My Lab had two heartworm tests done this past week and both came back borderline positive. I've never missed a dose of heartworm preventative and give it the same day each month. My vet has checked with an internist to see if there would be anything else that could cause a possible false positive. At this point, I don't know if my boy actually has heartworms or if some anomaly has occurred. If he truly has heartworms, then it's the result of a preventative failure. My vet has suggested changing from what I was using (HeartGard Plus) to Revolution and retesting in six months. Apparently Revolution can kill adult heartworms. He also said we could do a chest x-ray, an ultrasound and an echocardiogram, but if my dog does have heartworms, it's a very mild case and therefore those tests may not show anything.
Has anyone else ever had anything like this happen?
Your veterinarian should contact manufacturers to report a possible product failure. They will have protocols for additional testing and treatment at their expense if it is a true product failure.
Borderline positive for heartworm is like being borderline pregnant. I suspect your dog is infected. Preventative failure is becoming more common even if you dose every 30 days. Not sure the manufacturer will pay for treatment anymore as heartworm larvae is becoming resistant to ivermectin. Many websites promoted extending the time interval between dosing to a month and a half and this contributes to drug resistance. Always dose every thirty days. There is also controversy about the correct reporting of ivermectin effectiveness in the first place.
