Heartworm disease causes severe cardiovascular damage and is potentially fatal, but is entirely preventable with consistent preventative medication.
Heartworm disease causes progressive, chronic suffering as the cardiovascular system is increasingly compromised by worm burden. Dogs with advanced heartworm infection experience exercise intolerance, respiratory distress, and heart failure — a gradual decline in quality of life over months to years. The welfare impact is compounded by the fact that treatment itself causes significant welfare compromise: dogs must be strictly rested for months while dead worms are resorbed, and complications including pulmonary embolism can be life-threatening. The preventability of this entire welfare burden through consistent monthly or annual preventative medication makes it one of the clearest examples of owner responsibility directly determining animal welfare outcomes.