Heartworm infection without detectable microfilaremia is called occult dirofilariasis. Diagnosis of dog heartworm disease is done by drawing a blood sample and looking for microfilaria using a microscope. A more reliable method is to take x-rays. When heartworm disease in confirmed, a treatment program is set up to remove both adult worms and microfilariae. Heartworm disease in cats is less frequent than in dogs.
Cats are susceptible, but appear to be poorer hosts than the dog.
The most prominent clinical signs include coughing, dyspnea, vomiting, lethargy, and anorexia. Acute collapse and death can occur. During the last 20 years, about 80 cases of human pulmonary dirofilariasis have been reported from Florida. More than 70 of the nearly 3,000 known species of mosquitoes world-wide have been identified as capable of sustaining the development of dog heartworm microfilariae to the infective stage. In Florida, about 20 species are potential vectors.