GM virus puts mice off sex

Australia's first GM mammal virus is poised to slash millions of dollars off grain spoilage figures, if medium-scale mouse-limitation trials go according to plan.

The newly developed virus, a GM strain of mouse herpes, has been designed to block sperm from entering the eggs of sexually active females. This would dramatically cut the numbers of mice breeding in any season and help cut down on mouse plagues, asserted Dr Tony Peacock, CEO of the Pest Animal Control Cooperative Research Centre (CRC).

One breeding pair of mice and their offspring have the potential to produce 500 mice in just 21 weeks, a figure which explodes exponentially into plague proportions every four years or so. During a plague year, mice can spoil a staggering amount of grain by both consumption and contamination -- in 1993 a major mouse plague in South Australia and Victoria spoiled an estimated $AUD55 million worth of stocks.

The fact that the mating of sexually prolific but vaccinated and thus infertile females will help to spread the virus is a bonus -- it is a highly secure and highly targeted method of virus transmission, claimed Peacock.

"The transmission and spread of the disease are vitally important issues, given the territorial behaviour of mice in the wild. The spread of this disease is normally mouse to mouse only, but we need to look at insect behaviour from infected mice too. We will have to investigate the effects of mosquitos, fleas and so on," he said.

Peacock said once the OGTR had given the go-ahead, the next stage in the research would involve trials at specially secured bird and rodent-proof sites in Victoria and Queensland. This would help assess the effectiveness of the virus, and its possible effect on other rodents.

"We need a great deal of certainty before we go ahead with the next phase of trials, and expect to apply to the OGTR for permission to go ahead within the next three months - but we will need to find out much more before we apply," he noted.

Product in three years

The research to date has cost the underwriter, the Grains Research and Development Board, about $1 million since the project's inception in 1996. Some 20-25 researchers have been working on the task across two labs at the University of Western Australia and at the CRC's own facility in Canberra. Additional work was started on an ectromelia virus solution, but this was judged to be less promising than the herpes solution.

If the project does prove feasible, safe and controllable mouse population control, a deliverable product could be ready for release in three years, claimed Peacock.

"It is likely we will release the final virus on an 'industry good' basis. However, there is the possibility we could commercialise some of the research and apply it to other parts of the world in the area of rat control. There is a huge potential for such a product in Asia where rats destroy enough food each year to feed Indonesia," he said.

How it works

The self-spreading vaccine will incorporate a genetically modified virus with a fertility control gene. The virus being studied by the mouse research team is called murine cytomegalovirus (MCMV). MCMV was chosen because it is spread by direct contact, is highly specific to mice and already infects 80%-100% of the mouse population in Australia - thus avoiding introducing a new virus into the mouse community.

Researchers inserted a gene (mouse zona pellucida 3 or ZP3) from a mouse egg into MCMV and demonstrated that lab mice infected with the modified virus were infertile for longer than six months. Research is now concentrating on selecting the most suitable strains of MCMV, the most suitable gene (egg or sperm protein), and confirming the specificity of MCMV for mice.