Do you know these creepy facts about heartworm disease?

Heartworm disease is a serious and potentially fatal disease. The good news is that it is preventable!

Heartworm is just what it sounds like. Blood-borne parasites known as Dirofilariaimmitis are worms that live in the heart, lungs and adjacent blood vessels of affected animals. This can cause potentially fatal heart disease, lung disease and damage to other organs.

Dogs are considered the natural host of heartworms, but cats can also be infected.

Heartworm disease in dogs can be very serious. Since dogs are natural hosts, the worms live happily in the blood stream reproducing year after year. Dogs can carry hundreds of heartworms in their body. This can lead to severe damage of the heart and lungs, with effects that can last long after the disease is treated. Heartworm prevention is the best way to keep your dog healthy. Treatment, when needed, should be initiated as quickly as possible.

Cats are an atypical host for heartworms so most worms do not live to the adult stage. Unlike dogs, cats with heartworms normally host only 1 or 2 adult worms and many only host immature worms. Despite being immature, these parasites can still cause severe respiratory problems.

Prevention is the only real way to protect cats from heartworm disease, as the medication used to treat dogs is not safe for use in cats.

Unfortunately, many cats with heartworms go undiagnosed.

How is heartworm disease transmitted?

Heartworms need an intermediate host in order to transfer from one animal to another. So, an infected animal cannot directly pass heartworms to another animal.

In this case the host is the mosquito. Adult female heartworms produce microfilariae, basically microscopic baby worms that circulate in the infected animal’s bloodstream. Whena mosquito bites the animal it ingests the microfilariae. They develop into infective larvae in the mosquito for 10 -14 days. When the mosquito bites another animal, the infective larvae enter the bloodstream through the bite.

It will take approximately 6 months for the larvae to develop into mature heartworms. For the first three months the larvae travel through the animal’s body, eventually arriving in the blood vessels of the lungs. In the next three months they continue to mature into adults, eventually growing to lengths of up to 14 inches. The worms can live 5-7 years in a dog and 2-3 years in a cat.

The mature worms are found mainly in the pulmonary arteries, the arteries surrounding the lungs, but severe infections may also have worms in the heart. The worms damage blood vessels and decrease the heart’s ability to pump blood. This results in serious, potentially fatal lung and heart disease.

The mature worms mate, producing microfilariae. Often, the animal’s body will mount an immune response to the microfilariae in the blood. This can cause damage to other organs.

Heartworms are found everywhere in the United States, as well as in other parts of the world. All unprotected dogs and cats are at risk for contracting heartworm disease.

What are the signs of heart worm disease?

Animals that have been recently infected with heartworm disease may have no clinical signs, making early diagnosis difficult. As time goes on and the infection gets worse animals will often begin to cough, have difficulty breathing, become lethargic and have a decreased appetite. Dogs often seem to tire easily, even with mild amounts of exercise. Cats may vomit or show signs of weight loss.

In severe infections both dogs and cats may collapse suddenly and die.

Testing for heartworm disease

Luckily, there is a test to diagnose heartworm disease, even if your pet is not showing signs. The American Heartworm Society recommends that all dogs be tested for heartworm disease yearly. There is a quick blood test that your veterinarian can run in clinic to test for heartworm infection in your dog. This test is very reliable. If the test comes back positive your vet will likely send blood to an outside lab to confirm the diagnosis. Your vet may also want to take chest X-rays, run a full blood panel and have an echocardiogram done on your dog. These tests will help evaluate the severity of the heartworm disease and will help your veterinarian know what the best course of action is for treatment.

Diagnosis in cats is more difficult, as are most things when it comes to cats. Due to the small worm load in cats, it may be much more difficult to diagnose the infection. Your veterinarian will want to run the same tests as with dogs. Even with those tests the answer may not be conclusive.  

How is heartworm disease treated?

As with many things it is easier to prevent heartworm disease than it is to treat it. We will discuss prevention in just a moment.

If your dog is diagnosed with heartworm disease, there is a treatment available. The goal of this treatment is to kill all of the worms in the dog’s body. This comes with some risk to the dog and it is important to follow all instructions from the veterinarian when your dog is being treated. The worms are dying within your pet’s body and his immune system is mounting a response to remove them. The dog’s body is being asked to do quite a bit of work. Your dog will need to be on strict cage rest while on treatment and likely for a while afterwards. He may also need to be on other medications to manage clinical symptoms and reduce the risk of complications.

There is currently no treatment for heartworm disease in cats. If your cat is diagnosed with heartworm disease your veterinarian may recommend medications to manage the symptoms. Occasionally surgery may be recommended to remove the worms. This surgery is high risk, but in severe cases it may be the only way to save an animal’s life.

How do you prevent heartworm disease?

Luckily, heartworm infection is preventable! There are a number of heartworm preventatives that have been approved by the FDA on the market and your veterinarian can help you decide which is right for your pet. These medications do not kill off worms that are present in the animal’s body, they just help prevent any new ones from infecting the animal. It is important to get your pet tested before starting heartworm preventative to ensure they are not infected.

The medications come as either chewable tablets, topical treatments or injections. Some even combine heartworm prevention with prevention for other parasites, making it simple to protect your pet.

It is imperative that you remember to give your pet every dose of the medication. Skipping or putting off a dose reduces the efficacy of the medication and can lead to infection.

There are reports of animals becoming infected with heartworms despite being on preventatives, so it is still important to get your pet tested yearly.