How Heartworms Develop in Pets
While you may know heartworms are transmitted to pets via the bites of infected mosquitoes, you may not realize that mammals are an essential part of the heartworm life cycle as well. In honor of National Heartworm Awareness Month, we’re sharing how important your pet is to the heartworm life cycle.
Where do adult heartworms live?
If heartworms had a choice, they would pick a canine host to grow and reproduce in. Cats, however, are not ideal hosts, even though they can develop a heartworm infection. That means your dog and wild canines act as the greatest reservoir of adult heartworms. Inside your pet’s pulmonary artery, the female heartworms give birth to tiny larvae (L1) called microfilariae.
How are mosquitoes responsible for infecting pets with heartworms?
As the L1 larvae circulate in an animal’s bloodstream, they wait for a mosquito to transport them to a new host. The L1 larvae cannot complete their development into adult heartworms without first being passed through a mosquito, meaning the microfilariae cannot grow up in the host pet in which they are born.
Once a mosquito picks up the circulating microfilariae (L1) from an infected pet, the heartworm larvae mix with the gastric juices in the mosquito’s stomach, stimulating the larvae to molt to the L2 stage.
Then the L2 larvae migrate to the mosquito’s salivary glands, where they molt to the infective L3 stage. This molting process takes 10 to 20 days, but it is vital to a heartworm’s life cycle.
After the microfilariae have reached the L3 stage, they can infect a new host animal via a mosquito bite.
How long does it take heartworm larvae to reach adulthood?
Once inside a pet, the L3 larvae molt into L4 larvae in seven to 14 days, then to L5 larvae in 45 to 60 days. During this time, the L4 larvae travel through bodily tissues, first to the abdomen, then passing out through the diaphragm to the lungs. The L5 larvae will penetrate the small arteries in the outer parts of the lungs on their way to the heart and eventually become adult heartworms.