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Four related research projects are currently investigating means of extending the usefulness of RHDV as a biological control agent for rabbits in Australia RHD Boost RHD Boost is a research program to import and evaluate new RHD virus strains to strengthen rabbit biocontrol. RFA funding support for RHD Boost was instrumental in the Invasive Animals Cooperative Research Centre's successful bid to obtain $1.5 million project funding from the Commonwealth 'Caring for Country' program for the period 2009-2012. RHD Boost aims to identify new Rabbit Haemorrhagic Disease Virus (RHDV) strains with high lethality to rabbits immune to endemic Australian Rabbit Calicivirus (RCV-A1) and rabbits resistant to infection with Czech 351 derived RHDV strains. The project is a strategic response to the apparent rising genetic resistance to the RHDV CZ 351 strain released, and its limited effectiveness in temperate regions due to the endemic RCV-A1, which protects many rabbits from the RHDV strain. In Europe, new RHDVa strains are out-competing the original RHDV strains in the field and strongly suppressing wild rabbit populations in cooler, wetter regions. The project will evaluate new candidate RHDV strains. This includes screening to determine which candidate RHDV strains overcome rabbits with immunity to CZ351 derived RHDV and RCV-A1, and research to confirm the competitive advantage of the new candidate RHDV strains. A decision framework to optimise the impacts from releasing candidate RHDV strains will also be developed. The research is being conducted at the Elizabeth Macarthur Agriculture Institute in NSW. Contact: Dr Peter Kirkland, Elizabeth Macarthur Agriculture Institute, 61-2-4640 6331 peter.kirkland@industry.nsw.gov.au Enhancing RHD effectiveness: RHDV genetic diversityA second project being conducted within the IA CRC, by Biosecurity SA, is investigating the genetic diversity of field strains of RHDV currently circulating in wild rabbits in Australia. While it is believed that increasing the genetic diversity of RHDV in Australia will lead to higher infection/mortality rates, we also need to understand what viruses we already have in Australia to guide the choice of strains selected for importation, to guide the choice of strains for release, and to monitor the establishment, spread and persistence of released strains. The current project will provide genetic information by sequencing samples from field outbreaks of RHDV around Australia. The project will also provide serological support for ongoing epidemiological field studies to determine how infection or mortality rates are changing in wild rabbits. The Turretfield site in SA is the only site where epidemiology of RHDV has been studied in detail before and during the period of emerging genetic resistance to RHD, has a high level of genetic resistance, and offers potential for assessing the processes by which Australian rabbit populations are recovering, and hence the likely effect of releasing new strains of RHDV. Contacts: Greg Mutze, Biosecurity SA, 61-8-83039505, greg.mutze@sa.gov.au Dr Ron Sinclair, Biosecurity SA, 61-8-83039506, ron.sinclair@sa.gov.au Enhancing RHDV effectivenessRHD has been less effective in controlling rabbits in the wetter, cooler parts of southern Australia than in the arid inland. One reason appears to be that pre-existing related caliciviruses, collectively referred to as RCV-A1, are providing some protection against RHDV. Their role in limiting the impact of RHDV is currently being investigated by an Invasive Animals CRC project being conducted by CSIRO. The project has isolated RCV-A1 from rabbits at several sites in eastern Australia and demonstrated that infection by RCV-A1 reduces mortality from subsequent RHDV infection. The geographic distribution and genetic diversity of RCV-A1 is being further investigated and specific antibody tests are being developed to study virus epidemiology in the field, the degree of protection offered against RHD infection in wild rabbits, and how the introduction of new RHDV strains might be used to overcome the problem. Contact: Dr Tanja Strive, CSIRO Entomology, 61-2-62464176, Tanja.Strive@csiro.au RHD genetic resistance
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