How Heartworm Prevention Works in Your Pet


Along with regular vaccinations and wellness exams, heartworm prevention is an essential part
of keeping your pet healthy and disease-free. Since heartworm disease has been diagnosed in
every U.S. state, and mosquitoes don’t take a break during the winter, keeping your four-legged
friend on year-round heartworm prevention is crucial.

The heartworm life cycle

Any mammal can be infected with heartworms, although these parasites prefer canine hosts.
When a mosquito bites an infected animal, they ingest microfilariae, or heartworm larvae (L1),
from the blood vessels. The mosquito’s gastric juices stimulate the larvae to molt to the L2
stage, and they then migrate to the mosquito’s salivary glands and molt to infective L3 larvae.
When the mosquito feeds, the L3 larvae swim under the pet’s subcutaneous tissue. Over time,
the larvae molt through two stages, traveling toward the pet’s heart until they finally arrive in
the main pulmonary artery, where they reach adulthood and reproduce.

How heartworm prevention works

Inside the pet, the mosquito goes through multiple larval stages, but only two larval stages are
susceptible to heartworm prevention. Once heartworm larvae reach juvenile or adult stages,
preventives can no longer kill them, and they need treatment with an arsenic-containing drug,
which is costly and harsh.


By giving your pet a monthly heartworm preventive, whether an oral chewable or topical liquid,
you effectively kill off the heartworm larvae before they develop into a more hardy life stage.
Since immature larvae can molt into the adult stage in as little as 51 days, monthly prevention
that does not allow the life cycle to progress and harm your pet is critical. Injections with a
slow-release mechanism that ensures heartworm larvae are killed before they molt can also be
administered every 6 or 12 months. While heartworm prevention does not prevent mosquitoes
from biting your pet, or heartworm larvae transmission, it ultimately prevents life-threatening
heartworm disease.

In honor of National Heartworm Awareness Month, investigate heartworm preventive options
for your pet. Give our team a call to discuss the heartworm preventive that will best keep your
four-legged pal safe from disease.