Scientists hunt for possum-specific poison

June 2006
The total number of possums in New Zealand first released in 1837 to establish a fur industry - is probably many tens of millions.

They are found in about 90% of the country, causing extensive damage to native and exotic forests and threatening the habitat and survival of some native bird species.

Importantly for pastoral agriculture, possums carry bovine tuberculosis, which they can pass to cattle and deer, with severe implications for our meat and dairy product exports.

Poisons currently used to kill possums in New Zealand (with the best known being cyanide and 1080) are also toxic to humans, farm animals, companion animals and birds. One aim of this biocontrol research project is to discover a marsupial-specific toxin.

Hunting for a possum-specific toxin

Toxins work by disrupting some vital mechanism in the body, causing death. Dr Bernie Dr Grant Butt and scientists from Otago Universitys physiology department are looking for a mechanism specific to marsupials, which can be targeted.

Several have been found for vital processes crucial for survival that are remarkably different from other animals, with the one being targeted relating to how marsupials secrete water across their intestine.

All animals move about 25% of their total body water through the body every 24 hours as saliva, gastric juices and water and absorb the same amount.

If the amount of water secreted is greater than the amount absorbed, the animal is in trouble. The only remaining place it can readily mobilise (a small amount of) water from is the blood. The result is a drop in blood pressure which rapidly affects all organs in the body, causing death.

An example of this is cholera toxin, which kills by switching on the mechanism that causes secretion, which then cant be shut down.

Scientists identify vital gene

The next step in the research is understanding how the mechanism controlling water secretion across possums gut works.

In any animals small intestine (as well as the large intestine, lungs and other vital organs) there is a single layer of cells that acts as a barrier to prevent the entry of pathogens into the body, and also controls the uptake of nutrients, drugs and the movement of water.

Every protein in the body is produced by a specific gene. This study has identified a gene which produces a possum transporter protein that controls the movement of water from the outside of the small intestine (from the blood) to the inside.

The next success was growing out cell lines which express the transporter protein. These lines of cells will be used to determine just how that transporter protein works and will also be screened for compounds that might switch it on, inducing the water secretion process.

The toxins will also be tested to check they have no effect on humans, farm and domestic animals and birds.

The scientists are now halfway through this five-year project