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1 Rabies and Wildlife Zoonoses Group, WHO Collaborating Centre for the Characterisation of Rabies and Rabies-Related Viruses, Veterinary Laboratories Agency – Weybridge, Woodham Lane, Addlestone, Surrey KT15 3NB, UK
2 IDT Biologika GmbH, Am Pharmapark, D-06861 Dessau-Roßlau, Germany
3 Institute for Epidemiology, WHO Collaborating Centre for Rabies Surveillance and Research, Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, Seestrasse 55, D-16868 Wusterhausen, Germany
4 Zoologisches Institut, Eberhard Karls University, Auf der Morgenstelle 28, 72076 Tuebingen, Germany
5 Centre for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta GA30333, USA
Correspondence
N. Johnson
n.johnson2{at}vla.defra.gsi.gov.uk
| ABSTRACT |
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| INTRODUCTION |
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EBLV-2 has been isolated from six Daubenton's bats in the UK between 1996 and 2007 (Harris et al., 2007
) and serosurveys of bat populations throughout England and Scotland suggest that the virus is endemic in the species but prevalence is low (Brookes et al., 2005a
). The Daubenton's bat belongs to the family Vespertilionidae and is found throughout Europe as far south as Greece, with a northern limit of central Finland. Colonies of Daubenton's bats have been found throughout the UK, where it is the third most abundant bat species after the common pipistrelle (Pipistrellus pipistrellus) and the brown long-eared bat (Plecotus auritis). All bats within the UK are protected by both national and European legislation, although the Daubenton's bat is not considered to be under threat and numbers may be increasing. After two well-documented cases of spill-over to humans, in both cases causing rabies, it is clear that the virus has the capacity for transmission to humans. In both cases, the individuals were unvaccinated and had recent contact with Daubenton's bats. This implies that bite transmission, in a similar manner to North American bats (Messenger et al., 2002
), is the principal means of dissemination of this virus.
Cross-neutralization and cross-protection studies have demonstrated that current anti-rabies vaccines provide protection against EBLV-2 (Brookes et al., 2005b
) and all bat handlers in the UK are required to receive vaccination. A limited number of pathogenesis studies have been conducted on the EBLVs using a range of animal models (Vos et al., 2004
; Johnson et al., 2006a
; Brookes et al., 2007
). These have suggested that EBLV-2 is less virulent in animal models including mouse, sheep and fox, when compared directly with EBLV-1, and both are less virulent than rabies virus (RABV). However, it is not clear if this is true for the virus within its reservoir host. The case-reports of EBLV-2-infected bats indicate that unprovoked biting is commonly associated with rabies in bats (Table 1
). This contrasts strongly with studies in Spain where apparently healthy bats have been shown to excrete EBLV-1 in saliva (Echevarria et al., 2001
; Vazquez et al., 2006
), suggesting the possibility that an asymptomatic carrier state could exist in lyssavirus-infected bats. From a public health perspective it is important to confirm or exclude this possibility.
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| METHODS |
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Thirty-three bats were assigned into five groups and housed in purpose-built metal-framed cages (75 cmx75 cmx75 cm) with fine-mazed wire gauzed side sheets. The remaining bat was not considered to be sufficiently healthy to enter the study and was retained by a bat rehabilitator. Two cages were held within one scantainer (Scanbur), which provided a closed, filtered-air system with constant temperature and humidity. Three scantainers were held within a secure containment laboratory under negative air pressure and controlled access. Animals were inspected daily to monitor their condition and development of disease.
Virus.
The EBLV-2 isolate used in this study was obtained from a Daubenton's bat found in Lancashire (Johnson et al., 2003
) and designated RV1332. Virus was passaged three times by intracerebral (i.c.) inoculation in female 5-week-old Swiss OF-1 mice (Charles River Laboratories, France) until a titre of 4.9 log10(MLD50) per ml was reached. A 20 % mouse brain homogenate was prepared and clarified by centrifugation at 3200 g for 10 min, then immediately frozen at –80 °C until required.
Inoculation and monitoring.
Four routes of inoculation of 20 µl of EBLV-2 infected mouse brain homogenate were used. Intranasal (i.n.) and i.c. inoculations were performed under light ether anaesthesia. For i.n. inoculation, the inocula was placed on the nasal passage and inhaled. For intramuscular (i.m.) inoculation, either EBLV-2 or negative control mouse brain homogenate was injected into the pectoral muscle. Subdermal (s.d.) inoculation was performed by injecting EBLV-2 homogenate under the skin in the scruff of the neck. This gave a final inoculation dose of 3.2 log10(MLD50) that consistently induced disease in mice through both i.c. and s.d. routes. Lower doses of virus have produced variable outcomes in the murine model. All animals were monitored closely for one hour after inoculation. Subsequently, all animals were observed twice daily for 120 days. Saliva swabs were taken 1 week prior to inoculation and at weekly intervals, or daily if individual bats showed signs of disease. A cotton swab was held within the mouth until moistened and placed in 0.4 ml minimal essential medium with gentamicin (50 mg ml–1) and amphotericin B (2.5 mg ml–1). All swabs were frozen immediately and stored at –20 °C until processing. Body weight was measured at weekly intervals throughout the study.
Blood samples were taken either from the vena brachialis during the study period, or by cardiac puncture on the development of severe disease (paralysis) or at the completion of the experiment (terminal bleed after euthanasia). Serum samples were prepared and stored at –20 °C until testing. Bat carcasses were frozen immediately and stored at –20 °C until necropsy. One animal from each group was fixed in formalin immediately after death for pathological examination.
Virus detection.
The fluorescent antibody test (FAT) was performed following standard protocols (Dean & Abelseth, 1973
). Virus isolation from saliva swabs (200 µl) was performed using the rapid tissue culture inoculation test (RTCIT) as described previously (Webster & Casey, 1996
). At least three consecutive passages were conducted to prove a negative result by RTCIT.
Detection of EBLV-2 RNA.
RNA was extracted from organ samples using Trizol (Invitrogen) following the manufacturer's protocol. RNA was extracted from saliva swabs (200 µl) using an RNeasy column (Qiagen) following the manufacturer's protocol. For detection of virus genome, two RT-PCR methods were utilized. The first was the nested RT-PCR described by Heaton et al. (1997)
. Amplicons were separated on 1 % agarose gels and visualized by ethidium bromide (1 µg µl–1) staining and UV illumination. The second assay was a probe-based real-time (q)RT-PCR assay described by Wakeley et al. (2005)
. This was modified using primers Jw12 (5'-ATGTAACACCYCTACAATG-3') and N165-146 (5'-GCAGGGTAYTTRTACTACTCATA-3') where indicated, to incorporate SyBr green using the SyBr green JumpStart Taq ReadyMix assay (Sigma) to enable quantification of genome copies as described by Johnson et al. (2006a)
. β-actin primers (Wakeley et al., 2005
) and 18S RNA primers (Ambion) were used to detect host mRNA within samples.
Rapid fluorescent focus inhibition test (RFFIT).
Virus neutralizing antibody (VNA) against EBLV-2 was measured with a modified RFFIT (Cox & Schneider, 1976
) by replacing challenge virus standard (RABV) with EBLV-2. Samples were tested in duplicate with twofold serum dilutions starting at 1 : 10. A heterologous WHO international standard immunoglobulin (2nd human rabies immunoglobulin preparation, National Institute for Standards and Control, Potters Bar, UK), adjusted to 1.5 IU ml–1, served as a positive control. The VNA titre was expressed as the reciprocal of the serum dilution showing a 50 % reduction in concentration of the EBLV-2 test virus in vitro. Sera from bats were assessed prior to inoculation and at the end of the study.
Immunohistochemistry.
Following fixation in 10 % buffered formalin, brain, spinal cord, salivary glands, liver, kidney, lung, spleen and intestinal samples were blocked and routinely processed to paraffin wax. Immunohistochemical detection of lyssavirus nucleocapsid was performed as described by Hicks et al. (2008)
. Briefly, serial 4 µm sections were hydrated and successively incubated with hydrogen peroxide block (BHD), normal goat serum block, primary antibody anti-rabies nucleocapsid mAb HAM (obtained from the Swiss Rabies Centre, Bern, Switzerland), biotinylated goat–anti-mouse secondary antibody, avidin–biotin-peroxidase conjugate (Vector Laboratories) and 3,3-diaminobenzidine (Sigma). Sections were then counterstained with Meyer's haematoxylin (Surgipath) and mounted.
| RESULTS |
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Two animals died during the 123 day experimental period, although these could not be attributed to EBLV-2 infection and were considered non-specific. The remaining animals survived to the end of the experiment. Both nested RT-PCR and a qRT-PCR assay corroborated the antigen detection assays, with both detecting EBLV-2 genes in all five bats from the i.c. group and the single bat from the s.d. group (Table 3
).
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| DISCUSSION |
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The data obtained in this study are limited, with only one of seven bats inoculated by the s.d route developing disease and all bats challenged by the i.m. route surviving to the end of the experiment. This implies that the reservoir species is surprisingly resilient to infection. In most lyssavirus challenge models, the i.m. route is effective at inducing disease (Moreno & Baer, 1980
) so the relative differences in efficacy of inoculation may reflect differences in innervation at particular sites in the Daubenton's bat. The inability of EBLV-2 to infect bats by i.n. inoculation repeats a previous observation made for EBLV-1 in Eptesicus fuscus bats (Franka et al., 2008
). In roosts of European bats, in contrast with those observed in bat species in other parts of the world, the number of individuals of species such as the Daubenton's bat is relatively small (<100 individuals). This would not favour aerosol spread and thus EBLV-2 could have evolved away from transmission by this route. When directly compared under experimental conditions, RABV proved more effective than EBLV-2 at infecting mice by the airborne route (Johnson et al., 2006c
), although a mouse is not the natural host for lyssaviruses, so these results should be interpreted with caution.
One possible explanation for sustained transmissibility could be that EBLV-2, like the silver-haired bat rabies variant (SHBRV) in North America, has become adapted to replication at the relatively lower body temperatures that are found in the dermis. SHBRV was shown to replicate faster at 34 °C than a RABV variant isolated from a coyote (Morimoto et al., 1996
). Superficial bites from Daubenton's bats were believed to be responsible for both human cases of EBLV-2 (Fooks et al., 2003b
). Another possible factor could be an extended incubation period. All of the Daubenton's bats in our study developed rabies within 32 days, with the animals inoculated by the i.c. route developing disease between 12 and 14 days. In one case of a naturally infected Daubenton's bat, an incubation period of 8 weeks was reported (Johnson et al., 2003
). Although a 90 day observation period was planned, this was extended to 123 days to lengthen the opportunity to detect disease after a longer incubation period; however, none occurred and there was no evidence of salivary excretion of virus without development of disease as has been reported for RABV (Aguilar-Setien et al., 2005
) and EBLV-1 (Echevarria et al., 2001
). However, much longer incubation periods have been observed for RABV infections (Smith et al., 1991
).
In the single case of rabies following peripheral inoculation of EBLV-2 registered in our study, viral RNA was detected in saliva 2 days before the development of disease. Similar observations have been made for RABV infection in both insectivorous (Bell et al., 1969
) and vampire (Moreno & Baer, 1980
) bats and Eurasian bat lyssaviruses in E. fuscus (Hughes et al., 2006
). This indicates that EBLV-2 shows similar pathogenic characteristics under experimental conditions to other lyssaviruses. Within this experiment, we did not find evidence for an asymptomatic carrier state with virus excretion. However, virus excretion from an apparently healthy bat was observed by detection of viral RNA; the bat then developed clinical signs of rabies over the next 2 days. This reinforces the need for those that have contact with bats to have rabies pre-exposure vaccination and to wear protective gloves to prevent being exposed to a bite.
| ACKNOWLEDGEMENTS |
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| REFERENCES |
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Bell, J. F., Moore, G. J. & Raymond, G. H. (1969). Protracted survival of a rabies-infected insectivorous bat after infective bite. Am J Trop Med Hyg 18, 61–66.
Bourhy, H., Kissi, B., Lafon, M., Sacramento, D. & Tordo, N. (1992). Antigenic and molecular charactisation of bat rabies virus in Europe. J Clin Microbiol 30, 2419–2426.
Brookes, S. M., Aegerter, J. N., Smith, G. C., Healy, D. M., Joliffe, T. A., Swift, S. M., Mackie, I. J., Pritchard, S., Racey, P. A. & other authors (2005a). European bat lyssavirus in Scottish bats. Emerg Infect Dis 11, 572–578.[Medline]
Brookes, S. M., Parsons, G., Johnson, N., McElhinney, L. M. & Fooks, A. R. (2005b). Rabies human diploid cell vaccine elicits cross-neutralising and cross-protecting immune responses against European and Australian bat lyssavirus. Vaccine 23, 4101–4109.[CrossRef][Medline]
Brookes, S. M., Klopfleisch, R., Müller, T., Healy, D., Teifke, J. P., Lange, E., Kleimt, J., Johnson, N., Johnson, L. & other authors (2007). Susceptibility of sheep to European bat lyssavirus type-1 and -2 infection: a clinical pathogenesis study. Vet Microbiol 125, 210–223.[CrossRef][Medline]
Cox, J. H. & Schneider, L. G. (1976). Prophylactic immunization of humans against rabies by intradermal inoculation of human diploid cell culture vaccine. J Clin Microbiol 3, 96–101.
Dean, D. J. & Abelseth, M. K. (1973). The fluorescent antibody test. In Laboratory Techniques in Rabies, 3rd edn, pp. 73–84. Edited by M. M. Kaplan & H. Koprowski. Geneva: World Health Organisation.
Echevarria, J. E., Avellon, A., Juste, J., Vera, M. & Ibanez, C. (2001). Screening of active Lyssavirus infection in wild bat populations by viral RNA detection on oropharyngeal swabs. J Clin Microbiol 39, 3678–3683.
Fooks, A. R., McElhinney, L. M., Pounder, D. J., Finnegan, C. J., Mansfield, K. L., Johnson, N., Brookes, S. M., Parsons, G., White, K. & other authors (2003a). Case report: isolation of a European bat lyssavirus type 2a from a fatal human case of rabies encephalitis. J Med Virol 71, 281–289.[CrossRef][Medline]
Fooks, A. R., Brookes, A. R., Johnson, N., McElhinney, L. M. & Hutson, A. M. (2003b). European bat lyssavirus: an emerging zoonosis. Epidemiol Infect 131, 1029–1039.[CrossRef][Medline]
Fooks, A. R., Seldon, D., Brookes, S. M., Johnson, N., Marston, D. A., Jolliffe, T. A., Wakeley, P. R. & McElhinney, L. M. (2004a). Identification of a European bat lyssavirus type 2 in a Daubenton's bat found in Lancashire. Vet Rec 155, 606–607.[Medline]
Fooks, A. R., McElhinney, L. M., Marston, D. A., Seldon, D., Joliffe, T. A., Wakeley, P. R., Johnson, N. & Brookes, S. M. (2004b). Identification of a European bat lyssavirus type 2 in a Daubenton's bat found in Staines, Surrey, UK. Vet Rec 155, 434–435.[Medline]
Fooks, A. R., Marston, D. A., Parsons, G., Earl, D., Dicker, A. & Brookes, S. M. (2006). Isolation of EBLV-2 in a Daubenton's bat (Myotis daubentonii) found in Oxfordshire. Vet Rec 159, 534–535.
Franka, R., Johnson, N., Müller, T., Vos, A., Neubert, L., Freuling, C., Rupprecht, C. E. & Fooks, A. R. (2008). Susceptibility of North American big brown bats (Eptesicus fuscus) to infection with European bat lyssavirus type 1. J Gen Virol 89, 1998–2010.
Freuling, C., Grossmann, E., Schameitat, A., Kliemt, J., Auer, E. & Müller, T. (2007). EBLV-2 infection confirmed in a Daubenton's bat in Germany. Rabies Bulletin Europe 31, 5
Harris, S. L., Mansfield, K. L., Marston, D. A., Johnson, N., Pajamo, K., O'Brien, N. O., Black, C., McElhinney, L. M. & Fooks, A. R. (2007). Isolation of European bat lyssavirus type 2 from a Daubenton's bat (Myotis daubentonii) in Shropshire. Vet Rec 161, 384–386.
Heaton, P. R., Johnstone, P., McElhinney, L. M., Cowley, R., O'Sullivan, E. & Whitby, J. E. (1997). Hemi-nested PCR assay for the detection of six genotypes of rabies and rabies-related viruses. J Clin Microbiol 35, 2762–2766.[Abstract]
Hicks, D. J., Núñez, A., Healy, D. M., Brookes, S. M., Johnson, N. & Fooks, A. R. (2008). Comparative pathological study of the murine brain after experimental infection with classical rabies virus and European bat lyssaviruses. J Comp Pathol In press
Hughes, G. J., Kuzmin, I. V., Schmitz, A., Blanton, J., Manangan, J., Murphy, S. & Rupprecht, C. E. (2006). Experimental infection of big brown bats (Eptesicus fuscus) with Eurasian bat lyssaviruses Aravan, Khujand, and Irkut virus. Arch Virol 151, 2021–2035.[CrossRef][Medline]
Johnson, N., Seldon, D., Parsons, G. & Fooks, A. R. (2002). European bat lyssavirus type 2 in a bat found in Lancashire. Vet Rec 151, 455–456.[Medline]
Johnson, N., Seldon, D., Parsons, G., Healy, D., Brookes, S. M., McElhinney, L. M., Hutson, A. A. & Fooks, A. R. (2003). Isolation of a European bat lyssavirus type 2 from a Daubenton's bat in the United Kingdom. Vet Rec 152, 383–387.
Johnson, N., McKimmie, C. S., Mansfield, K. L., Wakeley, P. R., Brookes, S. M., Fazakerley, J. K. & Fooks, A. R. (2006a). Lyssavirus infection activates interferon gene expression in the brain. J Gen Virol 87, 2663–2667.
Johnson, N., Wakeley, P. R., Brookes, S. M. & Fooks, A. R. (2006b). European bat lyssavirus type 2 RNA distribution in Myotis daubentonii. Emerg Infect Dis 12, 1142–1144.[Medline]
Johnson, N., Phillpotts, R. & Fooks, A. R. (2006c). Airborne transmission of lyssaviruses. J Med Microbiol 55, 785–790.
King, A., Davies, P. & Lawrie, A. (1990). The rabies viruses of bats. Vet Microbiol 23, 165–174.[CrossRef][Medline]
Kuzmin, I. V., Franka, R. F. & Rupprecht, C. E. (2008). Experimental infection of big brown bats (Eptesicus fuscus) with West Caucasian bat virus (WCBV). Dev Biol (Basel) 131, 327–337.[Medline]
Lumio, J., Hillbom, M., Roine, R., Ketonen, L., Halthia, M., Valle, M., Neuvonen, E. & Lahdevirta, J. (1986). Human rabies of bat origin in Europe. Lancet 1, 378[Medline]
Marston, D. A., McElhinney, L. M., Johnson, N., Müller, T., Conzelmann, K. K., Tordo, N. & Fooks, A. R. (2007). Comparative analysis of the full genome sequence of European bat lyssavirus type 1 and type 2 with other lyssaviruses and evidence for a conserved transcription termination and polyadenylation motif in the G-L 3' non-translated region. J Gen Virol 88, 1302–1314.
Messenger, S. L., Smith, J. S. & Rupprecht, C. E. (2002). Emerging epidemiology of bat-associated cryptic cases of rabies in humans in the United States. Clin Infect Dis 35, 738–747.[CrossRef][Medline]
Mohr, W. (1957). Die Tollwut. Med Klin 52, 1057–1060.
Moreno, J. A. & Baer, G. M. (1980). Experimental rabies in the vampire bat. Am J Trop Med Hyg 29, 254–259.
Morimoto, K., Patel, M., Corisdeo, S., Hooper, D. C., Fu, Z. F., Rupprecht, C. E., Koprowski, H. & Dietzschold, B. (1996). Characterisation of a unique variant of bat rabies virus responsible for newly emerging human cases in North America. Proc Natl Acad Sci U S A 93, 5653–5658.
Müller, T., Johnson, N., Freuling, C. M., Fooks, A. R., Selhorst, T. & Vos, A. (2007). Epidemiology of bat rabies in Germany. Arch Virol 152, 273–288.[CrossRef][Medline]
Scatterday, J. E. (1954). Bat rabies in Florida. J Am Vet Med Assoc 124, 125[Medline]
Seidler, M., Brehmer, H.-J., Pott, B., Cox, J. H. & Zinke, H. (1987). Tollwut bei Fledermausen in Niedersachsen. Berl Munch Tierarztl Wochenschr 100, 199–203.[Medline]
Smith, J. S., Fishbein, D. B., Rupprecht, C. E. & Clark, K. (1991). Unexplained rabies in three immigrants in the United States. A virologic investigation. N Engl J Med 324, 205–211.[Abstract]
Tignor, G. H., Murphy, F. A., Clark, H. F., Shope, R. E., Madore, P., Bauer, S. P., Buckley, S. M. & Meredith, C. D. (1977). Duvenhage virus: morphological, biochemical, histopathological and antigenic relationships to the rabies serogroup. J Gen Virol 37, 595–611.
Van der Poel, W. H. N., Van der Heide, R., Verstraten, E. R., Takumi, K., Lina, P. H. C. & Kramps, J. A. (2005). European bat lyssaviruses, the Netherlands. Emerg Infect Dis 11, 1854–1859.[Medline]
Vazquez, S., Ibanez, C., Juste, J. & Echevarria, J. E. (2006). EBLV-1 circulation in natural bat colonies of Eptesicus serotinus: a six year study. Dev Biol (Basel) 125, 257–261.[Medline]
Vos, A., Müller, T., Cox, J., Neubert, L. & Fooks, A. R. (2004). Susceptibility of ferrets (Mustela putorius furo) to experimentally induced rabies with European bat lyssaviruses. J Vet Med B Infect Dis Vet Public Health 51, 55–60.[Medline]
Wakeley, P. R., Johnson, N., McElhinney, L. M., Marston, D. A., Sawyer, J. & Fooks, A. R. (2005). Development of a real-time, TaqMan reverse transcription-PCR assay for detection and differentiation of lyssavirus genotypes 1, 5 and 6. J Clin Microbiol 43, 2786–2792.
Webster, W. A. & Casey, G. A. (1996). Virus isolation in neuroblastoma cell culture. In Laboratory Techniques in Rabies, 4th edn, pp. 93–104. Edited by F. X. Meslin, M. M. Kaplan & H. Koprowski. Geneva: World Health Organisation.
Whitby, J. E., Heaton, P. M., Black, E. M., Wooldridge, M., McElhinney, L. M. & Johnstone, P. (2000). First isolation of a rabies-related virus from a Daubenton's bat in the United Kingdom. Vet Rec 147, 385–388.
Wiktor, T. J. & Koprowski, H. (1978). Monoclonal antibodies against rabies virus produced by somatic cell hybridization: detection of antigenic variants. Proc Natl Acad Sci U S A 75, 3938–3942.
Received 2 May 2008;
accepted 16 July 2008.
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