INTRODUCTION:Vector-borne diseases (VBDs) pose a growing threat to human and animal health, driven by complex interactions among and between vectors, hosts, pathogens, and the environment. The Nordic region is warming at twice the global average rate, creating novel ecological conditions that reshape VBD transmission dynamics. OBJECTIVES AND METHODS:This narrative review synthesises current knowledge regarding major tick- and mosquito-borne diseases in the Nordic region, with a focus on Finland, based primarily on outputs from the VECLIMIT project (2020-2023), supported by other Nordic studies. RESULTS:The most prevalent human VBDs are Lyme borreliosis (LB), tick-borne encephalitis (TBE), tularaemia, and Sindbis virus (SINV) infections. Over the past decade, LB and particularly TBE incidence have increased, whereas SINV and tularaemia show cyclical patterns. The principal tick vectors Ixodes ricinus and Ixodes persulcatus are expanding geographically, while key mosquito vectors, Aedes cinereus/geminus and Culex pipiens/torrentium, are widespread. Rising temperatures and extended growing seasons promote vector activity and pathogen development, whereas heterogenous environments, such as wetlands and urban green spaces, support vector and host populations. While small mammals serve as key reservoirs for tick-borne pathogens, cervids drive tick propagation, and avian hosts maintain vector-borne enzootic cycles. Substantial gaps remain in prevention and awareness across public, medical, and veterinary sectors. CONCLUSIONS:Climate warming is likely to increase the spread of many endemic and invasive vectors and pathogens, yet surveillance remains limited and understanding of VBD drivers incomplete. Addressing these gaps requires coordinated One Health frameworks leveraging citizen science and cross-border Nordic collaboration.

The circulation of tick-borne pathogens is influenced by the availability of ticks, the hosts of ticks and pathogens, and the environmental conditions that affect both the ticks and their hosts. Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato and transmitted by Ixodes spp. ticks, is the most common tick-borne disease in the Northern Hemisphere. Understanding the spatio-temporal dynamics of human LB incidence regarding abundance of ticks and hosts and environmental factors is essential for effective disease risk management. We analyzed long-term (1997–2018) and spatially extensive (277 municipalities covering 230,000 km2) data on human LB incidence in Finland. Using dynamic species distribution models, we assessed the effects of (i) the abundance of pathogen reservoir hosts used by immature ticks (voles and squirrels), (ii) abundance of the key reproductive hosts for adult ticks (moose and deer), (iii) landscape characteristics, and (iv) climatic variables on the risk of LB. LB presence and incidence varied across the study area and exhibited a clear increasing trend. While host species showed temporal and regional variation in abundance, their relationships with LB risk were inconsistent. In contrast, environmental variables showed more consistent patterns: increased forest fragmentation, longer growing seasons, and higher humidity were generally associated with elevated LB risk. Our study suggests that the factors explaining LB epidemiology cannot be generalized spatially but depend on local climate, landscape, and host community. Given the available data, environmental conditions seem to play a more predictable role in LB epidemiology than the estimated abundances of hosts at the municipality level, yet we cannot exclude host abundance effects. Hence, the key to enhancing our understanding of the complex mechanisms underlying the epidemiology of LB and other tick-borne infections is to clarify how tick distribution and abundance respond to alterations in the host community, habitat features, and local climate.

Despite advances in understanding infectious diseases, the persistence and re-emergence of wildlife pathogens continue to raise public and veterinary health concerns. This study investigates the relationship between biodiversity and rodent-borne diseases in Europe, focusing on habitat alterations and their impact on rodent diversity. We present host-pathogen data from 21 temperate forest sites and eight urban green spaces throughout five European countries, environments where rodents are abundant and human/domestic animals-wildlife interactions are likely to occur. From 2020 to 2022, 3766 specimens comprising 15 different small mammal species were analyzed. Samples were screened for bacteria via 16S rRNA sequencing or PCR, and for viral antibodies using immunofluorescent assays. Pathogens from several genera, including Bartonella, Borrelia, Mycoplasma, Anaplasma, Neoehrlichia, Leptospira, Orthohantavirus, and Orthopoxvirus, were detected at non-negligible prevalence in 11 host species. Host community composition differed between habitats, with more urban adapters in parks than in forests. Pathogen richness increased with an increase in host species diversity, supporting the "host-diversity begets parasite-diversity" hypothesis, though not with anthropization. The absence of some vector-transmitted parasites in urban areas suggests a shift in pathogen community driven by human impact. Host species and intrinsic factors were dominant explanatory variables for Mycoplasma species and Sarcocystidae, while extrinsic environmental and climatic factors influenced variations in several vector-transmitted pathogens. Apodemus sylvaticus and Clethrionomys glareolus served as important connector hosts in urban spaces and temperate forests, respectively. These results improve our understanding of the complex local host-pathogen system, aiding future management decisions and supporting the public health sector.

BACKGROUND:Hantaviruses are rodent-borne zoonoses causing haemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome. In Europe, Puumala virus (PUUV) and Dobrava virus (DOBV) account for most recognized disease; Seoul virus (SEOV) is relevant to ports and urban settings. The 2026 MV Hondius cruise-ship cluster of Andes hantavirus (ANDV) infections, involving passengers from 23 countries, has highlighted urgent gaps in European preparedness for both endemic and imported hantavirus disease. OBJECTIVES:To review hantavirus epidemiology, ecology, clinical recognition, diagnostics, and preparedness in Europe, with emphasis on endemic PUUV, DOBV, and SEOV, and to clarify the separate relevance of imported ANDV infection for travel medicine and maritime response. SOURCES:We conducted a structured narrative review of literature published from January 2000 to May 2026, prioritizing surveillance reports, systematic and narrative reviews, rodent ecology studies, diagnostic evaluations, external quality assessment studies, and outbreak investigations. WHO, European Centre for Disease Prevention and Control, and International Health Regulations guidance documents were also reviewed. CONTENT:European hantavirus epidemiology is heterogeneous and shaped by reservoir ecology, biome-specific rodent dynamics, clinical awareness, diagnostic capacity, and surveillance practice. Climate effects are indirect and regionally variable, mediated by mast years, predator-prey dynamics, winter conditions, land use, reservoir density, and human exposure. Diagnostic preparedness is uneven, particularly for molecular detection. Imported ANDV infection is rare in Europe but relevant to travel medicine and high-consequence preparedness because it can cause severe hantavirus cardiopulmonary syndrome and, unlike endemic European hantaviruses, has documented person-to-person transmission. IMPLICATIONS:European preparedness should prioritize PUUV, DOBV, and SEOV through rodent biomonitoring, harmonized surveillance, improved molecular diagnostics, and locally calibrated early warning.

Abstract Background The Norwegian lemming (Lemmus lemmus) is a small rodent endemic to the Fennoscandian alpine and arctic tundra. The species is known for cyclic population outbreaks and mass movements during peak years. Previous research based on microsatellites revealed high genetic variation but a weak population structure in the Norwegian lemming. Results In this study, we revisit the population structure of the species using genome-wide data. To do this, we generated a high-quality de novo reference genome for Lemmus lemmus, and resequenced genomes to 2.5–5 × coverage, from 86 lemmings sampled across the species’ entire geographic distribution. Our results reveal that the population is geographically structured into distinct subpopulations, with an overall pattern characterised by isolation-by-distance among subpopulations. Furthermore, our results are consistent with earlier work suggesting that the species survived the last ice age within a northern refugium. Conclusions Together, these findings provide a genome-wide perspective on today’s population structure of the Norwegian lemming. In addition, we provide a de novo reference genome, which we believe will be a valuable resource to the research community.

Paramyxoviruses can infect a variety of host species and cause infections among wildlife and humans. Some of these viruses can also cause severe zoonotic infections. Although new paramyxoviruses, such as jeilongviruses, are being recognized, little is known about their host species variation and pathogenesis. The current screening methods to detect paramyxoviruses are either laborious conventional PCR methods or costly next-generation sequencing methods. Therefore, we designed a new pan-jeilong-RT-qPCR assay to detect jeilong- and parajeilongviruses from wildlife samples and screened rat, shrew, and bat samples from Finland and Latvia. With this new real-time PCR assay, we detected jeilongviruses in Finnish urban rat populations during 2020-2023 with a 13% positivity rate, including beilong virus (Jeilongvirus beilongi). This finding highlights the abundance of jeilongvirus in rats and the need for continued surveillance and more detailed characterization of these novel pathogens to evaluate the zoonotic potential of these viruses in rat and other rodent populations.

The transmission dynamics of the tick-borne encephalitis virus (TBEV) remain enigmatic. New lineages of the European TBEV-variant have been emerging in areas where it was not expected to circulate, questioning their origins. Although Ixodes ricinus and I. persulcatus are primary vectors for TBEV, other tick species have also been proposed to transmit the virus. Under natural conditions, I. trianguliceps can maintain Anaplasma phagocytophilum and Babesia microti circulation, but not Borrelia burgdorferi sensu lato. As I. trianguliceps is reported to be a vector for TBEV, we investigated whether it can sustain a cryptic TBEV transmission in areas without I. ricinus and/or I. persulcatus. Sera from 951 bank voles from six sites in Finland, where I. trianguliceps, but neither I. ricinus nor I. persulcatus, have been observed, were negative for TBEV antibodies, and B. burgdorferi s.l., but positive for A. phagocytophilum and B. microti. In contrast, 32 bank voles from two endemic TBEV-foci, where I. ricinus/I. persulcatus are abundant, were positive for TBEV-antibodies as well as B. burgdorferi s.l., A. phagocytophilum and B. microti. Our results provide no evidence that TBEV would circulate alone by I. trianguliceps under natural conditions. Our results corroborate previous findings that A. phagocytophilum and B. microti, but neither TBEV nor B. burgdorferi s.l., can be sustained in the absence of I. ricinus/I. persulcatus. Whether TBEV can circulate in cryptic cycles or whether I. trianguliceps contributes to the maintenance of TBEV in the rodent - tick cycle, remains unresolved, but warrants further investigations.

Rodents have co-existed with humans for centuries, and frequently exchange pathogens. Historically, rodent-driven plague outbreaks scoured the Old World, resulting in substantial human mortality. Although such pandemics have not occurred for centuries, serious threats from rodent-borne infections, such as the global emergence of mpox, still exist. Moreover, endemic and emerging rodent infections continue to cause substantial human morbidity and mortality in low-income and middle-income countries. Efforts by the medical community to control rodent-borne zoonoses primarily focus on treating or preventing symptoms in humans using biomedical interventions (eg, vaccination). Such approaches are geared towards preparedness and response but are insufficient for prevention. In this Personal View, we identify three key pillars that drive rodent-borne zoonotic spillover: ecology of rodent infections; use of human habitation by rodents (synanthropy); and the influence of humans on the ecological proliferation of rodents in our landscape (rodentation). The challenge is to leverage these pillars as entry points for interventions, to prevent spillover and reduce disease burden. Given shortcomings of rodent culling, we advocate for integrated countermeasures that are socially and ecologically grounded, apply systems thinking, and leverage emerging technologies to prevent spillover driven by persistent human-rodent interactions and global change.

Rodents constitute a significant proportion of mammalian diversity, with their adaptability and wide distribution making them indispensable study organisms across various biological disciplines. While the laboratory mouse remains a predominant model rodent, the bank vole (Clethrionomys glareolus) offers a unique perspective as a wild rodent within the large subfamily Arvicolinae. Recognized for its relevance to studynatural ecology, the bank vole provides insights into complex ecological interactions, evolutionary adaptations, and disease dynamics. Despite recent recognition of its importance in specific research areas, there is a lack of a comprehensive and up-to-date exploration of its role as a model organism. This review addresses this gap by offering a holistic examination of the bank vole’s applications in ecology, evolution, biogeography, disease dynamics, and host–pathogen interactions. We emphasize novel insights into genetic variation, adaptation to climate change, population dynamics, experimental evolution, host-parasite co-evolution, and disease dynamics studies. By consolidating diverse research findings, this review provides a unique and comprehensive perspective on the bank vole’s contributions to understanding ecology and evolution, underscoring its importance as a model organism in shaping future biological research.

The present study aims at clarifying the poorly known phylogenetic relationships and systematics of cestodes of the family Davaineidae Braun, 1900 (Cyclophyllidea), primarily the genus Raillietina Fuhrmann, 1920 and of the subfamily Inermicapsiferinae (Anoplocephalidae) from mammals (mostly rodents, 31 new isolates) and birds (eight new isolates). Phylogenetic analyses are based on sequences of the large subunit ribosomal RNA gene (28S) and mitochondrial NADH dehydrogenase subunit 1 gene ( nad1 ). The main phylogenetic pattern emerging from the present analysis is the presence of three independent lineages within the main clade of the subfamily Davaineinae, one of which is almost entirely confined to species from rodents and the other two show a mixture of species from birds and mammals. It is suggested that the major diversification of the main clade took place in birds, possibly in galliforms. The subsequent diversification included repeated host shifts from birds to mammals and to other birds, and from rodents to other mammals, showing that colonisation of new host lineages has been the main driver in the diversification of davaineine cestodes. It is also shown that all isolates of Inermicapsifer Janicki, 1910, mainly from rodents, form a monophyletic group positioned among Raillietina spp. in the "rodent lineage", indicating that the genus Inermicapsifer is a member of the family Davaineidae. This means that the subfamily Inermicapsiferinae and the family Inermicapsiferidae should be treated as synonyms of the Davaineidae, specifically the subfamily Davaineinae. Three additional genera generally included in the Inermicapsiferinae, i.e. Metacapsifer Spasskii, 1951, Pericapsifer Spasskii, 1951 and Thysanotaenia Beddard, 1911, are also assigned here to the Davaineidae (subfamily Davaineinae). Raillietina spp. were present in all three main lineages and appeared as multiple independent sublineages from bird and mammalian hosts, verifying the non-monophyly of the genus Raillietina and suggesting a presence of multiple new species and genera.

ABSTRACT Introduction Hantaviruses cause two kinds of clinical syndromes. Hemorrhagic fever with renal syndrome is caused by Hantaan virus in Asia, Puumala virus (PUUV) and Dobrava virus in Europe, and Seoul virus worldwide. Hantavirus cardiopulmonary syndrome is caused by Sin Nombre virus in North America and Andes virus and related viruses in Latin America. All hantaviruses are carried by rodents and insectivores. Humans are infected via inhaled aerosols of rodent excreta. In the history, there are several epidemics of acute infectious diseases during many wars, which have been suggested or proven to be caused by various hantaviruses. Materials and Methods Literature review of 41 original publications and reviews published between 1943 and 2022 was performed. Among them, 23 publications handle hantavirus infections among military forces, and the rest 17 hantavirus infections themselves. Results A large epidemic during World War II in 1942 among German and Finnish soldiers in Northern Finland with more than 1,000 patients was most probably caused by PUUV. During Korean War in 1951–1954,∼ 3,200 cases occurred among United Nations soldiers in an epidemic caused by Hantaan virus. During Balkan war from 1991 to 1995, numerous soldiers got ill because of hantavirus infection caused by PUUV and Dobrava virus. Several other reports of cases of various hantavirus infections especially among U.S. soldiers acting in South Korea, Germany, Bosnia, and Kosovo have been described in the literature. Conclusions Military maneuvers usually include soil removal, spreading, digging with accompanied dust, and living in field and other harsh conditions, which easily expose soldiers to rodents and their excreta. Therefore, the risks of hantavirus infections in military context are obvious. All military infections have been caused by hantaviruses leading to hemorrhagic fever with renal syndrome.

Reports of fading vole and lemming population cycles and persisting low populations in some parts of the Arctic have raised concerns about the spread of these fundamental changes to tundra food web dynamics. By compiling 24 unique time series of lemming population fluctuations across the circumpolar region, we show that virtually all populations displayed alternating periods of cyclic/non-cyclic fluctuations over the past four decades. Cyclic patterns were detected 55% of the time (n = 649 years pooled across sites) with a median periodicity of 3.7 years, and non-cyclic periods were not more frequent in recent years. Overall, there was an indication for a negative effect of warm spells occurring during the snow onset period of the preceding year on lemming abundance. However, winter duration or early winter climatic conditions did not differ on average between cyclic and non-cyclic periods. Analysis of the time series shows that there is presently no Arctic-wide collapse of lemming cycles, even though cycles have been sporadic at most sites during the last decades. Although non-stationary dynamics appears a common feature of lemming populations also in the past, continued warming in early winter may decrease the frequency of periodic irruptions with negative consequences for tundra ecosystems.

To prevent foodborne infections from pigs and cattle, the whole food chain must act to minimize the contamination of products, including biosecurity measures which prevent infections via feed and the environment in production farms. Rodents and other small mammals can be reservoirs of and key vectors for transmitting zoonotic bacteria and viruses to farm animals, through direct contact but more often through environmental contamination. In line with One Health concept, we integrated results from a sampling study of small mammals in farm environments and data from a capture-recapture experiment into a probabilistic model which quantifies the degree of environmental exposure of zoonotic bacteria by small mammals to farm premises. We investigated more than 1200 small mammals trapped in and around 38 swine and cattle farm premises in Finland in 2017/2018. Regardless of the farm type, the most common species caught were the yellow-necked mouse (Apodemus flavicollis), bank vole (Clethrionomys glareolus), and house mouse (Mus musculus). Of 554 intestine samples (each pooled from 1 to 10 individuals), 33% were positive for Campylobacter jejuni. Yersinia enterocolitica was detected in 8% of the pooled samples, on 21/38 farm premises. Findings of Salmonella and the Shiga-toxin producing Escherichia coli (STEC) were rare: the pathogens were detected in only single samples from four and six farm premises, respectively. The prevalence of Campylobacter, Salmonella, Yersinia and STEC in small mammal populations was estimated as 26%/13%, 1%/0%, 2%/3%, 1%/1%, respectively, in 2017/2018. The exposure probability within the experimental period of four weeks on farms was 17-60% for Campylobacter and 0-3% for Salmonella. The quantitative model is readily applicable to similar integrative studies. Our results indicate that small mammals increase the risk of exposure to zoonotic bacteria in animal production farms, thus increasing risks also for livestock and human health.

Long-term studies of cyclic rodent populations have contributed fundamentally to the development of population ecology. Pioneering rodent studies have shown macroecological patterns of population dynamics in relation to latitude and have inspired similar studies in several other taxa. Nevertheless, such studies have not been able to disentangle the role of different environmental variables in shaping the macroecological patterns. We collected rodent time-series from 26 locations spanning 10 latitudinal degrees in the tundra biome of Fennoscandia and assessed how population dynamics characteristics of the most prevalent species varied with latitude and environmental variables. While we found no relationship between latitude and population cycle peak interval, other characteristics of population dynamics showed latitudinal patterns. The environmental predictor variables provided insight into causes of these patterns, as 1) increased proportion of optimal habitat in the landscape led to higher density amplitudes in all species and 2) mid-winter climate variability lowered the amplitude in Norwegian lemmings and grey-sided voles. These results indicate that biome-scale climate and landscape change can be expected to have profound impacts on rodent population cycles and that the macro-ecology of such functionally important tundra ecosystem characteristics is likely to be subjected to transient dynamics.

Rodents are major reservoirs of pathogens that can cause disease in humans and livestock. It is therefore important to know what pathogens naturally circulate in rodent populations, and to understand the factors that may influence their distribution in the wild. Here, we describe the occurrence and distribution patterns of a range of endemic and zoonotic pathogens circulating among rodent communities in northern France. The community sample consisted of 713 rodents, including 11 host species from diverse habitats. Rodents were screened for virus exposure (hantaviruses, cowpox virus, Lymphocytic choriomeningitis virus, Tick-borne encephalitis virus) using antibody assays. Bacterial communities were characterized using 16S rRNA amplicon sequencing of splenic samples. Multiple correspondence (MCA), multiple regression and association screening (SCN) analyses were used to determine the degree to which extrinsic factors (study year and site; host habitat, species, sex and age class) contributed to pathogen community structure, and to identify patterns of associations between pathogens within hosts. We found a rich diversity of bacterial genera, with 36 known or suspected to be pathogenic. We revealed that host species is the most important determinant of pathogen community composition, and that hosts that share habitats can have very different pathogen communities. Pathogen diversity and co-infection rates also vary among host species. Aggregation of pathogens responsible for zoonotic diseases suggests that some rodent species may be more important for transmission risk than others. Moreover, we detected positive associations between several pathogens, including Bartonella , Mycoplasma species, Cowpox virus (CPXV) and hantaviruses, and these patterns were generally specific to particular host species. Altogether, our results suggest that host and pathogen specificity is the most important driver of pathogen community structure, and that interspecific pathogen-pathogen associations also depend on host species.

Major advances in the understanding of infectious diseases have been achieved in the last decades. However, the persistence and re-emergence of pathogens continue to raise public and veterinary health concerns, of which the recent COVID-19 pandemic may be one of the most dramatic examples. Understanding the impact of habitat alterations and concomitant biodiversity loss on pathogen transmission and emergence from wildlife remains challenging. Here, we aim to elucidate the interlinkages between biodiversity and rodent-borne diseases at local and European scales. We present recently collected host-pathogen data from 21 temperate forest sites and eight urban green spaces throughout five European countries, environments where rodents are abundant and human/domestic animals – wildlife interactions are likely to occur. 3766 specimens were analyzed during the period from 2020 to 2022 comprising 15 different small mammal species. Different organ tissues of each specimen were screened for bacteria by either 16S rRNA amplicon sequencing or specific PCR. The presence of antibodies to different families of viruses was screened using immunofluorescent assays. A multitude of pathogens of zoonotic potential from several genera including Bartonella, Borrelia, Mycoplasma, Anaplasma, Neoehrlichia, Leptospira , Orthohantavirus and Orthopoxvirus were detected at non-negligible prevalence in 11 different terrestrial mammal species. A shift in host community composition was observed along the anthropization gradient with more urban adapters in more anthropized sites. Pathogen richness increased with an increase in host species diversity, following the “host-diversity begets parasite-diversity” hypothesis. The absence of some vector-transmitted parasites in urban areas suggests a shift in pathogen community along the anthropization gradient. Host species and host intrinsic factors were dominant explanatory variables for endoparasitic Mycoplasma species and Sarcocystidae , while extrinsic environmental and climatic factors where influential in explaining variations in occurrences of several vector-transmitted pathogens. Apodemus sylvaticus and Clethrionomys glareolus were important connector host species in respectively urban green spaces and temperate forests. Increased host diversity, but not anthropization, correlated with a richer pathogen community. These results ultimately lead to an increased understanding of the complex host-pathogen system at the local landscape that can aid future management decisions and support the public health sector. ### Competing Interest Statement The authors have declared no competing interest.

Abstract Evidence for divergent selection and adaptive variation across the landscape can provide insight into a species' ability to adapt to different environments. However, despite recent advances in genomics, it remains difficult to detect the footprints of climate‐mediated selection in natural populations. Here, we analysed ddRAD sequencing data (21,892 SNPs) in conjunction with geographic climate variation to search for signatures of adaptive differentiation in twelve populations of the bank vole (Clethrionomys glareolus) distributed across Europe. To identify the loci subject to selection associated with climate variation, we applied multiple genotype‐environment association methods, two univariate and one multivariate, and controlled for the effect of population structure. In total, we identified 213 candidate loci for adaptation, 74 of which were located within genes. In particular, we identified signatures of selection in candidate genes with functions related to lipid metabolism and the immune system. Using the results of redundancy analysis, we demonstrated that population history and climate have joint effects on the genetic variation in the pan‐European metapopulation. Furthermore, by examining only candidate loci, we found that annual mean temperature is an important factor shaping adaptive genetic variation in the bank vole. By combining landscape genomic approaches, our study sheds light on genome‐wide adaptive differentiation and the spatial distribution of variants underlying adaptive variation influenced by local climate in bank voles.

The Eurasian golden jackal ( Canis aureus ) has been rapidly expanding its distribution range in Europe. Whether jackals will be able to adapt to new environmental conditions in northern Europe remains largely unresolved. Herein we provide additional evidence for the species’ ability to colonize northern environments by presenting the new records of golden jackal occurrence in Finland. During 2018–2022, golden jackals were recorded at six localities of which one located in southern, four in central and one in northern Finland. We drafted potential main routes of dispersal movements by jackals in northern Europe, and discuss ecology and management of this newly colonizing species in Finland.