Australia's War Against Rabbits: The Story of Rabbit Haemorrhagic Disease

By Brian Douglas Cooke

The management of wild rabbits is a vexing problem worldwide. In countries such as Australia and New Zealand, wild rabbits are regarded as serious pests to agriculture and the environment, while in many European countries they are considered an important hunting resource, and are a cornerstone species in Mediterranean ecosystems, modifying habitats and supporting important predator populations such as the Iberian lynx. The introduction of two viral diseases, myxomatosis and rabbit haemorrhagic disease, as biological control agents in Australia has been met favourably, yet their spread in southern Europe threatens natural rabbit populations. Despite this, scientists with very different goals still work together with a common interest in understanding rabbit biology and epidemiology.

Australia's War Against Rabbits uses rabbit haemorrhagic disease as an important case study in understanding how animal populations adapt to diseases, caused in this case by an RNA virus. Looking at rabbit haemorrhagic disease (RHD) in an ecological framework enables insights into both virus and rabbit biology that are relevant for understanding other emerging diseases of importance to humans.

This book provides up-to-date information on recent advances in areas ranging from virus structure and disease mechanics through to the sociological implications of using biological control agents and the benefits to the economy and biodiversity. It is a compelling read for wildlife disease researchers, wildlife managers, rabbit biologists, people working in the public health and education sectors, and landholders and farmers with experience or interest in RHD.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: May 29, 2014
• ISBN: 9781486301751

Book preview

Prologue

Bloody instructions, which, being taught, return

To plague th’inventor; this even-handed justice

Commends the ingredients of our poisoned chalice

To our own lips.

William Shakespeare, Macbeth, Act 1

Mao Li Lin turned the dead rabbit over. She had commented only the morning before how healthy it seemed as she watched it investigate then avidly nibble the cabbage leaves thrown into the hutch. Now it lay stretched out on the cage floor; still warm, head thrown back, jaundiced eyes unseeing. Even so, the nestlings the rabbit had been suckling seemed active enough. This prompted Li Lin to gently transfer them to the nest of another rabbit feeding a small litter of about the same age. ‘What should I do with the carcase?’ she thought, unaware that it was the first of many deaths to come.

The emergence in 1984 of a new, highly lethal rabbit disease in China was destined to be controversial. The first reports of the disease involved a few angora stud rabbits recently imported from Eastern Germany. Soon it was spreading quickly, from rabbitry to rabbitry. It struck not only where households kept a few rabbits in small crowded courtyards, but also within large rabbit farms. The toll quickly mounted to hundreds of rabbits, then thousands, then millions (Liu et al. 1984).

China dominated international trade in rabbit meat, exporting over 50 000 tonnes annually. But slowness in pinpointing the cause of the disease, inadequate animal hygiene measures and a lack of international notification inevitably meant that contaminated rabbit meat was exported. The Republic of Korea was the next country where the disease was reported, and a Chinese shipment of rabbit meat to Mexico City triggered an outbreak among domestic rabbits there (Gregg et al. 1991).

When the disease appeared in more distant Italy in 1985 it was initially referred to as ‘malattia X’ or ‘disease X’ for lack of understanding that it was the same scourge as rabbit haemorrhagic ‘pneumonia’ in China. As it was found in more and more countries across Europe, the official name became rabbit haemorrhagic disease, usually abbreviated to RHD. By 1990 a virus was identified as the cause; it was referred to as RHDV.

As its name implies, RHD is confined to rabbits, and the European rabbit Oryctolagus cuniculus at that. The virus is not known to cause disease in any other species, even other closely related rabbits and hares. Perhaps because of this, and because it was handled by veterinarians, the initial outbreak and spread was largely overlooked when it came to analysing and understanding newly emerging diseases. There has been much more intense interest in new diseases that have transferred from animals to humans, such as H5N1 avian influenza and severe acute respiratory syndrome (SARS) in 2002. In many ways, experiences with RHD might have provided a preview of the difficulties of east–west communication over newly emerging diseases. Unfortunately, it seems, attention focuses on such issues only when spread into humans brings matters to a personal level. Indeed, RHD did not fit the expected model at all well. Its emergence was not linked to live animal markets, the so-called ‘wet markets’ in China and South-east Asia, which were then thought to be a cradle of new diseases transmissible to humans. Quite to the contrary, Chinese authorities firmly believed that the initial outbreak, so closely linked to rabbits from East Germany, indicated a very different origin.

Controversy over the causative virus, first thought to be a Parvovirus, then a Picornavirus, but eventually shown to be a Calicivirus, continued until its detailed structure was adequately described. Caliciviruses are so-named because they have 32 cup-like depressions on their outer surface. The Latin calyx, or in its plural form calices, is a readily recognised precursor of chalice in not-so-modern-day English.

Meanwhile, the story became even more complex and took several new twists and turns. Rabbits are not only valuable because they are farmed for meat and fur, but they are also an important natural wildlife species, reputed to be a keystone species in the Mediterranean shrublands of south-western Europe. Their importance lies not only in their role as landscape engineers, in maintaining vegetation and landscapes through their nibbling and digging, but also in being a major prey of endangered iconic predators such as the imperial eagle and Iberian lynx.

These same characteristics also make wild rabbits major pests where they have been introduced to become widely established and abundant. They destroy native vegetation that is not adapted to withstand their grazing and they compete with native animals and with livestock for food. Southern Australia, New Zealand, Central Chile and parts of Argentina are most affected, but increasingly it is understood that rabbits also cause significant damage to unique vegetation in the Azores and Canary Islands.

Australia’s problems with rabbits had been so desperate that the viral disease myxomatosis had been introduced in 1950 to address the problem. It had made an enormous difference by reducing rabbits to a tiny fraction of their prior abundance but, over a decade or two, the myxoma virus had attenuated into less virulent strains while rabbits had developed genetic resistance that could be passed on to their all-too-numerous progeny. As a result, rabbits were becoming a conspicuous pest once more. This meant that Australian scientists were on the lookout for ways to re-kindle the effectiveness of myxomatosis or find an additional biological control agent.

One of the projects that seemed promising at the time was the introduction of additional insects that might better transmit myxomatosis from rabbit to rabbit. This was seen as especially important for arid inland Australia, where the normal mosquito vectors of myxomatosis were scarce. That had involved me in looking for arid-adapted rabbit fleas in Spain’s dry south-eastern provinces to add to the mix of virus vectors available. By sheer chance, this led to my first encounter with RHD in wild rabbits, and from that experience sprang a new idea. This acute disease, plainly a pestilence in Europe, could be used in another way. It was potentially a new agent for the biological control of wild rabbits in Australia.

So while Europe sought ways to suppress the disease, the virus was actively promoted for use in Australia – although not without major national and international controversies as events unfolded. The idea of introducing a virus to kill wild rabbits in Australia was not always accepted by observers in other countries and often they said so, bluntly and clearly. For their part, proponents of the use of RHDV in Australia argued their case equally strongly, and there could have been no clearer demonstration that, as far as this particular virus was concerned, one country’s threat could be another’s remedy.

The escape of the virus from an island quarantine compound during testing and the illegal smuggling of the virus into New Zealand heightened the controversy, and those events were feasted upon by the press for weeks. Indeed, some journalists dined out for some time on the mix of hard news and tall stories generated by the spread of the virus.

International debate by no means ended at that point either. Further controversy arose when scientists genetically engineered new recombinant viruses that might be used for managing rabbits. Spanish scientists inserted genetic material that coded for the coat protein of RHDV into an attenuated myxoma virus and showed that this might be used not only to protect rabbits against severe myxomatosis but also against rabbit haemorrhagic disease. Added to this, the recombinant virus was reportedly able to spread from rabbit to rabbit as a live vaccine. Consequently, by catching and inoculating a few wild rabbits, it might be possible to immunise whole rabbit populations against both diseases. Clearly, such a strategy might help conserve rabbits in south-western Europe, but the inadvertent release of the same recombinant virus in Australia or New Zealand could catastrophically undo the investments and benefits of hard-won advances in rabbit control.

Figure 1. Author examining a wild rabbit at CSIRO Gungahlin. (Photo: Alex Bagnara)

RHDV has been a pathway to a parallel research revolution. Away from the hullabaloo, some scientists began to explore other uses for the virus. By using unique properties of the virus coat protein, new ways of delivering vaccines or gene treatments for animals and possibly for humans were being discovered. If successful, this work could produce major medical advances.

Despite all controversy, it remains remarkable that researchers have largely collaborated and exchanged scientific ideas freely. Most have sought to fully understand the details of the virus and the disease it causes, irrespective of their contrasting goals. It has not mattered whether they wished to suppress it as an unwanted disease or use it as a biological control agent. Figuratively, the ‘chalice’ has been sought by many despite its contents dealing, from different points of view, either medicine or venom. Every researcher has considered the virus in a unique way, interpreting what they saw differently. In that sense, each viewpoint reflects a different facet of this complex study.

Put together, the picture is cohesive, and within the space of 30 years an unknown, newly emergent disease has become one of the best researched animal diseases. It has also generated important ideas and applications that go far beyond its importance as a scourge of rabbits; it has remarkably contributed to other disciplines such as medicine, evolutionary biology and conservation.

It is such detail that makes this story essential background for understanding the complexity of other emerging diseases, each with its own attendant social, economic and environmental implications. Even more, it is also a story about people who are curious about the world they live in and would like to know more about how things work and where things are going in the future. The fortunes of humans, their cultures and their interactions with rabbits and viruses are a recurrent and inescapable theme in this book.

1

Almería awakening

Man’s mind, once stretched by a new idea, never regains its original dimensions.

Oliver Wendell Holmes

Don Antonio Gil carefully made his way up over the broken rocks, a loaded but open shotgun cradled across his arm. He threaded his way between the esparto tussocks atop the mesa, watching for rabbits to bolt from cover. It was not yet mid-morning yet the intense Almería sun was already whitening the sky and bleaching the landscape. The grey, half crystalline, half plaster-like soil was beginning to shimmer. Away to the south-east, the leaden-blue Mediterranean Sea was calm and hazy; the scattered fishing villages along its beaches were barely discernible while the rounded headland of Cabo de Gata was just an obscure shape where the horizon should have been.

Beads of perspiration shone on Don Antonio’s deep-tanned forehead and wet the dark curls of his hair. Sweat darkened the seams of his meticulously patched suit-coat. That dark blue coat was a symbol of his status as the most important and toughest game-guard in the area, and was seldom shed even on the hottest days. Symbol or not, the coat inevitably took a lot of punishment from the spiny shrubs. This was especially so when all attention was concentrated on the quarry. Don Antonio had several large hunting reserves to look after, mainly for absentee landlords, and apart from controlling rabbit predators such as foxes and mongooses he also had to be one step ahead of poachers – furtivos he called them – who came from the nearby villages. They watched his daily movements and seized opportunities in his absence to use their ferrets, nets and snares to catch rabbits. Care was needed, however. It was rumoured that, if Don Antonio chanced upon them, a cartridge load of saltpetre aimed at the rump of a scurrying victim was a strong possibility.

That day Don Antonio should have had an easier task. Dr Ramon Soriguer and I had arranged to meet him on a hunting reserve east of El Alquian to collect some rabbits. We were to complete the last of a series of forays, made every few months across a year, to obtain rabbit blood samples, ticks and fleas. As on previous occasions, we expected that Don Antonio would stride ahead, bagging a rabbit from time to time, while we struggled along after him laden with blood sampling kits, alcohol-filled sample bottles, flea combs and a wide-mouthed vacuum flask containing ice. Worst of all was a cumbersome white plastic box into which freshly shot rabbits were quickly dropped to prevent their parasites escaping before we could collect them.

Unexpectedly, as if to make things more difficult, Don Antonio insisted on heading for the high ground to begin shooting. Previously, we simply moved off along the flat, dry river bed, or rambla, where we parked the cars. He was right. Half a dozen rabbits later, he explained that shooting on the high ground had been the only option; a mysterious disease had recently killed many, many rabbits in areas where they had previously been so abundant. Hundreds had died along the ramblas far below and so we would have little luck there. Indeed, we would go back to our cars through such an area to see what he meant.

When we eventually began slipping and sliding down into the rocky gullies leading back to the dry river bed we began to encounter one rabbit carcase after another lying in the open. So many rabbits had died that the scavenging birds and foxes were satiated. They had left most rabbit carcases untouched. Don Antonio confided that the disease also caused the rabbits to ‘fight’. He had heard several rabbits squealing, as they sometimes did when fighting, but the reason was unclear. Others that he disturbed had run for 20 or 30 m before unexpectedly collapsing and rolling to a sprawling, lifeless stop.

Ramon and I picked up and carefully examined the remains of several rabbits, dry and almost mummified by the hot air. None showed outward signs of disease but many lay on their sides with forelegs curiously extended and their heads thrown back sharply. Was it a particularly acute form of myxomatosis, the disease most likely to cause such high mortality? We spoke in English while we considered this possibility, but Don Antonio understood the essence of what was being said and growled emphatically in the background: ‘No es la mixomatosis!’ – ‘It’s not myxomatosis!’

Indeed, Antonio Gil was again correct. It certainly wasn’t myxomatosis. Two weeks later I was back in Australia and had begun gleaning reports of a new rabbit disease that had reportedly spread from China and was causing the loss of tens of thousands of domestic rabbits in Italy. Almost simultaneously, Ramon sent a telex message to tell me that veterinary reports on wild rabbits found dead between Almería and Malaga had confirmed an outbreak of ‘la enfermedad hemorrhagica virica’ or viral haemorrhagic disease, as it was then called.

In retrospect, that hot morning in 1988 in the rough, dry hills and arroyos of Almería was pivotal. It led to the first clear evidence that rabbit haemorrhagic disease or RHD was well established in wild rabbits in Europe and it initiated concerns in Spain, Portugal and France that wild rabbits were under threat from another lethal disease to add to the woes caused by myxomatosis. Simultaneously it sowed the seed of a further idea. A virus capable of devastating wild rabbits in arid Spain was well worth investigating for use against the burgeoning myxomatosis-resistant rabbit populations of inland Australia.

The flood gates were slowly but irreversibly opening. I was about to be swallowed up in a tide that would carry me along and dictate the course I followed for the next two decades or more.

2

The Coffee Brothers

Good communication is just as stimulating as black coffee, and just as hard to sleep after.

Anne Morrow Lindbergh, Gift from the sea, 1955

Rabbit haemorrhagic disease was first officially recognised in Europe when a new disease of domestic rabbits was demonstrated to be spreading rapidly through Italy in 1988. Although it clearly differed from other common rabbit diseases, it was initially called ‘malattia X’ or ‘disease X’ because there was considerable uncertainty about its cause. A plethora of possibilities and opinions confronted those trying to understand this mysterious malady and it took some time to sort things out.

Although rabbit meat was widely produced in Italy for the domestic market, rising demand had seen a shortfall in supply. This had been made up by importing both live rabbits and rabbit meat. These products came mostly from Central and Eastern Europe, but also on a smaller scale from the People’s Republic of China. Wherever virulent RHDV originated, be it in China, or in East Germany as the Chinese insisted (Liu et al. 1984), Italy seems to have been an inevitable early recipient and was the first of many European countries where the disease was eventually encountered.

It was not until several years later that Dr Norbert Nowotny and colleagues suggested that virus samples from Italy were genetically most similar to those from Eastern and Central Europe while the viruses subsequently collected in Spain and parts of France had greater affinity with those from China, Korea and Mexico (Nowotny et al. 1999). The rapid confirmation of the disease in the USSR, Czechoslovakia, Poland and Hungary soon after its appearance in Italy also heightened the possibility that Eastern Europe was a possible transit route, if not a source of the disease.

The best evidence available only confirms that the disease was present in the Ukraine and eastern Slovakia in 1987 (Rodak et al. 1991) and that it spread westwards across the Czech Republic in a little more than 12 months. It spread into Silesia and the Krakow regions of Poland in 1988 (Górski et al. 1994), resulting in the deaths of over 27 000 domestic rabbits. Whether that spread had emanated from the Ukraine is still unclear and, given the discontent and social turmoil within the Soviet Union at that time, we may never know. Moves towards more open government through the policies of glasnost and perestroika were certainly underway at the time but were suddenly reduced to minor importance in April 1986, when the catastrophic Chernobyl nuclear reactor meltdown completely dominated world news. With high-level attempts being made to cover up a nuclear reactor disaster, the simultaneous spread of a new disease among domestic rabbits would hardly have raised an official eyebrow.

Even so, the unfolding of events in Chernobyl did inevitably colour the emergence of the new disease. In Italy, over 300 rabbit farms recorded major losses to malattia X just as radioactive smoke from the burning nuclear reactor began to tint western European skies. As radioactive particles settled on Europe’s fields, radiation poisoning was briefly suspected. Italian newspapers were quick to exploit the possibility and an experimental trial was run in which radio-contaminated hay was fed to rabbits to see if a disease similar to malattia X could be induced.

The lack of positive results from those experiments, along with evidence that the new disease had been present well before the Chernobyl disaster, quickly ruled out the idea that radioactivity was a direct cause of deaths. Nonetheless, the prospect of some other unknown poison or contaminant remained. This was especially so because the liver degeneration seen in sick rabbits was similar to that caused by toxins or even metabolic disorders. Things clearly needed careful handling to allay fears among an increasingly suspicious public. The problem was not quickly resolved, however, because further scientific irregularities arose. Tissues from dead rabbits, ground finely and filtered to remove broken cells and bacteria, should have been infective if a virus was present. The tests didn’t always produce clear-cut results. In some cases the inoculated rabbits became infected and quickly died, while in others the inoculated rabbits remained healthy and showed no apparent response at all.

There were many contributors to these initial investigations. Names such as Cancellotti, Renzi, Marcato, Benazzi and others loom large, but in terms of providing insights and research methods to help understand the whole spectrum of virus and disease behaviour – from rabbit farms to international issues – none surpassed the work of Dr Lorenzo Capucci and Dr Antonio Lavazza and their colleagues from the Istituto Zooprofilattico Sperimentale della Lombardia e del’Emilia-Romagna (IZSLER) in Brescia, Italy.

Capucci and Lavazza have now worked closely together for over two decades and it was inevitable, with names so linked to a famous style and equally famous brand of Italian coffee, that they would become affectionately known as the ‘Coffee Brothers’. But other brands of coffee are important too, and they are quick to point out that their work has always depended on a wider ‘brotherhood’. Other individuals from their work team are included in this larger group as well as other units of the Istituti Zooprofilattici, other European institutes, and colleagues in the wider world.

Lavazza, a veterinarian specialising in electron microscopy, searched hard for evidence of virus particles in rabbit tissues; but even with a microscope capable magnifying over 40 000 times he initially found it impossible to detect a virus. The essential breakthrough was made when the specialised techniques needed to make the particles visible were developed. In particular, serum from rabbits that had recovered from the disease was used to clump together complexes of virus particles and make them more readily detectable under the microscope. Lavazza was then able to collaborate closely with researchers in University of Bologna and other institutes by producing photographs of the clusters of virus particles in rabbit liver cells to confirm that a virus was the likely disease-causing agent. He also participated further afield, attending the world rabbit conference in Budapest in 1988 where the recent recognition of the new disease in rabbits in Hungary was the dominant interest. At the same conference, presentations given by invited Chinese scientists who studied the virus thought to cause ‘rabbit haemorrhagic pneumonia’ were particularly important in confirming that everyone was dealing with the same disease.

Figure 2: Electron micrograph of RHDV particles showing cup-shaped surface depressions. (Image: Antonio Lavazza)

Taking things even further, Lavazza quickly saw the link between RHD and a disease of European hares, called European brown hare syndrome, or EBHS. The hare disease also caused high mortality associated with haemorrhages in internal organs and liver damage. Lavazza is credited with being the first to show that viral particles in hares suffering from EBHS were similar to those in rabbits with rabbit haemorrhagic disease. This paved the way to an understanding that these rabbit and hare viruses, now collectively called lagoviruses, belonged to a separate genus within the Caliciviridae family.

Lorenzo Capucci, the son of a mining engineer, had a difficult school-age transition following his father’s premature death. His mother, who originally came from northern Italy, took the family from the semi-rural life of Sardinia back to Brescia, and Lorenzo had to work extremely hard to catch up in the more rigorous education system. He successfully made that transition to become a scientist of international repute, but he never lost his love for exploring the wilder rural parts of Italy and being with everyday people.

When Lavazza’s work showed that RHDV and EBHSV were closely related viruses, the scientists set out to investigate things further by closely investigating the immunological responses of hares and rabbits to these viruses. Effectively, the immune systems of rabbits and hares, like all mammals, produce a vast array of individual cells uniquely capable of identifying almost any new protein, a string of amino acids, that is likely to appear when a new virus or bacterium causes an infection. Cells that respond to these foreign protein sequences proliferate and stimulate the production of antibodies and other defences to help fight off the infection. In the laboratory, using immunised mice, it is possible to derive specialised cell lines stimulated by individual RHDV proteins and peptides and subsequently produce enough specific antibodies – called monoclonal antibodies – for experimental and diagnostic use. In the case of RHDV and EBHSV, Capucci and his colleagues were able to produce a dozen or so mouse monoclonal antibodies that interacted with fragments of different virus proteins and these provided a useful way of comparing the two viruses (Capucci et al. 1991).

The outer shells of these two related viruses are generally very different, so some antibodies that recognise RHDV bind very poorly to EBHSV and vice versa, but deeper inside the two viruses, where basic functions are similar, the virus proteins are more similar and are said to be well conserved in terms of their likeness and function. The antibodies that bind to RHDV protein from within these inner domains will often bind well to the equivalent proteins of EHBSV. Consequently, based on the reactivity of different monoclonal antibodies, it was possible to say that the two viruses differed markedly in some respects but were closely related in others. Indeed, once the genetic codes of both viruses were fully described, it was confirmed that the rabbit and hare viruses showed approximately 70% genetic relatedness, although differences were much greater in some sections of their genetic coding than others (Wirblich et al. 1994).

Using some of these highly specific monoclonal antibodies, Capucci and his team went on to design a system of tests for measuring the amount of virus in rabbit and hare tissues and the amount of antibody in the blood of those animals that survived the disease (Barbieri et al. 1996). These tests are commonly referred to as ELISAs, for ‘enzyme-linked immuno-sorbent assays’. The array of ELISAs that Capucci and colleagues produced included some that enabled the quantity or ‘titres’ of antibodies of three different immunoglobulin types to be broadly estimated.

The antibody titres are based on the number of times rabbit serum can be diluted until the antibodies become only weakly detectable. A very low titre might be, say, a 1:40 dilution, whereas high titres might be detectable at 1:40 960 dilutions – achieved by making many successive dilutions of the original serum.

Capucci and his colleagues also knew that different immunoglobulin types of antibodies were produced during the infection process. Antibodies of immunoglobulin-M, immunoglobulin-A and immunoglobulin-G (IgM, IgA and IgG) are produced at different times following infection and each of these persists for different periods of time. As a consequence, their initial increases and subsequent declines are often good indicators of the time elapsed since surviving rabbits have recovered from the disease. By using IgM, IgA or IgG ELISAs to follow the rise and fall of antibody titres, it is possible to confirm that one rabbit is recovering from infection while another rabbit might show evidence of having been recently re-exposed to the virus.

The titres of IgM, IgA and IgG are particularly useful when it comes to understanding whether or not young rabbits have been infected with RHD. Many young rabbits acquire antibodies passed across the placenta from their mothers before they are born, and potentially these might be confused with antibodies resulting from infection. However, since the antibodies of maternal origin are almost exclusively IgG, any young rabbits that also carry antibodies of IgM or IgA can be taken as being RHDV recoveries.

Largely as a result of their pioneering work, in 1991 the Brescia laboratory was asked by the World Organization of Animal Health (then known as the International Office of Epizootology or OIE) to take on the role of the world reference laboratory for RHD. This in turn led to increasing international collaboration and in the long run to a very special scientific collaboration with Australian researchers. In the last decade or so, Antonio Lavazza and Lorenzo Capucci’s names have appeared among the authors of many publications about RHD and EBHS that have been produced by researchers from many different countries.

Once the pace of initial investigations slowed, Dr Capucci eventually returned to ask why some rabbits in earlier confusing tests had developed RHD after inoculation with cadavers’ tissues while others had shown no ill effects. His new diagnostic tools and careful experiments helped him to show that, circulating silently on many domestic rabbit farms, there was a third lagovirus that caused no observable disease. Capucci called this non-pathogenic virus ‘rabbit calicivirus’ or RCV, and with his research team he was able to isolate it and describe many of its characteristics (Capucci et al. 1996). Rabbits infected by RCV were effectively immunised against highly virulent RHDV. This meant that on rabbit farms where management practices had unconsciously allowed the non-pathogenic virus to circulate, RHD was unlikely to break out. Later, Capucci was to add a further highly virulent virus variant, RHDVa, to his list of discoveries (Capucci et al. 1998).

As Lavazza had done earlier, Capucci’s description of two additional forms of lagovirus again expanded the genus and in doing so showed that virulent RHDV, by then spreading worldwide, had not appeared mysteriously but had almost certainly originated from a family of viruses associated with rabbits and hares in Europe. Nonetheless, its time in China seemed to have polished its lethal characteristics so that, on arrival in Western Europe, it effectively behaved like a new disease.

Although Capucci and Lavazza were highly successful in their initial work with RHD, Capucci’s work with lagovirus was suddenly heavily curtailed after 2001. It was almost inevitable that, as head of the diagnostic laboratory, he was expected to take on new lines of research in response to the European ‘mad cow disease’ (bovine spongiform encephalopathy or BSE) crisis. This had developed, principally in Britain, when people who had eaten contaminated beef developed a fatal variant of Creutzfeldt-Jacob disease, and there was increasing evidence the disease could spread to other countries among residents who had spent time in Britain or consumed British beef.

By 2005 Capucci was designated as head of the Molecular Biology Department of IZSLER. However, in 2008, once a solution had been found for the mad cow disease crisis, Lorenzo found it increasingly difficult to reconcile administrative and research directives, finally resigning from this position to once again resume research work on the viruses of lagomorphs.

Creditably, throughout the time that Lorenzo was heavily preoccupied by research into mad cow disease, he maintained a high interest in RHD and with Antonio Lavazza was always available to give advice on technical questions on RHD and its diagnosis. Certainly, from an Australian perspective they supplied the practical and intellectual support necessary to establish a sound understanding of the epidemiology of RHD in the field. They continue to be closely involved in Australian RHD research.

3

A new disease

A plague o’ both your houses!

William Shakespeare, Romeo and Juliet, Act 3

With RHD spreading on several fronts across the globe, it was essential to know more about the virus that caused it and how it spread. Work in China and the investigation of a Mexican outbreak by scientists from the United States of America at first suggested the new disease was caused by a parvovirus. Its true identity was independently, but almost simultaneously, established by two separate groups of European scientists. The teams, Drs Parra and Prieto at the University of Oviedo in Spain, and Drs Ohlinger, Thiel and Meyer at the Federal Research Centre for Virus Diseases of Animals, Tübingen, in Germany, separately confirmed that the world was dealing with a previously undescribed calicivirus (Ohlinger et al. 1991; Parra and Prieto 1990).

Precisely how the virus spread from rabbit to rabbit was unknown, but within the domestic rabbit industry the spread was linked to poor hygiene. This included inadequate quarantine after taking stud rabbits to shows and poor cleaning of cages taken from farm to farm while collecting rabbits to be taken to abattoirs. Even the movement of domestic cats in and out of barns where rabbits were kept was one suggested possibility, although transmission via cats was not verified. Transmission between domestic and wild rabbits also seemed inevitable: waste from small rabbit farms was commonly dumped in the fields, while food for hutch rabbits could be cheaply supplemented with grasses and thistles collected from roadsides where wild rabbits lived. The disease even spread quickly on well maintained rabbit farms, especially where cages were closely spaced. It was soon realised that aerosol transmission – virus in tiny water droplets breathed out by sick