WA mice more susceptible to rodent killer


Rat poison is more effective in WA rodents. Picture credit:Photo by Zdeněk Macháček on Unsplash

WA mice are genetically very different to their overseas counterparts and “surprisingly” susceptible to rat poisons, scientists have found.

Edith Cowan University ecologists say they tested 34 mice for resistance to rodenticides from across Perth and found that they lack a key gene that provides resistance to rat poison.

Edith Cowan University ecologist Bridget Duncan said her colleagues were surprised to discover the lack of the mutation gene in West Australian mice, compared to mice around the world.

“Mice in Europe, the United States and Canada have all been found to carry this mutation and we assumed that mice in Western Australia would be the same,” Ms Duncan said.

“It is possible that Western Australian mice arrived on the early settler ships before this genetic mutation arose in the British population,” she said.

Ms Duncan said this was surprising as potent rat poisons are much more accessible to consumers in Australia than elsewhere in the world.

The scientists say a lack of mutation in VKORC1 gene, that produces an enzyme that is important for blood clotting, rendered stronger ‘second generational’ rodenticides much more effective at killing WA mice at lower doses.

Second-generational rodenticides are problematic as they stay in the animal’s body longer than first-generation chemicals, posing a threat to native wildlife that predates on rodents.


Rat poisons are a multi-million dollar industry and have been used for decades to control rodents.  But, as mice developed resistance, a new generational and more-potent form of rat poison was developed.

Called second-generational rat poisons, the baits use chemicals like brodifacoum which quickly kill and now scientists have shown these chemicals are spreading through the ecosystem and having a devastating impact on the Western Australian native species.

“Second generational poisons are horrible for wildlife as a study in 2018 found that 37 species of Australian native animals were affected by rodenticides,” Ms Duncan said.

ECU vertebrate biologist Dr Robert Davies said rodenticides have a major impact on most aspects of the food chain and the more it has been looked at, the more concerning it becomes.

“Concerningly, we found detectable rodenticides in all species,” Dr Davies said.

“91 per cent of dugites (that are rat and mice predators) contained second generation anticoagulant rodenticides.

“Even more concerning was detection in 60 per cent of bobtails which eat primarily plants, fruit, slugs and snails and tiger snakes that primarily eat frogs,” he said.

Dr Davies said that this indicates that there is a deep penetration of rat poison into the entire ecosystem and even species not directly eating poisoned rats or mice are being affected.

“We flag the very real concern that this means that there is a possible human health risk,” he said.

A rodenticide review, from Dr Robert Davies and ECU, PhD student, Michael Lohr, discuss the aspects that Australian Indigenous people, culturally and economically consume Australian reptiles such as the goanna.

“Rodenticides can show through unknown routes into the food chains of things that we eat,” Dr Davies said.