The decline of the humble rabbit, Oryctolagus cuniculus, across many areas of the UK has been notable. This has been reported by many country folk, hunters and conservationists. Yet the dearth of rabbits in distinct areas is matched by reports from some areas that the rabbit is alive and kicking in healthy numbers. So what’s going on?
There is a specific reason for the rabbit famine, of course. A very worrying reason. The proliferation of any ‘species-specific’ disease is cause for concern. Even more so when there is suspicion of deliberate introduction into the UK for purely commercial reasons. No, I’m not talking about myxomatosis this time. I’m talking about both RHDV1 and RHDV2. The rabbit haemorrhagic disease viruses.
Viruses that effect rabbits or hares are known as lagoviruses. In China (in 1984) a new lagovirus emerged amongst a population of Angoran rabbits which had been imported from Germany just days before the outbreak. The new disease proved unstoppable and wiped out around 140 million farmed and domestic rabbits in Asia. The disease was RHDV1. In 1986, it turned up again in Europe and spread like wildfire from Italy to Scandinavia. By 1988 it had infected the European wild rabbit population. In 1990, the disease reached the famous rabbit population on the island of Gotland in Sweden. Almost the entire population was dead within one week. The start of the spread of the disease two decades ago was largely attributed to contaminated rabbit meat … a popular product in Europe. Our Antipodean friends, as they did with myxomatosis, saw RHVD as a potential for biological pest control (not as a threat). Unfortunately the Australian Government’s experiments on Warranga Island (4km off the mainland) resulted in accidental transmission to the mainland, probably through flies. The New Zealand government, to be fair, decided not to adopt RHVD as a pest control medium. So someone introduced it illegally in 1997!
It is now spread by many different vectors. Insects, flies and fleas can carry the virus from infected host rabbits to other rabbits. It travels in animal faeces. Birds such as carrion eaters can carry it in their beaks, mammals such as fox, dog or badger can carry it in their mouths and their faeces. It transmits by ‘aerosol’ means too (breath, sneezing, breeze). One of the most important vectors for the spread of RHVD is us, humans. We can carry the virus on our hands and on our footwear.
The virus is extremely robust. Chinese experiments have shown that it survived in rabbit livers frozen at -20oC for 560 days. It also survived temperature of +50oC for 60 minutes. It can survive on clothing at 20oC for over 100 days. In short, RHVD is the rabbits worst nightmare. So what is the difference between RHVD1 and RHVD2? And why does the virus seem to have completely missed many geographical areas of Britain?
To answer the first question, RHVD2 (sometimes called RHVD Variant) emerged in France in 2010. Latter research has shown that it has been in the UK since 2010, too. It ‘variance’ is allowing it to attack rabbit populations which had previously built up resistance the RHVD2 and many rabbits are now exposed to the new lagovirus. The most devastating property of RHVD2 is that newly born rabbits have no resistance to the virus. With RHVD1, kits under 5 weeks of age contracting the virus had a naturally immunity which would stay with them for life. That at least gave a life-line for survival for the wild rabbit. There is a worry that this new strain may carry its pathogens to other Lagomorphs, which could have huge consequences for the Brown Hare.
What of the second question, though? The random spread of the epidemic? There are two threads of research that may offer the answer to this enigma, yet neither are conclusive at the moment. Both relate to Rabbit Calicivirus (RCV).
The first possible explanation is the immunity built up to RCV. Many of us will recall the emergence of RCV during the mid-nineties?. A disease closely related to RHVD but non-pathogenic. Many rabbits survived RCV and built up anti-bodies which rejected the RHVD virus. So, ironically, it is possible that many colonies that have resisted the first wave of RHVD could be those who were strengthened by infection by RCV in their community.
The second possibility relates to research undertaken in Australia in 2014 which suggests that climatic conditions influenced the spread of RCV and has therefore reduced the pathogenicity of RHVD. A quick and simple summary of the research is that RCV was most infectious in the cool and damp areas of South East Australia. Therefore resistance to RHVD is most prevalent in those same areas. Great Britain has many areas with cool, damp micro-climates. Are these where the rabbits are holding out in numbers? If so, how long will it be before the new variant affects these colonies?
The rabbit became an established staple in the British countryside centuries ago and is sorely missed where it has lost its foothold. I know that from personal experience. I haven’t shot a rabbit for four months as I write this. Not that I haven’t seen a few here and there but you simply don’t shoot what has become rare. You only harvest what is abundant. That should be a hunters apothegm. But I don’t just miss the rabbit as ‘quarry’. As a primary prey species its loss will have an detrimental consequence on many other species and a knock-on effect, too. The fox and stoat, in the absence of rabbits, turn their attention to the hen-house or the ground nest. The buzzard, to the poults.
The British Countryside without the ubiquitous ‘coney’ would be unthinkable.
Copyright Ian Barnett, Wildscribbler, March 2018