|
Introducing
a new virus for biological control
Jean Macnamara must be given the credit for finally getting myxomatosis tested in Australia. She had graduated in medicine in Melbourne in 1922, in the same class as Macfarlane Burnet, and later she was to help him on the epidemiological side of studies of psittacosis and poliomyelitis. In 1931 she received a Rockefeller Foundation grant to travel around the world to study the treatment of poliomyelitis. Because of her association with Burnet, she also visited several virus laboratories, including that of Richard Shope at the Princeton laboratories of the Rockefeller Institute. A few years earlier Shope had isolated fibroma virus from cottontail rabbits in New Jersey. When she visited he was comparing this virus with myxoma virus, which was causing a lethal disease in colonies of European rabbits in California. He had just shown that his fibroma virus, which produced a localized lump, a fibroma, in both cottontail and European rabbits, was serologically related to myxoma virus, which was almost always lethal for European rabbits. Macnamara knew what a problem rabbits were in Australia, and she determined to get the myxoma virus. Shope gave her a sample, which she sent to her fiancée, who was working at the Walter and Eliza Hall Institute. However, on the instructions of Dr JHL Cumpston, the Director of Quarantine, it was destroyed on arrival. Nothing daunted, she went to London and obtained an interview with the Australian High Commissioner, former Prime Minister Viscount Stanley Bruce. As a result, she prepared a detailed letter setting out the virtues of the virus for rabbit control, which Bruce sent to Sir David Rivett, the Head of CSIR. Importation was once again refused by Cumpston, but in 1934 Rivett persuaded Sir Charles Martin to trial it in large enclosures of rabbits in Cambridge, where Martin had retired. The Brits were not as worried about exotic viruses as the Australians. After a trial in a large enclosure near Cambridge, Martin concluded that the virus was worth further trials in Australia. Lionel Bull, soon to be Chief of Animal Health of CSIR, was travelling around the world at the time and brought the virus back. Again Cumpston expressed his objections, saying, among other things that, “the introduction of a new virus will be associated with dangers at present unimaginable". However, he granted Bull permission to test it in domestic animals and in Australian wild animals and birds, none of which were susceptible to infection. Bull also showed, as had Aragao before him with cat fleas, that myxoma virus could be transmitted mechanically by mosquitoes. In 1937 Cumpston authorized field trials on Wardang Island, South Australia and these were begun at the end of the year. By January 1939 many rabbits had died but the population had renewed itself and the disease had died out. Rumours about the lethal virus spread among farmers, and they lobbied the Government to allow further trials. Reluctantly, Cumpston agreed to these, as long as they were far from human habitation. In 1942 field trials were commenced on three pastoral properties in inland South Australia, an area which had suffered a severe drought in the previous two years. Again, there were many deaths but the disease died out and the populations built up again. Because of the War, no further work was done until 1949, when Clunies Ross, new Chairman of CSIRO, told Francis Ratcliffe to make myxomatosis the first priority of the new Wildlife Survey Section. Jean Macnamara, now a Dame of the British Empire, took up the cudgels again, with critical letters to the rural and metropolitan press, chiding CSIRO for not doing trials in what she called “good country”. By early 1950 Ratcliffe had recruited enough staff (including Bunny Fennessy, John Calaby and Ken Myers) to start trials, but for various reasons these were delayed until May. The first trial was at Gunbower in north-central Victoria. In spite of a very dense population, the virus died out. In September 1950 further trials were initiated at four sites near the Murray River in eastern NSW and Victoria. Again, careful counts of live and diseased rabbits showed that although transmission continued for four generations, by the end of November the rabbit population had grown back to its original numbers and myxomatosis appeared to have died out. Ratcliffe let his staff, who had been in the field for several months, go home for Christmas. Then, late in December, came telephone calls that many sick rabbits were being seen at one of the release sites and also at Corowa Common, over ten miles away. In January 1951 dead and sick rabbits were seen along the Murray, the Lachlan, the Murrumbidgee and the Darling Rivers and by late March it had spread throughout the Murray-Darling Basin. I had returned to Australia in February 1950 as Professor of Microbiology at the John Curtin School and was working on mycobacterial diseases in the Hall Institute, where Burnet had lent the ANU two laboratories. I wanted to get back to virology, and myxomatosis presented a wonderful opportunity. According to Burnet’s diary, I told him of my intentions in February 1951 and immediately set about recruiting staff. The first appointments were Gwen Woodroofe and Ian Marshall, both of whom are here tonight and Kath Sutton, later to marry Ian, was a lab technician. We worked on myxomatosis from then until about 1965, in very close collaboration with scientists of CSIRO Wildlife. To get back to the outbreak. Although myxomatosis appeared to have disappeared during the winter, in October-November 1951 outbreaks occurred again throughout the Basin. For this reason, returning to my early comment on the title of this dinner, I believe that the naming of 2001 as the Golden Jubilee of Myxomatosis is justified, because this was the year of the first great spread and the demonstration that it would persist and recur when the vector mosquito population had built up again. I have been asked to compare the difficulties associated with the introduction of myxomatosis with the hurdles facing those anxious to introduce a new agent for the biological control of a vertebrate pest nowadays. What were the principal difficulties over the period 1918 to 1951, principally 1936-51? There were really only two barriers: first, the strong opposition of the Director-General of Health, Dr Cumpston, who was Chief Quarantine Officer and second, the absence of even a small group of field workers dedicated to the task of studying rabbits. At that time the general public were not consulted, although farmers who had heard of the disease pushed strongly for its use and when encephalitis occurred in the Murray Valley, the Mayor of Mildura challenged Burnet to inject himself with myxoma virus to show that it was harmless. Before comparing the
situation then with the situation now, it is instructive to look at the
experience with the introduction of rabbit haemorrhagic disease virus
(RHDV) in the 1990s. Brian Cooke, then of the South Australian Animal
and Plant Control Commission, had witnessed the first outbreak of a new
disease, rabbit haemorrhagic disease, in wild rabbits in Spain in July
1988, when he was looking for a heat-tolerant rabbit flea. On his return
he suggested to Brian Walker that RHDV might be useful in inland Australia. To initiate studies of RHDV, presentations were made by Brian Cooke to a meeting of the Council of Nature Conservation Ministers in July 1989, and Barry Jones, then Minister for Science, recommended that funding should be provided for further investigations. As a first step, Harvey Westbury from AAHL was sent to Europe and USA to obtain up-to-date information on the virus, and Brian Cooke, who was returning to Spain to finalize arrangements for the importation of the Spanish rabbit flea, was asked to make a preliminary study of the epidemiology of the disease. In July 1990 the meeting of the newly formed Australian and New Zealand Environment and Conservation Council considered the reports of Cooke and Westbury and voted $750,000 for a three-year laboratory investigation at AAHL. A comprehensive Working Party was set up to oversee the work, and in August 1991 the quarantine authority issued a permit for the importation of the virus to AAHL, where a small breeding colony of wild rabbits had been established. In August 1992 the Working Party, augmented by representatives of animal welfare societies, considered preliminary findings and planned the next steps, which included the obligation to increase public awareness of the proposal. In September 1993 a three-day workshop was held at AAHL, at which a 127-page discussion paper was made available to delegates. This analysed the steps that would need to be taken prior to granting of authority to release the virus. Initially these steps included satisfying the requirements of the Quarantine Act (1908), the Wildlife Protection Act (1982), the Biological Control Act (1984), the Environment Protection Act (1974) and the Endangered Species Protection Act (1992). In April 1994 the Ministerial Council approved a $3 million budget and set up three new committees, a Government Assessment Facilitation Committee, a Proponent Committee and a Research Committee. The approved program comprised six stages: 1. Laboratory assessment,
1992-94, In relation to stage 2, public consultation, in November 1995 a call for public comment was published in the Commonwealth Gazette and in the national newspapers, and a range of leaflets containing information of various aspects of rabbit control and RHDV were very widely distributed. A special Rabbit Calicivirus Human Health Group was set up to examine risks to the public. To provide for stage 6, monitoring and release sites were established throughout southern Australia. As we all know, these steps were short-circuited at step 3, limited pen trials, by the escape of RHDV from Wardang Island to the mainland in October 1995, but they illustrate the nature of the steps that would now have to be taken before the release of a new infectious agent for biological control of vertebrate pests. In addition, if the release of a genetically engineered virus or bacterium was planned, it would be necessary to satisfy the requirements of the Office of the Gene Technology Regulator, which I would expect to be very demanding. All in all, the regulatory steps nowadays are very much more stringent that they were in the first half of the twentieth century, when only the Quarantine authorities were concerned and there was no need to consult the general public. I wish any of you who face such a task the best of luck! |
|
|
|