RADIOGRAPHIC AND 2-D ECHOCARDIOGRAPHIC FINDINGS IN 18 CATS EXPERIMENTALLY EXPOSED TO D-IMMITIS VIA MOSQUITO BITES

Eighteen cats were exposed to Dirofilaria immitis infected mosquitoes. Thoracic radiography was performed prior to exposure and at 5, 7, and 9 month intervals following exposure. Immunologic testing for adult h eartworm antigen was performed on days 168, 195, 210, 224, 237, 254 an d 271 post infection. Necropsies were performed on all cats. Adult hea rtworms were found in 61% of the exposed cats. Radiographic findings i n heartworm positive cats included bronchointerstitial lung disease, l obar pulmonary arterial enlargement and pulmonary hyperinflation. In m ost heartworm positive cats, lobar arterial enlargement resolved as th e disease progressed while pulmonary hyperinflation progressively beca me more common. Pulmonary patterns in heartworm positive cats remained abnormal throughout the study while abnormal pulmonary patterns resol ved in over 50% of the heartworm negative cats. Cardiomegaly was seen in less than 50% of the cats with adult heartworms at necropsy. This s tudy suggests that the radiographic appearance of heartworm disease is variable and radiographic changes are dependent on the time post infe ction at which cats are evaluated. Echocardiographic examinations were randomly performed on 16 of 18 cats. Heartworms were identified in 7 cats. No false positive identifications were made. Persistent pulmonar y disease accompanied by resolving vascular disease in heartworm cats with pulmonary hyperinflation may be difficult to distinguish from cat s with feline allergic lung disease. Echocardiograms may be helpful in identifying adult heartworms in cats in which the radiographic signs or immunodiagnostic data are insufficient to provide a diagnosis.