Determination of anthelmintic efficacy against Toxocara canis in dogs by use of capsule endoscopy

Abstract

Industry guidelines for anthelmintic testing call for postmortem inspection of animals to verify treatment efficacy. A previous study showed that capsule endoscopy (CE) can be performed on dogs in vivo to quantify hookworms in the small intestine. Adoption of a minimally invasive procedure such as this could reduce the need for necropsy in efficacy trials. The present study employed CE to enumerate Toxocara canis in dogs, with two main goals: to determine if multiple capsule examinations improves the accuracy of worm counts compared to a single examination, and to establish if the efficacy of an anthelmintic compound is the same whether calculated using CE or necropsy data. To avoid needless animal sacrifice, the study was carried out on beagle dogs already in a product development trial with a planned terminal endpoint. Dogs were infected by oral inoculation with T. canis eggs. Untreated control dogs (n=8) were evaluated by CE three times while dogs treated with test compounds (3 groups of 4) were examined only once. Utilizing either the average count or just the last complete capsule examination, a robust correlation was found between CE and postmortem numbers (r=0.94, p<0.001). Calculated anthelmintic efficacy was essentially identical for the two enumeration methods, ranging from 94% to 100% for the three research compounds. CE may therefore be a viable alternative to necropsy for T. canis parasiticide trials.