Residues of an anthelmintic veterinary drug (closantel) detected in red foxes (Vulpes vulpes) in Scotland

Abstract

The contamination of the environment by some veterinary medicines and their impact on wild animals is ofincreasing concern. However, there is a lack of information about their residues in wildlife. The sentinel animalsmost commonly used for monitoring the level of environmental contamination are birds of prey, and informationon other carnivores and scavengers scarce. This study examined the livers from 118 foxes for residues of a rangeof 18 veterinary medicines (16 anthelmintic agents and 2 metabolites) used on farm livestock. The samples werecollected from foxes, primarily in Scotland, shot during legal pest control activities conducted between 2014 and2019. Closantel residues were detected in 18 samples, and the concentrations found ranged from 6.5 μgkg 1 to1383 μgkg 1. No other compounds were found in significant quantities. The results show a surprising frequencyand level of closantel contamination, raising concerns about both the route of contamination and the potentialimpacts on wild animals and the environment, such as the potential for significant wildlife contamination tocontribute to the development of closantel-resistant parasites. The results also suggest that red fox (Vulpes vulpes)could be a useful sentinel species for detecting and monitoring some veterinary medicine residues in theenvironment.