Genetic resistance to anticoagulant rodenticides and pathways of non-target exposure in Ontario

Abstract

Genetic resistance to anticoagulant rodenticides (ARs) is a worldwide phenomenon that has never been investigated in Canada’s commensal rodents. Additionally, the pathways of non-target rodent AR exposure and secondary poisoning are unknown in Ontario. The VKORC1 gene of 55 house mouse (Mus musculus) and 54 Norway rat (Rattus norvegicus) samples collected from 3 regions of Ontario was examined for known and novel resistance mutations. Resistance was absent from rats, but present in 98% of mice, with mutations known to cause resistance to first-generation ARs and bromadiolone. Homozygous resistant mice were more common in heavily developed, low-income, high population density areas. Additionally, only 11 out of 111 non-target Peromyscus leucopus trapped near ongoing urban rodenticide operations tested positive for an anticoagulant. Given these findings, we recommend that second-generation anticoagulant rodenticides (SGARs) be used only for the control of house mice where non-target rodents are absent.