Heartworm disease causes serious cardiopulmonary damage in dogs and is fatal without treatment. Prevention is straightforward; treatment of established infection involves significant welfare burdens that make prevention far preferable.
Heartworm welfare involves a stark contrast between prevention and treatment. Prevention with monthly antiparasitic medication costs a few dollars per month and has minimal welfare burden. Treatment of established infection is lengthy, expensive, painful, and carries significant risk — melarsomine injections are given into the lumbar muscles and are painful; strict activity restriction for 6–8 weeks is necessary to prevent fatal pulmonary thromboembolism as worms die; and dogs may experience respiratory compromise throughout. Severe clinical heartworm disease causes progressive exercise intolerance, coughing, and respiratory distress before treatment — months of suffering from a preventable condition. In endemic areas, missing even a few months of prevention can result in infection. Owners who cannot afford monthly prevention should discuss alternatives with their vet — annual injectable moxidectin provides 12 months of coverage from a single dose. Shelters and veterinary outreach programmes providing prevention to low-income pet owners address the welfare equity dimension.