Heartworm disease in dogs is a serious and potentially fatal disease. Though effective heartworm preventive medications are readily available and easy to use, there are still many dogs which become infected with heartworms yearly. For these dogs, a decision of whether to treat the heartworm infection will need to be made.
Classes of Heartworm Disease in Dogs
Before making the decision to treat a heartworm infection, the severity of the disease must be evaluated. Heartworm disease is broken into three classes:
- Class one - asymptomatic to mild heartworm disease symptoms
- Class two - moderate heartworm disease symptoms
- Class three - severe heartworm disease symptoms
Classes of heartworm disease are determined based on clinical signs and results from basic blood testing and chest radiographs.
Treatment Options for Heartworm Disease in Dogs
Once the decision to treat has been made, a treatment protocol must be determined. The only medication currently labeled to treat heartworm disease in dogs is Immiticide®. Immiticide® is an arsenic compound which must be injected into the lumbar muscle of the infected dog.
Two treatment protocols exist when using Immiticide® as a treatment for heartworm disease in dogs.
- The first option is a series of two injections of Immiticide® administered 24 hours apart.
- The second option is a series of three injections, with one injection of Immiticide® given initially and then followed 30 days later with two injections of Immiticide® given 24 hours apart.
The second option offers a slower kill rate of heartworms, which often results in less damage to the lungs and less risk of complications resulting from treatment. Some veterinarians feel that the three injection technique should be the standard of care but there is still disagreement within the veterinary community regarding this topic. In cases where finances are an issue, the two injection technique is sometimes chosen as a viable alternative if the infected dog is classed in group one and exhibiting few to no signs of heartworm disease.
Often, other medications are given concurrently with the Immiticide® injections as well. Some veterinarians prefer to start treatment with an ivermectin product such as Heartgard Plus® 2-3 months prior to treatment with Immiticide®. Some also prefer to medicate with doxycycline for 30-60 days prior to treatment with Immiticide®. This is an area where research is still ongoing and there is still a great deal of disagreement between veterinarians regarding the best protocol.
Risks of Heartworm Treatment in Dogs
Immiticide® is an arsenic compound and because it is injected into the body of the infected dog, the potential for toxicity exists. One of the major complicating factors with treating heartworm disease in dogs is the fact that as the adult heartworms in the heart begin to die off, they can cause emboli to the lungs, leading to damage within the lung tissue. This complication can be quite serious and even fatal. Severely restricted exercise is the primary technique used to combat this complication and usually means cage restriction for many weeks for the infected dog during the course of the treatment for heartworm disease.
Another risk involved with treating heartworms in dogs is the possibility that treatment may not successfully kill all adult heartworms living within the dog's heart. Some dogs remain positive for heartworms even after treatment. The decision between undergoing another round of Immiticide® injections and simply waiting can be a difficult choice.
Other Alternatives to Heartworm Treatment in Dogs Infected with Heartworms
Some dogs exist which are not good candidates for heartworm treatment even though they may be infected. Often these are the dogs which are experiencing severe clinical signs of heartworm disease and Immiticide® injections have been deemed to be too dangerous to the dog's health. For these dogs, a viable option is beginning a monthly routine with an ivermectin-based heartworm preventive medicine.
Ivermectin is chosen over other heartworm preventive medications because it has a lower risk for complications in heartworm infected dogs. However, heartworm positive dogs should be observed closely for at least 8-12 hours after administering the ivermectin heartworm preventive in case an adverse reaction occurrs.
Ivermectin-based monthly heartworm preventive medications kill the microfilaria form of the heartworm which circulates in the blood stream of infected dogs, making the dog non-infectious for other dogs in the immediate area.
Eventually, the adult worms living inside the dog's heart will die and disappear. However, this process can take months to years and the risk of further damage to the dog's heart exists while adult heartworms are still present.
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