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Rethinking myxomatosis in rabbits Categories : RVNs Date : September 1, 2013

Glen Cousquer, BSc(Hons), BVM&S, CertZooMed, PGDOE, MSc, MRCVS, reflects on veterinary attitudes surrounding rabbit diseases

READERS will be familiar with the two infectious rabbit diseases of most concern to the profession – myxomatosis and rabbit haemorrhagic viral disease (RHVD). But is there more to these than meets the eye? This article will review the history of myxomatosis and the ways in which the rabbit, humans and the virus have constructed this particular phenomenon. Preventive medicine and, in particular, vaccination will be broached. In doing so, a seemingly unproblematic subject will be turned on its head and the reader asked to consider what the role of the veterinary profession is, might be and should be in promoting rabbit welfare.

Rabbit – friend or foe? A short history of rabbit infectious disease Of the many diseases man has wittingly or unwittingly transported across the Atlantic, perhaps the two most devastating have been smallpox and myxomatosis. The former devastated the indigenous people of the Americas (Wilson, 1995), the latter ravaged the wild rabbit populations of Australia and Europe (Bartrip, 2008; Fenner and Ratcliff, 2009). As such, and in view of their aetiological cause, they were, quite literally, “poxes” on the population that suffered them. Frank Fenner, delivering the Florey lecture to the Royal Society in 1983, highlighted some of the parallels between these two terrible diseases.

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In 1983, he said of myxomatosis: “[It] is a benign disease in Sylvilagus rabbits in South America transmitted mechanically by mosquitoes. In the European rabbit, Oryctolagus, which is a pest in Australia and England, the virus from Sylvilagus produces a generalised disease that is almost always lethal. Myxomatosis was deliberately introduced into Australia in 1950 and into Europe in 1952. It was at first spectacularly successful in controlling the rabbit pest, but biological adjustments occurred in the virulence of the virus and the genetic resistances of rabbits. After 30 years of interaction, natural selection has resulted in a balance at a fairly high level of viral virulence.” This may sound objective and factual. The opening sentence describes the disease as benign in Latin America, the last implies that a balance will establish itself and that natural selection will have its way. A more careful reading of the text, however, will start to see this account as far more subjective and problematic. This reflects what is perhaps the most fundamental issue in morality and epistemology, namely our ongoing struggle to transcend ourselves and attain what Thomas Nagel (1986) describes as “the view from nowhere”. The story and all the facts it purports to present are human constructs. The typical veterinary professional, trained in the veterinary sciences, a field that, arguably, has yet to fully acknowledge, let alone shed, the predominant realist ontological view of the world1 (a view that is perhaps most evidenced by our current obsession with evidence-based medicine and quantifying welfare), might wish to reread that last sentence. In doing so, the reader may want to try identifying some of these subjective elements that could include: • “transmitted mechanically by mosquitos”; • “is a pest in Australia and England”; • “spectacularly successful in controlling”; and • “natural selection has resulted in a balance”. The language used reduces the complex interactions of rabbit and insect parasite to a mechanical process and uncritically accepts the characterisation of the rabbit as a pest that needs to be controlled. Using the verb “control” is benign, especially when compared to alternatives such as “mercilessly exterminate” or “kill in their thousands”. The final quote implies acceptance of two of the most popular ideas in medical sciences, that of “natural selection” and “balance”, which, while useful as explanatory theories, are not unproblematic, especially when it is assumed they can be used as reliable measures of the health of an individual or system (Canguilhem, 2012; Nordenfelt, 2006). Then there is the matter of power for it is power that allows this particular account of “reality” to be put forward. When interviewed, in 1993, about his work on myxomatosis, Prof Fenner is quoted as saying:

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“Myxomatosis has done a marvellous job in controlling the rabbit pest in Australia. In many areas of the country it has virtually disappeared. But in the dry outback areas, where mosquito activity is minimal and you only get a mosquito plague every few years, the rabbit causes major problems in promoting erosion and destroying habitat for indigenous, native mammals of Australia (Australian Academy of Science, no date). When asked about its introduction to New Zealand he is quoted as saying: “There have been several proposals to introduce myxomatosis for rabbit control there. A recent strong one was refused on the grounds that the flea which would have to be introduced at the same time to spread the virus – because there are not sufficient mosquitoes in that particular area on the South Island – might get on the kiwis. As a sop, I suppose, to the landholders who wanted to have the virus introduced, they were told that rabbit haemorrhagic disease virus might be introduced instead. I think that might cause some problems with the animal welfare lobbies there. We’ll see.” (Australian Academy of Science, no date). These two quotes reflect the embeddedness of our actions in complex socio-biological systems that can be characterised in many ways. At the same time as Australian officials were preparing to conduct this trial, a similar rabbit eradication scheme was being considered by the British Government and the Ministry for Agriculture and Fisheries (MAF; Bartrip, 2010). One of MAF’s senior scientists voiced strong concerns and is quoted by Dr Bartrip as saying: “The symptoms of this disease are distressing… Infected rabbits die in the open. Public opinion in this country is becoming increasingly antagonistic to cruelty to wild animals… Because of this, it is improbable that virus dissemination could ever become a recognised method of control here, even if it were a possible one. There is another hindrance. The disease, if disseminated, would probably become permanently established and, unless particularly effective, might become more of an embarrassment than a help as it would affect domesticate rabbits as well as wild rabbits.” Following the introduction of myxomatosis into Australia in 1951, it was introduced into France a year later (by a physician seeking to rid his garden of rabbits) and then spread across Europe and into the UK. At the same time, scientists working for the North of Scotland College of Agriculture released a strain of the virus into the Hebrides (Allan, 1956; Bartrip, 2010). The spread of the virus was thus fed by individuals, scientists and others, some of whom set up rabbit clearance societies (Bartrip, 2009). This phenomenon was met with a mixed response by the UK public, some of whom relied on wild rabbits as a source of food. The resulting collapse in rabbit numbers also impacted heavily on habitats and especially on species that could not easily change to an alternative food source (Sumption and Flowerdew, 1985). In Spain, the collapse of the Iberian Lynx and Spanish Imperial Eagle populations have been attributed to the virtual wiping out of rabbits (Ferrer and Negro, 2004). Therefore, the story of myxomatosis tells us much about our confused relationship with nature, rabbits, science and technol ogy, society, value systems and our ideas of how we should relate to

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and act in and on the world. How did such weapons come to be launched against the rabbit? To answer this question we could look at actor network theory and material semiotics (Law, 2009). To understand the work of social theorists working on science and technology, it helps to consider how Bruno Latour (1988) dismantled the claim that Louis Pasteur was a genius, demonstrating instead that his was a role within a network of discourses. Essentially Pasteur was an effect rather than a cause, for he was able to conduct his work because the network enabled it. To show this he charts how a network of domesticated farms, technicians, laboratories, veterinarians, statistics and bacilli was generated. He describes how they were shaped (in some cases created) in this network, and he shows how the result was generative. Farms were turned into laboratories, vaccines made from attenuated bacteria, cattle stopped dying of anthrax, and Pasteur became a great man (Law, 2009). A wider appreciation of the networks that come together around us, “a sensibility to the messy practices of relationality and materiality of the world” (Law, 2009) is likely to promote humility and wonder as we try to make sense of actions, of how they relate to those of others, to social structures, to our understanding of veterinary practice, to non-humans and to the material world. This shifting collection of many things interacts in ways that are complex (Fioretti, 1996; Kauffman, 1993) and have been characterised as an assemblage (Bennett, 2005 for an account of the North American blackout or Thompson’s 2002 account of the ways elephants stand for competing models of nature). Where does myxomatosis fit into all this? Annemarie Mol (2002) points out in her study on the diagnosis and treatment of atherosclerosis, that there are many realities produced by the different practices brought to bear on the one body. Myxomatosis is not one disease, but many and we need to be conscious of how we construct and work with it. Today, we vaccinate rabbits annually, sometimes six monthly, in an attempt to protect domestic rabbits against both of these two infectious and highly dangerous diseases. That is one situation, but there are many others, for this reality is constructed by the practices of vets, of the pharmaceutical industry, of rabbit owners and their busy family lives, of rabbit feed merchants and the pet industry, of rabbits, mosquitos, fleas, of the myxoma virus, the weather and so many other factors.

Rabbit vaccination The recent launch of a combination RHVD and myxomatosis vaccine has made life a little easier for rabbit and rabbit owner. It means one, perhaps two fewer visit(s) to the vet and there is no risk,

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for the vet, associated with the self-injection of mineral oil. Onset of immunity is said to occur within three weeks of vaccination and lasts 12 months, representing a significant advance over the previous product. It is recommended vaccination be programmed before the summer peak in insect activity and viral transmission. Previously the vaccine used in the UK made use of the Shope fibroma virus that was known to provide good cross-protection. The new vaccine is different and makes use of a novel approach to the disablement of the myxomatosis virus. This attenuated virus also has the ability to protect against RHVD. This represents an impressive technical leap forward. The value of annual vaccination is not in doubt, but how does the network of veterinary practices, pharmaceutical industry representatives and members of the pet trade, animal care industry and society influence rabbit vaccination? I suspect many rabbits never see a vet. It could be argued veterinary practice and pet sales are revenue-driven and animal welfare is a secondary priority. Vaccines and drugs sell better than education, pellets sell better than hay and grass and so on. Currently, vaccination is coupled to an annual health check and, in my view, there is little opportunity to properly address the various concerns that continue to impact on rabbit welfare. We only have to consider the superior welfare of rabbits living in less urbanised parts of the world, where they are afforded more space and a diet better suited to their needs, to realise that we are failing rabbits in this country. Rabbit welfare in the UK and owner understanding of the needs of rabbits is, sadly, generally poor (Edgar and Mullan, 2011) and I believe there has been a surprising lack of initiatives to address this.

Radical suggestion My following radical suggestion could address both the uptake of vaccines and the welfare of rabbits across the UK. Vaccination could be made available, either free or at cost price, to all new rabbits. This might involve devolving this duty to veterinary nurses or some other suitably qualified person. Such practices are common in human medicine across the world, where vaccine uptake rather than profit is the true priority. To really improve welfare, this initiative should be tied in to a requirement that owners undertake an approved course on rabbit husbandry, nutrition, handling and health care. Attendance could be made mandatory and understanding assessed prior to vaccination. Veterinary nurses would be very well-placed and qualified to undertake this and it would provide them with a valuable opportunity to engage with communities, develop their teaching skills and promote good practice. Veterinary practices would, in turn, pick up more follow-up work through the responsible provision of advice on neutering, ongoing health care and future vaccinations.

Conclusion

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The new vaccine will transform the way we vaccinate rabbits and will benefit those who can afford to pay for it. It is up to vets and wider society to decide how much further they wish to push these changes. We need to rethink how rabbit welfare is promoted in this country and how we can better reach out to the many rabbits we fail to reach. We also need to rethink the concept of practice – of veterinary practice, of rabbit keeping as a practice and of various other “practices” we unwittingly are affected by and affect. This includes the “practice” of the myxoma virus that has given rise to myxomatosis.

Footnote

1. There are wide-ranging views about what reality consists of (ontology) and how we can come to know about any such realities (our epistemology – or theory of knowledge). Each individual will have his or her own way of thinking about such questions (the nature of reality and the nature of knowledge) and it is useful to consciously reflect on how we relate to the world, for it is a truly interesting subject of reflection – am I a realist? To what extent am I a positivist? How much of what is real constructed?

References and further reading Allan R M (1956). A study of the populations of the rabbit flea Spilopsyllus cuniculi (dale) on the wild rabbit (Oryctolagus cuniculus) in the north-east of Scotland, Proceedings of the Royal Entomological Society of London, Series A, General Entomology 31: 145-52. Australian Academy of Sciences (no date). Interviews with Australian scientists: Professor Frank Fenner (1914-2010). Retrieved July 28, 2013 from: http://science.org.au/scientists/interviews/f/ff.html Bartrip P W J (2008). Myxomatosis in 1950s Britain, Twentieth Century British History 19(1): 83-105. doi: 10.1093/tcbh/hwm016 Bartrip P W J (2009). The arrival, spread and impact of myxomatosis in Scotland during the 1950s. The Scottish Historical Review 88(1): 134–153. doi: 10.3366/E0036924109000602 Bartrip P W J (2010). Changing attitudes to risk. Managing myxomatosis in 20th century Britain. In B M Hutter (ed) Anticipating Risks and Organising Risk Regulation. Cambridge University Press, Cambridge: 68-89. Bennett J (2005). The agency of assemblages and the North American blackout, Public Culture 17(3): 445. Canguilhem G (2012). Writings on Medicine. Fordham University Press. Cooke B (2008). Managing the European rabbit: converging interests between Australian research for rabbit control and European research for their conservation. In Alves P D P C, Ferrand P D N and Hackländer P D K (eds), Lagomorph Biology. Springer Berlin Heidelberg: 317-326.

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Edgar J L and Mullan S M (2011). Knowledge and attitudes of 52 UK pet rabbit owners at the point of sale, Veterinary Record 168(13): 353. Fenner F (1983). The Florey Lecture, 1983: biological control, as exemplified by smallpox eradication and myxomatosis, Proceedings of the Royal Society of London. Series B. Biological Sciences 218(1,212): 259-285. doi: 10.1098/rspb.1983.0039 Fenner F and Ratcliffe F (2009). Myxomatosis. Cambridge University Press, Cambridge. Ferrer M and Negro J J (2004). The near extinction of two large European predators: super specialists pay a price, Conservation Biology 18(2): 344-349. Fioretti G (1996). A concept of complexity for the social sciences, IIASA discussion paper. Kauffman S (1995). At Home in the Universe: The Search for the Laws of Self-organization and Complexity. Oxford University Press, Oxford. Kerr P J and Best S M (1998). Myxoma virus in rabbits, Rev Sc Tech 17(1): 256-268. Latour B (1988). The Pasteurization of France (MA). Harvard University Press, Cambridge. Law J (2009). Actor network theory and material semiotics. In Turner B S (ed) The New Blackwell Companion to Social Theory. John Wiley and Sons, Chichester, UK. Mol A (2002). The Body Multiple: Ontology in Medical Practice. Duke University Press, Durham, NC. Nordenfelt L (2006). Animal and Human Health and Welfare: A Comparative Philosophical Analysis. CABI, Wallingford, Oxfordshire, UK. Sumption K J and Flowerdew J R (1985). The ecological effects of the decline in rabbits (Oryctolagus cuniculus L) due to myxomatosis, Mammal Review 15(4): 151-186. doi: 10.1111/j.1365-2907.1985.tb00396.x Thompson C (2002). When elephants stand for competing models of nature. In Law J and Mol A (eds) Complexity in Science, Technology and Medicine. Duke University Press, Durham, NC. Wilson M E (1995). Travel and the emergence of infectious diseases, Emerging Infectious Diseases 1(2): 39-46.

Myxomatosis Aetiology A viral disease caused by the myxoma virus, a member of the Poxviridae. Transmission The virus can be transmitted via biting insects including both mosquitos and fleas. There is, however, no replication of the virus within the vector. Rabbitto-rabbit transmission has also been reported and fomites, including straw from affected farms, may be implicated.

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Epidemiology Environmental conditions that promote insect feeding activity, especially of Culicidae and Aedes mosquitoes, are likely to increase transmission. The flea is a good reservoir, as its life cycle is longer than that of mosquitoes, with fleas feeding for as long as a year compared to three to four weeks for a mosquito. Overwintering fleas can act as a reservoir of infection early in the subsequent year. Host susceptibility and the virulence of the viral strain have had significant effects on the epidemiology and impact of the disease. Very young rabbits are particularly susceptible and will die unless they have good passive immunity. Outdoor rabbits are also more vulnerable due to their greater exposure to a range of factors, including biting insects and wild rabbits. Indoor rabbits are not completely safe as they are vulnerable to mosquito bites, hitch-hiking rabbit fleas coming into the home on cats and dogs, and to virus on contaminated straw. Clinical signs In the natural host (Sylvilagus brasiliensis), the myxoma virus causes a benign cutaneous fibroma (Kerr and Best, 1998). In the European rabbit (Oryctolagus cuniculus), however, it causes considerable morbidity and mortality, producing what we call “myxomatosis”. Typical clinical signs may start with runny eyes that could be confused with a conjunctivitis. Swollen genitals often allow myxomatosis to be distinguished from a conjunctivitis. Signs progress and worsen; the eyes become swollen and closed and there is typically a heavy mucopurulent discharge from the eyes and nose. Nodules may appear on the ears, head, body and limbs, at the site of infection; these may become congested and necrotic. Two atypical forms of myxomatosis are also reported. The first produces respiratory signs (following aerosol infection), the second nodular skin changes. Vaccination A yearly subcutaneous vaccine protecting against both myxomatosis and RHVD was launched in 2012. Previous vaccination with a myxomatosis vaccine could potentially interfere with protection against RHVD; in view of this, it may be wiser to continue with the previous vaccine regimen in older rabbits. See also www.future-of-vaccination.co.uk/myxomatosis-rabbit-disease.asp

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Classic myxomatosis starts with runny eyes and in the very early stages can be confused with other causes of conjunctivitis. It rapidly progresses to a severe conjunctivitis that causes blindness and is accompanied by lumpy (nodular) swellings on the head, plus lumps on the body. Excessive amounts of thick pus discharges from the nose and swollen eyes (which are often sealed shut).

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Classic myxomatosis starts with runny eyes and in the very early stages can be confused with other causes of conjunctivitis. It rapidly progresses to a severe conjunctivitis that causes blindness and is accompanied by lumpy (nodular) swellings on the head, plus lumps on the body. Excessive amounts of thick pus discharges from the nose and swollen eyes (which are often sealed shut). Photo: Rae Todd, RWAF

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Of myxomatosis, the author asks: “How did such weapons come to be launched against the rabbit?”

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