ARCHIVE: Bat research

Prevalence of European Bat Lyssavirus-2 (EBLV-2) in Daubenton’s Bats in England (2004-2006)

In 2004, a three year study, funded by Defra, began in England. Further work is also being conducted in Scotland by the Scottish Government and Scottish Natural Heritage. The Defra study is now complete.

This surveillance has indicated that there are antibodies to rabies in a very small proportion of Daubenton’s bats in England. This indicates that they have been exposed to the rabies virus at some time during their lives. There is therefore a small risk of rabies infection from contact with bats.

A single serotine bat was found to be EBLV1 antibody positive in 2004 but none was found to have antibodies to EBLV 1 in 2005 or 2006.

Transmission of European Bat Lyssavirus-2 (EBLV-2) Between Bat and Host (2005-2008)

European Bat Lyssavirus (EBLV) is a strain of rabies virus that is found in European bats. In particular, European Bat Lyssavirus type-2 has been detected in Myotis daubentonii (commonly referred to as Daubenton’s bat). The number of Daubenton’s bats in Great Britain (GB) is estimated at 150,000 and is not regarded as a threatened species.  Rabies virus, including EBLV, can be transmitted to humans and to other animals. One such example was the tragic death of a Scottish bat conservationist from rabies caused by EBLV-type 2 in 2002. Bats can also succumb to this infection; in GB for example there have been a small number of confirmed cases of rabies in Daubenton’s bats due to EBLV-type 2. In addition a limited survey has shown about 2% of this species in England to be seropositive and this indicates that these bats have been exposed to the virus.

There has been little information available on how bats transmit EBLV-type 2 or the relationship between the virus and its bat host. It is possible that bat variants of rabies virus, including EBLV-type 2, are less virulent than classical strains of rabies virus (e.g. dog rabies). This suggests that EBLV-type 2 might have a longer incubation period than other strains of rabies virus before being intermittently excreted in saliva. Of particular concern is the public health aspect where it could be found that a healthy Daubenton’s bat may be infected with EBLV-type 2 and be capable of transmitting the disease without showing signs of rabies.

Research has therefore been carried out to examine the susceptibility and pathogenicity of EBLV-2 in its natural host.  This has helped provide firm scientific evidence to support the current approach on bat rabies and confirms the advice to be given to bat handlers and the general public on any risks to which they may be exposed when coming into direct contact with bats. The results will also be used to obtain a better understanding of what type of surveillance is worthwhile. The particular importance of carrying out this research in the natural host was supported by international organisations such as the OIE – the World Organisation of Animal Health, and Eurobats.

A research study was therefore undertaken to further our understanding of these issues using live Daubenton’s bats caught under licence from English Nature (now Natural England). The results of the research have been published and there is now information available about this study.

Background

The research was led by internationally recognised scientists at the Veterinary Laboratories Agency in a multi-centre collaborative study and was jointly funded by Defra and the German Ministry of Nutrition, Agriculture and Consumer Protection.  The study itself was undertaken in Germany as the UK did not have the capacity in its specialised facilities to undertake this work.

Research findings

The main findings of this experiment were:

  • This single study on a small, but statistically valid, number of bats provided no evidence to support the notion that Daubenton’s bats carry EBLV 2 without showing clinical signs of bat rabies.
  • Virus excretion was only observed immediately before the onset of clinical signs.
  • Healthy Daubenton’s bats appear to be resilient to challenge with EBLV 2.
  • Inhalation and oral routes (similar to grooming between bats) are not effective means of transmitting EBLV-2.
  • One bat succumbed to EBLV2 infection after injection under the skin (similar to a bite or scratch). But only minute amounts of virus was found in the saliva of that bat, indicating that it is likely to be difficult to transmit EBLV 2 following human exposure via a bite from an infected bat.
  • Daubenton’s bats are not susceptible to infection by inoculation directly into the muscle.
  • Bats inoculated with virus did not develop an immune response to infection.

Even though transmission to humans is likely to continue to be very rare, these results support the view that the right level of risk mitigation is in place through our current approach of investigation and advice, as well as prompt precautionary post exposure prophylaxis. The study has therefore been extremely valuable in providing a stronger scientific base for our policy of a precautionary approach to possible contacts with bats by bat workers and others handling bats on a routine basis as well as any incident where a human has come into contact with a bat.

Defra advice to bat workers and members of the public remains the same and this view has been endorsed by the Health Protection Agency (HPA).

Further research

Defra has no current plans for further surveillance. 

Further papers resulting from the current research are being considered for future publication.

Further information

 

Page published: 29 October, 2010