Symptoms of Heartworm Disease
Visible signs of heartworm disease may not appear until a full year after being bitten by infected mosquitoes. In fact, the disease may be well advanced before the dog shows any symptoms. Dogs with typical heartworm disease fatigue easily, cough, and appear rough and not thriving. Blood and worms from ruptured vessels may be coughed up. Blockage of major blood vessels can cause the animal to collapse suddenly and die within a few days.
Dogs with 50-100 mature worms exhibit moderate to severe heartworm disease. Dogs with 10-25 worms that receive little exercise may never show signs of heartworm disease, and one may not be able to find microfilariae in the blood. Heartworm infection without detectable microfilaremia is called occult dirofilariasis.
Diagnosing Heartworm Disease
Diagnosis of canine heartworm infection depends on an accurate patient history, clinical signs, and use of several diagnostic procedures that may include detection of microfilariae in a blood sample, X-rays, or ultrasound.
It is much more difficult to diagnose feline heartworm infection than canine heartworm infection. Routine tests for the microfilariae are not useful in cats because the presence of heartworm offspring in the blood is temporary in cats. There are several tests used together for diagnosing heartworm in cats, including physical exam, ultrasound readings of the heart, complete blood count, blood testing, microfilaria testing, and in some cases, necropsy.