Epidemiology of bat rabies in Germany

Phylogeographic Aspects of Bat Lyssaviruses in Europe: A Review

During the last few decades, bat lyssaviruses have become the topic of intensive molecular and epidemiological investigations. Since ancient times, rhabdoviruses have caused fatal encephalitis in humans which has led to research into effective strategies for their eradication. Modelling of potential future cross-species virus transmissions forms a substantial component of the recent infection biology of rabies. In this article, we summarise the available data on the phylogeography of both bats and lyssaviruses in Europe and the adjacent reg ions, especially in the contact zone between the Palearctic and Ethiopian realms. Within these zones, three bat families are present with high potential for cross-species transmission and the spread of lyssaviruses in Phylogroup II to Europe (part of the western Palearctic). The lack of effective therapies for rabies viruses in Phylogroup II and the most divergent lyssaviruses generates impetus for additional phylogenetic and virological research within this geographical region.

Discovery of a novel bat lyssavirus in a Long-fingered bat (Myotis capaccinii) from Slovenia

Lyssaviruses are the causative agents of rabies, a zoonotic, fatal disease that is thought to be ancestral to bats. In the last decade, the detection of bat associated lyssaviruses is increasing also in Europe. Within a retrospective bat associated lyssavirus surveillance study a total of 225 dead bats of 21 bat species were collected in Slovenia between 2012 and 2019 and tested by specific real-time RT-PCR method. The first lyssavirus positive sample in bats in Slovenia was detected using the real-time RT-PCR, the fluorescent antibody test, and next generation sequencing, while the rabies tissue culture inoculation test was unsuccessful due to sample degradation and storage conditions. The nearly complete genome of Divača bat lyssavirus from Slovenia consists of 11,871 nucleotides and reflects the characteristic gene organization known for lyssaviruses, encoding the five viral proteins. Phylogenetic analysis of Divača bat lyssavirus revealed that it belongs to phylogroup I lyssaviruses and is most closely related to Kotalahti bat lyssavirus (KBLV) with 87.20% nucleotide and 99.22% amino acid identity. Together with KBLV, Khujand virus, European bat lyssavirus 2, Bakeloh bat lyssavirus, and Aravan virus, Divača bat lyssavirus was detected in the genus Myotis suggesting its key role in the transmission and maintenance of certain lyssaviruses.

Retrospective Enhanced Bat Lyssavirus Surveillance in Germany between 2018-2020

Lyssaviruses are the causative agents for rabies, a zoonotic and fatal disease. Bats are the ancestral reservoir host for lyssaviruses, and at least three different lyssaviruses have been found in bats from Germany. Across Europe, novel lyssaviruses were identified in bats recently and occasional spillover infections in other mammals and human cases highlight their public health relevance. Here, we report the results from an enhanced passive bat rabies surveillance that encompasses samples without human contact that would not be tested under routine conditions. To this end, 1236 bat brain samples obtained between 2018 and 2020 were screened for lyssaviruses via several RT-qPCR assays. European bat lyssavirus type 1 (EBLV-1) was dominant, with 15 positives exclusively found in serotine bats (Eptesicus serotinus) from northern Germany. Additionally, when an archived set of bat samples that had tested negative for rabies by the FAT were screened in the process of assay validation, four samples tested EBLV-1 positive, including two detected in Pipistrellus pipistrellus. Subsequent phylogenetic analysis of 17 full genomes assigned all except one of these viruses to the A1 cluster of the EBLV-1a sub-lineage. Furthermore, we report here another Bokeloh bat lyssavirus (BBLV) infection in a Natterer's bat (Myotis nattereri) found in Lower Saxony, the tenth reported case of this novel bat lyssavirus.

Update on Potentially Zoonotic Viruses of European Bats

Bats have been increasingly gaining attention as potential reservoir hosts of some of the most virulent viruses known. Numerous review articles summarize bats as potential reservoir hosts of human-pathogenic zoonotic viruses. For European bats, just one review article is available that we published in 2014. The present review provides an update on the earlier article and summarizes the most important viruses found in European bats and their possible implications for Public Health. We identify the research gaps and recommend monitoring of these viruses.

Full-Genome Sequences and Phylogenetic Analysis of Archived Danish European Bat Lyssavirus 1 (EBLV-1) Emphasize a Higher Genetic Resolution and Spatial Segregation for Sublineage 1a

European bat lyssavirus type 1 (EBLV-1) is the causative agent for almost all reported rabies cases found in European bats. In recent years, increasing numbers of available EBLV-1 full genomes and their phylogenetic analyses helped to further elucidate the distribution and genetic characteristics of EBLV-1 and its two subtypes, namely EBLV-1a and EBLV-1b. Nonetheless, the absence of full-genome sequences from regions with known detections of EBLV-1 still limit the understanding of the phylogeographic relations between viruses from different European regions. In this study, a set of 21 archived Danish EBLV-1 samples from the years 1985 to 2009 was processed for the acquisition of full-genome sequences using a high-throughput sequencing approach. Subsequent phylogenetic analysis encompassing all available EBLV-1 full genomes from databases revealed the Danish sequences belong to the EBLV-1a subtype and further highlighted the distinct, close phylogenetic relationship of Danish, Dutch and German isolates in this region. In addition, the formation of five putative groups nearly exclusively formed by Danish isolates and the overall increased resolution of the EBLV-1a branch indicate a higher genetic diversity and spatial segregation for this sublineage than was previously known. These results emphasize the importance of phylogenetic analyses of full-genome sequences of lyssaviruses for genetic geography.

Experimental Lagos bat virus infection in straw-colored fruit bats: A suitable model for bat rabies in a natural reservoir species

Rabies is a fatal neurologic disease caused by lyssavirus infection. Bats are important natural reservoir hosts of various lyssaviruses that can be transmitted to people. The epidemiology and pathogenesis of rabies in bats are poorly understood, making it difficult to prevent zoonotic transmission. To further our understanding of lyssavirus pathogenesis in a natural bat host, an experimental model using straw-colored fruit bats (Eidolon helvum) and Lagos bat virus, an endemic lyssavirus in this species, was developed. To determine the lowest viral dose resulting in 100% productive infection, bats in five groups (four bats per group) were inoculated intramuscularly with one of five doses, ranging from 100.1 to 104.1 median tissue culture infectious dose (TCID50). More bats died due to the development of rabies after the middle dose (102.1 TCID50, 4/4 bats) than after lower (101.1, 2/4; 101.1, 2/4) or higher (103.1, 2/4; 104.1, 2/4) doses of virus. In the two highest dose groups, 4/8 bats developed rabies. Of those bats that remained healthy 3/4 bats seroconverted, suggesting that high antigen loads can trigger a strong immune response that abrogates a productive infection. In contrast, in the two lowest dose groups, 3/8 bats developed rabies, 1/8 remained healthy and seroconverted and 4/8 bats remained healthy and did not seroconvert, suggesting these doses are too low to reliably induce infection. The main lesion in all clinically affected bats was meningoencephalitis associated with lyssavirus-positive neurons. Lyssavirus antigen was detected in tongue epithelium (5/11 infected bats) rather than in salivary gland epithelium (0/11), suggesting viral excretion via the tongue. Thus, intramuscular inoculation of 102.1 TCID50 of Lagos bat virus into straw-colored fruit bats is a suitable model for lyssavirus associated bat rabies in a natural reservoir host, and can help with the investigation of lyssavirus infection dynamics in bats.

Phylogeny of Hungarian EBLV-1 strains using whole-genome sequence data

European bat lyssavirus 1 (EBLV-1) is a widespread lyssavirus across Europe, whose epizootic cycle is linked to a few bat species. Occasionally, EBLV-1 infection may occur in domestic animals and humans. EBLV-1 can be classified into two subtypes, where subtype EBLV-1a shows a wide geographic distribution between France and Russia whereas subtype EBLV-1b is distributed between Spain and Poland. In this study, we determined the genome sequence of two recent EBLV-1a strains detected in Hungary and analysed their adaptive evolution and phylodynamics. The data set that included 100 EBLV-1 genome sequences identified positive selection at selected sites in genes coding for viral proteins (N, codon 18; P, 141 and 155; G, 244 and 488; L, 168, 980, 1597 and 1754). A major genetic clade containing EBLV-1a isolates from Hungary, Slovakia, Denmark and Poland was estimated to have diverged during the 19th century whereas the divergence of the most recent ancestor of Hungarian and Slovakian isolates dates back to 1950 (time span, 1930 to 1970). Phylogeographic analysis of the EBLV-1a genomic sequences demonstrated strong evidence of viral dispersal from Poland to Hungary. This new information indicates that additional migratory flyways may help the virus spread, a finding that supplements the general theory on a west-to-east dispersal of EBLV-1a strains. Long-distance migrant bats may mediate the dispersal of EBLV-1 strains across Europe; however, structured surveillance and extended genome sequencing would be needed to better understand the epizootiology of EBLV-1 infections in Europe.

Bats and Viruses: Emergence of Novel Lyssaviruses and Association of Bats with Viral Zoonoses in the EU

Bats in the EU have been associated with several zoonotic viral pathogens of significance to both human and animal health. Virus discovery continues to expand the existing understating of virus classification, and the increased interest in bats globally as reservoirs or carriers of zoonotic agents has fuelled the continued detection and characterisation of new lyssaviruses and other viral zoonoses. Although the transmission of lyssaviruses from bat species to humans or terrestrial species appears rare, interest in these viruses remains, through their ability to cause the invariably fatal encephalitis—rabies. The association of bats with other viral zoonoses is also of great interest. Much of the EU is free of terrestrial rabies, but several bat species harbor lyssaviruses that remain a risk to human and animal health. Whilst the rabies virus is the main cause of rabies globally, novel related viruses continue to be discovered, predominantly in bat populations, that are of interest purely through their classification within the lyssavirus genus alongside the rabies virus. Although the rabies virus is principally transmitted from the bite of infected dogs, these related lyssaviruses are primarily transmitted to humans and terrestrial carnivores by bats. Even though reports of zoonotic viruses from bats within the EU are rare, to protect human and animal health, it is important characterise novel bat viruses for several reasons, namely: (i) to investigate the mechanisms for the maintenance, potential routes of transmission, and resulting clinical signs, if any, in their natural hosts; (ii) to investigate the ability of existing vaccines, where available, to protect against these viruses; (iii) to evaluate the potential for spill over and onward transmission of viral pathogens in novel terrestrial hosts. This review is an update on the current situation regarding zoonotic virus discovery within bats in the EU, and provides details of potential future mechanisms to control the threat from these deadly pathogens.

Mechanisms for lyssavirus persistence in non-synanthropic bats in Europe: insights from a modeling study

Bats are natural reservoirs of the largest proportion of viral zoonoses among mammals, thus understanding the conditions for pathogen persistence in bats is essential to reduce human risk. Focusing on the European Bat Lyssavirus subtype 1 (EBLV-1), causing rabies disease, we develop a data-driven spatially explicit metapopulation model to investigate EBLV-1 persistence in Myotis myotis and Miniopterus schreibersii bat species in Catalonia. We find that persistence relies on host spatial structure through the migratory nature of M. schreibersii, on cross-species mixing with M. myotis, and on survival of infected animals followed by temporary immunity. The virus would not persist in the single colony of M. myotis. Our study provides for the first time epidemiological estimates for EBLV-1 progression in M. schreibersii. Our approach can be readily adapted to other zoonoses of public health concern where long-range migration and habitat sharing may play an important role.

Pathogenesis of bat rabies in a natural reservoir: Comparative susceptibility of the straw-colored fruit bat (Eidolon helvum) to three strains of Lagos bat virus

Rabies is a fatal neurologic disease caused by lyssavirus infection. People are infected through contact with infected animals. The relative increase of human rabies acquired from bats calls for a better understanding of lyssavirus infections in their natural hosts. So far, there is no experimental model that mimics natural lyssavirus infection in the reservoir bat species. Lagos bat virus is a lyssavirus that is endemic in straw-colored fruit bats (Eidolon helvum) in Africa. Here we compared the susceptibility of these bats to three strains of Lagos bat virus (from Senegal, Nigeria, and Ghana) by intracranial inoculation. To allow comparison between strains, we ensured the same titer of virus was inoculated in the same location of the brain of each bat. All bats (n = 3 per strain) were infected, and developed neurological signs, and fatal meningoencephalitis with lyssavirus antigen expression in neurons. There were three main differences among the groups. First, time to death was substantially shorter in the Senegal and Ghana groups (4 to 6 days) than in the Nigeria group (8 days). Second, each virus strain produced a distinct clinical syndrome. Third, the spread of virus to peripheral tissues, tested by hemi-nested reverse transcriptase PCR, was frequent (3 of 3 bats) and widespread (8 to 10 tissues positive of 11 tissues examined) in the Ghana group, was frequent and less widespread in the Senegal group (3/3 bats, 3 to 6 tissues positive), and was rare and restricted in the Nigeria group (1/3 bats, 2 tissues positive). Centrifugal spread of virus from brain to tissue of excretion in the oral cavity is required to enable lyssavirus transmission. Therefore, the Senegal and Ghana strains seem most suitable for further pathogenesis, and for transmission, studies in the straw-colored fruit bat.

Rabies is a neurologic disease that causes severe suffering and is almost always fatal. The disease is caused by infection with a virus of the genus Lyssavirus, of which 16 species are known. These viruses replicate in neurons, are excreted in the mouth, and are transmitted by bites. Dogs are the most important source of rabies for humans, but recently there is a relative increase in people contracting the disease from bats. To better understand the development of human rabies caused by these bat-acquired viruses, we need to study this disease in its bat host under controlled circumstances. To do so, we chose a naturally occurring lyssavirus–host combination: Lagos bat virus in straw-colored fruit bats. We compared three available strains of Lagos bat virus (all isolated from brains of this bat species) for their ability to mimic a natural infection. We used intracranial inoculation to ensure infection of the brain. All three strains infected brain neurons, resulting in fatal neurologic disease, however only two of the strains showed the ability to reach the site of excretion—the mouth—and were considered a suitable virus to use for further studies of this disease in bats.

The Recently Discovered Bokeloh Bat Lyssavirus: Insights Into Its Genetic Heterogeneity and Spatial Distribution in Europe and the Population Genetics of Its Primary Host

In 2010, a novel lyssavirus named Bokeloh bat lyssavirus (BBLV) was isolated from a Natterer's bat (Myotis nattereri) in Germany. Two further viruses were isolated in the same country and in France in recent years, all from the same bat species and all found in moribund or dead bats. Here we report the description and the full-length genome sequence of five additional BBLV isolates from Germany (n=4) and France (n=1). Interestingly, all of them were isolated from the Natterer's bat, except one from Germany, which was found in a common Pipistrelle bat (Pipistrellus pipistrellus), a widespread and abundant bat species in Europe. The latter represents the first case of transmission of BBLV to another bat species. Phylogenetic analysis clearly demonstrated the presence of two different lineages among this lyssavirus species: lineages A and B. The spatial distribution of these two lineages remains puzzling, as both of them comprised isolates from France and Germany; although clustering of isolates was observed on a regional scale, especially in Germany. Phylogenetic analysis based on the mitochondrial cytochrome b (CYTB) gene from positive Natterer's bat did not suggest a circulation of the respective BBLV sublineages in specific Natterer's bat subspecies, as all of them were shown to belong to the M. nattereri sensu stricto clade/subspecies and were closely related (German and French positive bats). At the bat host level, we demonstrated that the distribution of BBLV at the late stage of the disease seems large and massive, as viral RNA was detected in many different organs.

Parasite diversity of European Myotis species with special emphasis on Myotis myotis (Microchiroptera, Vespertilionidae) from a typical nursery roost

Background

Bats belong to one of the most species-rich orders within the Mammalia. They show a worldwide distribution, a high degree of ecological diversification as well as a high diversity of associated parasites and pathogens. Despite their prominent and unique role, the knowledge of their parasite-host-relationships as well as the mechanisms of co-evolutionary processes are, partly due to strict conservation regulations, scarce.

Methods

Juvenile specimens of the greater mouse-eared bat (Myotis myotis) from a roosting colony in Gladenbach (Hesse, Germany) were examined for their metazoan endo-and ectoparasite infections and pathogens. Morphometric data were recorded and the individuals were checked for Lyssavirus-specific antigen using a direct immunofluorescence test. For unambiguous species identification, the bats were analysed by cyt-b sequence comparison.

Results

Myotis myotis were parasitized by the six insect and arachnid ectoparasite species, i.e. Ixodes ricinus, Ischnopsyllus octactenus, Ichoronyssus scutatus, Steatonyssus periblepharus, Spinturnix myoti and Cimex dissimilis. Additionally, the nematode Molinostrongylus alatus and the cestode Vampirolepis balsaci were recorded. Each bat was parasitized by at least four species. The parasites showed partially extreme rates of infection, never recorded before, with more than 1,440 parasites per single host. Ichoronyssus scutatus, Steatonyssus periblepharus, Vampirolepis balsaci and Molinostrongylus alatus are recorded for the first time in Germany. A checklist for Europe is presented containing records of 98 parasite species of 14 Myotis species.

Conclusions

The Myotis myotis from Gladenbach (Hesse, Germany) were parasitized by a diverse parasite fauna with high infestation rates. We assume that in juvenile Myotis the number of parasites is generally higher than in adults due to only later acquired immune competence and behavioural adaptations. Our results revealed new insights into parasite fauna of M. myotis and European bats in general. The finding of endoparasitic cyclophyllidean cestodes that have a two-host lifecycle is, considering the stationary behaviour of the juvenile bats, rather unusual and suggests a non-predatory transmission mechanism (e.g. via autoinfection).

A new insight gained from the collated literature was that the European wide composition of the Myotis parasite fauna is dominated by a few specific taxonomic groups in Europe.

Real-Time RT-PCR for the Detection of Lyssavirus Species

The causative agents of rabies are single-stranded, negative-sense RNA viruses in the genus Lyssavirus of Rhabdoviridae, consisting of twelve classified and three as yet unclassified species including classical rabies virus (RABV). Highly neurotropic RABV causes rapidly progressive encephalomyelitis with nearly invariable fatal outcome. Rapid and reliable diagnosis of rabies is highly relevant for public and veterinary health. Due to growing variety of the genus Lyssavirus observed, the development of suitable molecular assays for diagnosis and differentiation is challenging. This work focused on the establishment of a suitable real-time RT-PCR technique for rabies diagnosis as a complement to fluorescent antibody test and rabies tissue culture infection test as gold standard for diagnosis and confirmation. The real-time RT-PCR was adapted with the goal to detect the whole spectrum of lyssavirus species, for nine of which synthesized DNA fragments were used. For the detection of species, seven probes were developed. Serial dilutions of the rabies virus strain CVS-11 showed a 100-fold higher sensitivity of real-time PCR compared to heminested RT-PCR. Using a panel of thirty-one lyssaviruses representing four species, the suitability of the protocol could be shown. Phylogenetic analysis of the sequences obtained by heminested PCR allowed correct classification of all viruses used.

European bats as carriers of viruses with zoonotic potential

Bats are being increasingly recognized as reservoir hosts of highly pathogenic and zoonotic emerging viruses (Marburg virus, Nipah virus, Hendra virus, Rabies virus, and coronaviruses). While numerous studies have focused on the mentioned highly human-pathogenic bat viruses in tropical regions, little is known on similar human-pathogenic viruses that may be present in European bats. Although novel viruses are being detected, their zoonotic potential remains unclear unless further studies are conducted. At present, it is assumed that the risk posed by bats to the general public is rather low. In this review, selected viruses detected and isolated in Europe are discussed from our point of view in regard to their human-pathogenic potential. All European bat species and their roosts are legally protected and some European species are even endangered. Nevertheless, the increasing public fear of bats and their viruses is an obstacle to their protection. Educating the public regarding bat lyssaviruses might result in reduced threats to both the public and the bats.

Bat rabies in France: a 24-year retrospective epidemiological study

Since bat rabies surveillance was first implemented in France in 1989, 48 autochthonous rabies cases without human contamination have been reported using routine diagnosis methods. In this retrospective study, data on bats submitted for rabies testing were analysed in order to better understand the epidemiology of EBLV-1 in bats in France and to investigate some epidemiological trends. Of the 3176 bats submitted for rabies diagnosis from 1989 to 2013, 1.96% (48/2447 analysed) were diagnosed positive. Among the twelve recognised virus species within the Lyssavirus genus, two species were isolated in France. 47 positive bats were morphologically identified as Eptesicus serotinus and were shown to be infected by both the EBLV-1a and the EBLV-1b lineages. Isolation of BBLV in Myotis nattereri was reported once in the north-east of France in 2012. The phylogenetic characterisation of all 47 French EBLV-1 isolates sampled between 1989 and 2013 and the French BBLV sample against 21 referenced partial nucleoprotein sequences confirmed the low genetic diversity of EBLV-1 despite its extensive geographical range. Statistical analysis performed on the serotine bat data collected from 1989 to 2013 showed seasonal variation of rabies occurrence with a significantly higher proportion of positive samples detected during the autumn compared to the spring and the summer period (34% of positive bats detected in autumn, 15% in summer, 13% in spring and 12% in winter). In this study, we have provided the details of the geographical distribution of EBLV-1a in the south-west of France and the north-south division of EBLV-1b with its subdivisions into three phylogenetic groups: group B1 in the north-west, group B2 in the centre and group B3 in the north-east of France.

Enhanced passive bat rabies surveillance in indigenous bat species from Germany--a retrospective study

In Germany, rabies in bats is a notifiable zoonotic disease, which is caused by European bat lyssaviruses type 1 and 2 (EBLV-1 and 2), and the recently discovered new lyssavirus species Bokeloh bat lyssavirus (BBLV). As the understanding of bat rabies in insectivorous bat species is limited, in addition to routine bat rabies diagnosis, an enhanced passive surveillance study, i.e. the retrospective investigation of dead bats that had not been tested for rabies, was initiated in 1998 to study the distribution, abundance and epidemiology of lyssavirus infections in bats from Germany. A total number of 5478 individuals representing 21 bat species within two families were included in this study. The Noctule bat (Nyctalus noctula) and the Common pipistrelle (Pipistrellus pipistrellus) represented the most specimens submitted. Of all investigated bats, 1.17% tested positive for lyssaviruses using the fluorescent antibody test (FAT). The vast majority of positive cases was identified as EBLV-1, predominately associated with the Serotine bat (Eptesicus serotinus). However, rabies cases in other species, i.e. Nathusius' pipistrelle bat (Pipistrellus nathusii), P. pipistrellus and Brown long-eared bat (Plecotus auritus) were also characterized as EBLV-1. In contrast, EBLV-2 was isolated from three Daubenton's bats (Myotis daubentonii). These three cases contribute significantly to the understanding of EBLV-2 infections in Germany as only one case had been reported prior to this study. This enhanced passive surveillance indicated that besides known reservoir species, further bat species are affected by lyssavirus infections. Given the increasing diversity of lyssaviruses and bats as reservoir host species worldwide, lyssavirus positive specimens, i.e. both bat and virus need to be confirmed by molecular techniques.

Lyssavirus infection: 'low dose, multiple exposure' in the mouse model

The European bat lyssaviruses (EBLV-1 and EBLV-2) are zoonotic pathogens present within bat populations across Europe. The maintenance and transmission of lyssaviruses within bat colonies is poorly understood. Cases of repeated isolation of lyssaviruses from bat roosts have raised questions regarding the maintenance and intraspecies transmissibility of these viruses within colonies. Furthermore, the significance of seropositive bats in colonies remains unclear. Due to the protected nature of European bat species, and hence restrictions to working with the natural host for lyssaviruses, this study analysed the outcome following repeat inoculation of low doses of lyssaviruses in a murine model. A standardized dose of virus, EBLV-1, EBLV-2 or a 'street strain' of rabies (RABV), was administered via a peripheral route to attempt to mimic what is hypothesized as natural infection. Each mouse (n=10/virus/group/dilution) received four inoculations, two doses in each footpad over a period of four months, alternating footpad with each inoculation. Mice were tail bled between inoculations to evaluate antibody responses to infection. Mice succumbed to infection after each inoculation with 26.6% of mice developing clinical disease following the initial exposure across all dilutions (RABV, 32.5% (n=13/40); EBLV-1, 35% (n=13/40); EBLV-2, 12.5% (n=5/40)). Interestingly, the lowest dose caused clinical disease in some mice upon first exposure ((RABV, 20% (n=2/10) after first inoculation; RABV, 12.5% (n=1/8) after second inoculation; EBLV-2, 10% (n=1/10) after primary inoculation). Furthermore, five mice developed clinical disease following the second exposure to live virus (RABV, n=1; EBLV-1, n=1; EBLV-2, n=3) although histopathological examination indicated that the primary inoculation was the most probably cause of death due to levels of inflammation and virus antigen distribution observed. All the remaining mice (RABV, n=26; EBLV-1, n=26; EBLV-2, n=29) survived the tertiary and quaternary inoculations although the serological response did not necessarily reflect the repeated exposure. We conclude that despite repeated exposure, neither clinical disease nor serological response can be predicted and that further studies are required to understand the mechanisms behind survival following multiple exposures to lyssaviruses.

Lyssavirus distribution in naturally infected bats from Germany

In Germany, to date three different lyssavirus species are responsible for bat rabies in indigenous bats: the European Bat Lyssaviruses type 1 and 2 (EBLV-1, EBLV-2) and the Bokeloh Bat Lyssavirus (BBLV) for which Eptesicus serotinus, Myotis daubentonii and Myotis nattereri, respectively, are primary hosts. Lyssavirus maintenance, evolution, and epidemiology are still insufficiently explored. Moreover, the small number of bats infected, the nocturnal habits of bats and the limited experimental data still hamper attempts to understand the distribution, prevalence, and in particular transmission of the virus. In an experimental study in E. serotinus a heterogeneous dissemination of EBLV-1 in tissues was detected. However, it is not clear whether the EBLV-1 distribution is similar in naturally infected animals. In an attempt to further analyze virus dissemination and viral loads within naturally infected hosts we investigated tissues of 57 EBLV-1 positive individuals of E. serotinus from Germany by RT-qPCR and compared the results with those obtained experimentally. Additionally, tissue samples were investigated with immunohistochemistry to detect lyssavirus antigen in defined structures. While in individual animals virus RNA was present only in the brain, in the majority of E. serotinus viral RNA was found in various tissues with highest relative viral loads detected in the brain. Interestingly, viral antigen was confirmed in various tissues in the tongue including deep intralingual glands, nerves, muscle cells and lingual papillae. So, the tongue appears to be a prominent site for virus replication and possibly shedding.

Bat rabies surveillance in Finland

Background

In 1985, a bat researcher in Finland died of rabies encephalitis caused by European bat lyssavirus type 2 (EBLV-2), but an epidemiological study in 1986 did not reveal EBLV-infected bats. In 2009, an EBLV-2-positive Daubenton’s bat was detected. The EBLV-2 isolate from the human case in 1985 and the isolate from the bat in 2009 were genetically closely related. In order to assess the prevalence of EBLVs in Finnish bat populations and to gain a better understanding of the public health risk that EBLV-infected bats pose, a targeted active surveillance project was initiated.

Results

Altogether, 1156 bats of seven species were examined for lyssaviruses in Finland during a 28–year period (1985–2012), 898 in active surveillance and 258 in passive surveillance, with only one positive finding of EBLV-2 in a Daubenton’s bat in 2009. In 2010–2011, saliva samples from 774 bats of seven species were analyzed for EBLV viral RNA, and sera from 423 bats were analyzed for the presence of bat lyssavirus antibodies. Antibodies were detected in Daubenton’s bats in samples collected from two locations in 2010 and from one location in 2011. All seropositive locations are in close proximity to the place where the EBLV-2 positive Daubenton’s bat was found in 2009. In active surveillance, no EBLV viral RNA was detected.

Conclusions

These data suggest that EBLV-2 may circulate in Finland, even though the seroprevalence is low. Our results indicate that passive surveillance of dead or sick bats is a relevant means examine the occurrence of lyssavirus infection, but the number of bats submitted for laboratory analysis should be higher in order to obtain reliable information on the lyssavirus situation in the country.

Twenty years of active bat rabies surveillance in Germany: a detailed analysis and future perspectives

In Germany, active bat rabies surveillance was conducted between 1993 and 2012. A total of 4546 oropharyngeal swab samples from 18 bat species were screened for the presence of EBLV-1- , EBLV-2- and BBLV-specific RNA. Overall, 0·15% of oropharyngeal swab samples tested EBLV-1 positive, with the majority originating from Eptesicus serotinus. Interestingly, out of seven RT–PCR-positive oropharyngeal swabs subjected to virus isolation, viable virus was isolated from a single serotine bat (E. serotinus). Additionally, about 1226 blood samples were tested serologically, and varying virus neutralizing antibody titres were found in at least eight different bat species. The detection of viral RNA and seroconversion in repeatedly sampled serotine bats indicates long-term circulation of the virus in a particular bat colony. The limitations of random-based active bat rabies surveillance over passive bat rabies surveillance and its possible application of targeted approaches for future research activities on bat lyssavirus dynamics and maintenance are discussed.

Molecular diagnostics for the detection of Bokeloh bat lyssavirus in a bat from Bavaria, Germany

A brain sample of a Natterer's bat tested positive for rabies with classical virological techniques. Molecular techniques confirmed the presence of Bokeloh bat lyssavirus (BBLV) in Germany for the second time. Sequence analysis revealed a close genetic relationship to the initial German BBLV case. Using a TaqMan RT-PCR specific for BBLV viral RNA was detected in various other organs albeit with differences in the relative viral load.

Ecological factors associated with European bat lyssavirus seroprevalence in spanish bats

Bats have been proposed as major reservoirs for diverse emerging infectious viral diseases, with rabies being the best known in Europe. However, studies exploring the ecological interaction between lyssaviruses and their natural hosts are scarce. This study completes our active surveillance work on Spanish bat colonies that began in 1992. Herein, we analyzed ecological factors that might affect the infection dynamics observed in those colonies. Between 2001 and 2011, we collected and tested 2,393 blood samples and 45 dead bats from 25 localities and 20 bat species. The results for dead confirmed the presence of EBLV-1 RNA in six species analyzed (for the first time in Myotis capaccinii). Samples positive for European bat lyssavirus-1 (EBLV-1)-neutralizing antibodies were detected in 68% of the localities sampled and in 13 bat species, seven of which were found for the first time (even in Myotis daubentonii, a species to date always linked to EBLV-2). EBLV-1 seroprevalence (20.7%) ranged between 11.1 and 40.2% among bat species and seasonal variation was observed, with significantly higher antibody prevalence in summer (July). EBLV-1 seroprevalence was significantly associated with colony size and species richness. Higher seroprevalence percentages were found in large multispecific colonies, suggesting that intra- and interspecific contacts are major risk factors for EBLV-1 transmission in bat colonies. Although bat-roosting behavior strongly determines EBLV-1 variability, we also found some evidence that bat phylogeny might be involved in bat-species seroprevalence. The results of this study highlight the importance of life history and roost ecology in understanding EBLV-1-prevalence patterns in bat colonies and also provide useful information for public health officials.

Bat Rabies

The lyssaviruses are a diverse group of viruses capable of causing rabies, which is an invariably fatal encephalitic disease in both humans and animals. Currently, the lyssavirus genus consists of 12 species with 11 of these distinct species having been isolated from bats. The basis for the apparent geographical segregation of bat lyssavirus infection between the Old and New World is poorly understood. In the New World species of insectivorous, frugivorous, and hematophagous bats, all represent important reservoirs of rabies virus. In contrast, rabies virus has never been detected in Old World bat populations, despite being endemic in terrestrial mammals. Instead, both insectivorous and frugivorous bat species across the Old World appear to act as reservoirs for the non-rabies lyssaviruses. In this chapter, we describe the association of the different lyssaviruses with different bat species across the world, classifying bat species by their feeding behavior.

Interspecies protein substitution to investigate the role of the lyssavirus glycoprotein

European bat lyssaviruses type 1 (EBLV-1) and type 2 (EBLV-2) circulate within bat populations throughout Europe and are capable of causing disease indistinguishable from that caused by classical rabies virus (RABV). However, the determinants of viral fitness and pathogenicity are poorly understood. Full-length genome clones based on the highly attenuated, non-neuroinvasive, RABV vaccine strain (SAD-B19) were constructed with the glycoprotein (G) of either SAD-B19 (SN), of EBLV-1 (SN-1) or EBLV-2 (SN-2). In vitro characterization of SN-1 and SN-2 in comparison to wild-type EBLVs demonstrated that the substitution of G affected the final virus titre and antigenicity. In vivo, following peripheral infection with a high viral dose (10⁴ f.f.u.), animals infected with SN-1 had reduced survivorship relative to infection with SN, resulting in survivorship similar to animals infected with EBLV-1. The histopathological changes and antigen distribution observed for SN-1 were more representative of those observed with SN than with EBLV-1. EBLV-2 was unable to achieve a titre equivalent to that of the other viruses. Therefore, a reduced-dose experiment (10³ f.f.u.) was undertaken in vivo to compare EBLV-2 and SN-2, which resulted in 100 % survivorship for all recombinant viruses (SN, SN-1 and SN-2) while clinical disease developed in mice infected with the EBLVs. These data indicate that interspecies replacement of G has an effect on virus titre in vitro, probably as a result of suboptimal G–matrix protein interactions, and influences the survival outcome following a peripheral challenge with a high virus titre in mice.

Bat rabies surveillance in Europe

Rabies is the oldest known zoonotic disease and was also the first recognized bat associated infection in humans. To date, four different lyssavirus species are the causative agents of rabies in European bats: the European Bat Lyssaviruses type 1 and 2 (EBLV-1, EBLV-2), the recently discovered putative new lyssavirus species Bokeloh Bat Lyssavirus (BBLV) and the West Caucasian Bat Virus (WCBV). Unlike in the new world, bat rabies cases in Europe are comparatively less frequent, possibly as a result of varying intensity of surveillance. Thus, the objective was to provide an assessment of the bat rabies surveillance data in Europe, taking both reported data to the WHO Rabies Bulletin Europe and published results into account. In Europe, 959 bat rabies cases were reported to the RBE in the time period 1977-2010 with the vast majority characterized as EBLV-1, frequently isolated in the Netherlands, North Germany, Denmark, Poland and also in parts of France and Spain. Most EBLV-2 isolates originated from the United Kingdom (UK) and the Netherlands, and EBLV-2 was also detected in Germany, Finland and Switzerland. Thus far, only one isolate of BBLV was found in Germany. Published passive bat rabies surveillance comprised testing of 28 of the 52 different European bat species for rabies. EBLV-1 was isolated exclusively from Serotine bats (Eptesicus serotinus and Eptesicus isabellinus), while EBLV-2 was detected in 14 Daubenton's bats (Myotis daubentonii) and 5 Pond bats (Myotis dasycneme). A virus from a single Natterer's bat (Myotis nattereri) was characterized as BBLV. During active surveillance, only oral swabs from 2 Daubenton's bats (EBLV-2) and from several Eptesicus bats (EBLV-1) yielded virus positive RNA. Virus neutralizing antibodies against lyssaviruses were detected in various European bat species from different countries, and its value and implications are discussed.

Molecular epidemiology of bat lyssaviruses in Europe

Bat rabies cases in Europe are principally attributed to two lyssaviruses, namely European bat lyssavirus type 1 (EBLV-1) and European bat lyssavirus type 2 (EBLV-2). Between 1977 and 2011, 961 cases of bat rabies were reported to Rabies Bulletin Europe, with the vast majority (>97%) being attributed to EBLV-1. There have been 25 suspected cases of EBLV-2, of which 22 have been confirmed. In addition, two single isolations of unique lyssaviruses from European insectivorous bats were reported in south-west Russia in 2002 (West Caucasian bat virus) and in Germany in 2010 (Bokeloh bat lyssavirus). In this review, we present phylogenetic analyses of the EBLV-1 and EBLV-2 using partial nucleoprotein (N) gene sequences. In particular, we have analysed all EBLV-2 cases for which viral sequences (N gene, 400 nucleotides) are available (n = 21). Oropharyngeal swabs collected from two healthy Myotis daubentonii during active surveillance programmes in Scotland and Switzerland also yielded viral RNA (EBLV-2). Despite the relatively low number of EBLV-2 cases, a surprisingly large amount of anomalous data has been published in the scientific literature and Genbank, which we have collated and clarified. For both viruses, geographical relationships are clearly defined on the phylogenetic analysis. Whilst there is no clear chronological clustering for either virus, there is some evidence for host specific relationships, particularly for EBLV-1 where more host variation has been observed. Further genomic regions must be studied, in particular for EBLV-1 isolates from Spain and the EBLV-2 isolates to provide support for the existence of sublineages.

Bat rabies, public health and European bat conservation

Most records of European bat lyssaviruses (EBLVs) are confined to three species - the serotine bat for EBLV1 (900 records) and Daubenton's bat and the pond bat for EBLV2 (25 records). High levels of seroprevalence, which may vary from year to year, are also recorded. All bat vectors of EBLVs are synanthropic, some exclusively so. Despite this, there have been only five cases of human rabies resulting from EBLV infection in the 590 million people of greater Europe during the last 35 years. These have triggered major programmes of surveillance in many European countries. The emphasis on active versus passive surveillance and the intensity with which they have been carried out has varied from country to country. Both involve cooperation between bat researchers, virologists and public health officials and the latter, in particular, engages amateur bat workers and members of the public. Bat NGOs throughout Europe have worked to persuade the public not to handle bats or to do so only with gloved hands and, in the case of bat workers, to receive pre-exposure immunization. They have also countered negative media coverage of bat rabies. Householders with bat roosts in their dwellings have in general been persuaded to retain their bats. Attempts have been made to persuade all European countries to establish comparable EBLV surveillance programmes. In the last 25 years, virologists, public health officials, bat biologists and conservationists, both amateur and professional have worked closely and collaboratively for the protection of the public and the conservation of bats, with little polarization of views.

Infektionskrankheiten

Virale Infektionen zählen immer noch weltweit, besonders in den Entwicklungsländern, zu den häufigsten Todesursachen. Durch internationale systematische Impfkampagnen der WHO ist die Welt Pocken-frei geworden. Die Inzidenz der Infektionen, die durch eine Immunprophylaxe verhindert werden können, wurde drastisch gesenkt (Poliomyelitis, Tollwut). In den 1980er Jahren trat eine neue Tierseuche beim Rind auf, die bovine spongyforme Enzephalopathie (BSE), die mit der neuen Variante der Creutzfeldt-Jakob-Krankheit (vCJK) in Zusammenhang steht (Nahrungskette). Im selben Zeitraum begann die explosionsartige weltweite Verbreitung eines neuen Retrovirus, des HIV. Trotz intensiver Aufklärungskampagnen und neuen therapeutischen Möglichkeiten (HAART, hoch aktive antiretrovirale Therapie) ist es bis zur Jahrtausendwende nicht gelungen, die weitere Ausbreitung der HIV-Infektion zu verhindern. Seit 2007 ist eine allmähliche Eindämmung der Infektion zu erkennen, die Neuinfektionen sind weltweit rückläufig. Durch den breiteren Einsatz der HAART sind Lebensqualität und Lebenserwartung enorm gestiegen, die Sterberate der AIDS-Infizierten ist seit 2005 um mehr als 50 % zurückgegangen.

Diseases and causes of death in European bats: dynamics in disease susceptibility and infection rates

BACKGROUND

Bats receive increasing attention in infectious disease studies, because of their well recognized status as reservoir species for various infectious agents. This is even more important, as bats with their capability of long distance dispersal and complex social structures are unique in the way microbes could be spread by these mammalian species. Nevertheless, infection studies in bats are predominantly limited to the identification of specific pathogens presenting a potential health threat to humans. But the impact of infectious agents on the individual host and their importance on bat mortality is largely unknown and has been neglected in most studies published to date.

METHODOLOGY/PRINCIPAL FINDINGS

Between 2002 and 2009, 486 deceased bats of 19 European species (family Vespertilionidae) were collected in different geographic regions in Germany. Most animals represented individual cases that have been incidentally found close to roosting sites or near human habitation in urban and urban-like environments. The bat carcasses were subjected to a post-mortem examination and investigated histo-pathologically, bacteriologically and virologically. Trauma and disease represented the most important causes of death in these bats. Comparative analysis of pathological findings and microbiological results show that microbial agents indeed have an impact on bats succumbing to infectious diseases, with fatal bacterial, viral and parasitic infections found in at least 12% of the bats investigated.

CONCLUSIONS/SIGNIFICANCE

Our data demonstrate the importance of diseases and infectious agents as cause of death in European bat species. The clear seasonal and individual variations in disease prevalence and infection rates indicate that maternity colonies are more susceptible to infectious agents, underlining the possible important role of host physiology, immunity and roosting behavior as risk factors for infection of bats.

Novel lyssavirus in Natterer's bat, Germany

A virus isolated from a Natterer’s bat (Myotis nattererii) in Germany was differentiated from other lyssaviruses on the basis of the reaction pattern of a panel of monoclonal antibodies. Phylogenetic analysis supported the assumption that the isolated virus, Bokeloh bat lyssavirus, may represent a new member of the genus Lyssavirus.

Bats and lyssaviruses

Numerous bat species have been identified as important reservoirs of zoonotic viral pathogens. Rabies and rabies-related viruses constitute one of the most important viral zoonoses and pose a significant threat to public health across the globe. Whereas rabies virus (RABV) appears to be restricted to bats of the New World, related lyssavirus species have not been detected in the Americas and have only been detected in bat populations across Africa, Eurasia, and Australia. Currently, 11 distinct species of lyssavirus have been identified, 10 of which have been isolated from bat species and all of which appear to be able to cause encephalitis consistent with that seen with RABV infection of humans. In contrast, whereas lyssaviruses are apparently able to cause clinical disease in bats, it appears that these lyssaviruses may also be able to circulate within bat populations in the absence of clinical disease. This feature of these highly encephalitic viruses, alongside many other aspects of lyssavirus infection in bats, is poorly understood. Here, we review what is known of the complex relationship between bats and lyssaviruses, detailing both natural and experimental infections of these viruses in both chiropteran and nonchiropteran models. We also discuss potential mechanisms of virus excretion, transmission both to conspecifics and spill-over of virus into nonvolant species, and mechanisms of maintenance within bat populations. Importantly, we review the significance of neutralizing antibodies reported within bat populations and discuss the potential mechanisms by which highly neurovirulent viruses such as the lyssaviruses are able to infect bat species in the absence of clinical disease.

Active surveillance of bat rabies in France: a 5-year study (2004-2009)

Active surveillance of bats in France started in 2004 with an analysis of 18 of the 45 bat species reported in Europe. Rabies antibodies were detected in six indigenous species, mainly in Eptesicus serotinus and Myotis myotis, suggesting previous contact with the EBLV-1 rabies virus. Nineteen of the 177 tested bats were shown serologically positive in seven sites, particularly in central and south-western France. Neither infectious viral particles nor viral genomes were detected in 173 and 308 tested oral swabs, respectively. The presence of neutralising antibodies in female bats (18.6%) was significantly higher than in males (5.6%).

Reassessing the risk from rabies: a continuing threat to the UK?

The threat of re-introduction of rabies virus into the United Kingdom exists on several levels. Firstly, importation of live animals into the UK continues to challenge the regulations in place to ensure that the virus does not enter the country. Secondly, the indigenous bat population is known to carry a virus genetically related to rabies virus, the European bat lyssavirus (EBLV). Molecular characterization of this virus has further characterized it as being EBLV type 2, genetically distinct from a similar virus that has caused several human deaths across Europe. Finally, a lack of awareness of the threat of rabies and related viruses to travelers visiting endemic areas also constitutes a re-introduction threat to the UK population. This review will address the most recent cases of lyssavirus infection, in both humans and animals, either contracted within the UK or from abroad. We highlight the current diagnostic necessity for testing indigenous and foreign cases and comment on current UK government policy in light of a European call to harmonise rabies legislation across Europe.

Human rabies due to lyssavirus infection of bat origin

Rabies is a fatal viral encephalitis and results from infection with viruses belonging to the genus Lyssavirus. Infection usually results from a bite from a dog infected with classical rabies virus. However, a small number of cases result from contact with bats. It is within bats that most lyssavirus variants, referred to as genotypes, are found. The lyssaviruses found in bats have a distinct geographical distribution and are often restricted to specific bat species. Most have been associated with rabies in humans and in some cases spill-over to domestic animals. Many diagnostic techniques are unable to differentiate rabies virus from other genotypes so it is possible that some human and animal cases go unreported. Furthermore, current vaccines have limited efficacy against some genotypes.

Repeated detection of European bat lyssavirus type 2 in dead bats found at a single roost site in the UK

In August 2007, European bat lyssavirus type 2 (EBLV-2) was isolated from a Daubenton’s bat found at Stokesay Castle. In September 2008, another bat from the same vicinity of Stokesay Castle also tested positive for EBLV-2. This is the first occurrence of repeated detection of EBLV-2 from a single site. Here, we report the detection of low levels of viral RNA in various bat organs by qRT-PCR and detection of viral antigen by immunohistochemistry. We also report sequence data from both cases and compare data with those derived from other EBLV-2 isolations in the UK.

Antibodies induced by vaccination with purified chick embryo cell culture vaccine (PCECV) cross-neutralize non-classical bat lyssavirus strains

Tissue-culture vaccines like purified chick embryo cell vaccine (PCECV) have been shown to provide protection against classical rabies virus (RABV) via pre-exposure or post-exposure prophylaxis. A cross-neutralization study was conducted using a panel of 100 human sera, to determine, to what extent after vaccination with PCECV protection exists against non-classical bat lyssavirus strains like European bat lyssavirus (EBLV) type 1 and 2 and Australian bat lyssavirus (ABLV). Virus neutralizing antibody (VNA) concentrations against the rabies virus variants CVS-11, ABLV, EBLV-1 and EBLV-2 were determined by using a modified rapid fluorescent focus inhibition test. For ABLV and EBLV-2, the comparison to CVS-11 revealed almost identical results (100% adequate VNA concentrations >or=0.5 IU/mL; correlation coefficient r(2)=0.69 and 0.77, respectively), while for EBLV-1 more scattering was observed (97% adequate VNA concentrations; r(2)=0.50). In conclusion, vaccination with PCECV produces adequate VNA concentrations against classical RABV as well as non-classical lyssavirus strains ABLV, EBLV-1, and EBLV-2.

Experimental infection of serotine bats (Eptesicus serotinus) with European bat lyssavirus type 1a

The serotine bat (Eptesicus serotinus) accounts for the vast majority of bat rabies cases in Europe and is considered the main reservoir for European bat lyssavirus type 1 (EBLV-1, genotype 5). However, so far the disease has not been investigated in its native host under experimental conditions. To assess viral virulence, dissemination and probable means of transmission, captive bats were infected experimentally with an EBLV-1a virus isolated from a naturally infected conspecific from Germany. Twenty-nine wild caught bats were divided into five groups and inoculated by intracranial (i.c.), intramuscular (i.m.) or subcutaneous (s.c.) injection or by intranasal (i.n.) inoculation to mimic the various potential routes of infection. One group of bats was maintained as uninfected controls. Mortality was highest in the i.c.-infected animals, followed by the s.c. and i.m. groups. Incubation periods varied from 7 to 26 days depending on the route of infection. Rabies did not develop in the i.n. group or in the negative-control group. None of the infected bats seroconverted. Viral antigen was detected in more than 50% of the taste buds of an i.c.-infected animal. Shedding of viable virus was measured by virus isolation in cell culture for one bat from the s.c. group at 13 and 14 days post-inoculation, i.e. 7 days before death. In conclusion, it is postulated that s.c. inoculation, in nature caused by bites, may be an efficient way of transmitting EBLV-1 among free-living serotine bats.

Detection of high levels of European bat lyssavirus type-1 viral RNA in the thyroid gland of experimentally-infected Eptesicus fuscus bats

Two common bat lyssavirus species have been identified in many European countries: European bat lyssavirus type-1 and -2 (EBLV-1 and EBLV-2). Only limited knowledge on the susceptibility of the natural EBLV-hosts, insectivorous bats, to lyssavirus infection is available. Our study was undertaken to evaluate the susceptibility and pathology associated with an EBLV-1 infection in Eptesicus fuscus following different routes of virus inoculation including intracranial (n = 6), intramuscular (n = 14), oral (n = 7) and intranasal (n = 7). Blood and saliva samples were collected from all bats on a monthly basis. Four bats inoculated intracranially developed rabies with a mean of 11 days to death, whilst seven bats inoculated intramuscularly developed rabies, with an extended incubation period prior to death. We did not observe any mortality in the oral (p.o.) or intranasal (i.n.) groups and both groups had detectable levels of virus neutralizing antibodies (data not shown). Virus shedding was demonstrated in the saliva by virus isolation and the detection of viral RNA in ill bats, particularly immediately prior to the development of disease. In addition, the presence of virus and viral RNA was detected in the thyroid gland in bats challenged experimentally with EBLV-1, which exceeded that detected in all other extra-neural tissue. The significance of detecting EBLV-1 in the thyroid gland of rabid bats is not well understood. We speculate that the infection of the thyroid gland may cause subacute thyroiditis, a transient form of thyroiditis causing hyperthyroidism, resulting in changes in adrenocortical activity that could lead to hormonal dysfunction, thereby distinguishing the clinical presentation of rabies in the rabid host.

Experimental infection of foxes with European Bat Lyssaviruses type-1 and 2

Background

Since 1954, there have been in excess of 800 cases of rabies as a result of European Bat Lyssaviruses types 1 and 2 (EBLV-1, EBLV-2) infection, mainly in Serotine and Myotis bats respectively. These viruses have rarely been reported to infect humans and terrestrial mammals, as the only exceptions are sheep in Denmark, a stone marten in Germany and a cat in France. The purpose of this study was to investigate the susceptibility of foxes to EBLVs using silver foxes (Vulpes vulpes) as a model.

Results

Our experimental studies have shown that the susceptibility of foxes to EBLVs is low by the intramuscular (IM) route, however, animals were sensitive to intracranial (IC) inoculation. Mortality was 100% for both EBLV-1 (~4.5 logs) and EBLV-2 (~3.0 logs) delivered by the IC route. Virus dissemination and inflammatory infiltrate in the brain were demonstrated but virus specific neutralising antibody (VNA) was limited (log(ED₅₀) = 0.24–2.23 and 0.95–2.39 respectively for specific EBLV-1 and EBLV-2). Foxes were also susceptible, at a low level, to peripheral (IM) infection (~3.0 logs) with EBLV-1 but not EBLV-2. Three out of 21 (14.3%) foxes developed clinical signs between 14 and 24 days post-EBLV-1 infection. None of the animals given EBLV-2 developed clinical disease.

Conclusion

These data suggest that the chance of a EBLV spill-over from bat to fox is low, but with a greater probability for EBLV-1 than for EBLV-2 and that foxes seem to be able to clear the virus before it reaches the brain and cause a lethal infection.

Experimental study of European bat lyssavirus type-2 infection in Daubenton's bats (Myotis daubentonii)

European bat lyssavirus type 2 (EBLV-2) can be transmitted from Daubenton's bats to humans and cause rabies. EBLV-2 has been repeatedly isolated from Daubenton's bats in the UK but appears to be present at a low level within the native bat population. This has prompted us to investigate the disease in its natural host under experimental conditions, to assess its virulence, dissemination and likely means of transmission between insectivorous bats. With the exception of direct intracranial inoculation, only one of seven Daubenton's bats inoculated by subdermal inoculation became infected with EBLV-2. Both intramuscular and intranasal inoculation failed to infect the bats. No animal inoculated with EBLV-2 seroconverted during the study period. During infection, virus excretion in saliva (both viral RNA and live virus) was confirmed up to 3 days before the development of rabies. Disease was manifested as a gradual loss of weight prior to the development of paralysis and then death. The highest levels of virus were measured in the brain, with much lower levels of viral genomic RNA detected in the tongue, salivary glands, kidney, lung and heart. These observations are similar to those made in naturally infected Daubenton's bats and this is the first documented report of isolation of EBLV-2 in bat saliva. We conclude that EBLV-2 is most likely transmitted in saliva by a shallow bite.

Susceptibility of North American big brown bats (Eptesicus fuscus) to infection with European bat lyssavirus type 1

The aim of this study was to determine the susceptibility of insectivorous bats (using the big brown bat as a model) to infection with European bat lyssavirus type 1a (EBLV-1a), to assess the dynamics of host immune responses and to evaluate the opportunity for horizontal viral transmission within colonies. Two isolates of EBLV-1a, originating from Slovakia (EBLV-1aSK) and Germany (EBLV-1aGE), were tested. Four different routes of inoculation were used with isolate EBLV-1aSK [10(4.8) mouse intracerebral median lethal dose (MICLD(50)) in 50 mul]: intramuscular (i.m.) in the deltoid area or masseter region, per os (p.o.) and intradermal (i.d.) scratches. Isolate EBLV-1aGE (10(3.2) and 10(2.2) MICLD(50) in 20 mul) was inoculated via the intranasal (i.n.), i.m. (low- and high-dose groups, into pectoral muscles); p.o. and intracerebral (i.c.) routes. None of the bats infected by the i.n., p.o. or i.d. route with either virus isolate developed disease during the experiments (91 or 120 days, respectively). Incubation periods were 9-12 days for i.c.-inoculated bats (66 % mortality), 12-33 days for bats inoculated i.m. with the higher dose (23-50 % mortality) and 21-58 days in bats inoculated i.m. with the lower dose of virus (57 % mortality). Virus or viral RNA in bat saliva was detected occasionally, as early as 37 days before death. All i.d.-inoculated and the majority of i.m.-inoculated bats seroconverted within 7-10 days of inoculation. These observations suggest that exposure of bats to varying doses of EBLV-1 from rabid conspecifics via natural (i.d.) routes could lead to an abortive infection and serve as a natural mode of immunization resulting in the presence of virus-neutralizing antibodies in free-ranging bats.

Phylogeny of Lagos bat virus: challenges for lyssavirus taxonomy

Lagos bat virus (LBV) belongs to genotype 2 of the Lyssavirus genus. The complete nucleoprotein (N), phosphoprotein (P), matrixprotein (M) and glycoprotein (G) genes of 13 LBV isolates were sequenced and phylogenetically compared with other lyssavirus representatives. The results identified three different lineages of LBV. One of these lineages demonstrated sufficient sequence diversity to be considered a new lyssavirus genotype (Dakar bat lyssavirus). The suggested quantitative separation of lyssavirus genotypes using the N, P, M and G genes was also investigated using P-distances matrixes. Results indicated that the current criteria should be revised since overlaps between intergenotypic and intragenotypic variation occur.

First isolation of EBLV-2 in Germany

In Europe, rabies in bats is caused by European Bat Lyssavirus (EBLV) type 1 (EBLV-1) or type 2 (EBLV-2) which form two distinct genotypes (gt 5 and 6) within the genus Lyssavirus of the family of Rhadoviridae. Spill-over infections of EBLV in humans have caused fatal rabies encephalitis and highlighted the relevance of this wildlife disease for public health. The vast majority of the 831 European bat rabies cases reported between 1977 and 2006 were identified as EBLV-1. Only few virus isolates originating from Switzerland, The Netherlands and the United Kingdom were characterized as EBLV-2. Here we report the first EBLV-2 case detected in Germany in a Daubenton's bat (Myotis daubentonii) in August 2007. The bat showed clinical signs of disorders of the central nervous system and subsequently tested positive for rabies. The virus was isolated and characterized as EBLV-2 based on its antigen pattern and by nucleotide sequencing. Phylogenetic analysis indicated an association to EBLV-2 isolates from Switzerland which correlates with the origin of the bat close to the Swiss border.

Identification of European bat lyssavirus isolates with short genomic insertions

Molecular typing has consistently identified European bat lyssaviruses from Germany as EBLV type 1a (EBLV-1a). This report confirms the presence of the closely related EBLV-1b in southern Germany, a group previously reported from The Netherlands, France and Spain. Furthermore, two of three German EBLV-1b isolates contain a 6 base pair insertion within the 3' untranslated region (UTR) of the nucleoprotein gene. This feature was shared with a third EBLV-1b isolate from a region of France adjacent to the French-German border. Further investigation revealed a two base pair insertion in a single isolate of EBLV-2 at the same genomic location. Although the length of the nucleoprotein gene 3'UTRs do vary between lyssavirus genotypes, such insertions have not been recorded within genotypes and could be the result of duplications within the nucleoprotein mRNA transcript polyadenylation signal.