News you can use: Heartworm disease- What you really need to know!!

What is heartworm and what disease can it cause in our pets?

Heartworms are large worms (potentially up to one foot long) that live in the pulmonary arteries of dogs or cats (the blood vessels that carry blood from the heart to the lungs), but can also be found in the heart and lungs themselves.  Heartworms can be found in dogs, cats and ferrets as well as some wild animals such as wolves or coyotes.  Since dogs are a natural host for heartworm, adult worms living inside dogs can mate and produce offspring that can be transmitted to other dogs.  Heartworms in dogs can cause damage to not only the heart, but also the lungs and arteries.  Signs of heartworm disease in dogs can include cough, exercise intolerance and weight loss.  When large numbers of worms are present they can back up into the right side of the heart severely affect the amount of blood that can enter the heart and be pumped to the lungs, this is known as caval syndrome and can be life threatening.  Cats, however, are not a natural host and those that become infected often only have a small number of worms that often do not mature to adults.  Heartworm disease in cats is more respiratory in nature but is still a serious concern.

How is heartworm spread between pets?

In order for transmission of heartworm between animals to occur mosquitos must be present.  When a mosquito bites an infected dog and ingests blood from that animal they can pick up immature heartworms called microfilaria that are being produced by the adult heartworms.  Within the mosquito the microfilaria will mature to a stage that can then be transmitted to a new dog or cat when this mosquito bites them.  It takes 6 months for the heartworms to mature within the tissues and the blood of the newly infected animal, but once mature they can live for a significant period of time.

What is the risk of your pet acquiring heartworm disease and how can you prevent it?

At this time it is difficult to determine what factors may increase the risk of heartworm transmission in a given area.  However, we do know that heartworm disease has been diagnosed in all 50 states and infection rates can vary.  The American Heartworm Society recommends ensuring your pet has a heartworm preventative for all 12 months of the year.  A variety of heartworm preventatives exist for both dogs and cats.  All heartworm preventatives target only the immature heartworms, not the adults.  It is important that both outdoor and indoor pets are given a heartworm preventative as mosquitos can easily enter the home. Prevention is extremely important in cats as the disease can be difficult to diagnose and the treatment currently used in dogs cannot be used in cats.  All heartworm preventatives target only the immature heartworms.  Your veterinarian can recommend and prescribe the product that is best for your pet to help protect them from heartworm disease all year long. 

How do you test for heartworm?

Testing should be performed annually for dogs even if they are on a monthly heartworm preventative to ensure that the medication is working correctly.  All dogs, except for puppies under 7 months of age, should be tested before they are started on a heartworm preventative or if they have been off a heartworm preventative for any length of time.  The timing of testing is different with cats because diagnosis of heartworm in cats is more difficult.  The test in dogs is a simple blood test that can sometimes be run right in the clinic.  In cats testing also includes diagnostic imaging because they typically have such low numbers of worms present when they are infected.  It takes a minimum of 6 months for an animal to have a positive test after they have been infected with heartworm. 

How is heartworm disease treated?

Your veterinarian will come up with a specific treatment plan for your pet once the diagnosis of heartworm disease has been confirmed.  It is important to note that the larger the worm burden is the more severe disease can be and the more difficult it may be to treat.  Treatment is different for cats and dogs, but can involve multiple medications and take several weeks to complete.  6 months after the treatment regimen is completed a repeat heartworm test will be performed to confirm the success of treatment. 

For more information on heartworm disease and how to prevent it in your pet please seek the advice of your veterinarian or access the American Heartworm Society website. 

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Rebecca Mycock, DVM