How Dog Get Heartworm

franklin falls animal clinic heartworm disease

Heartworm disease is a serious and potentially fatal condition that affects dogs, cats, and ferrets. It’s caused by parasitic worms called Dirofilaria immitis that live in the heart, lungs, and associated blood vessels of affected animals. Understanding how dogs contract heartworm is crucial for prevention.

The heartworm life cycle requires an intermediate host: the mosquito. Dogs don’t get heartworm directly from other dogs. Instead, the following process unfolds:

Infection of a Mosquito: A mosquito bites an animal already infected with heartworm. This infected animal, usually a dog, has adult heartworms residing in its heart and lungs. These adult worms produce microscopic larvae called microfilariae, which circulate in the bloodstream. When the mosquito feeds on the infected dog, it ingests these microfilariae.
Development within the Mosquito: Inside the mosquito, the microfilariae undergo development over a period of 10 to 14 days, depending on environmental temperature. They transform into infective larvae, known as L3 larvae. This developmental process is crucial, as only these L3 larvae can infect a new host.
Transmission to a New Host: When the infected mosquito bites a dog, the L3 larvae are deposited onto the dog’s skin through the mosquito’s bite wound. The larvae then enter the dog’s body through the bite site. This transmission occurs during mosquito feeding.
Migration and Maturation: Once inside the dog, the L3 larvae migrate through the dog’s tissues, undergoing two more molts. They become L4 larvae and then immature adult worms. This migration process takes several months.
Arrival in the Heart and Lungs: After several months, the immature adult worms migrate to the dog’s heart and pulmonary arteries (blood vessels leading from the heart to the lungs). Here, they mature into adult heartworms, which can grow to be several inches long.
Reproduction and Continued Cycle: Once in the heart and lungs, the adult heartworms reproduce, releasing microfilariae into the dog’s bloodstream. This completes the life cycle, as the dog can now serve as a reservoir for future mosquito infections. The entire process, from the initial mosquito bite to the presence of adult heartworms producing microfilariae, typically takes about six to seven months in dogs.

It’s important to note that the severity of heartworm disease depends on several factors, including the number of worms present, the duration of the infection, the dog’s size and activity level, and the dog’s overall health. Symptoms can range from mild coughing and fatigue to severe heart failure and death.

Because heartworm disease is transmitted through mosquitoes, it is prevalent in areas with high mosquito populations. Prevention is key to protecting dogs from this devastating disease. Year-round heartworm preventatives, prescribed by a veterinarian, are highly effective in killing the heartworm larvae before they can mature into adult worms. Regular veterinary checkups and heartworm testing are also essential for early detection and treatment, if necessary.