What's In Your Dog's Heart?

Let's talk about something that's near and dear to my heart and your dog's...literally. This is a hot topic of discussion among many veterinarians and dog owners in the southern US right now; we're talking about Heartworm disease. According to the newest guidelines published by the American Heartworm Society..."It is estimated that currently more than 1 million dogs in the United States are infected with heartworms. This potentially fatal disease has been found in dogs native to all 50 states. Even as diagnostic methods advance, preventive therapies improve and disease awareness increases among veterinary professionals and pet owners, heartworm continues to present a serious threat to dogs’ health."

Heartworm disease is a deadly and devastating, parasitic infection affecting the heart. The parasite responsible for this disease is a long, slender worm called Dirofilaria Immitus. D. Immitus is the only worm that infects dogs in this way. The disease is not contagious; however, the disease is transmitted through a mosquito bite and cohabitating dogs may easily all be infected. Here in the state of Mississippi, the disease is widespread due to our overwhelming mosquito population. For some time, there have been products available to prevent heartworm disease. Almost all of these products are inexpensive and administered monthly. Speak to your veterinarian for specific product recommendations.

Life Cycle
The dog is infected by a mosquito bite, which transmits the heartworm larvae. (The mosquito is the only vector for transmission because the first stages of larval development must occur inside the mosquito.) From this point, the heartworm larvae mature and migrate to the pulmonary artery of the heart. After approximately six months, the larvae mature into an adult stage heartworm. These mature heartworms reside in the pulmonary artery and right side of the heart and feed off the blood in the heart. Adult male and female worms reproduce. Over the course of another 3-9 months (depending upon the size of the dog, season, etc.) these adults have multiplied from a few worms to possibly hundreds of worms.

Disease Stages
The heartworm can be readily picked up on a routine screen test at early stage disease. However, the dog will be asymptomatic (not showing signs of infection) during the early to middle stages. This is due to the fact that a low number of worms can be present and detected on a test but not cause enough damage or occlusion to create a problem in the dog. For this reason, we at Brandon Veterinary Clinic perform heartworm tests on every annual vaccination visit. Unfortunately, dogs that are not on heartworm prevention and that do not have routine, yearly tests may be infected without the owner realizing it. As the number of worms increases, the disease state also advances. If untreated, the large number of worms in the heart eventually begins to physically obstruct the chambers of the heart. The heart enlarges somewhat to compensate, but eventually is left severely strained and debilitated. At this point, the heart can no longer compensate by its normal mechanisms and blood begins to back up in the system. The overloaded blood vessels in the lung tissue begin to leak. This leads to congestive heart failure, which is fluid accumulation in the lungs and ultimately in the abdomen due to heart disease. The dog then begins to develop a cough (from the fluid accumulation and heart enlargement) and becomes lethargic, reluctant to exercise, and easily “winded”. Unfortunately, these signs only develop late in the course of disease. Thus emphasizing the importance of heartworm prevention and testing. If left untreated, the disease can be severely debilitating and even fatal.

Treatment
Heartworm treatment consists of a series of injections with a drug called “Immiticide”. It is currently the only FDA approved drug available for the safe and effective treatment of heartworm disease. The treatment is effective but can be costly, reaching into the thousands of dollars; severly affected dogs will be at considerable risk with treatment. Dogs must be evaluated thoroughly prior to the start of a treatment protocol; this includes blood work, x-rays, and a physical examination. Typically, one or more pre-treatment medications will be started to facilitate a safe and effective outcome. Dogs must also be confined and put on restricted activity during and after treatment. Many dogs have been treated successfully, but the treatment process is long, can be complicated, and is expensive.

Prevention
There are many heartworm prevention products on the market, most of which are very inexpensive, relative to the cost of treatment. Most prevention products are given monthly as a treat or as a topical application and although these products are effective, if heartworm prevention is not given every 30 days, a heartworm infection is likely to develop.

"As the United States economy continues to struggle, we as Americans closely inspect our monthly spending for what is and isn't necessary. It's tempting to cut preventative heartworm care for pets, but the cost of prevention is still relatively low compared to the cost of treatment if heartworm disease is diagnosed. Both dogs and cats may needlessly suffer and possibly die from this completely preventable disease. The risk from the increased mosquito population makes the need for prevention even greater this year," says Dr. Sheldon Rubin, American Heartworm Society president and Chicago area practitioner.

Heartworm Disease in Cats

Yes, your cat can get heartworm disease. Although it's really a canine specific parasite, the cat is the second most reported domestic species that can acquire the parasite. The cat is not very tolerant of the parasite either; it only takes a few worms to cause a devastating respiratory disease in cats. There is currently no FDA approved treatment for heartworm disease in the cat, however there are preventive products that are safe, effective and FDA approved for the cat.

As you can see, it is critical to keep your pet on monthly heartworm prevention to avoid this devastating disease.

To watch a video animation of heartworm disease click here.

For more information on heartworm disease visit http://www.heartwormsociety.org/

The American Heartworm Society, headquartered in Batavia, Illinois, is the global resource for the prevention, diagnosis and treatment of heartworm disease and was formed during the Heartworm Symposium of 1974. The American Heartworm Society stimulates and financially supports research, which furthers knowledge and understanding of the disease.