Strychnine poisoning in nontarget species in western Canada: A retrospective case series (2014 to 2023).

Background: Strychnine is a highly toxic, plant-derived alkaloid. It has historically been used in western Canada as a rodenticide for control of Richardson's ground squirrels; and in Alberta, as a predacide against wolves, coyotes, black bears, and skunks. However, nontarget species poisonings with strychnine have been widely documented in Canada and elsewhere. Poisonings manifest as acute neuroexcitation and are usually fatal. In March 2023, strychnine was banned in Canada for control of Richardson's ground squirrels, with concerns over wildlife poisonings cited. However, fatal poisonings have occurred in animals since the ban.

Objective: To retrospectively characterize cases of nontarget species poisoning by strychnine in western Canada (British Columbia, Alberta, Saskatchewan, and Manitoba) based on diagnostic case records.

Procedure: Diagnostic information from confirmed cases of strychnine poisoning from 2014 to 2023 was compiled from the records of Prairie Diagnostic Services (Saskatoon, Saskatchewan). Where available, epidemiologic data pertaining to year and month of submission, province, location of submitting veterinary clinic/enforcement office, species/breed, age, sample submitted, strychnine concentration, and case history were collected.

Results: Prairie Diagnostic Services confirmed 51 cases of strychnine poisoning in western Canada from 2014 to 2023. Strychnine poisoning was diagnosed in dogs (n = 38), horses (n = 5), and wildlife (n = 8). Most poisonings occurred in Alberta (n = 23) and Saskatchewan (n = 25). Poisonings occurred annually (average: 6/y), with the highest numbers of cases occurring in 2015 (n = 9) and 2017 (n = 9). Poisoning in dogs occurred predominantly in medium and large breeds and in smaller population centers. Poisonings were diagnosed after the national ban was in effect.

Conclusion and clinical relevance: This paper highlights the prevalence of nontarget species strychnine toxicosis in western Canada. Despite the recent national ban of strychnine, poisonings of nontarget species have continued.