Anthelmintic resistance in canine parasitology: a critical review of an emerging global challenge.

Anthelmintic resistance (AR) in canine parasitology is rapidly emerging as a significant health challenge. Growing reports of multidrug resistance in the canine hookworm Ancylostoma caninum, as well as macrocyclic lactone resistance in the heartworm Dirofilaria immitis, and isolated cases in Dipylidium caninum, highlight the increasing importance of AR. Unlike livestock, AR in dogs develops under different dynamics, shaped by unique epidemiological and biological features, including lower treatment frequencies, smaller parasite populations, and distinct husbandry practices. Nevertheless, frequent prophylactic deworming, widespread use of fixed-dose combinations, and intense drug exposure in environments such as kennels create strong selection pressures that may accelerate resistance. Treatment failures in clinical settings, particularly among greyhounds and shelter dogs, suggest canine parasitology is entering the same 'resistance crisis' faced in production animals. This paper comprehensively reviews current evidence on AR in canine helminths, covering geographical distribution, mechanistic insights, and diagnostic methods. We highlight the applications and limitations of AR-detecting assays and discuss advances in molecular diagnostics, including polymerase chain reaction and next-generation sequencing. Overall, the evidence demonstrates that AR in canine parasitology is no longer anecdotal but an emerging issue, demanding improved diagnostics, targeted therapies, and judicious drug use to preserve treatment efficacy and mitigate broader health risks.