italy: molecular analysis, relationships with density and seasonal dynamics of Ixodes ricinus

Ixodes ricinus ticks were collected from dragging vegetation and from shot roe deer in the province of Trento and Belluno in northern Italy. Ticks were pooled for analyses and from 1060 pools of ticks collected in the province of Belluno and 12390 tick samples collected in Trentino, four proved positive by immunofluorescence microscopy using a tick-borne encephalitis (TBE)-specific antiserum. The identity of the virus isolates was determined by RT-PCR cycle sequencing and they were all found to be closely similar (> 98% nucleotide identity) to typical western European TBE complex viruses as found in Austria. The isolates from Trentino differed from the Neudorfl strain of western European TBE virus at eight nucleotide positions but as these nucleotide substitutions were all synonymous, there were no amino acid changes. These results imply that the virus isolates in Trentino have changed slightly from the typical European strains isolated in nearby Austria. The abundance of questing ticks and ticks feeding on roe deer was greater in TBE positive hunting districts than in hunting districts where TBE complex viruses were only probable or believed to be absent. In TBE positive and probable districts synchrony in the seasonal dynamics of larvae and nymphs of L. ricinus was observed. This study provides evidence to suggest that roe deer may have an important role to play in the maintenance of tick density and in the persistence of TBE virus.

Heterogeneity in the host preference of Japanese encephalitis vectors in Chiang Mai, northern Thailand

Experiments, using the capture-mark-release-recapture technique inside large nets, were carried out in Chiang Mai, northern Thailand, to examine heterogeneity in the host preference of Japanese encephalitis (JE) vectors. A significantly higher proportion of the vector species that were initially attracted to a cow fed when released into a net with a cow than when released into a net containing a pig. However, Culex vishnui individuals that had been attracted to a pig had a higher feeding rate in a net containing a pig rather than a cow. When mosquitoes were given a choice by being released into a net containing both animals, they exhibited a tendency to feed on the host to which they had originally been attracted. This feeding preference was, however, not shown by the offspring of pig-fed individuals. We have therefore shown evidence of physiological/behavioural conditioning in the host preference of JE vectors rather than genetic variability. Our results suggest that effective control of JE might be achieved by increasing the availability of cows (the dead-end hosts of JE virus) to deflect the vectors from pigs (the amplifying host). The behavioural imprinting which we have found would tend to re-inforce the initial tendency of the vectors to bite cows.

[The results of the serological examination of medium-sized mammals in the natural foci of arbovirus infections in central Siberia]

The serological survey of white hares (n = 8), squirrels (n = 118), and Asian chipmunks (n = 486) in the dark coniferous forests of Middle Siberia revealed tick-borne encephalitis virus antihemagglutinins only in the former two species (37.5 +/- 17.1 and 7.6 +/- 2.4%, respectively) and in the squirrel, there is a close seasonal relation between the parameters of immune interbred and those virophoricity of taiga tick nymphs.

Natural foci of tick-borne encephalitis in central Europe and the relationship of the incidence of Ixodes ricinus to original ecosystems

Based on reports of the national epidemiological service on tick-borne encephalitis (TBE) morbidity in 1953-1987, data in the literature, and results of the author's own field research on the occurrence of the common tick, Ixodes ricinus, foci of this disease have been identified on the territory of Czechoslovakia. In Bohemia a significant focus of TBE in the Central Bohemian Region is located in the Krivoklát area with forests and in the Berounka, mid-Vltava, and lower-Sázava river basins, in the Brdy area and the Czech Karst continuing southwards via the Vltava basin to foci in the South Bohemian region in the districts of Písek and Ceské Budĕjovice and west of the Berounka river basin to a focus in the central part of the West Bohemian region. In the North Bohemian and East Bohemian regions only smaller isolated foci of TBE were detected. In Moravia foci of TBE are in the districts of Opava and Bruntál in the North Moravian region and in the central and southern areas of the South Moravian region. The foci in Bohemia are isolated from foci in neighboring countries, those of Moravia are connected with foci in Poland and Austria. On the territory of the Czech Republic foci of TBE are found in localities of pristine oakwood agglomerations. Original beechwood agglomerations even when located below the upper limit of occurrence of the common tick, i.e. less than 700 meters above sea level, do not offer favourable conditions for this arthropod and they do not harbour natural foci of TBE.(ABSTRACT TRUNCATED AT 250 WORDS)

[Differences in the distant transmission of the tick-borne encephalitis virus by ixodid ticks of 2 subfamilies]

Simultaneous but separate feeding of ticks on nonviremic animal (guinea pig) has shown that Amblyomminae ticks are practically unable to transmit distantly tick-borne encephalitis virus (TBEV) to the specimens of their own subfamily and to Ixodinae as well. Ixodes persulcatus and I. ricinus displayed their ability as donors and recipients of TBEV (adults and nymphs) not only for their own subfamily representatives but also as donors for recipients of Amblyomminae subfamily (nymphs and adults of Dermacentor and Rhipicephalus and nymphs of Haemaphysalis). Experimental and literature data analysis permits the authors to conclude that the very important role of TBEV circulation in nature belongs to the distant virus transmission. The absence of such type of virus exchange among Amblyomminae excludes this group of ticks from active virus circulation in TBEV foci.

[Prognosis in tick-borne encephalitis]

The paper presents a review of suggested and used methods of predicting the number of the main vector and its infection with the tick-borne encephalitis virus. It has been suggested that most practically important are long-term prognoses of tendencies in the changes of the parasitic system on the basis of retrospective estimation of the recurrence of its changes, that is, the definition of probability of recurrence of most important characters (states) of a parasitic system in the presence of appropriate external conditions.