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Posted on 07-14-2017

Heartworm Disease

What is heartworm disease?

Heartworm disease is a serious and potentially fatal disease in pets that can result in lung disease, heart failure and other organ damage.  It is caused by long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets.  It can affect many different types of animals, but we’re concerned about your dog or cat and this article centers on the prevention and care of your dog or cat should it be affected by heartworms.

The heartworm is spread through the bite of a mosquito.  The dog is the definitive host, meaning that the worms mature into adults, mate, and produce offspring while living inside a dog.  The mosquito is the intermediate host, meaning that the worms live inside the mosquito for a short period of time.

The worms are called “heartworms” because the adults live in the heart, lungs, and associated blood vessels of an infected animal.

DOGS  The dog is a natural host for heartworms. If left untreated, heartworm numbers can increase, and dogs have been known to harbor several hundred worms in their bodies.  Heartworm disease causes lasting damage to the heart, lungs and arteries, and can affect the dog’s health and quality of life long after the parasites are gone.  For this reason, prevention is the best option, and treatment—when needed—should be administered as early in the course of the disease as possible.

CATS     Heartworm disease in cats is very different from heartworm disease in dogs. The cat is an atypical host for heartworms, and most worms in cats do not survive to the adult stage.  Cats with adult heartworms typically have just one to three worms, and many cats affected by heartworms have no adult worms. While this means heartworm disease often goes undiagnosed in cats, it’s important to understand that even immature worms cause real damage in the for

m of a condition known as heartworm associated respiratory disease (HARD). Moreover, the medication used to treat heartworm infections in dogs cannot be used in cats, so prevention is the only means of protecting cats from the effects of heartworm disease.

How is heartworm disease transmitted from one pet to another?

The mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic baby worms called ‘microfilaria’ that circulate in the bloodstream.  When a mosquito bites and takes a blood from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal's skin and enter the new host through the mosquito’s bite wound.  Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms.  Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

What are the signs of heartworm disease in dogs?

In the early stages of heartworm disease, many dogs show few symptoms or no symptoms at all.  The longer the infection persists, the more likely symptoms will develop.  Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced clinical signs.

Signs may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss.  As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen.  Dogs with large numbers of heartworms can develop a sudden blockages of blood flow within the heart leading to a life-threatening form of cardiovascular collapse.

What are the signs of heartworm disease in cats?

Signs of heartworm disease in cats can be very subtle or very dramatic. Symptoms may include coughing, asthma-like attacks, periodic vomiting, lack of appetite, or weight loss. Occasionally an affected cat may have difficulty walking, experience fainting or seizures, or suffer from fluid accumulation in the abdomen. Unfortunately, the first sign in some cases is sudden collapse of the cat, or sudden death.

How can I determine if my dog or cat has heartworms?

The most common test to check for heartworms is called an antigen test.  This is a blood test the detects specific proteins, called antigens, which are released by the adult female heartworms.  Antigen test can accurately detect infections with one or more adult female heartworms that are a least 7 to 8 months old.  The test generally does not detect infections that are less than five months old.

There are tests that detect the microfilariae in a dog’s bloodstream, but again this is after 6 to 7 months after it is bitten by an infected mosquito.

When should I test my dog for heartworms?

Dogs older than 6 to 7 months of age should be tested for heartworms before starting heartworm prevention medication.  Remember, prevention is the best cure to stopping heartworm disease.  Heartworm preventives do not kill heartworms.  Giving a dog preventive medication that may have heartworms may be harmful or deadly to the dog.  Any infected dog must be treated to kill and remove the heartworms before any preventive measures can take place.

An annual testing for heartworms is recommended.  April is Heartworm Prevention Month and is a good time to have your dog tested for heartworms.

What is the treatment should my dog have heartworms?

A powerful drug called Immiticide has been approved by the FDA to kill adult heartworms in dogs.  Immiticide contains arsenic, which kills the heartworm, and is given by deep injection into the dog’s back muscles.  Other FDA approved drugs called Imidacloprid and Moxidectin are used to rid any microfilariae in the dog’s bloodstream.  These drugs are a topical solution applied to the dog’s skin.

Any treatment for heartworm disease is not easy on the dog or the owner.  Treatment can be potentially toxic to the dog’s body and can cause serious complications.  Treatment is expensive because it requires multiple visits to the clinic, bloodwork, x-rays, hospitalization, and a series of injections with Immiticide.

There is no FDA-approved drug for the treatment of heartworm disease in cats, although symptoms may be managed with medications.  You need to talk with your veterinarian about the treatment of heartworms in your cat.

The Best Treatment is Prevention!  Year-round prevention is the best!

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