2. The Daubenton's bat

so contact with humans is minimal making them both an elusive species to study and a rare source of zoonotic pathogens [3]. Key amongst these is the European bat lyssaviruses (EBLVs), members of the genus Lyssavirus, family Rhabdoviridae. The type species of the genus is rabies lyssavirus (RABV), the virus responsible for virtually all cases of rabies in the world. The genus contains a growing number of viruses, the majority associated with bat species [4] (Table 1). All can cause encephalitis in mouse models of infection and it is suspected that all are capable of causing rabies in humans. Of these, five have been reported from Europe. European bat lyssavirus type-1 (EBLV-1), EBLV-2, West Caucasian bat lyssavirus (WCBV), Bokeloh bat lyssavirus (BBLV) and Lleida bat lyssavirus (LLEBV). Despite the close association with bats, the first recognised isolation of EBLV-2 was derived from a human case of rabies. The patient was a bat ecologist working in Finland when he developed rabies [5]. Shortly afterward, a related virus was isolated from the brain of a pond bat (Myotis dasycneme). Since then there has been one further case of EBLV-2 infection in a human [6] and continual reports of the virus

The ability to discriminate between different lyssaviruses was only achieved with the advent of monoclonal antibody panels that show different binding patterns to particular viruses. This first alerted researchers that the viruses present in European bats were distinct from RABV found in North American bats [7]. Antigenic typing has now been superseded by genetic

Virus species Bat reservoir Human infection

Eptesicus serotinus Yes

Myotis daubentonii Yes

Miniopterus schreibersii No

Yes

Rabies lyssavirus Numerous insectivorous, frugivorous and hematophagous bat

Lagos bat lyssavirus Various species including Eidolon helvum and Rousettus aegyptiacus No Mokola lyssavirus Not known Yes Duvenhage lyssavirus Nycteris thebaica Yes

Bokeloh bat lyssavirus Myotis nattereri No Aravan lyssavirus Myotis blythii No Irkut lyssavirus Murina leucogaster Yes Khujand lyssavirus Myotis mystacinus No

Australian bat lyssavirus Various species including Pteropus alecto and Saccolaimus flaviventris Yes Shimoni bat lyssavirus Hipposideros commersoni No Gannoruwa bat lyssavirus Pteropus medius No Taiwan bat lyssavirus Pipistrellus abramus No Lleida bat Lyssavirus Miniopterus schreibersii No

Table 1. Known lyssaviruses and their association with particular bat species.

infection of Daubenton's bats (Myotis daubentonii).

species

European bat lyssavirus

European bat lyssavirus

West Caucasian bat lyssavirus

type-1

102 Bats

type-2

The Daubenton's bat was first described by the German naturalist and zoologist, Heinrich Kuhl [1797–1821] in his monograph, Die deutschen Fledermäuse, published in 1817. The name selected for the species was derived from the French naturalist Louis Jean-Marie Daubenton [1716–1800]. Kuhl went on to take part in an expedition to Java to study the islands fauna but developed a fever that subsequently killed him. He was buried in the Botanical Gardens of Bogor to the south of Jakarta where his gravestone can still be located.

Daubenton's bats are considered a medium-sized insectivorous bat with an adult wingspan of up to 27.5 cm and a body length up to 5.5 cm. Adults weigh between 7 and 12 g and have a reddish brown pelt. The common name of the species is the 'water bat' due to its feeding habit. This involves flying low across the surface of water bodies such as lakes, rivers and canals, feeding on a range of water-associated flies. These include chironomid midges, caddisflies and mayflies. Daubenton's bats echolocate in a call range between 35 and 85 kHz, and generally feed within 6 km of their roost. Roost sites range from natural sites such as tree holes to manmade structures, including houses [19]. During the summer, there is a degree of segregation between maternity colonies, dominated by a single male and bachelor roosts [20]. Hibernation takes place over the winter months, usually in caves, tunnels and mines.

Daubenton's bats are found from Ireland in the west, across Europe, Asia and the islands that form the Japanese archipelago. In Europe, the species can be found in the Iberian Peninsula and north of the Alps. Populations are also reported as far north as southern Sweden and Finland, almost as far as the Arctic Circle. Mating occurs in late autumn and is preceded by a behaviour termed swarming where bats congregate and fly near the entrance to a hibernation site. Daubenton's bats are not the only species that demonstrate this behaviour but they are commonly found early in the swarming season. In Britain, this is typically between August and October [21]. The behaviour is thought to be a form of lecking due to the male bias observed during trapping at swarming sites and may proceed mating.

demonstrate aerosol transmission were unsuccessful for EBLV-2 [30]. However, once in the brain, EBLV-2 shows similar characteristics to rabies lyssavirus, infecting neurons, stimulating innate immune responses [31] and triggering signs of viral encephalitis [32, 33]. In order to confirm some of these observations, a series of experimental studies were established to investigate the methods of EBLV transmission in bats and characterised EBLV-induced disease in the natural host [34–36]. These studies demonstrated that subcutaneous inoculation was the most efficient means of infecting insectivorous bats with EBLVs. Clinical signs exhibited by infected bats ranged from sudden death with no apparent disease to a spectrum including

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Field studies in the UK in response to the human case of EBLV-2 in 2002 provided evidence of virus circulation within the Scottish Daubenton's bat population [37]. Seroprevalence levels ranging from 0.05 to 3.8% were detected in colonies from across the country although oral swabs taken coincident with blood samples were all negative for EBLV-2. Subsequent surveillance in Daubenton's bat colonies in England found similar seroprevalence levels [38] suggesting that the virus affects bat populations across the country. This is supported by population genetic analysis of English Daubenton's bats [22] and the detection of EBLV-2 infected bats from locations across England, Scotland and Wales [39]. One location where EBLV-2 infected bats have been repeatedly detected is Stokesay Castle in Shropshire [40]. The tower of the castle (Figure 1) is known to host a summer maternity roost and there have been three bats found in the castle that have been infected with EBLV-2. Another infected bat was submitted from the nearby location of Newtown. A further practical question, bearing in mind the zoonotic potential of EBLV-2, was whether current vaccines developed against rabies lyssavirus would be protective against exposure following a bat bite. Cross-neutralisation and cross-protection studies in mice indicated that rabies vaccines would be protective [41].

Figure 1. A photograph of Stokesay Castle where EBLV-2 infected bats have been repeatedly detected. The site offers a number of features attractive to bats including the main tower where bats were roosting, a large pond in the foreground

that could provide a feeding site and extensive woodland that would provide alternative roosts.

weight loss and rapid progression to paralysis [35].

Investigation into the population structure of the Daubenton's bat, based on genetic data, between UK bats and those on the European mainland suggests that there is regular movement of bats across the English Channel [22]. This suggests panmixia between the two populations with no barriers to the spread of genetic haplotypes, and in theory to the transmission of EBLV-2. A similar situation has been proposed for the straw-coloured fruit bat, Eidolon helvum, and its association with certain zoonotic viruses across its range in Africa [23].

The first report of EBLV-2 in a Daubenton's bat occurred in Denmark in 1986 [24, 25]. The virus from this account was not isolated. Subsequently, EBLV-2 was isolated from pond bats from the Netherlands in 1987 [8] and Daubenton's bats from Switzerland in 1992 [16]. Descriptions of initial encounters with EBLV-2 infected bats typically report grounding, particularly near rivers or canals, although occasionally bats are reported to fly in daylight. Live bats vocalise, show signs of distress and can bite aggressively although this may in part be a result of distress caused by captivity. Infected bats often appear emaciated and dehydrated despite attempts at rehabilitation [26].
