Goals of Treating Heartworm Disease
Treating heartworm disease can be difficult and dangerous. The therapeutic goals are to kill all adult worms and microfilariae that are present in the dog’s bloodstream. Other goals are to resolve any associated complications that the dog is suffering from and to prevent future reinfection. In considering treatment options, owners and veterinarians must pay special attention to potential adverse drug reactions. They also must consider the possibility that dead and dying adult worms may plug up one or more of the dog’s heart chambers or critical blood vessels, which can lead to pulmonary hypertension, congestive heart failure and possibly death.
Dogs with acute respiratory and/or cardiac complications from adult heartworms need to be hospitalized, given oxygen and placed on strict bed rest. Steroids may be prescribed to reduce inflammation, and aspirin may be recommended to reduce the risk of blood clots (thromboembolisms). Several medical protocols are available to eliminate adult heartworms. A veterinarian is the best person to discuss these options with the dog’s owner. The decision involves consideration of the dog’s age and overall health, the presence of any associated medical complications (such as liver or kidney damage or heart failure), the owner’s financial resources and tolerance of treatment regimens, and whether microfilariae are present in the dog’s bloodstream. Some medications that kill adult heartworms contain arsenic and can cause toxic side effects, including vomiting, diarrhea, appetite loss, liver damage, kidney damage and even death. Older animals have a higher risk of suffering adverse side effects from drugs that kill the adult parasites.
Surgical procedures are also available to remove adult heartworms. This requires general anesthesia, which carries its own risks. The veterinarian will make an incision in the dog’s neck and pass a tong-like instrument down its jugular vein, through the superior vena cava and directly into the right side of its heart. She will pull the parasites out one by one, which requires use of X-rays and a great deal of technical skill. Surgery is reserved for critical cases that don’t respond to drug therapy.
Additional treatment options must be considered when immature heartworms are present. The drugs that kill circulating microfilariae are can cause serious adverse reactions in some dogs, including hypothermia, depression, weakness, vomiting, shock and collapse. Many veterinarians recommend waiting several weeks after treating a dog for adult heartworm infection before starting treatment to kill the microfilariae. Most dogs are hospitalized during microfilaricide therapy. Sometimes, microfilariae can be eliminated in 6 to 9 months by putting the dog on monthly heartworm preventatives. All dogs should be on exercise restriction during any heartworm treatment.
Dogs with heartworms usually have a good prognosis, especially if they haven’t shown severe signs of illness. Those with moderate to serious infection, including heart, lung, kidney or liver complications, have a poorer prognosis. Unfortunately, the prognosis for dogs with caval syndrome is guarded to grave, even with treatment.