Heartworm disease is caused by an internal blood-borne parasite that grows within an infected animal’s heart.  While many species can be infected, we veterinarians primarily are concerned about infections in your dog. It can only be transmitted through the bite of a mosquito. Once inside an animal it grows through several immature life stages and six months later emerges an adult that grows, lives and reproduces within the chambers of the heart and surrounding blood vessels. So many worms can be present that these chambers and vessels become blocked leading to heart failure, lung disease and death.  Infection can be prevented by the simple monthly, oral administration of a medication that will eliminate the immature worms before they can cause disease. There is also an injectable form that can protect for up to six months. Mosquitos are currently becoming active in our area, so it’s important to protect your animals now. There can often be a lot of confusion about this disease. I’ll set you straight by addressing some common questions or statements I hear in our hospital. 

“My dog doesn’t have heartworm. I haven’t seen any worms in her stool.”

While the juvenile forms live and migrate through many body tissues the adults live in the blood system. You’ll never see heartworms in the stool. Your veterinarian performs a blood test to check for evidence of the presence of adult worms in the heart. This test is so sensitive that it is able to detect only a few worms if present. A different blood test can detect juvenile worms circulating in the bloodstream.

“My dog doesn’t really go outside so he can’t get heartworm and I don’t need to worry about it.”

Duh. MOSQUITOES CAN GET IN YOUR HOUSE! I never quite understand this statement. Don’t all dogs in our area do their “business” outside?  A mosquito can find them and bite in under a minute. It only takes the bite of one carrier mosquito to cause an infection. All dogs in our area are at risk for heartworm disease. Even more so now as many dogs are being transported from the south through rescue organizations. Many of these dogs come infected with heartworm and spread it to the mosquito population putting our dogs at increased risk. There has been an increase in heartworm disease in the northeast ever since Hurricane Katrina led to rescue groups dispersing southern dogs throughout the country.

 “How can I tell if my dog has heartworm disease?”

Adult worms living in the heart cause blockage of the blood flow to the heart and lungs. This leads to congestive heart failure. Dogs with this will usually have a cough, shortness of breath, lethargy, exercise intolerance, weight loss and difficulty breathing.  Left untreated these can become fatal.

“Can it be treated?”

There is a treatment available for dogs that develop heartworm disease. Often the disease has been present for so long before signs develop that there can be irreversible changes in the heart. The treatment is there for difficult, lengthy and needs to be customized for each patient.  Recent research found that the worms themselves are infected with a bacterial parasite. This also needs to be treated with appropriate antibiotics before and during treatment as even the worm’s parasite can cause symptoms in the infected dog.  The drug used to treat heartworm has been in limited supply over the past year making prevention even more important. Of course all of this treatment is very costly. It is much more difficult and expensive to treat this disease than to prevent it.

Look for more questions and answers coming up in Part 2 next week. Please post your comments or questions  here so I can add those as well.



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