Date of Award
2024
Document Type
Thesis
Publisher
Edith Cowan University
Degree Name
Master of Science by Research
School
School of Science
First Supervisor
Quinton Burnham
Second Supervisor
Annette Koenders
Third Supervisor
Mike Lohr
Abstract
Anticoagulant rodenticides (ARs) have been the mainstay of rodent control since their inception more than seventy years ago. ARs interfere with the vitamin K cycle by targeting the VKOR protein and disrupting normal blood clotting, and death results from internal haemorrhage. Although widely used for many decades, there are issues associated with their use. Not only do ARs pose a significant risk to non-target organisms including children, pets and wildlife, but the continued use of ARs has resulted in the development of resistance in target rodents. Resistance is a challenge for pest management and can intensify exposure for non-target species if higher toxicity ARs are employed in response.
In Australia, ARs have few restrictions controlling their use, and second-generation ARs (SGARs) which bioaccumulate and biomagnify through the food chain are easily available to the public. High levels of SGAR residues have been detected in non-target taxa, including taxa which do not consume rodents, yet we do not understand the efficacy of ARs against target rodent populations. A feeding trial in the 1970s found Australian Rattus rattus resistant to the first-generation AR, warfarin. Resistance has not been further evaluated or monitored in introduced rats since, and aside from a recent investigation into genetic resistance in mice on Browse Island and Perth, Western Australia, there is no published evidence of genetic investigation into AR resistance. Resistance can be associated with single-nucleotide polymorphisms (SNPs) in the Vkorc1 gene, and screening of the gene has been used worldwide to establish the resistance status of rodents, including in Europe, UK and the USA. This thesis is an investigation of Vkorc1-mediated resistance in the four largest cities (by population) in Australia: Brisbane, Melbourne, Perth and Sydney.
The first step in investigating Vkorc1-mediated resistance in introduced rats in Australia was to clarify the species present. Via sequencing of the cytochrome b gene for 183 rats it was found that Rattus rattus, and Rattus norvegicus were present, which was expected, however there was also a third cryptic species, Rattus tanezumi (Lineage II) present in large numbers in Brisbane, which had not been previously reported.
In addition to sequencing the mitochondrial cytochrome b gene, the nuclear Vkorc1 gene was sequenced to identify any mutations present that may confer resistance to anticoagulant rodenticides. Of the 182 rats tested, three non-synonymous single nucleotide polymorphisms (nsSNPs) were identified in Rattus rattus, and one was found in one Rattus tanezumi. No non[1]synonymous mutations were found in Rattus norvegicus. Phe55Ile has not been previously reported and was detected in one rat, and Trp59Arg was found in two rats and is actually associated with increased susceptibility to anticoagulant rodenticides. However, the most common non-synonymous mutation which was found in R. rattus (51.5%; 51 of 99 R. rattus screened) and R. tanezumi (1 of 31 R. tanezumi screened), Tyr25Phe, has been linked to resistance to various anticoagulant rodenticides and may explain resistance previously reported in Rattus rattus. This is the first genetic evidence of potential resistance to anticoagulant rodenticides in rats on Australia’s mainland.
DOI
10.25958/zkf5-m738
Access Note
Access to this thesis is embargoed until 26th November 2025
Recommended Citation
Gorbould, A. (2024). Genetic detection of anticoagulant resistance in Australia's introduced rats. Edith Cowan University. https://doi.org/10.25958/zkf5-m738