Model-Based Prediction of Nephropathia Epidemica Outbreaks Based on Climatological and Vegetation Data and Bank Vole Population Dynamics

Impact of Environmental Factors on the Distribution Patterns of Nephropathia Epidemica Cases in Western Europe

BACKGROUND

Environmental factors, such as fluctuations of climatic conditions and land cover, play a pivotal role in driving infectious disease epidemics, particularly those originating from wildlife reservoirs. Orthohantavirus puumalaense, hosted by bank voles in Europe, is the causative agent of a form of hemorrhagic fever and renal syndrome called nephropathia epidemica. Despite two decades of consistent presence in western Europe, nephropathia epidemica outbreaks still pose challenges due to localized periodic occurrences and a lack of understanding of its environmental drivers.

OBJECTIVE

Our study aims to bridge this gap by investigating the specific ecological and climatic factors influencing nephropathia epidemica outbreaks in western Europe.

METHODS

We compiled monthly, serologically confirmed nephropathia epidemica case data obtained from public health authorities in Belgium, France, Germany, and the Netherlands for the period 2004-2012. Cases were georeferenced to the finest available administrative unit. We selected 28 covariates, including climatic variables, land cover, tree species distributions, and human population, and implemented a Bayesian spatiotemporal model using integrated nested Laplace approximation (INLA) with zero-inflated Poisson distribution, including fixed effects and spatial, temporal, and nonstructured random effects.

RESULTS

We identified key triggers for nephropathia epidemica outbreaks, particularly climate-mediated changes in all seasons up to 2 years before, favoring tree mast impacting bank vole abundance. Our findings revealed that while land-cover factors mostly determine hotspot locations, climatic fluctuation patterns rather tend to modulate outbreak intensity.

DISCUSSION

Crucially, our model allows for the generation of yearly maps showcasing nephropathia epidemica incidence and risk factors, aiding in public health preparedness against climate change-induced disease emergence. This work represents a significant step toward developing targeted forecasting tools for Orthohantavirus puumalaense outbreaks, offering valuable insights for epidemic control strategies. https://doi.org/10.1289/EHP15457.

High-resolution early warning system for human Puumala hantavirus infection risk in Germany

The fluctuation of human infections by the Puumala orthohantavirus (PUUV) in Germany has been linked to weather and phenology parameters that drive the population growth of its host species. We quantified the annual PUUV-outbreaks at the district level by binarizing the reported infections in the period 2006-2021. With these labels we trained a model based on a support vector machine classifier for predicting local outbreaks and incidence well in advance. The feature selection for the optimal model was performed by a heuristic method and identified five monthly weather variables from the previous two years plus the beech flowering intensity of the previous year. The predictive power of the optimal model was assessed by a leave-one-out cross-validation in 16 years that led to an 82.8% accuracy for the outbreak and a 0.457 coefficient of determination for the incidence. Prediction risk maps for the entire endemic area in Germany will be annually available on a freely-accessible permanent online platform of the German Environment Agency. The model correctly identified 2022 as a year with low outbreak risk, whereas its prediction for large-scale high outbreak risk in 2023 was not confirmed.

Small mammal community composition impacts bank vole (Clethrionomys glareolus) population dynamics and associated seroprevalence of Puumala orthohantavirus

Rodents are important reservoirs for zoonotic pathogens that cause diseases in humans. Biodiversity is hypothesized to be closely related to pathogen prevalence through multiple direct and indirect pathways. For example, the presence of non-host species can reduce contact rates of the main reservoir host and thus reduce the risk of transmission ("dilution effect"). In addition, an overlap in ecological niches between two species could lead to increased interspecific competition, potentially limiting host densities and reducing density-dependent pathogen transmission processes. In this study, we investigated the relative impact of population-level regulation of direct and indirect drivers of the prevalence of Puumala orthohantavirus (PUUV) in bank voles (Clethrionomys glareolus) during years with high abundance. We compiled data on small mammal community composition from four regions in Germany between 2010 and 2013. Structural equation modeling revealed a strong seasonality in PUUV control mechanisms in bank voles. The abundance of shrews tended to have a negative relationship with host abundance, and host abundance positively influenced PUUV seroprevalence, while at the same time increasing the abundance of competing non-hosts like the wood mouse (Apodemus sylvaticus) and the yellow-necked field mouse (Apodemus flavicollis) were associated with reduced PUUV seroprevalence in the host. These results indicate that for PUUV in bank voles, dilution is associated with increased interspecific competition. Anthropogenic pressures leading to the decline of Apodemus spp. in a specific habitat could lead to the amplification of mechanisms promoting PUUV transmission within the host populations.

Transmission modelling of environmentally persistent zoonotic diseases: a systematic review

Transmission of many infectious diseases depends on interactions between humans, animals, and the environment. Incorporating these complex processes in transmission dynamic models can help inform policy and disease control interventions. We identified 20 diseases involving environmentally persistent pathogens (ie, pathogens that survive for more than 48 h in the environment and can cause subsequent human infections), of which indirect transmission can occur from animals to humans via the environment. Using a systematic approach, we critically appraised dynamic transmission models for environmentally persistent zoonotic diseases to quantify traits of models across diseases. 210 transmission modelling studies were identified and most studies considered diseases of domestic animals or high-income settings, or both. We found that less than half of studies validated their models to real-world data, and environmental data on pathogen persistence was rarely incorporated. Model structures varied, with few studies considering the animal-human-environment interface of transmission in the context of a One Health framework. This Review highlights the need for more data-driven modelling of these diseases and a holistic One Health approach to model these pathogens to inform disease prevention and control strategies.

Detection and Genetic Characterization of Puumala Orthohantavirus S-Segment in Areas of France Non-Endemic for Nephropathia Epidemica

Puumala virus (PUUV) in Europe causes nephropathia epidemica (NE), a mild form of hemorrhagic fever with renal syndrome (HFRS). The incidence of NE is highly heterogeneous spatially, whereas the geographic distribution of the wild reservoir of PUUV, the bank vole, is essentially homogeneous. Our understanding of the processes driving this heterogeneity remains incomplete due to gaps in knowledge. Little is known about the current distribution and genetic variation of PUUV in the areas outside the well-identified zones of NE endemicity. We trapped bank voles in four forests in French regions in which NE is considered non-endemic, but sporadic NE cases have been reported recently. We tested bank voles for anti-PUUV IgG and characterized the S segment sequences of PUUV from seropositive animals. Phylogenetic analyses revealed specific amino-acid signatures and genetic differences between PUUV circulating in non-endemic and nearby NE-endemic areas. We also showed, in temporal surveys, that the amino-acid sequences of PUUV had undergone fewer recent changes in areas non-endemic for NE than in endemic areas. The evolutionary history of the current French PUUV clusters was investigated by phylogeographic approaches, and the results were considered in the context of the history of French forests. Our findings highlight the need to monitor the circulation and genetics of PUUV in a larger array of bank vole populations, to improve our understanding of the risk of NE.

Molecular and epidemiological characteristics of human Puumala and Dobrava-Belgrade hantavirus infections, Germany, 2001 to 2017

Introduction

Two hantavirus species, Puumala (PUUV) and Dobrava-Belgrade (DOBV) virus (genotype Kurkino), are endemic in Germany. Recent PUUV outbreaks raised questions concerning increasing frequency of outbreaks and expansion of PUUV endemic areas.

Aims

To describe the epidemiology of human PUUV and DOBV infections in Germany.

Methods

We conducted an observational retrospective study analysing national hantavirus surveillance data notified to the national public health institute and hantavirus nucleotide sequences from patients collected at the national consultation laboratory between 2001 and 2017. Matching molecular sequences with surveillance data, we conducted epidemiological, phylogenetic and phylogeographic analyses.

Results

In total, 12,148 cases of symptomatic hantavirus infection were notified 2001–17 (mean annual incidence: 0.87/100,000; range: 0.09–3.51). PUUV infections showed a highly variable space-time disease incidence pattern, causing large outbreaks every 2–3 years with peaks in early summer and up to 3,000 annually reported cases. Sex-specific differences in disease presentation were observed. Of 202 PUUV nucleotide sequences obtained from cases, 189 (93.6%) fall into well-supported phylogenetic clusters corresponding to different endemic areas in Germany. DOBV infections caused few, mostly sporadic cases in autumn and winter in the north and east of Germany.

Conclusions

The frequency of PUUV outbreaks increased between 2001 and 2017 but our data does not support the suggested expansion of endemic areas. The epidemiology of PUUV and DOBV-Kurkino infections differs in several aspects. Moreover, the latter are relatively rare and combining efforts and data of several countries to identify risk factors and develop specific recommendations for prevention could be worthwhile.

Tick-borne encephalitis incidence forecasts for Austria, Germany, and Switzerland

The forecast of human tick-borne encephalitis (TBE) incidence for the next years has been on the research agenda of epidemiologists since the discovery of this tick-borne zoonosis. Based on models to explain the trend as well as the low- and high-frequency oscillations in the Austrian TBE incidence series, TBE forecasts for Austria, Germany and Switzerland are presented here. For this purpose, generalized linear models (GLMs) of type negative binomial regression were calibrated with the TBE incidences of the period 1991-2018 to forecast the TBE incidences 2019 and 2020. The GLMs require only 4-5 predictors, 2 of which are large-scale synchronized over Central Europe and used for all 3 countries. Predictors used include the demographic parameters total population and net migration rate, the Scandinavian index which describes the large-scale atmospheric circulation patterns, the fructification index of the European beech (Fagus sylvatica) 2 years prior as a proxy for the intensity of the TBE virus transmission cycle, and the national TBE vaccination coverage. Since an official time series of TBE vaccination coverage is only available for Austria, the missing TBE vaccination coverages of Germany and Switzerland were reconstructed and presented as the first results. Model verification results in explained variances of 76% for Austria, 84% for Germany, and 89% for Switzerland. Thus, the best model fit was determined for the Swiss GLM which is able to predict the TBE incidence with a root-mean-square error of RMSE = 25 cases (19% of the mean TBE incidence 1991-2018 or 7% of the TBE incidence of 2018). Forecasting TBE incidences for 2019 and 2020 results in 92 ± 12 and 142 ± 26 TBE cases for Austria, 417 ± 71 and 670 ± 168 TBE cases for Germany as well as 235 ± 30 and 465 ± 91 TBE cases for Switzerland.

Identifying the patterns and drivers of Puumala hantavirus enzootic dynamics using reservoir sampling

Hantaviruses are zoonotic hemorrhagic fever viruses for which prevention of human spillover remains the first priority in disease management. Tailored intervention measures require an understanding of the drivers of enzootic dynamics, commonly inferred from distorted human incidence data. Here, we use longitudinal sampling of approximately three decades of Puumala orthohantavirus (PUUV) evolution in isolated reservoir populations to estimate PUUV evolutionary rates, and apply these to study the impact of environmental factors on viral spread. We find that PUUV accumulates genetic changes at a rate of ∼10⁻⁴ substitutions per site per year and that land cover type defines the dispersal dynamics of PUUV, with forests facilitating and croplands impeding virus spread. By providing reliable short-term PUUV evolutionary rate estimates, this work facilitates the evaluation of spatial risk heterogeneity starting from timed phylogeographic reconstructions based on virus sampling in its animal reservoir, thereby side-stepping the need for difficult-to-collect human disease incidence data.

Human infectious diseases and the changing climate in the Arctic

Climatic factors, especially temperature, precipitation, and humidity play an important role in disease transmission. As the Arctic changes at an unprecedented rate due to climate change, understanding how climatic factors and climate change affect infectious disease rates is important for minimizing human and economic costs. The purpose of this systematic review was to compile recent studies in the field and compare the results to a previously published review. English language searches were conducted in PubMed, ScienceDirect, Scopus, and PLOS One. Russian language searches were conducted in the Scientific Electronic Library "eLibrary.ru". This systematic review yielded 22 articles (51%) published in English and 21 articles (49%) published in Russian since 2012. Articles about zoonotic and vector-borne diseases accounted for 67% (n = 29) of the review. Tick-borne diseases, tularemia, anthrax, and vibriosis were the most researched diseases likely to be impacted by climatic factors in the Arctic. Increased temperature and precipitation are predicted to have the greatest impact on infectious diseases in the Arctic.

Emerging Rodent-Borne Viral Zoonoses in Trento, Italy

Rodent-borne hanta- and arenaviruses are an emerging public health threat in Europe; however, their circulation in human populations is usually underestimated since most infections are asymptomatic. Compared to other European countries, Italy is considered 'low risk' for these viruses, yet in the Province of Trento, two pathogenic hantaviruses (Puumala and Dobrava-Belgrade virus) and one arenavirus (Lymphocytic Choriomeningitis Virus) are known to circulate in rodent reservoirs. In this paper, we performed a follow-up serological screening in humans to detect variation in the prevalence of these three viruses compared to previous analyses carried out in 2002. We also used a statistical model to link seropositivity to risk factors such as occupational exposure, cutting firewood, hunting, collecting mushrooms, having a garden and owning a woodshed, a dog or a companion rodent. We demonstrate a significant increase in the seroprevalence of all three target viruses between 2002 and 2015, but no risk factors that we considered were significantly correlated with this increase. We conclude that the general exposure of residents in the Alps to these viruses has probably increased during the last decade. These results provide an early warning to public health authorities, and we suggest more detailed diagnostic and clinical investigations on suspected cases.

Characterization of the Temporal Trends in the Rate of Cattle Carcass Condemnations in the US and Dynamic Modeling of the Condemnation Reasons in California With a Seasonal Component

Based on the 2016 National Cattlemen's Beef Association statistics, the cattle inventory in the US reached 93.5 million head, from which 30.5 million were commercial slaughter in 2016. California ranked fourth among all the US states that raise cattle and calves, with 5.15 million head and approximately 1.18 million slaughtered animals per year. Approximately 0.5% of cattle carcasses in the US are condemned each year, which has an important economic impact on cattle producers.In this study, we first described and compared the temporal trends of cattle carcass condemnations in all the US states from Jan-2005 to Dec-2014. Then, we focused on the condemnation reasons with a seasonal component in California and used dynamic harmonic regression (DHR) models both to model (from Jan-2005 to Dec-2011) and predict (from Jan-2012 to Dec-2014) the carcass condemnations rate in different time horizons (3 to 12 months).Data consisted of daily reports of 35 condemnation reasons per cattle type reported in 684 federally inspected slaughterhouses in the US from Jan-2005 to Dec-2014 and the monthly slaughtered animals per cattle type per states. Almost 1.5 million carcasses were condemned in the US during the 10 year study period (Jan 2005-Dec 2014), and around 40% were associated with three condemnation reasons: malignant lymphoma, septicemia and pneumonia. In California, emaciation, eosinophilic myositis and malignant lymphoma were the only condemnation reasons presenting seasonality and, therefore, the only ones selected to be modeled using DHRs. The DHR models for Jan-2005 to Dec-2011 were able to correctly model the dynamics of the emaciation, malignant lymphoma and eosinophilic myositis condemnation rates with coefficient of determination (Rt2) of 0.98, 0.87 and 0.78, respectively. The DHR models for Jan-2012 to Dec-2014 were able to predict the rate of condemned carcasses 3 month ahead of time with mean relative prediction error of 33, 11, and 38%, respectively. The systematic analysis of carcass condemnations and slaughter data in a more real-time fashion could be used to identify changes in carcass condemnation trends and more timely support the implementation of prevention and mitigation strategies that reduce the number of carcass condemnations in the US.

Urban Rodent Surveillance, Climatic Association, and Genomic Characterization of Seoul Virus Collected at U.S. Army Garrison, Seoul, Republic of Korea, 2006-2010

Rodent-borne pathogens pose a critical public health threat in urban areas. An epidemiological survey of urban rodents was conducted from 2006 to 2010 at the U.S. Army Garrison (USAG), Seoul, Republic of Korea (ROK), to determine the prevalence of Seoul virus (SEOV), a rodent-borne hantavirus. A total of 1,950 rodents were captured at USAG, Yongsan, near/in 19.4% (234/1,206) of the numbered buildings. Annual mean rodent infestation rates were the highest for food service facilities, e.g., the Dragon Hill Lodge complex (38.0 rodents) and the Hartell House (18.8 rodents). The brown rat, Rattus norvegicus, accounted for 99.4% (1,939/1,950) of all the rodents captured in the urban area, whereas only 0.6% (11/1,950) of the rodents was house mice (Mus musculus). In November 2006, higher numbers of rats captured were likely associated with climatic factors, e.g., rainfall and temperatures as rats sought harborage in and around buildings. Only 4.7% (34/718) of the rodents assayed for hantaviruses was serologically positive for SEOV. A total of 8.8% (3/34) R. norvegicus were positive for SEOV RNA by reverse transcription polymerase chain reaction, of which two SEOV strains were completely sequenced and characterized. The 3' and 5' terminal sequences revealed incomplete complementary genomic configuration. Seoul virus strains Rn10-134 and Rn10-145 formed a monophyletic lineage with the prototype SEOV strain 80-39. Seoul virus Medium segment showed the highest evolutionary rates compared with the Large and Small segments. In conclusion, this report provides significant insights into continued rodent-borne disease surveillance programs that identify hantaviruses for analysis of disease risk assessments and development of mitigation strategies.

First insights into Puumala orthohantavirus circulation in a rodent population in Alsace, France

In-depth knowledge on the mechanisms that maintain infection by a zoonotic pathogen in an animal reservoir is the key to predicting and preventing transmission to humans. The Puumala orthohantavirus (PUUV), the most prevalent orthohantavirus in Western Europe, causes a mild form of haemorrhagic fever with renal syndrome (HFRS) in humans. In France, this endemic illness affects the north-eastern part of the country. We conducted a 4-year capture-mark-recapture study in a bank vole population, combined with molecular analyses, to explore the epidemiological situation of PUUV in Alsace, a French region where human cases have occurred, but for which no studies have been conducted on this reservoir host. PUUV-infected bank voles were detected in the 2 years that showed high bank vole density with a prevalence of 4%. The individual PUUV sequences identified in this study were similar from year to year and similar to other French sequences. On a very small spatial scale, the distribution of seropositive bank voles was very heterogeneous in time and space. The short distances travelled on average by bank voles resulted in spatial clusters of seropositive rodents, which spread only very gradually throughout the year.

Modelling human Puumala hantavirus infection in relation to bank vole abundance and masting intensity in the Netherlands

This paper deals with modelling the relationship between human Puumala hantavirus (PUUV) infection, the abundance and prevalence of infection of the host (the bank vole), mast, and temperature. These data were used to build and parametrise generalised regression models, and parametrise them using datasets on these factors pertaining to the Netherlands. The performance of the models was assessed by considering their predictive power. Models including mast and monthly temperature performed well, and showed that mast intensity influences vole abundance and hence human exposure for the following year. Thus, the model can aid in forecasting of human illness cases, since (1) mast intensity influences the vole abundance and hence human exposure for the following year and (2) monitoring of mast is much more feasible than determining bank vole abundance.

Validation of the Puumala virus rapid field test for bank voles in Germany

Puumala virus (PUUV) causes many human infections in large parts of Europe and can lead to mild to moderate disease. The bank vole (Myodes glareolus) is the only reservoir of PUUV in Central Europe. A commercial PUUV rapid field test for rodents was validated for bank-vole blood samples collected in two PUUV-endemic regions in Germany (North Rhine-Westphalia and Baden-Württemberg). A comparison of the results of the rapid field test and standard ELISAs indicated a test efficacy of 93-95%, largely independent of the origin of the antigens used in the ELISA. In ELISAs, reactivity for the German PUUV strain was higher compared to the Swedish strain but not compared to the Finnish strain, which was used for the rapid field test. In conclusion, the use of the rapid field test can facilitate short-term estimation of PUUV seroprevalence in bank-vole populations in Germany and can aid in assessing human PUUV infection risk.

Spatial and Temporal Epidemiology of Nephropathia Epidemica Incidence and Hantavirus Seroprevalence in Rodent Hosts: Identification of the Main Environmental Factors in Europe

In Europe, the increasing number of nephropathia epidemica (NE) infections in humans, caused by Puumala virus carried by bank voles (Myodes glareolus), has triggered studies of environmental factors driving these infections. NE infections have been shown to occur in specific geographical areas characterized by environmental factors that influence the distribution and dynamics of host populations and virus persistence in the soil. Here, we review the influence of environmental conditions (including climate factors, food availability and habitat conditions) with respect to incidence in humans and seroprevalence in rodents, considering both direct and indirect transmission pathways. For each type of environmental factor, results and discrepancies between studies are presented and examined in the light of biological hypotheses. Overall, food availability and temperature appear to be the main drivers of host seroprevalence and NE incidence, but data quality and statistical approaches varied greatly among studies. We highlight the issues that now need to be addressed and suggest improvements for study design in regard to the current knowledge on hantavirus epidemiology.

Temporal dynamics of Puumala hantavirus infection in cyclic populations of bank voles

Understanding the dynamics of zoonotic pathogens in their reservoir host populations is a prerequisite for predicting and preventing human disease epidemics. The human infection risk of Puumala hantavirus (PUUV) is highest in northern Europe, where populations of the rodent host (bank vole, Myodes glareolus) undergo cyclic fluctuations. We conducted a 7-year capture-mark-recapture study to monitor seasonal and multiannual patterns of the PUUV infection rate in bank vole populations exhibiting a 3-year density cycle. Infected bank voles were most abundant in mid-winter months during years of increasing or peak host density. Prevalence of PUUV infection in bank voles exhibited a regular, seasonal pattern reflecting the annual population turnover and accumulation of infections within each year cohort. In autumn, the PUUV transmission rate tracked increasing host abundance, suggesting a density-dependent transmission. However, prevalence of PUUV infection was similar during the increase and peak years of the density cycle despite a twofold difference in host density. This may result from the high proportion of individuals carrying maternal antibodies constraining transmission during the cycle peak years. Our exceptionally intensive and long-term dataset provides a solid basis on which to develop models to predict the dynamic public health threat posed by PUUV in northern Europe.

Beech Fructification and Bank Vole Population Dynamics--Combined Analyses of Promoters of Human Puumala Virus Infections in Germany

The transmission of wildlife zoonoses to humans depends, amongst others, on complex interactions of host population ecology and pathogen dynamics within host populations. In Europe, the Puumala virus (PUUV) causes nephropathia epidemica in humans. In this study we investigated complex interrelations within the epidemic system of PUUV and its rodent host, the bank vole (Myodes glareolus). We suggest that beech fructification and bank vole abundance are both decisive factors affecting human PUUV infections. While rodent host dynamics are expected to be directly linked to human PUUV infections, beech fructification is a rather indirect predictor by serving as food source for PUUV rodent hosts. Furthermore, we examined the dependence of bank vole abundance on beech fructification. We analysed a 12-year (2001-2012) time series of the parameters: beech fructification (as food resource for the PUUV host), bank vole abundance and human incidences from 7 Federal States of Germany. For the first time, we could show the direct interrelation between these three parameters involved in human PUUV epidemics and we were able to demonstrate on a large scale that human PUUV infections are highly correlated with bank vole abundance in the present year, as well as beech fructification in the previous year. By using beech fructification and bank vole abundance as predictors in one model we significantly improved the degree of explanation of human PUUV incidence. Federal State was included as random factor because human PUUV incidence varies considerably among states. Surprisingly, the effect of rodent abundance on human PUUV infections is less strong compared to the indirect effect of beech fructification. Our findings are useful to facilitate the development of predictive models for host population dynamics and the related PUUV infection risk for humans and can be used for plant protection and human health protection purposes.

Climate Variability and the Occurrence of Human Puumala Hantavirus Infections in Europe: A Systematic Review

Hantaviruses are distributed worldwide and are transmitted by rodents. In Europe, the infection usually manifests as a mild form of haemorrhagic fever with renal syndrome (HFRS) known as nephropathia epidemica (NE), which is triggered by the virus species Puumala. Its host is the bank vole (Myodes glareolus). In the context of climate change, interest in the role of climatic factors for the disease has increased. A systematic review was conducted to investigate the association between climate variability and the occurrence of human Puumala hantavirus infections in Europe. We performed a literature search in the databases MEDLINE, EMBASE and Web of Science. Studies that investigated Puumala virus infection and climatic factors in any European country with a minimum collection period of 2 years were included. The selection of abstracts and the evaluation of included studies were performed by two independent reviewers. A total of 434 titles were identified in the databases, of which nine studies fulfilled the inclusion criteria. The majority of studies were conducted in central Europe (Belgium, France and Germany), while only two came from the north (Sweden) and one from the south (Bosnia). Strong evidence was found for a positive association between temperature and NE incidence in central Europe, while the evidence for northern Europe so far appears insufficient. Results regarding precipitation were contradictory. Overall, the complex relationships between climate and hantavirus infections need further exploration to identify specific health risks and initiate appropriate intervention measures in the context of climate change.

Spatiotemporal heterogeneity analysis of hemorrhagic fever with renal syndrome in China using geographically weighted regression models

Hemorrhagic fever with renal syndrome (HFRS) is an important public health problem in China. The identification of the spatiotemporal pattern of HFRS will provide a foundation for the effective control of the disease. Based on the incidence of HFRS, as well as environmental factors, and social-economic factors of China from 2005–2012, this paper identified the spatiotemporal characteristics of HFRS distribution and the factors that impact this distribution. The results indicate that the spatial distribution of HFRS had a significant, positive spatial correlation. The spatiotemporal heterogeneity was affected by the temperature, precipitation, humidity, NDVI of January, NDVI of August for the previous year, land use, and elevation in 2005–2009. However, these factors did not explain the spatiotemporal heterogeneity of HFRS incidences in 2010–2012. Spatiotemporal heterogeneity of provincial HFRS incidences and its relation to environmental factors would provide valuable information for hygiene authorities to design and implement effective measures for the prevention and control of HFRS in China.

Identification of factors influencing the Puumala virus seroprevalence within its reservoir in aMontane Forest Environment

Puumala virus (PUUV) is a major cause of mild to moderate haemorrhagic fever with renal syndrome and is transmitted by the bank vole (Myodes glareolus). There has been a high cumulative incidence of recorded human cases in South-eastern Germany since 2004 when the region was first recognized as being endemic for PUUV. As the area is well known for outdoor recreation and the Bavarian Forest National Park (BFNP) is located in the region, the increasing numbers of recorded cases are of concern. To understand the population and environmental effects on the seroprevalence of PUUV in bank voles we trapped small mammals at 23 sites along an elevation gradient from 317 to 1420m above sea level. Generalized linear mixed effects models(GLMEM) were used to explore associations between the seroprevalence of PUUV in bank voles and climate and biotic factors. We found that the seroprevalence of PUUV was low (6%–7%) in 2008 and 2009, and reached 29% in 2010. PUUV seroprevalence was positively associated with the local species diversity and deadwood layer, and negatively associated with mean annual temperature, mean annual solar radiation, and herb layer. Based on these findings, an illustrative risk map for PUUV seroprevalence prediction in bank voles was created for an area of the national park. The map will help when planning infrastructure in the national park (e.g., huts, shelters, and trails).

Ecological niche modelling of bank voles in Western Europe

The bank vole (Myodes glareolus) is the natural host of Puumala virus (PUUV) in vast areas of Europe. PUUV is one of the hantaviruses which are transmitted to humans by infected rodents. PUUV causes a general mild form of hemorrhagic fever with renal syndrome (HFRS) called nephropathia epidemica (NE). Vector-borne and zoonotic diseases generally display clear spatial patterns due to different space-dependent factors. Land cover influences disease transmission by controlling both the spatial distribution of vectors or hosts, as well as by facilitating the human contact with them. In this study the use of ecological niche modelling (ENM) for predicting the geographical distribution of bank vole population on the basis of spatial climate information is tested. The Genetic Algorithm for Rule-set Prediction (GARP) is used to model the ecological niche of bank voles in Western Europe. The meteorological data, land cover types and geo-referenced points representing the locations of the bank voles (latitude/longitude) in the study area are used as the primary model input value. The predictive accuracy of the bank vole ecologic niche model was significant (training accuracy of 86%). The output of the GARP models based on the 50% subsets of points used for testing the model showed an accuracy of 75%. Compared with random models, the probability of such high predictivity was low (χ(2) tests, p < 10(-6)). As such, the GARP models were predictive and the used ecologic niche model indeed indicates the ecologic requirements of bank voles. This approach successfully identified the areas of infection risk across the study area. The result suggests that the niche modelling approach can be implemented in a next step towards the development of new tools for monitoring the bank vole's population.