By Jean Durbin
Heartworm disease is a silent invader that could pose a serious health risk to your canine companion, and could result in his or her death. Your pet is relying on you, his best friend, to see that he is protected.
Is your dog at risk? How do you know? If you find out your dog does have heartworms, what then?
Many pet owners have never even heard of heartworms; some have but have no idea what they are or how deadly they are. Many people believe that heartworms are a problem for dogs only in the Southern United States, or other warm summer locations. As it turns out, heartworms are found everywhere now, even coastal Humboldt County.
What are heartworms and why are they such a concern? The heartworm is an internal parasite that can grow into an adult some 10-12 inches long in only a year. The scientific name is Dirofilaria immitis. They live in the dog's heart chambers, larger blood vessels and lungs. Their presence greatly hampers normal respiratory function; they can, in time, completely fill the chambers of the dog's heart, making it impossible for adequate volumes of blood to be circulated. The adult heartworms can live inside the dog for up to seven years and a dog can harbor as many as 250 individual worms. Their presence can result in heart failure, liver, kidney and lung problems. Left untreated, any of these conditions will result in the pet's death.
The only way to be sure your pet does not get heartworms is to have a test done by your veterinarian, and, if the dog does not have them at that time, put the dog on a preventive program. There are several drugs available, both topical and ingestible; all are given periodically, usually monthly. All are prescription medications and should be obtained from your veterinarian, not from an online provider.
What if the test shows that your dog already has heartworms? Treatment is available for many cases and the precise method depends on the severity of the infection. The method most certain to effect a cure is very hard on the patient; it sometimes results in the death of the dog. As the worms die, they break up and move through the blood vessels. The chances for an embolism, or blood clot, are very high. The more serious the infection at the time of treatment, the more risk to the patient during treatment. Further, the dog must have severely restricted activity for up to 2 months since running or jumping increases the chance for fatal embolisms to occur. The treatment involves a series of injections of Imiticide, an arsenic compound. Dogs that have a very slight infection have a fairly high chance of successful treatment.
As the level of infection rises, so do the risks of a fatality. Once the infection has reached a level where there are outward symptoms (difficulty breathing, coughing, enlarged heart, enlarged liver, easily tiring during exercise, fluid retention), treatment is seldom considered a viable option. The dog simply is not well enough to tolerate it.
How does a dog get heartworms? Transmission occurs with a mosquito bite, if the mosquito is carrying the infective larval form. Mosquitos can become infected by biting an infected dog, or any member of the Canid family, or even humans. Dogs are much more easily infected than are cats and humans. After the larval form is transferred to the dog (also called the host), the larvae migrate through the body for several months and grow to maturity while traveling. When mature, they lodge in the heart, lung and associated blood vessels. Any one of a large number of mosquito species can carry the heartworm larvae.
Then, the adults mate and begin producing offspring, which are called microfilariae. The next time a mosquito bites the infected dog, the microfilariae are transmitted to the mosquito, where they undergo a slight change that makes them ready to infect a dog in about 2 weeks. The next time an infected mosquito bites this already-infected dog, the cycle begins again and the dog acquires more adult heartworms. The more bites from infective mosquitos, the more adult heartworms. It's easy to see that with repeated mosquito bites, a single dog could, in time, have several dozen adult heartworms living in its heart, lung and related blood vessels, resulting in those organs being barely able to function. By the time the symptoms of this effect show up, it's probably too late to try to cure the disease. At this point, the dog does not have long to live and it might be most humane to have it put to sleep.
This is why it's important to find out as soon as possible if your pet has already been infected; if caught early enough, it is treatable, though the treatment is rigorous and not without risk. If your pet has not been infected, then putting and keeping him on the preventive program will almost certainly assure he will not become infected.
You should have your veterinarian test your dog right away if your dog is not now on heartworm prevention. If he is positive, follow your vet's recommendations regarding treatment, and if he is negative, you can consider yourself very lucky! Then, put your pet on the preventive and rigorously stick to the dosage intervals. In this situation, as with so many others, "an ounce of prevention is worth a pound of cure".
If you wish to know more about heartworms in dogs, make an appointment with your dog's veterinarian. You can also find a lot of information on a superb website maintained by the American Heartworm Society at http://www.heartwormsociety.org/ Detailed information on this disease, which was the source of the factual material in this article, is on their web page: http://www.heartwormsociety.org/pet-owner-resources/learnmore.html.
I wish to thank the American Heartworm Society for maintaining a website that provides copious, easily understandable information about this deadly disease affecting an increasing number of our canine best friends, and for its generosity in allowing me to use material that appears on their website, including the diagram.