Mice
The wild house mouse (Mus domesticus) was introduced
from Europe with early settlement. Plagues periodically cause
major economic loss through crop and stored grain damage and damage
to infrastructure, as well as social distress.
One plague in 1993 (through South Australia and western Victoria)
was estimated to cost the agricultural industry AU$100
million. Densities can reach over 750 mice per hectare,
although more commonly are < 10 mice per hectare.
Mouse plagues usually occur when good climatic conditions produce
abundant high quality food, and good nesting sites are
plentiful.
Plagues have occurred in the grain-growing areas of Australia
since the turn of the century, on average every four
years. Between 1980 and 1995 there was an escalated
pattern of plagues - seven outbreaks occurred in southeast
Queensland, three in southern New South Wales, three in South
Australia and four in Victoria - thought to be the result of
altered farm management practices. However, due to
drought it has now been approximately ten years since the last
major plague and some experts predict that one is due in the next
autumn following on from heavy rains this last spring and
summer.
During plagues, severe economic, environmental and social damage
occurs. Apart from the crop losses, damage to stored grain
and reduced livestock production levels, there are also flow-on
effects such as spoiled stock in stores and damage to electrical
equipment and infrastructure. Environmental issues related to
the increased use of pesticides, especially unregistered
rodenticides can also occur. Households suffer stress
not only from lost income, but also from spoiled food, chewed
paper, damaged wiring and fouling for periods of up to six months
at a time.
Rats
Australia has around 60 native species of rat, occuring in a
wide range of habitats around the country. Only one causes
concern - the cane field rat, Rattus sordidus. This
grasslands rodent has increased its range , particularly in
northern Queensland, because of clearing and crop planting.
It can achieve high densities, and causes damage not only to
sugarcane crops but also to banana and teak plantations in the
tropical parts of Queensland.
Two species of invasive rat - the Black Rat or Roof Rat
(Rattus rattus) - responsible for London's Bubonic Plague
in 1665) and the Brown Rat (Rattus norwegicus). The
Black Rat is the one most people see in our cities and towns, and
is often responsible for the infestation of houses, sheds,
warehouses and storage facilities.
The ability of Black and Brown rats (and a half dozen or so
native rats) to breed up rapidly is due to their biology, which
includes rapid maturity (sexually mature by 10 weeks) and high
birth rates (up to 12 young per litter). Litters can be produced
every three weeks under ideal conditions.
Rats are an enormous problem in Southeast Asia where they cause
damage to many agricultural and horticultural crops, particularly
rice. This impacts on the ability of some countries to
provide sufficient food to meet growing populations.
A current conservative estimate is that rodents in rice-growing
regions typically cause annual pre-harvest losses of between 5 and
17%. A loss of 6% of rice production amounts to approximately
36 tonnes, enough rice to feed 215 million people (roughly the
population of Indonesia) for one year. Rat damage is
generally patchy, so it is not unusual for families or even
villages to lose more than 50% of their crop to rats.
Rats are also well-known for their role in the spread of
disease. Because of the increasing mobility of people between
rural and urban areas and between countries, and the increasing
clearance of natural habitats which allows further rodent-human
contact, there is real concern about a major disease
outbreak.
What are we doing?
The IA CRC (and formerly the Pest Animals Control CRC) spent
considerable research effort investigating the feasibility of
virally-vectored immuno-contraception for rodents. The
overarching concept was that the genes for proteins that are
critically involved in fertilisation or implantation could be
inserted into a virus that would infect mice. The inserted
genes would then be expressed in an animal infected with the
recombinant virus and the infected animal would simultaneously
raise antibodies to the virus and the reproductive protein.
In this way, fertilisation or implantation would be prevented
without affecting the animal's sexual activity or social status in
the population (Tyndale-Biscoe and Hinds, 2008).
The CSIRO team achieved considerable success in producing an
rMCMV-mZP3 vector that sterilised female mice. (MCMV is
a cytomegalovirus - a naturally occurring pathogen of the house
mouse, and mZP3 is a female fertility-associated
gene). The infertility was long lived, and in most
cases complete. Unfortunately, there were significant
barriers to the widespread use of the technology.
Attenuation of the virus prevented it transmitting naturally
through a population, meaning that extensive further work needed to
be done to try and find either a new strain of the virus or a
completely different vector if this was to be overcome. Due
to the extremely long time scale and high cost of this projected
research, the IA CRC had to abandon the project.
We are at present working with Animal Control Technologies
Australia (ACTA) to trial baiting programs in intensive crops and
industrial applications. The Australian Pesticides and
Veterinary Medicine Authority has approved the use of an
ACTA-developed product (RATTOFF) in the banana industry (after
knockdown rates of up to 80% achieved in mark/recapture
trials). ACTA has also had considerable success in reducing
rat damage to macadamia and teak plantations, and the product is
now approved under permit for both these applications - giving
growers a new method to treat rodent infestations with reduced risk
of secondary poisoning. A further benefit is reducing the
risk of leptospirosis for workers in the industry.
The University of Queensland (Gatton) is supporting enclosure
trials by ACTA of another bait product (MOUSEOFF) in intensive
crops - with promising results so far.
Read about the project <more>
