- Disease of the pulmonary vasculature and pulmonary parenchyma of cats caused by Dirofilaria immitis (Figure 1, above)
Figure 1. A single female heartworm in right ventricle of a cat. No other worms or fragments found. Diffuse lung disease was demonstrated. Photo courtesy of Dr. Ray Dillon
- Infection in cats is found in all 50 states, with greater prevalence in warmer climates.
- Because cats are not the natural host of D immitis and clearance of third-stage through fifth-stage infective larvae (ie, L3-L5, immature) can occur, prevalence of feline heartworm infection in endemic areas is ~10% that of infection in dogs1,2 (see Heartworm Infection: Cats vs Dogs).
- Approximately 25% of feline heartworm cases occur in purely indoor cats.3