Figure 7.

Combined use of different diagnostic tools is usually required to reach a diagnosis of feline heartworm disease (HWD) and in some cases confirmation is never obtained. Anti-Dirofilaria immitis antibody detection and thoracic radiography to look for compatible pulmonary lesions are sensitive methods for providing early information about possible feline HWD. However, antibody detection has limitations due to lower sensitivity in asymptomatic cats and lower specificity as time passes because antibodies persist for some time in cats that self-cure. A positive antigen test or the ultrasound visualisation of filarial worms are confirmatory, but their sensitivity is inadequate for ruling out HWD in the case of no antigen and worm detection. Occasionally, microfilariae are evident in blood (modified Knott test or millipore filter), and they have to be differentiated from those of Dirofilaria repens in regions where both species are found (eg, in many European countries)