Heart worms are parasites that live in animals' hearts. They typically reside in the right ventricle and surrounding blood vessels. Mosquitoes carry the parasites from host to host, infecting new dogs when they bite. Heart worms are dangerous to your dog. Unless it is on a monthly preventative medication, a dog is at risk for heart worms almost everywhere in the United States. If your dog becomes infected, it can die if left untreated. Unfortunately, treatment can also kill the dog, so knowing exactly what to do is very important.
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Signs
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If your dog has a heart worms infection, it will most likely have a cough. The cough will have a soft, dry sound. The dog will also seem lethargic and more reluctant to engage in physical activity. When it does become active, the exercise may trigger coughing episodes. Because the major signs of infection are similar to those presented with other diseases, you should take the dog to the vet for a definitive diagnosis. Your dog will need to be infected for about six months before a blood test will reliably reveal the presence of parasites.
Treatment
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Heart worms are easy to prevent but difficult to treat. It can be a delicate process to eradicate the worms without damaging the coronary system. The type of treatment depends on the dog's general state of health, the number of parasites present, whether they are mainly adult or still larval, side effects of the medication, and how the dog is tolerating the presence of the heart worms before and during treatment.
Adulticides
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There is no medication that is effective in killing both adult heart worms and microfilaria (larval stage). Treatment focuses first on killing adult heart worms by using one of two medications called adulticides. Both are derived from arsenic and can have severe side effects, including death. Caparsolate is the oldest heart worms treatment. It is usually effective, but has the potential to cause major harm to the kidneys and liver. It is delivered via IV and can damage the vein and surrounding tissue if it leaks.
Immiticide is a newer drug delivered through intramuscular injection. While Immiticide also has serious side effects, it appears to be safer than Caparsolate. Immiticide is usually the first drug of choice, and vets reserve Caparsolate for cases that don't respond to Immiticide. The medications tend to start killing the worms within five to 10 days. The bodies can block blood vessels, posing a risk. The dying worms cause inflammation, which can impair breathing. Your vet might prescribe an anti-inflammatory drug at this point. Sometimes, your dog will require a second round of adulticide to kill the younger adult heart worms that can be more resistant to treatment.
Microfilaria
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It usually takes at least a month for all the adult heart worms to die and for side effects to resolve. Once your dog is stable and in better health, your vet will address eliminating the microfilaria. This is done with one of two medications--Ivermectin or Milbemycin Oxime. These medications are also preventatives. Once your dog has had heart worms, it is even more important to keep it on preventative medication for the rest of its life. About four months after the start of treatments, the vet will retest your dog for heart worms. If the dog is negative, you will continue the preventative. If it still has heart worms, it will need another round of treatment.
Warning
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All dogs should be on some type of preventative for heart worms, but you shouldn't start treatment without first having a blood test to make sure the dog doesn't have the parasite. The only exception is if it is a puppy under seven months old, because adult heart worms can't form in this amount of time. Puppies should start on a preventative around eight to 12 weeks of age, and don't need to be tested for heart worms first.
Administering the preventative to an infected dog can result in the death of some of the heart worms, and they will accumulate in the heart and blood vessels, potentially blocking blood flow. The inflammatory process will be painful if the dog survives. It is important that all side effects from the worms dying be supervised by a veterinarian to minimize pain and the risk of death for your dog.
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