Quantitative ecology of ticks as a basis for transmission models of tick-borne pathogens

Tick population ecology is the basis of spatiotemporal variation in the risk of infection by tick-borne pathogens. The continental distribution of tick-borne encephalitis (TBE) in Europe is statistically associated with a specific pattern of the seasonal dynamics of Ixodes ricinus, and a particular characteristic of the seasonal land surface temperature profile. A tick population model would allow us to move from this statistical analysis to a biological, process-based model for TBE virus and the many other pathogens vectored by Ixodes spp. ticks in Europe and the United States. Long-term field data on I. ricinus are analyzed to provide empirical estimates of rates of the major demographic processes, development, questing, attachment to hosts, and mortality.     

Spatial synchrony of local populations has increased in association with the recent Northern Hemisphere climate trend

According to ecological theory, populations whose dynamics are entrained by environmental correlation face increased extinction risk as environmental conditions become more synchronized spatially. This prediction is highly relevant to the study of ecological consequences of climate change. Recent empirical studies have indicated, for example, that large-scale climate synchronizes trophic interactions and population dynamics over broad spatial scales in freshwater and terrestrial systems. Here, we present an analysis of century-scale, spatially replicated data on local weather and the population dynamics of caribou in Greenland. Our results indicate that spatial autocorrelation in local weather has increased with large-scale climatic warming. This increase in spatial synchrony of environmental conditions has been matched, in turn, by an increase in the spatial synchrony of local caribou populations toward the end of the 20th century. Our results indicate that spatial synchrony in environmental conditions and the populations influenced by them are highly variable through time and can increase with climatic warming. We suggest that if future warming can increase population synchrony, it may also increase extinction risk.     

The effect of climatic forcing on population synchrony and genetic structuring of the Canadian lynx

The abundance of Canadian lynx follows 10-year density fluctuations across the Canadian subcontinent. These cyclic fluctuations have earlier been shown to be geographically structured into three climatic regions: the Atlantic, Continental, and Pacific zones. Recent genetic evidence revealed an essentially similar spatial structuring. Introducing a new population model, the "climate forcing of ecological and evolutionary patterns" model, we link the observed ecological and evolutionary patterns. Specifically, we demonstrate that there is greater phase synchrony within climatic zones than between them and show that external climatic forcing may act as a synchronizer. We simulated genetic drift by using data on population dynamics generated by the climate forcing of ecological and evolutionary patterns model, and we demonstrate that the observed genetic structuring can be seen as an emerging property of the spatiotemporal ecological dynamics.     

Tick-borne borreliosis in the Iaroslavl region

The present paper characterizes a natural focus of tick-borne borreliosis in the Yaroslavl Region, analyzes the incidence of this infection in the Region, and thus concludes that the density of the population living in the areas of the natural foci of tick-borne borreliosis has a significant impact on its epidemic process. The incidence of tick-borne borreliosis in the Yaroslavl Region has remained a challenge in the past 7 years. By the number of cases, this infection heads the list of naturally focal infections recorded in the Region. Examining long-term changes in the incidence and prevalence of tick-borne borreliosis in the Region revealed its high incidence in the population residing in the tidal marshlands and forest areas. At the same time the potential activity of natural foci of borreliosis due to the conditions that maintain the population of Ixodes ticks is high in the forest-field, southern, and meadow-forest-field regions.     

Ecology and epidemiology of tick-borne borreliosis in the Ul'ianovsk region

The parameters that characterize the affection and spread of ticks in the Ulyanovsk Region are presented. A risk for Ixodes tick-borne borreliosis among the urban population is shown.     

Multi-year changes in the morbidity of tick-borne encephalitis in the Irkutsk region

Correlation and cluster analysis of data on the number of tick-borne encephalitis cases in the Irkutsk region collected for a 31-year period allowed the authors to distinguish three areas with various morbidity dynamics, physical and geographical conditions and level of land development. Long-term morbidity prognosis is presented.     

Snow conditions may create an invisible barrier for lynx

The dynamics of Canadian lynx (Lynx canadensis) abundance are geographically structured according to the influence of large-scale climatic regimes. Here we demonstrate that this structuring matches zones of differential snow conditions, in particular surface hardness, as determined by the frequency of winter warm spells. Through a modified functional response curve, we show that various features of the snow may influence lynx interaction with its main prey species, the snowshoe hare (Lepus americanus). This study highlights the importance of snow, and exemplifies how large-scale climatic fluctuations can mechanistically influence population biological patterns.     

Modeling relationships between climate and the frequency of human plague cases in the southwestern United States, 1960-1997

The relationships between climatic variables and the frequency of human plague cases (1960-1997) were modeled by Poisson regression for two adjoining regions in northeastern Arizona and northwestern New Mexico. Model outputs closely agreed with the numbers of cases actually observed, suggesting that temporal variations in plague risk can be estimated by monitoring key climatic variables, most notably maximum daily summer temperature values and time-lagged (1 and 2 year) amounts of late winter (February-March) precipitation. Significant effects also were observed for time-lagged (1 year) summer precipitation in the Arizona model. Increased precipitation during specific periods resulted in increased numbers of expected cases in both regions, as did the number of days above certain lower thresholds for maximum daily summer temperatures (80 degrees F in New Mexico and 85 degrees F in Arizona). The number of days above certain high-threshold temperatures exerted a strongly negative influence on the numbers of expected cases in both the Arizona and New Mexico models (95 degrees F and 90 degrees F, respectively). The climatic variables found to be important in our models are those that would be expected to influence strongly the population dynamics of the rodent hosts and flea vectors of plague.     

Temporal variation of Ixodes ricinus intensity on the rodent host Apodemus flavicollis in relation to local climate and host dynamics

The risk to humans of contracting tick-borne zoonotic diseases depends on the risk of a bite from an infected tick, which can be broken down into its component parts as the number of host-seeking ticks in the environment, in particular nymphs, and the prevalence of tick-borne pathogens they are carrying. In turn, the prevalence of tick-borne pathogens is dependent upon tick biting intensity on hosts that support transmission between ticks; namely rodents. These ticks once fed moult into the next life stage and search for the next blood meal, thus posing a zoonotic risk. Here, we analyse tick biting intensity on rodents in a known tick-borne encephalitis (TBE) focus in Trentino (northern Italy). We examine patterns of tick demography and the influence of host densities and climate on ticks' generation time, development rates, tick density and intensity. During the period 2000-2004, a population of the yellow-necked mouse, Apodemus flavicollis, the most important TBE transmission host, was intensively monitored. Ticks feeding on individual rodents were counted, distinguishing between the larval and nymph life-stages. Local temperature and relative humidity was calculated using both data-loggers in the field site and regional weather stations. We investigated which factors had a predictive value both on feeding tick intensity and on the overall density of larvae or nymphs feeding on rodents in a year. We observed a negative effect of rodent density on tick intensity, while temperature influenced positively both larvae and nymph intensity. Overall larval density was higher in the years and trapping grids where rodent density was higher, while for nymphs no such effect was observed. The best explanatory variable for nymph density was the larval density in the previous year, confirming the discrete nature of tick demography. This provides important information in terms of monitoring the risk to humans of acquiring pathogen-infected ticks.     

A model of Leptospirosis infection in an African rodent to determine risk to humans: seasonal fluctuations and the impact of rodent control

Human leptospirosis (Leptospira spp. infection) is a worldwide public health problem that is of greatest concern for humid tropical and subtropical regions. The magnitude of the problem in these areas is larger because of the climatic and environmental conditions the bacterium face outside their hosts but also because of the frequency of contacts between people and sources of infection. Rodents are thought to play the most important role in the transmission of human leptospirosis. We here model the dynamics of infection in an African rodent (Mastomys natalensis) that is thought to be the principal source of infection in parts of Tanzania. Our model, representing the climatic conditions in central Tanzania, suggests a strong seasonality in the force of infection on humans with a peak in the abundance of infectious mice between January and April in agricultural environments. In urban areas the dynamics are predicted to be more stable and the period of high numbers of infectious animals runs from February to July. Our results indicate that removal of animals by trapping rather than reducing the suitability of the environment for rodents will have the greater impact on reducing human cases of leptospirosis.     

我国蜱和人群中TBEV流行情况的Meta分析

目的 通过评价蜱、人群中蜱传脑炎病毒阳性率及血清抗体阳性率的情况,分析蜱传脑炎在我国的流行特点,明确我国现行蜱传脑炎预防控制措施疫苗接种的重要意义,为该病的预防控制提供科学依据。方法 检索PubMed、万方、维普和知网数据库搜集2000-2019年发表的关于蜱中蜱传脑炎病毒阳性率和人血清学调查的文章,通过Meta分析方法利用Stata15软件对选定的11篇和12篇相关文献进行汇总和分析,得到蜱传脑炎在我国蜱和人群中的流行特点。结果 2000-2019年我国TBEV阳性蜱主要分布在吉林、黑龙江和内蒙古。不同蜱种中TBEV阳性率不同,森林革蜱中TBEV阳性率最高为5%(95%CI:2%~10%,P<0.05)。人群特征分析显示:男性抗体阳性率高于女性,林区工人、军人和农民易感染。不同地区人群血清抗体阳性率差异很大,新疆地区的抗体阳性率最高为14%(95%CI:9%~21%,P<0.05)。结论 我国TBEV流行多在东北地区,阳性蜱以森林草蜱为主,感染人群多为林区工人、军人和农民。     

The species composition of mosquitoes and ticks in Armenia

Comprehensive epidemiological, entomological, virological, and parasitological studies were conducted to examine the species composition and size of bloodsucking arthropoda (mosquitoes and ticks). A total of 64,567 mosquitoes and 45,180 Ixodes ticks were collected. Among the mosquitoes, Anopheles maculipennis was a prevalent species (81.6%). In all climatic zones, Dermacentor marginatus was the largest in number and most abundant during flag collections from cattle and plants (62.5% and 95.5%, respectively). Virological studies of the collected field material identified 125 strains of arboviruses belonging to 10 viruses: Tyaginya, Sindbis, Batai, Dkhori, tick-borne encephalitis, West Nile fever, Tamdy, KGL, Geta, and Bkhandzha. The identified arboviruses are environmentally associated with both mosquitoes and ticks. The larger number and diversity of bloodsucking artropoda present a potential risk of outbursts of arbovirus infections on the territory of the republic.     

Roadside ecology and epidemiology of tick-borne diseases

When humans, pets and livestock walk along roads, they may encounter questing ticks and tick-borne pathogens. A new field of environmental science called road ecology can help researchers study the complex epidemiology of tick-borne diseases in the unique roadside environment. This paper reviews some of the important ways that roads alter the distribution, abundance and behaviour of wildlife species that are involved in the enzootic cycles of tick-borne diseases. Compared to the surrounding landscape, roadways often constitute a different environment and hence there is no assurance that disease risk along roads will be the same as in the adjacent landscape, or that disease control measures taken in the surrounding landscape will work in the adjacent roadway. Since roadways have their own special ecological conditions, are used extensively by the human populace and play strategic roles in community security, we believe that roadways should be one of the habitats where tick-borne diseases are studied. It is amazing that at this late period of human history, epidemiological research along such important corridors has been almost completely ignored.     

北京市首例莱姆病合并斑点热混合感染确诊病例的流行病学调查分析

目的 分析北京市首例莱姆病合并斑点热混合感染确诊病例的流行病学特征,为蜱传疾病防控工作提供科学依据。方法 通过现场流行病学个案调查,了解患者活动史、发病就诊过程, 临床表现以及实验室检测结果,并对其进行分析。结果 调查结果提示北京市郊可能存在莱姆病和斑点热重叠自然疫源地。结论 本起疫情是北京市首例莱姆病合并斑点热混合感染确诊病例,建议在相关地区开展人群和病媒生物监测,明确莱姆病和斑点热疫区范围,警惕人群感染蜱传疾病的风险。     

The possible consequences of the probable global warming of the climate for the spread of blood-sucking ectoparasites and the pathogens they transmit

The paper reviews the causes and possible consequences of the warming-up of global climate. Probable changes in the areas of vectors and blood-suckers, which are most important for Russia, are analyzed. The vectors of malaria and tick-borne pathogens were used as special subjects of prognostic survey. The paper shows it necessary to computer-aided simulate possible consequences of climatic warming-up for changes in the parasitological situation in the Russian Federation.     

Acquisition dynamics of Borrelia burgdorferi and the agent of human granulocytic ehrlichiosis at the host-vector interface

The population dynamics of two cotransmitted tick-borne pathogens, Borrelia burgdorferi and the agent of human granulocytic ehrlichiosis (aoHGE), were assessed at the skin-vector interface at intervals after tick attachment on infected mice. Quantitative real-time polymerase chain reaction targeting the B. burgdorferi flagellin gene revealed consistent decreases in spirochete numbers in skin at the sites of tick attachment compared with non-tick attachment sites. This phenomenon was found during early (2 weeks) and late (8 weeks) infection and at 24, 48, and 72 h after tick attachment. A nonspecific inflammatory stimulus, implantation of suture material, did not have this effect. In contrast to B. burgdorferi, copy numbers of an aoHGE p44 target gene target were significantly increased at the sites of tick attachment, compared with non-tick sites. The non-specific stimulus of suture material had the same effect on aoHGE recruitment as tick attachment in aoHGE infected mice. These results reinforce the concept that B. burgdorferi interfaces with its vector by virtue of its non-systemic dermatotropism, and not via systemic hematogenous acquisition. In contrast, results indicate that the aoHGE relies upon hematogenous acquisition. Thus, these two cotransmitted tick-borne pathogens utilize distinctly different means of vector acquisition.     

Organization and tactics of the ground tick control in the south of the Tyumen Region

Measures for protection of the general population from the attacks of vectors of natural and focal infections were implemented by OOO "Spetsbioservis" at the expense of the regional budget in the involving foci oftick-borne encephalitis (TBE) and Ixodes tick-borne encephalitis in the south of the Tyumen Region during 2002-2004. The organizational and tactical issues of ground antitick treatments were perfected during this work. The paper describes the maximum effective completeness of teams of disinfectors and their supply with materials and equipment, as applied to local conditions. This scheme of organizational and tactical measures for acaricidal treatments in the south of the Tyumen Region in 2002-2004 has indicated their high effectiveness and mobility. In 2002-2003, tick bites were not recorded in children's health facilities. In these years, the incidence of TBE in the population of Tyumen reduced by 39.3% as compared with 2001. The qualitative implementation of acaricidal treatments, their extended scopes, successively intensified sanitary educational work among the population, and introduced personal prophylactic agents (repellents and protective clothes) will substantially affect the epidemiological situation associated with tick-borne infections in the region.     

Ecological bases of the combination of natural foci of leptospirosis, tick-borne encephalitis, and ixodes tick-borne borrelioses in the ecosystems of a northern forest-steppe subzone in the Tyumen region

In the context of the present-day teaching of parasitocenoses and the proposition that the pathogen's population is the only compulsory and specific component of a natural focus, the authors bring to light the ecological bases of the combination of natural foci of leptospirosis and tick-borne encephalitis, leptospirosis and Ixodes tick-borne borrelioses. These foci are one-host population-combined. While analyzing the combination of the foci, it is expedient to consider in pairs since this provides a way of identifying the combination bases that are unique to these foci and determining the level, pattern, type, and degree of the combination of foci and, on their basis, the type of a combined focus. By determining the confined pattern of foci of leptospirosis, tick-borne encephalitis, and Ixodes tick-borne borrelioses to the same elements of a landscape, the morphological structure of the northern forest-steppe landscape of the Tyumen Region predetermines their relationship, by acting as the abiotic basis of the combination of foci. Despite the differences in the types of the parasitic systems and the absence of the same mechanism of transmission of causative agents, the natural foci of leptospirosis, tick-borne encephalitis, and Ixodes tick-borne borrelioses are, nevertheless, combined at the level of parasitocenosis of the co-acting populations of pathogenic organisms and their reservoir hosts act as the biotic bases of the combination of foci of leptospirosis, tick-borne encephalitis, and Ixodes tick-borne borrelioses. The susceptibility of Cl. rutilus and S. araneus to infection with the pathogens ofleptospirosis, tick-borne encephalitis, and Ixodes tick-borne borrelioses and multihost pattern of the causative agents act as the epizootic bases of a combination of the foci of leptospirosis, tick-borne encephalitis, and Ixodes tick-borne borrelioses. It has been shown that the biotic, epizootic, and abiotic bases of a combination of the natural foci of leptospirosis, tick-borne encephalitis, and Ixodes tick-borne borrelioses of the Javanica serogroup are, in the aggregate, the ecological bases of the combination of these foci.     

The current status of foci of tick-borne relapsing fever in the western Pamirs

For the first time in the last 20-50 years foci of tick-borne relapsing fever have been surveyed in the western Pamirs. Settlements in the Piandzha valley were shown to be (as in the 1930s and 1960s) affected by Ornithodoros papillipes Bir., the carrier of the infection. Though the number of ticks is still rather high, it is nowadays considerably reduced. The findings suggest a tendency towards a decrease in the infestation of the carrier population with the agent of the disease. The traditional type of construction (especially widespread in far-off regions), when houses are built in such a way that living rooms are joined with stables inhabited by ticks, ensures favourable conditions for the existence of tick-borne relapsing fever foci and the contact of people with the agent of the infection. This demonstrates high epidemiological danger of the infection foci in the western Pamirs.     

Tick-borne pulmonary disease: update on diagnosis and management.

Ticks are capable of transmitting viruses, bacteria, protozoa, and rickettsiae to man. Several of these tick-borne pathogens can lead to pulmonary disease. Characteristic clinical features, such as erythema migrans in Lyme disease, or spotted rash in a spotted fever group disease, may serve as important diagnostic clues. Successful management of tick-borne diseases depends on a high index of suspicion and recognition of their clinical features. Patients at risk for tick bites may be coinfected with two or more tick-borne pathogens. A Lyme vaccine has recently become available for use in the United States. Disease prevention depends on the avoidance of tick bites. When patients present with respiratory symptoms and a history of a recent tick bite or a characteristic skin rash, a differential diagnosis of a tick-borne pulmonary disease should be considered. Early diagnosis and appropriate antibiotic therapy for these disorders lead to greatly improved outcomes.