Puumala Hantavirus in the forest ecosystems of Western Europe

Viruses belonging to the genus Hantavirus are the only representative of the family Bunyaviridae that are not transmitted to Human by arthropod vectors but by small rodents. Some insectivores and bats are infected by hantaviruses but transmission to human has never been reported. In Europe, the hantavirus Puumala, transmitted by the bank vole (Myodes glareolus), is responsible for an increasingly important zoonosis Nephropathia Epidemica (NE), an attenuated form of Hemorrhagic Fever with Renal Syndrome. Humans become infected by inhalation of aerosols containing contaminated rodent excreta. Despite the continuous spatial distribution of M. glareolus throughout Europe, Nephropathia Epidemica incidence is highly variable at continental as well as regional scales. Endemic areas cover a large part of Northern Europe (Scandinavia, Finland, Baltic States) and are more fragmented in Belgium, North-Eastern France and Western Germany. A better understanding of the current distribution of Nephropathia Epidemica and its potential risk of extension is essential and must be based on a multidisciplinary approach taking into account the different actors involved in the transmission cycle (Human, bank voles and virus).Les virus du genre Hantavirus sont les seuls représentants de la famille des Bunyaviridae qui ne sont pas transmis à l’Homme par des vecteurs arthropodes mais par de petits rongeurs. Certains insectivores et chiroptères sont porteurs d’hantavirus mais aucun cas de transmission à l’Homme n’est connu à ce jour. En Europe, l’hantavirus Puumala qui a comme réservoir le campagnol roussâtre (Myodes glareolus), est responsable d’une zoonose d’importance croissante, la Néphropathie Epidémique, une forme atténuée de Fièvre Hémorragique à Syndrome Rénal. La contamination humaine s’effectue généralement par inhalation d’aérosols contenant des excrétas ou des sécrétions de rongeurs infectés. Malgré une zone de distribution continue des populations de campagnols roussâtres, la répartition de l’incidence de la Néphropathie Epidémique présente une forte variabilité aux échelles continentale et régionale. Les zones endémiques recouvrent une large partie de l’Europe du Nord (Scandinavie, Finlande, Pays Baltes) et de manière parcellaire la Belgique, le nord-est de la France et l’ouest de l’Allemagne. Une meilleure compréhension de la distribution actuelle de la Néphropathie Epidémique et de son risque d’extension est essentielle et doit s’appuyer sur une approche multidisciplinaire prenant en compte les différents acteurs impliqués dans le cycle de transmission (Homme, campagnol roussâtre et virus)

The Needs for Developing Experiments on Reservoirs in Hantavirus Research: Accomplishments, Challenges and Promises for the Future

Due to their large geographic distribution and potential high mortality rates in human infections, hantaviruses constitute a worldwide threat to public health. As such, they have been the subject of a large array of clinical, virological and eco-evolutionary studies. Many experiments have been conducted in vitro or on animal models to identify the mechanisms leading to pathogenesis in humans and to develop treatments of hantavirus diseases. Experimental research has also been dedicated to the understanding of the relationship between hantaviruses and their reservoirs. However, these studies remain too scarce considering the diversity of hantavirus/reservoir pairs identified, and the wide range of issues that need to be addressed. In this review, we present a synthesis of the experimental studies that have been conducted on hantaviruses and their reservoirs. We aim at summarizing the knowledge gathered from this research, and to emphasize the gaps that need to be filled. Despite the many di_culties encountered to carry hantavirus experiments, we advocate for the need of such studies in the future, at the interface of evolutionary ecology and virology. They are critical to address emerging areas of research, including hantavirus evolution and the epidemiological consequences of individual variation in infection outcomes

Recent data on hantaviruses and perspectives for research

The members of the genus Hantavirus are the only representatives of the family Bunyaviridae not transmitted by arthropod vectors but by small mammals. Hantaviruses transmitted by rodents (Order Rodentia) have been discovered at first because of their pathogenicity for humans. The first phylogenetic studies suggested a co-evolution between each hantavirus and its rodent reservoir species. However, further exploration of more animal reservoirs has evidenced that hantaviruses also circulate among insectivores (Order Soricomorpha) and bats (Order Chiroptera), without associated human pathology or even transmission demonstrated up to now. Documented co-circulation of the same hantavirus among sympatric rodent species and new phylogenetic data outlining host-switching events between closely related hantaviruses are currently weakening the concept of strict co-speciation. In addition, the closer analysis of clinical cases invites to moderate the dogma of a clearly distinct pathology in humans between Old World (Europe-Asia) hantaviruses that would provoke Haemorrhagic Fevers with Renal Syndrome (HFRS) and New World (Americas) hantaviruses that would result in a Cardio- Pulmonary Syndrome (HCPS). These topics are discussed because they open interesting perspectives for trans-disciplinary research, from compared immunology between mammals up to modelling of reservoir dynamics in natural environment and sociology of human populations at risk. The most recent data concerning the circulation and pathogenicity of hantaviruses in Europe and in the world are also presented as well as the new technologies for the serological and genetic investigations to discover without a priori new viruses « sleeping » in animal reservoirs and to evaluate their potential for future emergence(s) in manLes virus du genre Hantavirus sont les seuls représentants de la famille des Bunyaviridae qui ne sont pas transmis par des vecteurs arthropodes mais par des petits mammifères. Les hantavirus transmis par les rongeurs (Ordre Rodentia) ont été les premiers découverts en raison de leur pouvoir pathogène chez l’homme. Les premières études phylogénétiques ont suggéré une coévolution entre chaque hantavirus et son espèce de rongeur réservoir. Toutefois, l’exploration d’autres réservoirs animaux a montré que des hantavirus circulent aussi chez les insectivores (Ordre Soricomorpha) et les chauvessouris (Ordre Chiroptera), sans qu’aucune transmission pathogène à l’homme n’ait pu être mise en évidence jusqu’à aujourd’hui. Des observations naturelles de cocirculation d’un même hantavirus au sein de plusieurs espèces de rongeurs sympatriques, ainsi que de nouvelles données phylogénétiques qui soulignent des changements d’hôte (host-switching) entre hantavirus très proches, remettent actuellement en cause la cospéciation stricte. De même, l’observation plus fine de cas cliniques suggère de modérer le dogme d’une maladie distincte chez l’homme, les hantavirus de l’Ancien Monde (Europe- Asie) provoquant une fièvre hémorragique à syndrome rénal (FHRS) et ceux du Nouveau Monde (Amériques) conduisant à une hantavirose à syndrome cardio-pulmonaire (HSCP). Ces points sont discutés car ils ouvrent d’importantes perspectives en matière de recherche transdisciplinaire, depuis l’immunologie comparée chez les mammifères jusqu’à la modélisation de la dynamique des réservoirs dans leur milieu naturel, en passant par la sociologie des populations à risque. Les données récentes sur la circulation et le pouvoir pathogène des hantavirus en Europe et dans le monde sont aussi présentées, ainsi que les nouveaux outils d’investigation sérologique et génétique permettant la découverte sans a priori de nouveaux virus « dormants » dans des réservoirs et l’évaluation de leur potentiel d’émergence chez l’homm

Phylogeography of Puumala orthohantavirus in Europe

Puumala virus is an RNA virus hosted by the bank vole (Myodes glareolus) and is today present in most European countries. Whilst it is generally accepted that hantaviruses have been tightly co-evolving with their hosts, Puumala virus (PUUV) evolutionary history is still controversial and so far has not been studied at the whole European level. This study attempts to reconstruct the phylogeographical spread of modern PUUV throughout Europe during the last postglacial period in the light of an upgraded dataset of complete PUUV small (S) segment sequences and by using most recent computational approaches. Taking advantage of the knowledge on the past migrations of its host, we identified at least three potential independent dispersal routes of PUUV during postglacial recolonization of Europe by the bank vole. From the Alpe-Adrian region (Balkan, Austria, and Hungary) to Western European countries (Germany, France, Belgium, and Netherland), and South Scandinavia. From the vicinity of Carpathian Mountains to the Baltic countries and to Poland, Russia, and Finland. The dissemination towards Denmark and North Scandinavia is more hypothetical and probably involved several independent streams from south and north Fennoscandia

Phylogeography of Puumala orthohantavirus in Europe

Puumala virus is an RNA virus hosted by the bank vole (Myodes glareolus) and is today present in most European countries. Whilst it is generally accepted that hantaviruses have been tightly co-evolving with their hosts, Puumala virus (PUUV) evolutionary history is still controversial and so far has not been studied at the whole European level. This study attempts to reconstruct the phylogeographical spread of modern PUUV throughout Europe during the last postglacial period in the light of an upgraded dataset of complete PUUV small (S) segment sequences and by using most recent computational approaches. Taking advantage of the knowledge on the past migrations of its host, we identified at least three potential independent dispersal routes of PUUV during postglacial recolonization of Europe by the bank vole. From the Alpe-Adrian region (Balkan, Austria, and Hungary) to Western European countries (Germany, France, Belgium, and Netherland), and South Scandinavia. From the vicinity of Carpathian Mountains to the Baltic countries and to Poland, Russia, and Finland. The dissemination towards Denmark and North Scandinavia is more hypothetical and probably involved several independent streams from south and north Fennoscandia

Increasing importance of Bunyaviridae in public and veterinary health illustrated by hantaviruses, and the Schmallenberg and Rift Valley fever viruses

The virus family of Bunyaviridae is very important in terms of public health and veterinary medicine. With over 350 viruses identified to date, it includes viruses mainly transmitted by arthropods (arboviruses) or rodents (roboviruses), infecting mammals and plants for the genus Tospovirus. Humans can be infected by around 60 bunyaviruses sometime with very serious or even fatal consequences. The examples of Schmallenberg and Rift Valley fever viruses and hantavirus genus illustrate perfectly the many questions surrounding the Bunyaviridae family’s capacity to emerge, widely variable pathogenicity for different hosts, and capacity to persist in different vectors such as arthropods or rodents and more recently the soricomorph species (insectivores)La famille des Bunyaviridae est très importante en santé publique et vétérinaire. Avec plus de 350 virus identifiés à ce jour, elle regroupe des virus transmis principalement par des arthropodes (arbovirus) ou des rongeurs (robovirus), responsables d’infections chez les mammifères et chez les plantes pour le genre Tospovirus. L’homme peut être infecté par une soixantaine de ces Bunyaviridae, parfois avec des conséquences très graves, voire fatales. Les exemples du virus de Schmallenberg, du virus de la fièvre de la Vallée du Rift et du genre viral hantavirus illustrent parfaitement les nombreuses incertitudes concernant cette famille virale quant à leur potentiel d’émergence, leur pouvoir pathogène très varié pour des hôtes divers, et leur capacité à persister chez différents vecteurs appartenant aux arthropodes ou aux rongeurs et, plus récemment, aux soricomorphes (insectivores

Development of recombinant nucleoprotein-based diagnostic systems for lassa fever

Diagnostic systems for Lassa fever (LF), a viral hemorrhagic fever caused by Lassa virus (LASV), such as enzyme immunoassays for the detection of LASV antibodies and LASV antigens, were developed using the recombinant nucleoprotein (rNP) of LASV (LASV-rNP). The LASV-rNP was expressed in a recombinant baculovirus system. LASV-rNP was used as an antigen in the detection of LASV-antibodies and as an immunogen for the production of monoclonal antibodies. The LASV-rNP was also expressed in HeLa cells by transfection with the expression vector encoding cDNA of the LASV-NP gene. An immunoglobulin G enzyme-linked immunosorbent assay (ELISA) using LASV-rNP and an indirect immunofluorescence assay using LASV-rNP-expressing HeLa cells were confirmed to have high sensitivity and specificity in the detection of LASV-antibodies. A novel monoclonal antibody to LASV-rNP, monoclonal antibody 4A5, was established. A sandwich antigen capture (Ag-capture) ELISA using the monoclonal antibody and an anti-LASV-rNP rabbit serum as capture and detection antibodies, respectively, was then developed. Authentic LASV nucleoprotein in serum samples collected from hamsters experimentally infected with LASV was detected by the Ag-capture ELISA. The Ag-capture ELISA specifically detected LASV-rNP but not the rNPs of lymphocytic choriomeningitis virus or Junin virus. The sensitivity of the Ag-capture ELISA in detecting LASV antigens was comparable to that of reverse transcription-PCR in detecting LASV RNA. These LASV rNP-based diagnostics were confirmed to be useful in the diagnosis of LF even in institutes without a high containment laboratory, since the antigens can be prepared without manipulation of the infectious viruses.Instituto de Biotecnologia y Biologia Molecula

Three-way relationships between gut microbiota, helminth assemblages and bacterial infections in wild rodent populations

Despite its central role in host fitness, the gut microbiota may differ greatly between individuals. This variability is often mediated by environmental or host factors such as diet, genetics, and infections. Recently, particular attention has been given to the interactions between gut bacteriota and helminths, as these latter could affect host susceptibility to other infections. Further studies are still required to better understand the three-way interactions between gut bacteriota, helminths and other parasites, especially because previous findings have been very variable, even for comparable host-parasite systems. In our study, we used the V4 region of the 16S rRNA gene to assess the variability of gut bacteriota diversity and composition in wild populations of a small mammal, the bank vole Myodes glareolus. Four sites were sampled at a regional geographical scale (100 km) along a North-South transect in Eastern France. We applied analyses of community and microbial ecology to evaluate the interactions between the gut bacteriota, the gastro-intestinal helminths and the pathogenic bacteria detected in the spleen. We identified important variations of the gut bacteriota composition and diversity among bank voles. They were mainly explained by sampling localities and reflected the North/South sampling transect. In addition, we detected two main enterotypes, that might correspond to contrasted diets. We found geographic variations of the Firmicutes/Bacteroidetes ratio, that correlated positively with body mass index. We found positive correlations between the specific richness of the gut bacteriota and of the helminth community, as well as between the composition of these two communities, even when accounting for the influence of geographical distance. The helminths Aonchotheca murissylvatici, Heligmosomum mixtum and  the bacteria Bartonella sp were the main taxa associated with the whole gut bacteriota composition. Besides, changes in the relative abundance of particular gut bacteriota taxa were specifically associated with other helminths (Mastophorus muris, Catenotaenia henttoneni, Paranoplocephala omphalodes and Trichuris arvicolae) or pathogenic bacteria. Especially, infections with Neoehrlichia mikurensis, Orientia sp, Rickettsia sp and P. omphalodes were associated with lower relative abundance of the family Erysipelotrichaceae (Firmicutes), while coinfections with higher number of bacterial infections were associated with lower relative abundance of a Bacteroidales family (Bacteroidetes). These results emphasize complex interlinkages between gut bacteriota and infections in wild animal populations. They remain difficult to generalize due to the strong impact of the environment on these interactions, even at regional geographical scales. Abiotic features, as well as small mammal community composition and within host parasite coinfections, should now be considered to better understand the spatial variations observed in the relationships between gut bacteriota, gastro-intestinal helminths and bacterial infections