Correlation of TBE Incidence with Red Deer and Roe Deer Abundance in Slovenia

Tick-borne encephalitis (TBE) is a virus infection which sometimes causes human disease. The TBE virus is found in ticks and certain vertebrate tick hosts in restricted endemic localities termed TBE foci. The formation of natural foci is a combination of several factors: the vectors, a suitable and numerous enough number of hosts and in a habitat with suitable vegetation and climate. The present study investigated the influence of deer on the incidence of tick-borne encephalitis. We were able to obtain data from deer culls. Using this data, the abundance of deer was estimated and temporal and spatial analysis was performed. The abundance of deer has increased in the past decades, as well as the incidence of tick-borne encephalitis. Temporal analysis confirmed a correlation between red deer abundance and tick-borne encephalitis occurrence. Additionally, spatial analysis established, that in areas with high incidence of tick-borne encephalitis red deer density is higher, compared to areas with no or few human cases of tick-borne encephalitis. However, such correlation could not be confirmed between roe deer density and the incidence of tick-borne encephalitis. This is presumably due to roe deer density being above a certain threshold so that availability of tick reproduction hosts has no apparent effect on ticks'' host finding and consequently may not be possible to correlate with incidence of human TBE.     

The shifting landscape of tick-borne zoonoses: tick-borne encephalitis and Lyme borreliosis in Europe

The two major vector-borne diseases of northern temperate regions, tick-borne encephalitis (TBE) and Lyme borreliosis (LB), show very different epidemiological patterns, but both have increased significantly in incidence since the 1980s. Insight into the temporal dynamics of TBE, gained from statistical analysis of spatial patterns integrated with biological explanation, suggests that the recent increases in TBE cases in Central Europe and the Baltic States may have arisen largely from changes in human behaviour that have brought more people into contact with infected ticks. Under forecast climate change scenarios, it is predicted that enzootic cycles of TBE virus may not survive along the southern edge of their present range, e.g. in Slovenia, Croatia and Hungary, where case numbers are indeed decreasing. New foci, however, are predicted and have been observed in Scandinavia. At the same time, human impact on the landscape, increasing both the habitat and wildlife hosts of ticks, has allowed tick populations to multiply significantly. This probably accounts for a genuine emergence of LB, with its high potential transmission rate, in both the USA and Europe, although the rate of emergence has been exaggerated by improved surveillance and diagnosis.     

Effects of Landscape Fragmentation and Climate on Lyme Disease Incidence in the Northeastern United States

Lyme disease is the most frequently reported vector borne illness in the United States, and incidences are increasing steadily year after year. This study explores the influence of landscape (e.g., land use pattern and landscape fragmentation) and climatic factors (e.g., temperature and precipitation) at a regional scale on Lyme disease incidence. The study area includes thirteen states in the Northeastern United States. Lyme disease incidence at county level for the period of 2002–2006 was linked with several key landscape and climatic variables in a negative binomial regression model. Results show that Lyme disease incidence has a relatively clear connection with regional landscape fragmentation and temperature. For example, more fragmentation between forests and residential areas results in higher local Lyme disease incidence. This study also indicates that, for the same landscape, some landscape variables derived at a particular scale show a clearer connection to Lyme disease than do others. In general, the study sheds more light on connections between Lyme disease incidence and climate and landscape patterns at the regional scale. Integrating findings of this regional study with studies at a local scale will further refine understanding of the pattern of Lyme disease as well as increase our ability to predict, prevent, and respond to disease.     

Epidemiological and clinical features of 1,149 persons with Lyme disease identified by laboratory-based surveillance in Connecticut

Laboratory-based surveillance of Lyme disease in Connecticut during 1984 and 1985 identified 3,098 persons with suspected Lyme disease; 1,149 were defined as cases. Lyme disease incidence in Connecticut towns ranged from none to 1,407 cases per 100,000 population in 1985. A comparison of 1985 data with data from 1977 epidemiologic studies indicated that incidence increased by 129 percent to 453 percent in towns previously known to be endemic for Lyme disease and that Lyme disease had spread northward into towns thought to be free of Lyme disease in 1977. Children aged five to 14 years had the highest incidence. Of persons with Lyme disease, 83 percent had erythema migrans, 24 percent had arthritis, 8 percent had neurologic sequelae, and 2 percent had cardiac sequelae. The distribution of symptoms was age-dependent: case-persons less than 20 years old were almost twice as likely to have arthritis than older case-persons (35 percent versus 18 percent). Of persons with arthritis, 92 percent of those less than 20 years of age, compared to 68 percent of older persons, did not have antecedent erythema migrans. We conclude that Lyme disease is increasing in incidence and geographic distribution in Connecticut. Of those with Lyme disease, children may be more likely than adults to develop arthritis and have it as their first major disease manifestation.     

Are Patients with Erythema Migrans Who Have Leukopenia and/or Thrombocytopenia Coinfected with Anaplasma phagocytophilum or Tick-Borne Encephalitis Virus?

Lyme borreliosis (LB), tick-borne encephalitis (TBE) and human granulocytic anaplasmosis (HGA) are endemic in central part of Slovenia. We tested the hypothesis that patients with erythema migrans (EM) from this region, who have leukopenia and/or thrombocytopenia (typical findings in HGA and in the initial phase of TBE but not in patients with LB) are coinfected with Anaplasma phagocytophilum and/or with TBE virus, i.e. that cytopenia is a result of concomitant HGA or the initial phase of TBE. Comparison of clinical and laboratory findings for 67 patients with EM who disclosed leukopenia/thrombocytopenia with the corresponding results in sex- and age-matched patients with EM and normal blood cell counts revealed no differences. In addition, patients with typical EM and leukopenia and/or thrombocytopenia tested negative for the presence of IgM and IgG antibodies to TBE virus by ELISA as well as for the presence of specific IgG antibodies to A. phagocytophilum antigens by IFA in acute and convalescent serum samples. Thus, none of 67 patients (95% CI: 0 to 5.3%) with typical EM (the presence of this skin lesion attests for early Lyme borreliosis and is the evidence for a recent tick bite) was found to be coinfected with A. phagocytophilum or had a recent primary infection with TBE virus. The findings in the present study indicate that in Slovenia, and probably in other European countries endemic for LB, TBE and HGA, patients with early LB are rarely coinfected with the other tick-transmitted agents.     

Lyme disease in northwestern coastal California.

To determine the incidence of physician-diagnosed Lyme disease in an endemic area of California, an active surveillance program was implemented in Lake, Mendocino, Sonoma, and southern Humboldt counties. More than 200 medical care providers were called monthly for their list of suspected cases of Lyme disease. Pertinent information was abstracted from the medical record of each patient. Of 153 cases of possible early Lyme disease ascertained from July 1991 to December 1992, 37% consisted of physician-diagnosed erythema migrans. Only 58% of erythema migrans rashes were at least 5 cm in diameter. An additional 43 patients had suspicious rashes not classified as erythema migrans. Of 166 patients with possible late-stage Lyme disease, 31% had specific clinical symptoms and 75% had a positive serologic test. With an incident case defined as physician-diagnosed erythema migrans of at least 5 cm in diameter, the annual incidence of Lyme disease in northwestern coastal California according to active surveillance only was 5.5 per 100,000. The rate of Lyme disease in California is substantially lower than that in the Atlantic northeastern United States. Many suspected cases of Lyme disease in this endemic area do not meet surveillance criteria, which are intentionally restrictive. Although some of the illnesses not meeting surveillance criteria may be due to infection with Borrelia burgdorferi, it appears that Lyme disease is being overdiagnosed in this area.     

森林脑炎自然疫源地样本的监测及病毒的分离研究

为了解森林脑炎疫源地的分布变化趋势及样本分离病毒的特性,采集了森林脑炎高发区周边的森林全沟硬蜱、血蜱样本及森林脑炎患者的脑组织样本,用小白鼠脑内接种法检测、分离病毒分离的病毒经鉴别试验证明为森林脑炎病毒：蜱、脑两种标本检测的阳性率分别为50％和100％、结果表明森林脑炎的疫区有从林区向农业区扩散的趋势,且全沟硬蜱的带毒率较高;森脑患者的脑组织样本与蜱标本病毒的性状育差异     

Different Populations of Blacklegged Tick Nymphs Exhibit Differences in Questing Behavior That Have Implications for Human Lyme Disease Risk

Animal behavior can have profound effects on pathogen transmission and disease incidence. We studied the questing (= host-seeking) behavior of blacklegged tick (Ixodes scapularis) nymphs, which are the primary vectors of Lyme disease in the eastern United States. Lyme disease is common in northern but not in southern regions, and prior ecological studies have found that standard methods used to collect host-seeking nymphs in northern regions are unsuccessful in the south. This led us to hypothesize that there are behavior differences between northern and southern nymphs that alter how readily they are collected, and how likely they are to transmit the etiological agent of Lyme disease to humans. To examine this question, we compared the questing behavior of I. scapularis nymphs originating from one northern (Lyme disease endemic) and two southern (non-endemic) US regions at field sites in Wisconsin, Rhode Island, Tennessee, and Florida. Laboratory-raised uninfected nymphs were monitored in circular 0.2 m² arenas containing wooden dowels (mimicking stems of understory vegetation) for 10 (2011) and 19 (2012) weeks. The probability of observing nymphs questing on these stems (2011), and on stems, on top of leaf litter, and on arena walls (2012) was much greater for northern than for southern origin ticks in both years and at all field sites (19.5 times greater in 2011; 3.6–11.6 times greater in 2012). Our findings suggest that southern origin I. scapularis nymphs rarely emerge from the leaf litter, and consequently are unlikely to contact passing humans. We propose that this difference in questing behavior accounts for observed geographic differences in the efficacy of the standard sampling techniques used to collect questing nymphs. These findings also support our hypothesis that very low Lyme disease incidence in southern states is, in part, a consequence of the type of host-seeking behavior exhibited by southern populations of the key Lyme disease vector.     

Forest Structure and Roe Deer Abundance Predict Tick-Borne Encephalitis Risk in Italy

Background

The Western Tick-borne encephalitis (TBE) virus often causes devastating or lethal disease. In Europe, the number of human TBE cases has increased dramatically over the last decade, risk areas are expanding and new foci are being discovered every year. The early localisation of new TBE foci and the identification of the main risk factors associated with disease emergence represent a priority for the public health community. Although a number of socio-economic parameters have been suggested to explain TBE upsurges in eastern Europe, the principal driving factors in relatively stable western European countries have not been identified.

Methodology/Principal Findings

In this paper, we analyse the correlation between the upsurge of TBE in 17 alpine provinces in northern Italy from 1992 to 2006 with climatic variables, forest structure (as a proxy for small mammal reservoir host abundance), and abundance of the principal large vertebrate tick host (roe deer), using datasets available for the last 40 years. No significant differences between the pattern of changes in climatic variables in provinces where TBE has emerged compared to provinces were no clinical TBE cases have been observed to date. Instead, the best model for explaining the increase in TBE incidence in humans in this area include changes in forest structure, in particular the ratio of coppice to high stand forest, and the density of roe deer.

Conclusion/Significance

Substantial changes in vegetation structure that improve habitat suitability for the main TBE reservoir hosts (small mammals), as well as an increase in roe deer abundance due to changes in land and wildlife management practices, are likely to be among the most crucial factors affecting the circulation potential of Western TBE virus and, consequently, the risk of TBE emergence in humans in western Europe. We believe our approach will be useful in predicting TBE risk on a wider scale.     

Investigating disease severity in an animal model of concurrent babesiosis and Lyme disease

The incidence of babesiosis, Lyme disease and other tick-borne diseases has increased steadily in Europe and North America during the last five decades. Babesia microti is transmitted by species of Ixodes, the same ticks that transmit the Lyme disease-causing spirochete, Borrelia burgdorferi. B. microti can also be transmitted through transfusion of blood products and is the most common transfusion-transmitted infection in the U.S.A. Ixodes ticks are commonly infected with both B. microti and B. burgdorferi, and are competent vectors for transmitting them together into hosts. Few studies have examined the effects of coinfections on humans and they had somewhat contradictory results. One study linked coinfection with B. microti to a greater number of symptoms of overall disease in patients, while another report indicated that B. burgdorferi infection either did not affect babesiosis symptoms or decreased its severity. Mouse models of infection that manifest pathological effects similar to those observed in human babesiosis and Lyme disease offer a unique opportunity to thoroughly investigate the effects of coinfection on the host. Lyme disease has been studied using the susceptible C3H mouse infection model, which can also be used to examine B. microti infection to understand pathological mechanisms of human diseases, both during a single infection and during coinfections. We observed that high B. microti parasitaemia leads to low haemoglobin levels in infected mice, reflecting the anaemia observed in human babesiosis. Similar to humans, B. microti coinfection appears to enhance the severity of Lyme disease-like symptoms in mice. Coinfected mice have lower peak B. microti parasitaemia compared to mice infected with B. microti alone, which may reflect attenuation of babesiosis symptoms reported in some human coinfections. These findings suggest that B. burgdorferi coinfection attenuates parasite growth while B. microti presence exacerbates Lyme disease-like symptoms in mice.     

Why Lyme disease is common in the northern US,but rare in the south: The roles of host choice,host-seeking behavior,and tick density

Lyme disease is common in the northeastern United States, but rare in the southeast, even though the tick vector is found in both regions. Infection prevalence of Lyme spirochetes in host-seeking ticks, an important component to the risk of Lyme disease, is also high in the northeast and northern midwest, but declines sharply in the south. As ticks must acquire Lyme spirochetes from infected vertebrate hosts, the role of wildlife species composition on Lyme disease risk has been a topic of lively academic discussion. We compared tick–vertebrate host interactions using standardized sampling methods among 8 sites scattered throughout the eastern US. Geographical trends in diversity of tick hosts are gradual and do not match the sharp decline in prevalence at southern sites, but tick–host associations show a clear shift from mammals in the north to reptiles in the south. Tick infection prevalence declines north to south largely because of high tick infestation of efficient spirochete reservoir hosts (rodents and shrews) in the north but not in the south. Minimal infestation of small mammals in the south results from strong selective attachment to lizards such as skinks (which are inefficient reservoirs for Lyme spirochetes) in the southern states. Selective host choice, along with latitudinal differences in tick host-seeking behavior and variations in tick densities, explains the geographic pattern of Lyme disease in the eastern US.

Lyme disease is common in the northeastern United States, but rare in the southeast, even though the tick vector is found in both regions. This study shows that this is largely because the tick vectors attach abundantly to rodents (which are good hosts for the Lyme bacteria) in the north, and to lizards (which are relatively poor hosts for Lyme bacteria) in the south.     

Preparation and purification of recombinant outer surface protein A (rOspA) of Borrelia burgdorferi sensu stricto and Borrelia afzelii

The recombinant Outer surface protein A (rOspA) from Borrelia burgdorferi is a possible immunogen for protection of infected humans and animals against development of Lyme borreliosis (Lyme disease), a chronic tick-borne disease characterised by diverse dermatologic, neurologic, rheumatic, and cardiac manifestations. For several years, research and development have been directed towards a vaccine for the prevention of this debilitating disease. Numerous animal studies demonstrate that pre-existing antibodies against the outer surface proteins of B. burgdorferi can prevent infection and disease caused by this organism. In this communication, using recombinant DNA technology, genes from B. burgdorferi sensu stricto and B. afzelii were inserted into E. coli-expression vectors and the rOspA were produced. Our aim was to obtain rOspA protein in a purity and quantity desirable for immunization of experimental animals. rOspA is currently the most developed, molecularly-defined vaccine candidate for the prevention of Lyme borreliosis.     

First report of Borrelia burgdorferi sensu lato in two threatened carnivores: the Marbled polecat, Vormela peregusna and the European mink

ABSTRACT: BACKGROUND: Lyme disease is a widespread cosmopolitan zoonosis caused by species belonging to the genus Borrelia. It is transmitted from animal reservoir hosts to humans through hard - ticks of genus Ixodes which are vectors of the disease. CASE PRESENTATION: Borrelia burgdorferi sensu lato infection was identified in a marbled polecat, Vormela peregusna, and two European minks, Mustela lutreola, from Romania, by PCR. RFLP revealed the presence of a single genospecies, Borrelia burgdorferi sensu stricto. CONCLUSIONS: This is the first report of the Lyme disease spirochetes in the two mentioned hosts.     

Molecular phylogenetic analysis of ixodid ticks based on the ribosomal DNA spacer, internal transcribed spacer 2, sequences

An internal transcribed spacer (ITS2) sequence between the 5.8S and 28S rRNA genes was used to estimate the phyletic relationships among Ixodes spp. tick vectors of Lyme disease-causing Borrelia spirochetes. Analysis indicates that Borrelia burgdorferi sensu lato species associated with Lyme disease are found mainly in ticks of the Ixodes ricinus species complex. Other closely related tick species are not known to transmit the Borrelia-that cause Lyme disease in humans, but they appear to have a specific association with other closely related Borrelia species. There is a high degree of concordance in the phylogenetics of Borrelia taxa and the phylogenetic relationships among Ixodes ticks.     

Seroprevalence study of Tick-borne encephalitis, Borrelia burgdorferi, Dengue and Toscana virus in Turin Province

Tick borne encephalitis virus (TBEV) is present in some European countries and it is transmitted by a tick bite. Ixodes ricinus is the main vector of the infection in Italy, where fortunately clinical neurological manifestations, typical of the more serious phase of the disease, are very rarely observed. This behaviour is different from other endemic Euroasiatic areas where numerous cases of encephalitis are described. However TBE transmission has not been widely investigated in Italy and available epidemiological data have been obtained only by studies performed in Central and Northern Regions of the country. In addition seroepidemiological researches were made prevalently on subjects at high risk of tick bite, such as hunters or forest guards from Trentin and Central Italy. No precise information about TBE virus diffusion was available in the Piedmont before our investigations. We found that hunters and wild boar breeders seem to be particularly exposed to the risk of TBE virus infection in Turin Province and in particular in the Susa valley, although no neurological involvement was observed in our population. In particular a seroprevalence of about 5% was detected by the use of purified antigens ELISA test, amongst the subjects at high risk of tick bite. Moreover low risk individuals showed a seroprevalence of below 2%. In addition a parallel seroepidemiological study was performed in Turin Province for Borrelia burgdorferi, the aetiological agent of Lyme disease, also transmitted by tick bite (e.g. Ixodes ricinus), for Dengue and Toscana (TOS) arboviruses, respectively transmitted by Aedes mosquitoes and phlebotomes. Data reported here demonstrate only a sporadic presence in our population of antibodies against Borrelia and Dengue infection. Moreover using an ELISA test performed with viral purified nucleoprotein, we reported a total percentage of about 3% of subjects positive for TOSV.     

Mixed infection by tick-borne encephalitis virus and Borrelia in ticks

To investigate the relationships between tick-borne encephalitis (TBE) virus and the bacterial spirochaete Borrelia burgdorferi sensu lato in vectors with mixed infections, unfed adult Ixodes persulcatus ticks were collected by flagging from vegetation in southern-taiga forests of the Pre-Urals region of Russia where both infections circulate sympatrically. Prevalences of TBE and Borrelia infections in a total of 4234 ticks were compared over 5 years. No significant differences were revealed between the prevalence of Borrelia infection in ticks with and without TBE virus (29.4+/-7.8% vs 23+/-3.6%), or between the prevalence of TBE virus infection in ticks with and without Borrelia (24.0+/-6.6% vs 18.4+/-3.4%). In ticks with mixed infection (40/689 = 5.8%), concentrations of TBE virus and Borrelia were not significantly correlated with one another. Field observations showed parallel trends in the prevalence of these pathogens in tick populations from year to year (1993-1997) indicating that, in I. persulcatus with mixed infection, Borrelia and TBE virus do not seem to interfere with each other and are apparently not involved in any antagonistic relationships.     

Close to home: a history of Yale and Lyme disease

Yale scientists played a pivotal role in the discovery of Lyme disease and are credited as the first to recognize, name, characterize, and treat the affliction. Today, Lyme disease is the most commonly reported vector-borne illness in the United States, affecting approximately 20,000 people each year, with the incidence having doubled in the past 10 years [1]. Lyme disease is the result of a bacterial infection transmitted to humans through the bite of an infected deer tick, which typically results in a skin rash at the site of attack. While most cases, when caught early, are easily treated by antibiotic therapy, delayed treatment can lead to serious systemic side effects involving the joints, heart, and central nervous system. Here we review Yale's role in the discovery and initial characterization of Lyme disease and how those early discoveries are crucial to our current understanding of the disease.     

The Willingness to Pay for Vaccination against Tick-Borne Encephalitis and Implications for Public Health Policy: Evidence from Sweden

The increasing incidence of tick-borne encephalitis (TBE) in Sweden and several other European countries has sparked a discussion about the need for a public vaccination strategy. However, TBE vaccination coverage is incomplete and there is little knowledge about the factors influencing vaccination behavior. Based on a survey of 1,500 randomly selected respondents in Sweden, we estimate vaccination coverage in areas with different TBE risk levels and analyze the role of vaccine price and other factors influencing the demand for vaccination. First, we find that the average rate of TBE vaccination in Sweden is 33% in TBE risk areas and 18% elsewhere. Income, age and risk-related factors such as incidence of TBE in the area of residence, frequency of visits to areas with TBE risk, and experience with tick bites are positively associated with demand for TBE vaccine. Next, using contingent valuation methodology, we estimate the willingness to pay for TBE vaccination among the unvaccinated respondents and the effect of a possible subsidy. Among the unvaccinated respondents in TBE risk areas, we estimate the mean willingness to pay for the recommended three doses of TBE vaccine to be 465 SEK (approximately 46 euros or 40% of the current market price). We project that a subsidy making TBE vaccines free of charge could increase the vaccination rate in TBE risk areas to around 78%, with a larger effect on low-income households, whose current vaccination rate is only 15% in risk areas. However, price is not the only factor affecting demand. We find significant effects on vaccination behavior associated with trust in vaccine recommendations, perceptions about tick bite-related health risks and knowledge about ticks and tick-borne diseases. Hence, increasing knowledge and trust, as well as ease of access to vaccinations, can also be important measures for public health agencies that want to increase the vaccination rate.     

Integrated Assessment of Behavioral and Environmental Risk Factors for Lyme Disease Infection on Block Island,Rhode Island

Peridomestic exposure to Borrelia burgdorferi-infected Ixodes scapularis nymphs is considered the dominant means of infection with black-legged tick-borne pathogens in the eastern United States. Population level studies have detected a positive association between the density of infected nymphs and Lyme disease incidence. At a finer spatial scale within endemic communities, studies have focused on individual level risk behaviors, without accounting for differences in peridomestic nymphal density. This study simultaneously assessed the influence of peridomestic tick exposure risk and human behavior risk factors for Lyme disease infection on Block Island, Rhode Island. Tick exposure risk on Block Island properties was estimated using remotely sensed landscape metrics that strongly correlated with tick density at the individual property level. Behavioral risk factors and Lyme disease serology were assessed using a longitudinal serosurvey study. Significant factors associated with Lyme disease positive serology included one or more self-reported previous Lyme disease episodes, wearing protective clothing during outdoor activities, the average number of hours spent daily in tick habitat, the subject’s age and the density of shrub edges on the subject’s property. The best fit multivariate model included previous Lyme diagnoses and age. The strength of this association with previous Lyme disease suggests that the same sector of the population tends to be repeatedly infected. The second best multivariate model included a combination of environmental and behavioral factors, namely hours spent in vegetation, subject’s age, shrub edge density (increase risk) and wearing protective clothing (decrease risk). Our findings highlight the importance of concurrent evaluation of both environmental and behavioral factors to design interventions to reduce the risk of tick-borne infections.