Surveillance of Anticoagulant Rodenticides in Free-Roaming Outdoor Cats (Felis catus) in Chicago, Illinois, USA

Rats are managed using anticoagulant rodenticides (ARs) in cities worldwide, but these compounds cause morbidity and mortality in nontarget wildlife. Several cities also use free-roaming outdoor cat (Felis catus) colonies to help reduce rats, but there have been no investigations of how often these cats are exposed to ARs. In this study, our goal was to assess how often free-roaming domestic cats are exposed to ARs to 1) understand health risks for urban predators by using free-roaming cats as a proxy and 2) evaluate the health risks associated with using cats as rodent control. We tested blood samples from 57 cats that were part of trap-neuter-release cat colonies in Chicago, Illinois, USA. We found that 7% (4/57) of cats tested positive for one type of rodenticide at trace amounts. Free-roaming cats can therefore be exposed to ARs, although the prevalence and concentrations were lower than in wild carnivores. Future research is needed to understand how often cats may be exposed to ARs by killing or consuming rats and any health impacts. Stronger rodenticide regulations are needed to reduce health risks for urban predators, and owned cats should be kept indoors to minimize the risk of rodenticide exposure.