Heartworms: What's the big deal?

posted: by: Megan Sims, DVM Tags: "Clinic Specials" "News" 

Heartworms: What’s the big deal?


What are they?

 -Heartworms are parasites that live in the heart and lungs of unprotected dogs and, to a lesser extent, cats. They are highly prevalent in Texas and can potentially be life threatening to pets.

How are they transmitted?

- Heartworms are transmitted by mosquito bites. The mosquito injects the immature worm into the skin of dogs/cats. This immature form then migrates through the body of the affected host to eventually set up shop as adult worms in the heart and lungs. These worms (which can grow to be 10-12 inches long!) begin to reproduce, sending the immature worms throughout the bloodstream. If a mosquito then bites this dog or cat and the mosquito takes up some of these “baby” heartworms as part of their blood meal, then the cycle repeats.

How do I know if my dog or cat is infected with heartworms?

- Heartworm infection (known as “heartworm disease”) is a very insidious process. It can take months or even YEARS for an animal to begin to display clinical signs of the disease. For dogs- typically, clinical signs can include coughing, difficulty breathing, weight loss, reluctance to exercise and lethargy. Less common signs can include discolored urine, pale gums, and sudden collapse.  Cats tend to have less severe, more subtle signs of infection- asthma-like symptoms, weight loss, occasional vomiting or lack of appetite.

How are heartworms diagnosed?

- Here at Belton Small Animal Clinic, we recommend that all dogs be tested yearly for heartworm disease. This includes drawing a small amount of blood to perform a microscopic evaluation of the sample to look for microfilaria (the “baby worms” circulating in the bloodstream), as well as an American Heartworm Association approved laboratory SNAP test. This SNAP test demonstrates the presence of adult worms in the dog by detecting a specific protein made by adult female heartworms.

- For cats, there are fewer readily available tests for veterinarians to use. If heartworm disease is suspected (usually through the evaluation of chest x rays in clinically ill patients), we can send a blood sample to diagnostic laboratories for more information.

OK, my dog or cat tested positive, what’s next?

 - For dogs, the current recommendation from the American Heartworm Association is a series of THREE injections of an immiticide known as melarsomine. This medication is designed to kill adult heartworms that are living in the dog. The use of melarsomine is somewhat risky, however. If the dog is very active during the course of treatment, small pieces of these dying worms could potentially break off and cause “pulmonary emboli”- essentially, clots in lungs that could be life threatening. As such, it is absolutely imperative that the dog be kept in strict confinement during treatment and up to 6 weeks after the conclusion of treatment. Immiticide treatment typically includes hospital stays during and a few days after injections are given to monitor for reactions to treatment, including pain/swelling at the site of injection. Most dogs are heartworm negative after 1 full course of immiticide treatment, however, rarely multiple course of treatment are needed. The dog should be on approved, veterinary prescribed heartworm prevention from the time of diagnosis, through treatment, and for the rest of the dog’s life to prevent NEW infections from the local mosquito population.

 -Cats are typically treated much more conservatively. Cats, as a general rule, tend to have less severe infections with smaller numbers of worms. There is not an improved immiticide treatment for cats at this time, so treatment is directed at managing clinical signs.

 -The myth of the “slow kill” method: Some Internet resources may recommend the “slow kill” method for treating heartworm infections in dogs. This method involves placing the dog on heartworm prevention monthly, sometimes with intermittent courses of an antibiotic called Doxycycline.  In this protocol, there is no actual treatment of the existing worms; instead, the heartworm prevention simply prevents new infections as the existing worms live out a normal lifespan in the dog and die of old age (typical heartworm lifespan is 5-7 YEARS!). These existing worms cause structural and functional damage to the heart and lungs, which could lead to sudden death, heart failure, and other complications. The American Heartworm Society does not recommend this method.

 The good news is that this terrible disease can be PREVENTED! Prescription heartworm preventatives for cats and dogs provided by your veterinarian are incredibly effective at killing the microfilarial (“baby worms”) stage of heartworms, preventing them from growing to adults and causing structural heart and lung damage.

Ask your veterinarian which product is best suited for your pet and lifestyle.  Monthly oral and topical products are available.

For more information, please come in and see us at Belton Small Animal Clinic! Through the month of April, if you purchase 12 months of prevention your heartworm test is free.