How is the heartworm parasite Dirofilaria immitus primarily spread in dogs?

Dirofilaria immitis, commonly known as heartworm, primarily spreads in dogs through the bites of infected mosquitoes. When a mosquito bites an infected dog, it ingests microfilariae (the larval stage of the heartworm). Inside the mosquito, these microfilariae develop into a stage that can infect other dogs. When the mosquito subsequently bites a healthy dog, the larvae are transmitted through the mosquito’s saliva, leading to the establishment of an infection in the new host.

Understanding this transmission route is critical for public health and veterinary practices aimed at preventing heartworm disease in dogs. Mosquitoes are the only vectors that can transmit heartworm, making this knowledge essential for effective prevention strategies, such as regular heartworm testing and preventive medication.

Other methods of parasite transmission in dogs, such as through ticks or fleas, do not relate to heartworm transmission. Also, direct contact does not play a role in how heartworm spreads, which distinguishes it from other parasites that may be transmitted through physical contact or other vectors.