Myxomatosis constituted the major part of my personal research between 1952 and 1967. To put it in perspective, I will begin with a very brief outline of its history, which is covered in detail in Fenner and Fantini (1999). Myxomatosis was first recognized as a virus disease when it killed European rabbits (Oryctolagus cuniculus) in Giuseppe Sanarelli's laboratory in Montevideo, Uruguay, in 1896. In 1911, workers in the Oswaldo Cruz Institute in Rio de Janeiro observed the disease in their laboratory rabbits and correctly classified the causative agent as a large virus. Henrique de Beaurepaire Aragão, working at the Oswaldo Cruz Institute, showed that it could be transmitted mechanically by insect bite. In 1942, he showed that the reservoir host in Brazil was the local wild rabbit, Sylvilagus brasiliensis, in which the virus produced a localized nodule in the skin (Figure 6.1B). Knowing that the European rabbit was a major pest animal in Australia, and impressed by the lethality of the disease in these rabbits (Figure 6.1A), in 1919 Aragão wrote to the Australian government suggesting that it should be used here for rabbit control, but the quarantine authorities would not permit its importation.
The idea was revived by Jean Macnamara, a Melbourne paediatrician who had worked with Macfarlane Burnet and thus had an interest in virus diseases. In 1934, she went on a world tour to investigate poliomyelitis, which was her main professional interest. In America, she visited the laboratory of Richard Shope, in the Princeton branch of the Rockefeller Institute. He was investigating a tumour in local cottontail rabbits (Sylvilagus floridanus), which he showed was caused by a poxvirus related to myxoma virus. He called it fibroma virus. At the time there was an epizootic of myxomatosis in domestic European rabbits (O. cuniculus) in California, which was later found to have a different reservoir host (Sylvilagus bachmani). Shope found that fibroma virus would protect laboratory rabbits against myxomatosis. Learning of this fatal rabbit disease, Macnamara wrote to the Australian High Commissioner in London asking him to help her convince the Government to use the virus for rabbit control.
Francis Noble Ratcliffe
Born in Calcutta in 1904, Ratcliffe studied zoology at Oxford. In 1928, he came to the notice of the London representative of the Council for Scientific and Industrial Research (CSIR), and this led to his invitation to come to Australia as Sir David Rivett's ‘biological scout’, to study flying foxes and erosion in arid lands, as a result of which he produced a classic book, Flying Fox and Drifting Sand. He returned to Britain in 1932 as Lecturer in Zoology in Aberdeen, but was invited back to Australia as a scientific adviser to the CSIR Executive in 1935. In 1937, he was transferred to the Division of Economic Entomology to work on termites. In 1942, he joined the Australian Army and served with distinction as Assistant Director of Entomology. Since I was serving in New Guinea as a malariologist at that time, I saw quite a lot of him then. After demobilization he served briefly as assistant to the Chief of the Division of Entomology, but in 1948 he was appointed Officer-in-Charge of the newly created Wildlife Survey Section of CSIR. Initially he had to work on rabbit control, and after some disappointments succeeded in introducing myxomatosis. Study of this disease preoccupied the Section for several years, but later he was able to broaden studies of the biology of the rabbit and introduce biological studies of native animals as an important part of the work of the Section, which by then had been expanded to the Division of Wildlife and Ecology. He retired from CSIRO in 1969. He played a major role in setting up the Australian Conservation Foundation in 1964, and devoted a great deal of time to its expansion to become Australia's peak environmental non-government organization, until he had to retire for health reasons in 1970 (see Coman, 1998; Mackerras, 1971).
Figure 6.1a. European rabbit (Oryctolagus cuniculus) 10 days after infection with the Standard Laboratory Strain of myxoma virus.
Figure 6.1b. Brazilian rabbit (Sylvilagus brasiliensis) three weeks after infection with the Standard Laboratory Strain of myxoma virus.
The Chief Quarantine Officer was again very reluctant to allow its importation, but allowed scientists in CSIR (which was transformed into the Commonwealth Scientific and Industrial Research Organization, CSIRO, in 1949), to test its species sensitivity against a wide range of domestic and native animals; they found that it infected only European rabbits. Several field trials were carried out, in dry inland areas, but the virus died out. Then came World War II, and in 1943 all investigations were stopped.
With so many country boys in the army, rabbit control, such as it was, had been neglected throughout the period 1939 to 1945, and by 1946 rabbits had increased to unprecedented numbers. Jean Macnamara (now Dame Jean) wrote articles in the rural press highly critical of CSIR/CSIRO for not proceeding immediately to try myxomatosis for biological control of the pest. In 1948, a CSIR/CSIRO scientist, Francis Ratcliffe, was appointed Officer-in-Charge of the newly-established Wildlife Survey Section, but instead of studying the native fauna, Ian Clunies Ross, Chairman of the newly-formed CSIRO, insisted that he should first try out myxomatosis. Several field trials failed, but in the Christmas–New Year period of 1950–51 the disease escaped from one of the four trial sites in the Murray valley and spread all over the Murray-Darling basin, killing millions of rabbits.