Dogs that spend time outside are prone to heartworm infestation, spread by mosquitoes. Treatment is very lengthy and costly, and dogs can feel the effects of the disease for several years after treatment, so prevention is best. Although created as a heartworm preventative, Heartgard can also be used as a part of a two-part treatment plan for an infestation in progress.
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Heartworms
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Mosquitoes transmit heartworms from dog to dog. Although a dog catches heartworms from mosquitoes, the contagion is really dog-to-dog. When a mosquito bites an infected dog, immature heartworm larvae enter the mosquito with the dog's blood. When that mosquito bites another dog, the heartworms enter the bloodstream of the new dog, where they migrate to the heart and its major arteries. Once safely situated, the heartworms flourish and can grow up to 12 inches long, reproducing and sending larvae into the bloodstream along the way. Eventually, the adult heartworms grow large and numerous enough to clog the heart, interrupting blood flow, and causing death.
Heartgard
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Most dogs like the taste of Heartgard chewables. Heartgard is an Ivermectin-based chewable monthly heartworm preventative that most dogs will take easily. Ivermectin affects the neurologic function of the immature parasite, causing paralysis and eventually death, thereby preventing the development and transmission of the disease. Heartgard is effective against many common parasites, including heartworms, hookworms and roundworms.
Treatment
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If a dog is already infested with heartworms, Heartgard is sometimes used to kill the microfilaria (offspring) before removal of the adult worms can begin. Although Heartgard is not effective against adult heartworms, eliminating the microfilaria prevents them from replacing adults that will die as treatment continues. The American Heartworm Society advocates three monthly doses of Heartgard before elimination of adult worms can begin. Removing both the adults and the offspring at the same time would cause such a shock to the system from so many dead parasites circulating in the blood that serious illness could result, so treatment is taken in stages.
Side Effects
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Collies can experience a severe reaction to Ivermectin. Heartgard is safe and well-tolerated by most dogs, but collies and other herding breeds may be especially sensitive to Ivermectin. Heartgard is not recommended for these dogs. Administering Heartgard to a dog with heartworm disease can cause serious side effects in some cases, so dogs undergoing treatment should be regularly monitored by a veterinarian.
Alternatives
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Dogs taking milbemycin oxime should be closely monitored. Although Ivermectin is considered to be the most effective treatment for microfilaria in an active heartworm infection, milbemycin oxime drugs can also be used. These drugs tend to kill relatively large amounts of microfilaria at once, risking shock, so dogs undergoing this type of treatment should be closely monitored for any signs of illness or distress.
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