European bat lyssavirus type 2 in Finland: Surveillance, evolutionary analysis, and prevention with vaccination

European bat lyssavirus type 2 (EBLV-2) was first isolated in Finland from a Daubenton’s bat (Myotis daubentonii) in 2009. Rabies in bats was already suspected in 1985, when a Swiss biologist died in Finland of lyssavirus infection, later identified as EBLV-2 infection. However, the origin of the infection could not be confirmed at that time. In 2010–2011, during active surveillance study, samples from 774 bats were analyzed for EBLV viral RNA. In addition, sera from 423 bats were analyzed for the presence of lyssavirus antibodies. Antibodies were detected in 2010 and 2011 from two locations and from one location, respectively. All seropositive bats were Daubenton’s bats. No EBLV viral RNA was detected in any of these bats. In 2016, EBLV-2 was detected from a diseased Daubenton’s bat for the second time. These data provide proof that EBLV-2 is endemic in the Finnish Daubenton’s bat population. In phylogenetic analysis, the Finnish EBLV-2 strains formed a monophyletic group separate from other bat-type lyssaviruses with significant support. EBLV-2 shared the most recent common ancestry with Bokeloh bat lyssavirus (BBLV) and Khujand virus (KHUV). EBLV-2 showed limited diversity compared to rabies virus (RABV) and appears to be well adapted to its host bat species. The slow tempo of viral evolution was evident in the estimations of divergence times for EBLV-2: the current diversity was estimated to have built up during the last 2000 years. The Finnish EBLV-2 strains and a Swiss strain (1993) were estimated to have diverged from other EBLV-2 strains during the last 1000 years, and the Finnish strains (1985 and 2009) appear to have evolved from a common ancestor during the last 200 years. Rabies vaccine is used to protect against rabies virus before or after potential exposure. Since all the currently available vaccines are based on RABV, the vaccines are also used to protect against other lyssaviruses, and additionally against EBLV-2 infection based on cross-protection. We assessed the level of protection afforded by two commercial rabies vaccines, one for humans and one for animals, against intracerebral challenge in mice with EBLV-2 isolated from a bat in 2009. We compared this with protection using the same mouse model against challenge with RABV isolated from a Finnish raccoon dog in 1989. When challenged with RABV, all the vaccinated mice survived. When challenged with EBLV-2, 75% to 80% of the vaccinated mice survived. All vaccinated mice developed sufficient to high virus-neutralizing antibody (VNA) titers against RABV, ranging from 0.5 to 128 IU/ml. RABV-based vaccines also appear to offer good cross-protection against EBLV-2 circulating in the Finnish bat population. To investigate the factors influencing the response to rabies vaccination, we assessed the success of vaccination measured from the antibody response in dogs (n = 10 071) and cats (n = 722) sampled during 2009–2013. We examined the factors influencing the response to vaccination when animals failed to reach a rabies antibody titer of ≥0.5 IU/ml.