By Annette M. Dixon, DVM
Heartworm disease is one of the easiest diseases to prevent. However veterinarians throughout the area and the United States diagnose it regularly in dogs and cats. Why is such a preventable disease such a problem? Maybe it is because the owner does not see it as a threat.
Heartworms, or Dirofilaria immitis, are long, thread-like parasitic worms that live in the heart and pulmonary arteries of its host. The female heartworm can be up to 12 inches long while a male heartworm will only be up to seven inches long. A female heartworm can live in a dog for up to seven years. Heartworms were originally found in the tropical parts of the world. Heartworms are now found in Australia, Japan, Europe and in all fifty states of the US.
Dogs are the primary host for heartworms. However cats, ferrets, and even humans can be susceptible to infection. A mosquito is infected with microfilariae (baby heartworms) when it feeds (bites) on a heartworm infected host (dog). When that mosquito bites the next dog, it passes the microfilariae on. Research has shown that of the mosquitoes living around a heartworm infected dog, over 60% of the mosquitoes will be carriers of the disease.
Once the microfilariae are living in the dog, it takes them up to six months to develop into adult heartworms. After the adult heartworms take up residence in the heart and pulmonary arteries, they interfere with the normal blood flow. Over time heartworms will cause congestive heart failure and even cardiovascular collapse. Clinic signs of heartworms include exercise intolerance, persistent cough, lethargy, decreased appetite, weight loss and an enlarged, swollen abdomen. However many times heartworm disease is diagnosed in dogs with no symptoms.
A simple five minute blood test can be run at your veterinary office. Any dog over months of age that has not been on heartworm prevention needs to be tested before any preventive medication is started. A dog with heartworm disease can have a serious anaphylactic reaction to the preventive medication. Any dog that is currently on heartworm preventative needs to be tested annually. Just because your dog has been receiving the preventive medication monthly does not mean it has been 100% protected. Human error, forgetting to give a dose especially in the winter, is the number one reason for failure. The dog could also vomit up the medication and the owner never know. The manufacturer of Heartgard Plus guarantees the preventative if your dog is tested annually and you purchase your Heartgard Plus from your veterinarian. Even if your dog develops heartworms because you forgot to give the Heartgard Plus, the manufacturer will still pay for the full treatment.
If heartworm disease is caught early on, the dog can be treated. Treatment is costly to the owner and painful to the dog. Treatment is a series of two injections of an arsenic-based drug. These injections are given in the back muscles and are very irritating to the tissues. Once treated, the dog must be confined and under exercise restriction for six weeks. The heartworms slowly die inside the heart and vessels and then must be absorbed by the body. The dog is at risk of a pulmonary embolism in those first six weeks.
Nine weeks after initial heartworm treatment the dog needs to be retested. 95% of dogs will be cleared of heartworms at that time. The other 5% that are positive need to be monitored and retested again in six months. All treated dogs are started on the heartworm preventive regardless of test results.
All dogs should be on heartworm preventative year round. This is given monthly. To be effective the preventative needs to be given properly and timely. The heartworm preventative does not stop exposure but actually kills any microfilariae the dog has been infected with in the last 30 days. Once the microfilariae develops into the adult form, it is no longer affected by the preventative.
Heartworm preventative is a safe and affordable way to keep your dog free of heartworms. Many heartworm preventatives also aid in the control of certain intestinal parasites. Ask your veterinarian what is best for your pet.
And for those of you wondering about your cat, heartworm disease is deadly in cats. One adult heartworm can kill a cat. Most owners will just find their cat dead. There is a test for heartworms in cats but there is no treatment. Heartworms can be prevented in cats with a monthly preventative just like dogs. Again, talk to your veterinarian.
If you have any questions concerning heartworm disease or any thing else about your pet, please call Clarksville Veterinary Clinc at 573-242-3444 or Clarksville Grooming and Boarding at 573-560-3233. We care about the health of your pet!