External and internal parasites cause significant welfare harm to companion dogs through discomfort, disease, and organ damage, and modern preventive treatments provide safe and effective protection against the most important parasites.
Parasite prevention is foundational to companion dog welfare because parasites cause suffering through multiple mechanisms simultaneously: physical discomfort from skin irritation, systemic disease from pathogen transmission, organ damage from internal parasites, and the debilitating effects of chronic anemia from heavy infestation. The welfare burden of neglected parasite control accumulates over time as subclinical infestation compromises immune function, reduces quality of life, and creates vulnerability to other diseases. Modern veterinary preventives provide safe, effective broad-spectrum protection that makes most of this welfare harm preventable with minimal effort from owners. The challenge of affordable access to veterinary preventives means that dogs in underserved communities often bear higher parasite burdens despite living with owners who care deeply about their welfare. Making preventive veterinary care more accessible and affordable is therefore both a welfare and an equity concern.