About 1 in 406 dogs in Oregon test positive for heartworm disease. Gideon, a 2-year-old rescue Dalmatian from Oklahoma, has been receiving treatment for heartworm disease for a year. Oregon veterinarians say that climate change and an influx of rescued dogs from states with endemic heartworm disease could possibly bring more cases to Oregon. Prevention is key. Are your pets on heartworm preventive medication? Consult your DVM re: your pet's risks.