Cause
Infection with the Dirofilaria immitis parasite occurs when a mosquito that previously has bitten an infected animal bites another animal, thereby injecting worm larvae into the new host. Infections in cats are much less common than in unprotected dogs in the same locale. Possible reasons include a mosquito preference to feed from dogs versus cats, a difference in exposure to infected mosquitoes, and a lower number of infective larvae developing into adults within the cat.