Heartworm in Dogs

In spite of its name, heartworm don't always live in your dog's heart, but instead
make their home in the large arteries carrying blood from his heart to his lungs.

There, they cause inflammation to the lining of the arteries, which leads to blood
clots and blockages.

Your dog's heart will need to work harder to pump blood through the blocked arteries
which can ultimately lead to heart failure and death.

Immature heartworms are spread from dog to dog by mosquitos. For heartworm to become a problem in any given area, there need to be the right species of mosquito to transmit the infection, and the climate must be warm enough to let the worm larvae develop inside the mosquito. In some parts of the country, the weather is just too cold in winter for heartworm to be transmitted to dogs.

The heartworm has a very interesting lifecycle.

1. These worms don't lay eggs but give birth to live babies called microfilaria, or first stage larvae. They are carried around in the blood stream until they are taken up by a mosquito as it drinks your dog's blood.

2. When the microfilaria is inside the mosquito's body, it takes a few weeks to develop into second stage and then third stage larvae. Then, the mosquito is able to infect another dog when it feeds on it. This can take a few weeks. The climate plays a role in this stage of the lifecycle; if it is too cold, the mosquito will die before it can pass the third stage larvae to another dog.

3. When the larva is injected into a new host, it will spend a few months living in the dog's skin while it develops into a 4th and then 5th stage larva. At this point, the larva makes its way into the bloodstream and is carried to the heart and pulmonary arteries. It will then mate and produce another generation of microfilaria.

It takes around 6 months from when a dog is first infected with heartworm, until those heartworm reach adulthood and start producing microfilaria.

Testing for Heartworm

There are two tests available to check if your dog has acquired heartworm infection. The first involves looking for proteins on the adult worms and if it is positive, then you know that there are adults living in his arteries. The second test checks for microfilaria in his blood.

This means that you can't tell if your dog has heartworm until 6 months after he has been infected.

Prevention and Treatment of Heartworm Disease

It's important to differentiate between the terms "heartworm" and "heartworm disease". Your dog can have heartworm, but have no signs of illness caused by the worms. Symptoms of heartworm disease include lethargy, coughing and an enlarged abdomen.

It is possible to treat your dog to get rid of any heartworm in his body but it can be costly and the treatment may have its own side effects. A better option is to give him a preventative on a regular basis. You have the option of using a tablet once a month, or even a topical treatment that is applied to his skin. There is also an injection that will control heartworm for several months.

All of the preventatives on the market don't prevent infection, but instead they kill the third and fourth stage larvae so they don't develop into adults. Some drugs also kill young fifth stage larvae.

If you live in a heartworm area, it's essential that you treat your dog to prevent any larvae from developing into adult worms, and save him from the severe effects of heartworm disease. Your vet can help you choose a preventative that suits your budget and your lifestyle.