Heartworm disease causes significant suffering in infected dogs, and preventive medication represents one of the most cost-effective welfare investments available to dog owners in endemic regions.
Heartworm prevention is a clear case where a low-cost, highly effective intervention prevents significant future suffering. Dogs infected with heartworm develop progressive deterioration in cardiac and pulmonary function — exercise intolerance, coughing, and eventually heart failure over years. Treatment for established disease involves immobilizing arsenic-based injections, strict cage rest for weeks, and significant morbidity risk from dying worm fragments causing pulmonary embolism. The contrast with prevention — a monthly chewable tablet costing under a dollar per month — makes the welfare and economic case for prevention unambiguous. Climate change expanding the range of mosquito vectors is spreading heartworm disease to regions where it was previously uncommon, making prevention relevant to an increasingly broad geographic area. Year-round prevention in endemic areas is recommended over seasonal prevention to avoid missed doses.