Heartworm disease causes progressive, potentially fatal cardiac and pulmonary damage in dogs through a parasite transmitted by mosquitoes — yet it is almost entirely preventable with monthly medication.
Heartworm disease causes a slow, progressive deterioration in cardiac and pulmonary function that significantly reduces quality of life before clinical signs become obvious. Dogs with heartworm burden experience exercise intolerance, respiratory discomfort, and progressive weakening as their hearts work against an increasing parasite load. The profound disparity between the ease of prevention — one monthly tablet or topical — and the suffering of established infection makes non-prevention a welfare failure. Treatment is possible but involves prolonged restricted exercise, significant medication side effects, and expense. Prevention is both the welfare-optimal and economically rational choice.