Heartworm disease causes serious cardiac and pulmonary suffering in dogs; it is entirely preventable but treatment of established infections involves significant welfare costs.
Heartworm disease causes progressive and significant suffering. Early infection is asymptomatic, but as worm burden increases, dogs develop exercise intolerance, chronic cough, and eventually right-sided heart failure with respiratory distress. The welfare cost of treatment — strict cage rest during the 8-week treatment period while dead and dying worms risk causing potentially fatal pulmonary embolism — is significant. Dogs must be prevented from exercising to prevent thromboembolism from dying worms, meaning weeks of enforced inactivity that is psychologically difficult for active dogs. Monthly preventive medications taken consistently prevent all of this suffering at negligible cost and welfare impact — making prevention the clear welfare priority.