Learn About Heartworm Disease In Dogs

Heartworm is a severe and potentially fatal disease in dogs known as dirofilariasis. The leading cause of this disease is a blood-borne parasite called immitis.

Infected dogs have adult heartworms in their hearts, pulmonary arteries, and nearby large blood vessels. Worms may occasionally be discovered in other areas of the circulatory system. Female adult heartworms measure 1/8″ wide and 6-14″ long (15-36 cm) in length (3 mm).

The size of males is roughly half that of females. When diagnosed, a dog might have 300 worms present. Heartworms in adults can live for up to five years. Millions of microfilaria, the females’ offspring, are produced during this period. This microfilaria primarily inhabits tiny blood vessels. In this article, you will learn the details of heartworm disease in dogs.

Life Cycle of Heartworm

The heartworm’s life cycle is not simple as a mosquito is required to complete the life cycle. There are almost 30 species of mosquitoes that can transmit this heartworm disease.

The problem starts when a female mosquito bite the dog and microfilariae is ingested in the blood meal. Before entering the mosquito’s mouthparts, the microfilariae develop in the insect’s gut for 10 to 30 days. They are infective larvae and can fully develop when entering a dog. Infectious larvae are injected into the dog’s body when a mosquito bites a dog.

Areas Where Heartworm Disease Is Common

This heartworm is expected in the whole world among dogs. Once, the disease was limited to the south and southeast regions. The highest numbers of reported cases are still within 150 miles of the Gulf of Mexico and the Atlantic Ocean coastlines and along the Mississippi River and its tributaries.

However, the disease is spreading and is now found in most regions of the United States, including California, Oregon, and Washington.

How Heartworm Disease Spreads

The disease does not spread by dog-to-dog as a mosquito is needed as an intermediate host. It means this disease has a greater spread during the mosquito season. If the mosquito season is long in an area, the number of heartworm-infected dogs will also be more significant.

What Happens In Heartworm Disease?

Unfortunately, we cannot diagnose the disease in its early stages. It will take 5 to 7 years to mature and show any clinical signs. Adult heartworms clog heart vessels and interfere with the function of heart valves. They also reduce the blood flow to the lungs, liver, and kidneys. Consequently, decreased blood flow and oxygen to the body’s organs may lead to failure.


Melarsomine (trade name Immiticide®), an injectable medication, is administered to kill adult heartworms. Adult heartworms in the heart and surrounding vessels are killed by melarsomine. A series of injections are used to administer this medication.

Your vet will decide the precise injection schedule based on your dog’s health. Most dogs receive an initial injection, a 30-day rest period, two additional injections spaced 24 hours apart, and a third injection.


Heartworm is a fatal disease in dogs that spreads through mosquitoes and not from dog to dog. We cannot diagnose this disease at early stages before elapsing 5 – 7 years as the condition does not show any clinical signs before.

The dogs may suffer from vital organ failure during this disease. Melarsomine drug is injected into an affected dog as a treatment for heartworm.

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