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Rabies: an increasing threat?

by
01 May 2014, at 1:00am

Jayne Laycock reports on her ‘pick of the month’ CPD webinar presented on the topic of rabies by Professor Radford Davis of the Iowa State University College of Veterinary Medicine

RABIES was eradicated from the UK at the beginning of the 20th century, with the last human death from indigenous classical rabies occurring in 1902 and the last case of indigenous terrestrial animal rabies occurring in 1922.

This, of course, is the way we would like it to stay but with relaxed regulations on the movement of pets across borders in Europe, is there an increased risk of encountering this fatal disease at some point in the near future?

The Webinar Vet organised for Professor Radford Davis to lead a veterinary webinar discussing the topic of rabies, giving insights into how this disease could enter the UK and also advising on how to manage any suspect cases.

Rabies and rabies-related viruses 

Prof. Davis explained that a good background knowledge of the rabies- causing viruses was necessary in order to understand how rabies could once again enter the UK.

Initially it was thought that every case of rabies was caused by one “rabies” virus from the family Rhabdoviridae, but based on work performed back in the 1950s and 1970s scientists discovered there were a number of rabies-related viruses which all sit under the umbrella of the genus Lyssavirus.

To date there are now thought to be 14 or more species of Lyssavirus which include the most widespread “classical rabies virus” known to cause the most deaths associated with rabies around the world (about 55,000 recorded cases a year).

The European Bat Lyssavirus type 1 (EBLV type 1) and European Bat Lyssavirus type 2 (EBLV 2) are the most common Lyssaviruses found in Europe. Although it is the classical rabies virus which causes the majority of rabies deaths across the world, EBLV1 and EBLV2 will still cause rabies in exactly the same way as a classical rabies virus once the host becomes infected. 

The hosts

All species of mammals can be infected with Lyssaviruses and once infected will eventually develop an acute encephalitis which, once clinical signs develop, is 100% fatal. Exposure to these viruses can take place if bitten or scratched by an infected mammal or if infectious material such as saliva or nervous tissue comes in contact with compromised skin or mucous membranes. 

Once exposed, there is retrograde movement from the site of infection to the spinal cord, ganglia and brain which eventually causes the fatal encephalitis.

The hosts for these viruses fall into one of two categories: the reservoir host or the end host. The majority of the Lyssaviruses have the bat in common, being their principle reservoir host.

Prof. Davis explained that a reservoir host is not a chronic shedder and will eventually succumb to rabies but they are extremely good at shedding and transmitting the virus. The dog is also a reservoir host as well as the major source of transmitting infection to humans worldwide; within Europe, however, the bat is the most indigenous reservoir species. End hosts such as humans and livestock will again eventually succumb to rabies but are poor transmitters of the virus.

EBLVs

EBLV-1 and EBLV-2 are the most common Lyssaviruses found in Europe with insectivorous bats acting as their reservoir host. In the UK to date, there have only been 10 confirmed cases of EBLV-2 infection in bats which have been identified by the UK Veterinary Laboratories Agency through routine testing.

Currently it is rare for the EBLVs to cross the species barrier with no documented evidence of EBLV-2 being present in any terrestrial mammals and EBVL-1 only having been found in one sheep in Denmark, a stone marten in Germany and two cats in France.

To date there have only been five reported cases of humans having been infected with an EBLV since 1977 across Europe: one in Finland, two in the former Soviet Union and one in Scotland in 2002. All four of these people had been in close contact with bats and had not received post- exposure treatment.

Rabies entering the UK 

Cases of human rabies in the UK are extremely rare with only five cases having occurred since 2000. All had been acquired from abroad, usually through dog bites. There was also the aforementioned death in 2002 of a man in Scotland who worked closely with bats and had become infected with EBLV-2.

Prof. Davis explained the current concern for rabies entering back into the UK is focused on the illegal smuggling of dogs infected with the classical rabies virus, but he believes that it will take a lot more than the smuggling of 10-12 rabies infected dogs for the UK to lose its rabies-free status and to establish rabies enzootically.

Prof. Davis would be more concerned about EBLVs evolving so that, instead of rarely crossing the species barrier, they can be easily transmitted from bats to terrestrial mammals and, even worse, then passed from terrestrial mammal to terrestrial mammal.

He also explained that it may be possible for bats to pick up the classical rabies virus and travel into the UK where it can then be spread from terrestrial mammal to terrestrial mammal. According to Prof. Davis this could have the potential to be an emerging problem over the next 20-30 years.

Exposure to rabies

The speaker went into great depth covering the variety of clinical signs associated with rabies if exposed, and also reminded us that rabies is a notifiable disease and the relevant agencies should be contacted. 

In Europe, being bitten or scratched by a potentially EBLV infected bat is always a possibility and he explained that if there is any concern this may have occurred then, if possible, the bat should be captured (obviously ensuring your own safety – advice can be sought at the Bat Conservation Trust).

The presence of the virus can then be confirmed at post- mortem and post- exposure prophylaxis can be instigated. He also advised that if there is any suspicion that someone has been bitten or scratched by a rabid dog, cat or ferret, the animal in question should be quarantined for 10 days by which time it will either be near to death or will have succumbed to the disease if infected.

First aid for the affected person is also crucial and can be instigated by washing the bite or scratch with soap and water for at least 15 minutes.

Post-exposure prophylaxis (PEP) should also be instigated and according to Prof. Davis there has been no vaccine or treatment failures recorded in the US since 1979 when PEP is given promptly and appropriately prior to the development of clinical signs.

This protocol is explained in much greater depth within the webinar recorded on The Webinar Vet’s website. Vaccination is also recommended for people at high risk of contracting the virus and Prof. Davis explained that the majority of vets in the US will be rabies vaccinated. In the UK, if handling bats, then vaccination would also be appropriate.

Of course, we are fortunate to be living in the UK with its rabies-free status, but rabies is a disease which will continue to threaten us and, with a 100% mortality rate in people once clinical signs develop, we really need to know how to recognise and deal with a potential rabies case.

This was an excellent and thought- provoking webinar about a disease which I had, perhaps foolishly, put to the back of my mind and any discussion which helps to raise its awareness can only be a good thing.