Haemorrhagic Fever with Renal Syndrome: an analysis of the outbreaks in Belgium, France, Germany, the Netherlands and Luxembourg in 2005

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.

Cluster of human Puumala orthohantavirus infections due to indoor exposure?-An interdisciplinary outbreak investigation

Puumala orthohantavirus (PUUV) is the most important hantavirus species in Europe, causing the majority of human hantavirus disease cases. In central and western Europe, the occurrence of human infections is mainly driven by bank vole population dynamics influenced by beech mast. In Germany, hantavirus epidemic years are observed in 2- to 5-year intervals. Many of the human infections are recorded in summer and early autumn, coinciding with peaks in bank vole populations. Here, we describe a molecular epidemiological investigation in a small company with eight employees of whom five contracted hantavirus infections in late 2017. Standardized interviews with employees were conducted to assess the circumstances under which the disease cluster occurred, how the employees were exposed and which counteractive measures were taken. Initially, two employees were admitted to hospital and serologically diagnosed with hantavirus infection. Subsequently, further investigations were conducted. By means of a self-administered questionnaire, three additional symptomatic cases could be identified. The hospital patients' sera were investigated and revealed in one patient a partial PUUV L segment sequence, which was identical to PUUV sequences from several bank voles collected in close proximity to company buildings. This investigation highlights the importance of a One Health approach that combines efforts from human and veterinary medicine, ecology and public health to reveal the origin of hantavirus disease clusters.

Epidemiological study on the incidence of haemorrhagic fever with renal syndrome in five Western Balkan countries for a 10-year period: 2006-2015

BACKGROUND

Large-scale epidemics of haemorrhagic fever with renal syndrome (HFRS) have been reported mostly in Asia and Europe, with around 100,000 people affected each year. In the Southeast Europe, Balkan region, HFRS is endemic disease with approximately 100 cases per year. Our aim was to describe epidemiological characteristics of HFRS in five Western Balkan (WB) countries and to describe correlation between HFRS incidence and major meteorological event that hit the area in May 2014.

METHODS

National surveillance data of HFRS from Bosnia and Herzegovina, Croatia, Montenegro, North Macedonia and Serbia obtained from 1 January 2006 to 31 December 2015 were collected and analysed.

RESULTS

In a 10-year period, a total of 1,065 HFRS patients were reported in five WB countries. Cumulative incidence rate ranged from 0.05 to 15.80 per 100.000 inhabitants (in North Macedonia and Montenegro respectively). Increasing number of HFRS cases was reported with a peak incidence in three specific years (2008, 2012, and 2014). Average incidence for the entire area was higher in males than females (5.63 and 1.90 per 100.000 inhabitants respectively). Summer was the season with the highest number of cases and an average incidence rate of 1.74/100.000 inhabitants across 10-year period. Haemorrhagic fever with renal syndrome incidence was significantly increased (7.91/100.000 inhabitants) in 2014, when a few months earlier, severe floods affected several WB countries. A strong significant negative correlation (r = -.84, p < .01) between the monthly incidence of HFRS and the number of months after May's floods was demonstrated for the total area of WB.

CONCLUSION

Our findings demonstrate that the HFRS incidence had similar distribution (general, age, sex and seasonality) across majority of the included countries. Summer was the season with the highest recorded incidence. Common epidemic years were detected in all observed countries as well as a negative correlation between the monthly incidence of HFRS and the number of months after May's cyclone.

Puumala Virus Variants Circulating in Forests of Ardennes, France: Ten Years of Genetic Evolution

In Europe, Puumala virus (PUUV) transmitted by the bank vole (Myodes glareolus) is the causative agent of nephropathia epidemica (NE), a mild form of haemorrhagic fever with renal syndrome. In France, very little is known about the spatial and temporal variability of the virus circulating within bank vole populations. The present study involved monitoring of bank vole population dynamics and PUUV microdiversity over a ten-year period (2000–2009) in two forests of the Ardennes region: Elan and Croix-Scaille. Ardennes region is characterised by different environmental conditions associated with different NE epidemiology. Bank vole density and population parameters were estimated using the capture/marking/recapture method, and blood samples were collected to monitor the overall seroprevalence of PUUV in rodent populations. Phylogenetic analyses of fifty-five sequences were performed to illustrate the genetic diversity of PUUV variants between forests. The pattern of the two forests differed clearly. In the Elan forest, the rodent survival was higher, and this limited turn-over resulted in a lower seroprevalence and diversity of PUUV sequences than in the Croix-Scaille forest. Uncovering the links between host dynamics and virus microevolution is improving our understanding of PUUV distribution in rodents and the NE risk.

Genomic Epidemiology and Active Surveillance to Investigate Outbreaks of Hantaviruses

Emerging and re-emerging RNA viruses pose significant public health, economic, and societal burdens. Hantaviruses (genus Orthohantavirus, family Hantaviridae, order Bunyavirales) are enveloped, negative-sense, single-stranded, tripartite RNA viruses that are emerging zoonotic pathogens harbored by small mammals such as rodents, bats, moles, and shrews. Orthohantavirus infections cause hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome in humans (HCPS). Active targeted surveillance has elucidated high-resolution phylogeographic relationships between patient- and rodent-derived orthohantavirus genome sequences and identified the infection source by temporally and spatially tracking viral genomes. Active surveillance of patients with HFRS entails 1) recovering whole-genome sequences of Hantaan virus (HTNV) using amplicon (multiplex PCR-based) next-generation sequencing, 2) tracing the putative infection site of a patient by administering an epidemiological questionnaire, and 3) collecting HTNV-positive rodents using targeted rodent trapping. Moreover, viral genome tracking has been recently performed to rapidly and precisely characterize an outbreak from the emerging virus. Here, we reviewed genomic epidemiological and active surveillance data for determining the emergence of zoonotic RNA viruses based on viral genomic sequences obtained from patients and natural reservoirs. This review highlights the recent studies on tracking viral genomes for identifying and characterizing emerging viral outbreaks worldwide. We believe that active surveillance is an effective method for identifying rodent-borne orthohantavirus infection sites, and this report provides insights into disease mitigation and preparedness for managing emerging viral outbreaks.

Temporal Dynamics of Two Pathogenic Hantaviruses Among Rodents in Hungary

Hantaviruses are worldwide pathogens, which often cause serious or even fatal diseases in humans. Hosts are predominantly in the form of rodents and soricomorphs; however, bats are also described as an important reservoir. In Hungary, representatives of two human pathogenic species of the genus Orthohantavirus are present: the Dobrava-Belgrade orthohantavirus and Puumala orthohantavirus. In Hungarian forests, the dominant rodent species are Apodemus flavicollis, Apodemus agrarius, Apodemus sylvaticus, and Myodes glareolus, all of which are natural reservoirs comprising different hantaviruses. The aim of the study was to survey the prevalence of hantaviruses among rodent populations and examine the potential relationship regarding population densities, years, sex, and seroprevalence. Rodents were trapped at 13 sampling plots in a forest reserve located in the Mecsek Mountain range, Hungary, from March to October between 2011 and 2014. Rodent serum samples were tested for IgG antibodies against Dobrava-Belgrade virus and Puumala virus by enzyme-linked immunosorbent assay (ELISA) using a recombinant nucleocapsid protein. During the 4-year sampling period, 2491 specimens were tested and 254 (10.2%) proved seropositive for orthohantaviruses. In 2011, the seroprevalence among Apodemus spp. and M. glareolus was 17.2% (114/661) and 3.9% (3/77), respectively, although this rate had reversed itself in 2014. Seropositivity was substantiated in 18.4% (12/65) of Myodes voles, while only 3.6% (13/359) of the tested Apodemus rodents were found to be IgG positive. Seroconversion was observed in 58 cases, while seroreversion was only detected in 3 individual cases. A significant difference among the number of infected males and females was identified in the first 2 years of our study. Winter survival with respect to rodents was not negatively affected due to the hantavirus infection. Hantavirus seroprevalence was not directly influenced by host abundance. Consequently, we assume that high rodent density alone does not lead to an increased risk of hantavirus infection among the rodent host population.

The ecological dynamics of hantavirus diseases: From environmental variability to disease prevention largely based on data from China

Hantaviruses can cause hantavirus pulmonary syndrome (HPS) in the Americas and hemorrhagic fever with renal syndrome (HFRS) in Eurasia. In recent decades, repeated outbreaks of hantavirus disease have led to public concern and have created a global public health burden. Hantavirus spillover from natural hosts into human populations could be considered an ecological process, in which environmental forces, behavioral determinants of exposure, and dynamics at the human–animal interface affect human susceptibility and the epidemiology of the disease. In this review, we summarize the progress made in understanding hantavirus epidemiology and rodent reservoir population biology. We mainly focus on three species of rodent hosts with longitudinal studies of sufficient scale: the striped field mouse (Apodemus agrarius, the main reservoir host for Hantaan virus [HTNV], which causes HFRS) in Asia, the deer mouse (Peromyscus maniculatus, the main reservoir host for Sin Nombre virus [SNV], which causes HPS) in North America, and the bank vole (Myodes glareolus, the main reservoir host for Puumala virus [PUUV], which causes HFRS) in Europe. Moreover, we discuss the influence of ecological factors on human hantavirus disease outbreaks and provide an overview of research perspectives.

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.

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).

The hanta hunting study: underdiagnosis of Puumala hantavirus infections in symptomatic non-travelling leptospirosis-suspected patients in the Netherlands, in 2010 and April to November 2011

Leptospirosis and haemorrhagic fever with renal syndrome (HFRS) are hard to distinguish clinically since these two important rodent-borne zoonoses share hallmark symptoms such as renal failure and haemorrhage. Leptospirosis is caused by infection with a spirochete while HFRS is the result of an infection with certain hantaviruses. Both diseases are relatively rare in the Netherlands. Increased incidence of HFRS has been observed since 2007 in countries that border the Netherlands. Since a similar rise in incidence has not been registered in the Netherlands, we hypothesise that due to overlapping clinical manifestations, hantavirus infections may be confused with leptospirosis, leading to underdiagnosis. Therefore, we tested a cohort of non-travelling Dutch patients with symptoms compatible with leptospirosis, but with a negative diagnosis, during 2010 and from April to November 2011. Sera were screened with pan-hantavirus IgG and IgM enzyme-linked immunosorbent assays (ELISAs). Sera with IgM reactivity were tested by immunofluorescence assay (IFA). ELISA (IgM positive) and IFA results were confirmed using focus reduction neutralisation tests (FRNTs). We found hantavirus-specific IgG and/or IgM antibodies in 4.3% (11/255) of samples taken in 2010 and in 4.1% (6/146) of the samples during the 2011 period. After FRNT confirmation, seven patients were classed as having acute Puumala virus infections. A review of hantavirus diagnostic requests revealed that at least three of the seven confirmed acute cases as well as seven probable acute cases of hantavirus infection were missed in the Netherlands during the study period.

Hantavirus reservoirs: current status with an emphasis on data from Brazil

Since the recognition of hantavirus as the agent responsible for haemorrhagic fever in Eurasia in the 1970s and, 20 years later, the descovery of hantavirus pulmonary syndrome in the Americas, the genus Hantavirus has been continually described throughout the World in a variety of wild animals. The diversity of wild animals infected with hantaviruses has only recently come into focus as a result of expanded wildlife studies. The known reservoirs are more than 80, belonging to 51 species of rodents, 7 bats (order Chiroptera) and 20 shrews and moles (order Soricomorpha). More than 80genetically related viruses have been classified within Hantavirus genus; 25 recognized as human pathogens responsible for a large spectrum of diseases in the Old and New World. In Brazil, where the diversity of mammals and especially rodents is considered one of the largest in the world, 9 hantavirus genotypes have been identified in 12 rodent species belonging to the genus Akodon, Calomys, Holochilus, Oligoryzomys, Oxymycterus, Necromys and Rattus. Considering the increasing number of animals that have been implicated as reservoirs of different hantaviruses, the understanding of this diversity is important for evaluating the risk of distinct hantavirus species as human pathogens.

First molecular evidence for Puumala hantavirus in Poland

Puumala virus (PUUV) causes mild to moderate cases of haemorrhagic fever with renal syndrome (HFRS), and is responsible for the majority of hantavirus infections of humans in Fennoscandia, Central and Western Europe. Although there are relatively many PUUV sequences available from different European countries, little is known about the presence of this virus in Poland. During population studies in 2009 a total of 45 bank voles were trapped at three sites in north-eastern Poland, namely islands on Dejguny and Dobskie Lakes and in a forest near Mikołajki. S and M segment-specific RT-PCR assays detected PUUV RNA in three animals from the Mikołajki site. The obtained partial S and M segment sequences demonstrated the highest similarity to the corresponding segments of a PUUV strain from Latvia. Analysis of chest cavity fluid samples by IgG ELISA using a yeast-expressed PUUV nucleocapsid protein resulted in the detection of two seropositive samples, both being also RT-PCR positive. Interestingly, at the trapping site in Mikołajki PUUV-positive bank voles belong to the Carpathian and Eastern genetic lineages within this species. In conclusion, we herein present the first molecular evidence for PUUV in the rodent reservoir from Poland.

Alternative causes of hypopituitarism: traumatic brain injury, cranial irradiation, and infections

Hypopituitarism often remains unrecognized due to subtle clinical manifestations. Anterior pituitary hormone deficiencies may present as isolated or multiple and may be transient or permanent. Traumatic brain injury (TBI) is recognized as a risk factor for hypopituitarism, most frequently presenting with isolated growth hormone deficiency (GHD). Data analysis shows that about 15% of patients with TBI have some degree of hypopituitarism which if not recognized may be mistakenly ascribed to persistent neurologic injury and cognitive impairment. Identification of predictors for hypopituitarism after TBI is important, one of them being the severity of TBI. The mechanisms involve lesions in the hypothalamic-pituitary axis and inflammatory changes in the central nervous system (CNS). With time, hypopituitarism after TBI may progress or reverse. Cranial irradiation is another important risk factor for hypopituitarism. Deficiencies in anterior pituitary hormone secretion (partial or complete) occur following radiation damage to the hypothalamic-pituitary region, the severity and frequency of which correlate with the total radiation dose delivered to the region and the length of follow-up. These radiation-induced hormone deficiencies are irreversible and progressive. Despite numerous case reports, the incidence of hypothalamic-pituitary dysfunction following infectious diseases of the CNS has been underestimated. Hypopituitarism usually relates to the severity of the disease, type of causative agent (bacterial, TBC, fungal, or viral) and primary localization of the infection. Unrecognized hypopituitarism may be misdiagnosed as postencephalitic syndrome, while the presence of a sellar mass with suprasellar extension may be misdiagnosed as pituitary macroadenoma in a patient with pituitary abscess which is potentially a life-threatening disease.

Human puumala and dobrava hantavirus infections in the Black Sea region of Turkey: a cross-sectional study

This study was carried out to better understand the epidemiology of hantaviruses in a province of Turkey (Giresun) where human hantavirus disease has recently been detected. In this cross-sectional study, a total of 626 blood samples from healthy people aged 15 and 84 years old were collected both in urban and rural areas in 2009. The sera were tested by enzyme-linked immunosorbent assay (ELISA), immunoblotting assay, and the focus reduction neutralization test (FRNT). We screened the samples by an ELISA and found that 65/626 samples reacted positively for the presence of hantavirus-reactive immunoglobulin G (IgG). Twenty of the 65 ELISA-positive samples could be confirmed by an immunobloting assay, and the overall seroprevalence was thereby calculated to 3.2% (20/626). The seroprevalence of the people living in wood areas or adobe houses 9/17 (52.9%) was significantly higher than among people living in concrete houses 10/47 (21.3%) (p=0.014). Finally, 3 of the 20 immunoblot-positive sera were confirmed as specific for the Puumala hantavirus serotype by FRNT, 1 serum was confirmed as Dobrava virus-specific, whereas 1 serum was found to be equally reactive to Dobrava and Saaremaa viruses. We will now focus on further investigations of the ecology and epidemiology of hantaviruses in humans and their carrier animals in Turkey, studies that have already been started and will be further intensified.

In Search for Factors that Drive Hantavirus Epidemics

In Europe, hantaviruses (Bunyaviridae) are small mammal-associated zoonotic and emerging pathogens that can cause hemorrhagic fever with renal syndrome (HFRS). Puumala virus, the main etiological agent carried by the bank vole Myodes glareolus is responsible for a mild form of HFRS while Dobrava virus induces less frequent but more severe cases of HFRS. Since 2000 in Europe, more than 3000 cases of HFRS have been recorded, in average, each year, which is nearly double compared to the previous decade. In addition to this upside long-term trend, significant oscillations occur. Epidemic years appear, usually every 2-4 years, with an increased incidence, generally in localized hot spots. Moreover, the virus has been identified in new areas in the recent years. A great number of surveys have been carried out in order to assess the prevalence of the infection in the reservoir host and to identify links with different biotic and abiotic factors. The factors that drive the infections are related to the density and diversity of bank vole populations, prevalence of infection in the reservoir host, viral excretion in the environment, survival of the virus outside its host, and human behavior, which affect the main transmission virus route through inhalation of infected rodent excreta. At the scale of a rodent population, the prevalence of the infection increases with the age of the individuals but also other parameters, such as sex and genetic variability, interfere. The contamination of the environment may be correlated to the number of newly infected rodents, which heavily excrete the virus. The interactions between these different parameters add to the complexity of the situation and explain the absence of reliable tools to predict epidemics. In this review, the factors that drive the epidemics of hantaviruses in Middle Europe are discussed through a panorama of the epidemiological situation in Belgium, France, and Germany.

Sero-epidemiological study of the presence of hantaviruses in domestic dogs and cats from Belgium

Hantaviruses are worldwide rodent-borne pathogens infecting humans and other animals mainly through inhalation of aerosols contaminated with rodent excreta. Few data are available on hantavirus serology and geographical distribution in dogs and cats. We therefore screened sera from pet dogs (N=410) and cats (N=124) in two regions of Belgium, using IgG ELISA and IFA. We analysed the effect of the owner's address as well as pet gender and age on hantavirus status. Hantavirus antibodies were found in both species with a significantly higher seroprevalence in cats than in dogs (16.9% vs. 4.9%, P=0.001). More dogs were infected in highly forested southern Belgium (harbouring more rodents) than in northern Belgium (10.5% vs. 3.0%, P=0.002). In the south, hantavirus sero-positive cats were found in more densely forested localities than sero-negatives ones were (P=0.033). These results are consistent with the ecological variations of hantavirus risks in humans.

Concomitant influence of helminth infection and landscape on the distribution of Puumala hantavirus in its reservoir, Myodes glareolus

Background

Puumala virus, the agent of nephropathia epidemica (NE), is the most prevalent hantavirus in Europe. The risk for human infection seems to be strongly correlated with the prevalence of Puumala virus (PUUV) in populations of its reservoir host species, the bank vole Myodes glareolus. In humans, the infection risks of major viral diseases are affected by the presence of helminth infections. We therefore proposed to analyse the influence of both helminth community and landscape on the prevalence of PUUV among bank vole populations in the Ardennes, a PUUV endemic area in France.

Results

Among the 313 voles analysed, 37 had anti-PUUV antibodies. Twelve gastro-intestinal helminth species were recorded among all voles sampled. We showed that PUUV seroprevalence strongly increased with age or sexual maturity, especially in the northern forests (massif des Ardennes). The helminth community structure significantly differed between this part and the woods or hedgerows of the southern cretes pre-ardennaises. Using PUUV RNA quantification, we identified significant coinfections between PUUV and gastro-intestinal helminths in the northern forests only. More specifically, PUUV infection was positively associated with the presence of Heligmosomum mixtum, and in a lesser extent, Aonchotheca muris-sylvatici. The viral load of PUUV infected individuals tended to be higher in voles coinfected with H. mixtum. It was significantly lower in voles coinfected with A. muris-sylvatici, reflecting the influence of age on these latter infections.

Conclusions

This is the first study to emphasize hantavirus - helminth coinfections in natural populations. It also highlights the importance to consider landscape when searching for such associations. We have shown that landscape characteristics strongly influence helminth community structure as well as PUUV distribution. False associations might therefore be evidenced if geographic patterns of helminths or PUUV repartition are not previously identified. Moreover, our work revealed that interactions between helminths and landscape enhance/deplete the occurrence of coinfections between PUUV and H. mixtum or A. muris-sylvatici. Further experimental analyses and long-term individual surveys are now required to confirm these correlative results, and to ascertain the causal links between helminth and PUUV infection risks.

Temporal variation in individual factors associated with hantavirus infection in bank voles during an epizootic: implications for Puumala virus transmission dynamics

Puumala virus (PUUV), the causal agent of nephropathia epidemica in humans, is one of the many hantaviruses included in the list of emerging pathogens. Hantavirus infection is not distributed evenly among PUUV reservoir hosts (i.e., bank voles [Myodes glareolus]). Besides environmental factors and local population features, individual characteristics play an important role in vole PUUV infection risk. Identifying the relative importance of these individual characteristics can provide crucial information on PUUV transmission processes. In the present study, bank voles were monitored during the nephropathia epidemica outbreak of 2005 in Belgium. Vole sera were tested for presence of immunoglobulin G against PUUV, and a logistic mixed model was built to investigate the temporal variation in individual characteristics and their relative importance to PUUV infection risk in bank voles. Relative risk calculations for individual vole characteristics related to PUUV infection in the reservoir host show that reproductive activity dominates infection risk. The gender effect is only found in reproductively active voles, where reproductively active males have the highest infection risk. Results also revealed a clear seasonal variation in the importance of reproductive activity linked to PUUV infection. In contrast to the main effect found in other trapping sessions, no difference in infection risk ratio was found between reproductively active and nonactive voles in the spring period. Combined with increased infection risk for the reproductively nonactive group at that time, these results indicate a shift in the transmission process due to changes in bank vole behavior, physiology, or climate conditions. Hence, our results suggest that mathematical models should take into account seasonal shifts in transmission mechanisms. When these results are combined with the seasonal changes in population structure during the epizootic period, we identify vole reproductive activity and length of the breeding season as potential drivers of PUUV epizootics in west-central European regions.

Environmental risk factors for haemorrhagic fever with renal syndrome in a French new epidemic area

In France, haemorrhagic fever with renal syndrome (HFRS) is endemic along the Belgian border. However, this rodent-borne zoonosis caused by the Puumala virus has recently spread south to the Franche-Comté region. We investigated the space-time distribution of HFRS and evaluated the influence of environmental factors that drive the hantavirus reservoir abundance and/or the disease transmission in this area. A scan test clearly indicated space-time clustering, highlighting a single-year (2005) epidemic in the southern part of the region, preceded by a heat-wave 2 years earlier. A Bayesian regression approach showed an association between a variable reflecting biomass (normalized difference vegetation index) and HFRS incidence. The reasons why HFRS cases recently emerged remain largely unknown, and climate parameters alone do not reliably predict outbreaks. Concerted efforts that combine reservoir monitoring, surveillance, and investigation of human cases are warranted to better understand the epidemiological patterns of HFRS in this area.

Early diagnosis of hantavirus infection by family doctors can reduce inappropriate antibiotic use and hospitalization

OBJECTIVE

Hantavirus infections are emerging infections that cause either Hantavirus pulmonary syndrome or haemorrhagic fever with renal syndrome (HFRS). A recent Swedish outbreak of nephropathia epidemica, a European HFRS, was analysed to study the patient flow and clinical picture and to investigate the value of an early diagnosis in general practice. Design. In a retrospective design, medical records of verified cases of Hantavirus infection were studied.

SETTING

The study was conducted in the county of Norrbotten, Sweden.

SUBJECTS

Data from Hantavirus patients diagnosed between 2006 and 2008 were analysed.

MAIN OUTCOME MEASURES

Demographic data, level of care, treatment, clinical symptoms, and laboratory findings were obtained.

RESULTS

In total, 456 cases were included (58% males and 42% females). The majority of patients first saw their general practitioner and were exclusively treated in general practice (83% and 56%, respectively). When diagnosed correctly at the first visit, antibiotics and hospitalization were significantly lowered compared with delayed diagnosis (14% vs. 53% and 30% vs. 54%, respectively; p < 0.0001). The clinical picture was diverse. Early thrombocytopenia was found in 65% of the patients, and haemorrhagic manifestations were documented in a few cases. Signs of renal involvement--haematuria, proteinuria, and raised levels of serum creatinine--were found in a majority of patients.

CONCLUSIONS

Raised awareness in general practice regarding emerging infections and better diagnostic tools are desirable. This study of a Hantavirus outbreak shows that general practitioners are frontline doctors during outbreaks and through early and correct diagnosis they can reduce antibiotic treatment and hospitalization.

Hantavirus outbreak in Western Europe: reservoir host infection dynamics related to human disease patterns

Within Europe, Puumala virus (PUUV) is the causal agent of nephropathia epidemica (NE) in humans, a zoonotic disease with increasing significance in recent years. In a region of Belgium with a historically high incidence of NE, bank voles (the PUUV reservoir hosts), were monitored for PUUV IgG antibody prevalence in nine study sites before, during, and after the highest NE outbreak recorded in Belgium in 2005. We found that the highest numbers of PUUV IgG-positive voles coincided with the peak of NE cases at the regional level, indicating that a PUUV epizootic in bank voles directly led to the NE outbreak in humans. On a local scale, PUUV infection in voles was patchy and not correlated to NE incidence before the epizootic. However, during the epizootic period PUUV infection spread in the vole populations and was significantly correlated to local NE incidence. Initially, local bank-vole numbers were positively associated with local PUUV infection risk in voles, but this was no longer the case after the homogeneous spreading of PUUV during the PUUV outbreak.

Disease burden of Puumala virus infections, 1995-2008

Puumala virus (PUUV) causes mild haemorrhagic fever with renal syndrome, a rodent-borne zoonosis. To evaluate the disease burden of PUUV infections in Finland, we analysed data reported by laboratories to the National Infectious Disease Registry during 1995-2008 and compared these with data from other national registries (death, 1998-2007; hospital discharge, 1996-2007; occupational diseases, 1995-2006). A total of 22,681 cases were reported (average annual incidence 31/100,000 population); 85% were in persons aged 20-64 years and 62% were males. There was an increasing trend in incidence, and the rates varied widely by season and region. We observed 13 deaths attributable to PUUV infection (case-fatality proportion 0.08%). Of all cases, 9599 (52%) were hospitalized. Only 590 cases (3%) were registered as occupational disease, of which most were related to farming and forestry. The wide seasonal and geographical variation is probably related to rodent density and human behaviour.

Environmental and ecological potential for enzootic cycles of Puumala hantavirus in Great Britain

Puumala virus (PUUV) is a zoonotic rodent-borne hantavirus in continental Europe. Its reservoir host, the bank vole (Myodes glareolus), is ubiquitous in Great Britain (GB); however, there has been no reported incidence of virus in either animals or humans. In northwest Europe, increases in bank vole numbers, stimulated by increases in production of beech/oak crops (mast), are associated with outbreaks of nephropathia epidemica (NE) in humans. These so-called 'mast years' are determined by sequential climatic events. This paper investigates the contribution of a number of ecological and environmental factors driving outbreaks of PUUV in northwest Europe and assesses whether such factors might also permit enzootic PUUV circulation in GB. Analysis of GB climate data, using regression models, confirms that mast years in GB are stimulated, and can be predicted, by the same climatic events as mast years in PUUV-endemic regions of northwest Europe. A number of other possible non-climatic constraints on enzootic cycles are discussed.

Hantavirus disease (nephropathia epidemica) in Belgium: effects of tree seed production and climate

Recently, human cases of nephropathia epidemica (NE) due to Puumala virus infection in Europe have increased. Following the hypothesis that high reservoir host abundance induces higher transmission rates to humans, explanations for this altered epidemiology must be sought in factors that cause bank vole (Myodes glareolus) abundance peaks. In Western Europe, these abundance peaks are often related to high tree seed production, which is supposedly triggered by specific weather conditions. We evaluated the relationship between tree seed production, climate and NE incidence in Belgium and show that NE epidemics are indeed preceded by abundant tree seed production. Moreover, a direct link between climate and NE incidence is found. High summer and autumn temperatures, 2 years and 1 year respectively before NE occurrence, relate to high NE incidence. This enables early forecasting of NE outbreaks. Since future climate change scenarios predict higher temperatures in Europe, we should regard Puumala virus as an increasing health threat.