What is the primary route of transmission for Dirofilaria immitis in cats?

The primary route of transmission for Dirofilaria immitis, commonly known as heartworm, in cats is indeed through vector-borne transmission via mosquitoes. When a mosquito bites an infected animal, it ingests microfilariae, the larval stage of the heartworm. These larvae then develop within the mosquito before being transmitted to a new host—such as a cat—through the mosquito's bite. This process underscores the importance of mosquito control in preventing heartworm disease, especially in regions where these vectors are prevalent.

Other routes mentioned, like fecal-oral transmission or water contamination, are not relevant to the lifecycle of Dirofilaria immitis, as this parasite does not utilize these means to spread. Similarly, direct contact with dogs does not facilitate transmission because the vector required to bridge the gap between an infected host and a new victim is missing. Thus, understanding the specific vector-borne nature of heartworm transmission is crucial for effective prevention and management strategies.