Heartworm disease causes severe cardiopulmonary damage and is potentially fatal. Monthly prevention is highly effective and far superior to treatment in welfare and cost terms.
Heartworm disease causes progressive and ultimately severe welfare harm through cardiopulmonary damage, exercise intolerance, coughing, and eventually cardiac failure. The welfare case for consistent prevention is overwhelming — monthly preventive medications are safe, inexpensive, and highly effective when given year-round. The contrast with treatment, which requires weeks of exercise restriction, potentially dangerous arsenic-based injections, and risks of treatment complications, makes prevention clearly superior. Annual heartworm testing enables early detection of infections that break through in dogs with inconsistent prevention and allows early treatment when worm burden is low. Veterinary outreach programs targeting underserved communities to improve heartworm prevention access have significant welfare impact given the correlation between lower-resource communities and heartworm prevalence.