Treating Heartworm Disease in Dogs

Although it’s completely preventable, each year in the United States some 250,000 dogs test positive for heartworm. This nasty parasite lives inside the blood vessels and heart of your dog, and if left untreated, can cause heart failure and even death.

Being a parasite, a heartworm is unable to live independently and only exists inside the bodies of certain animals (mainly dogs, but also cats, wolves, and coyotes) and mosquitos. The life cycle of a heartworm begins inside the dog, where baby heartworms can be found in the blood stream. Strangely, baby heartworms living inside a dog cannot mature. When a mosquito bites an infected dog, the mosquito takes up some of the heartworms, and if conditions are right, they will transform into a new state that can cause an infection in a new dog. This critical step takes about 10-14 days and requires constant, warm temperatures. That is why the greatest risk of heartworm infection in most areas is between the months of April-October. If the temperature dips below 57 degrees F for any significant length of time, the baby heartworms cannot mature and infection is not possible.

When maturation does occur and a mosquito bites a new, uninfected dog, the bug injects the heartworms into the dog where they migrate to the blood vessels and heart. There they mature and begin reproducing. Female heartworms give birth to as many as 5,000 babies per day. The babies make the dog a risk to spread the infection to other dogs, but its the adults that cause problems. Living in the right ventricle of the heart, the worms will eventually cause heart failure and death if left untreated.

Early on, an infected dog exhibits no symptoms. In later stages, the disease may be characterized by tiring easily and a soft cough. The only way to know for sure if your dog has heartworm is by giving a blood test. If your dog tests positive, your veterinarian will order more tests to determine the extent of the infection and function of vital organs, like kidneys, liver, and heart. X-rays are used to determine signs of organ damage and the load of the infection. Advanced cases may require surgery, but if everything looks OK your vet will order treatment with a compound known as an adulticide which kills the adult heartworms.

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In most cases, the drug is given in two doses spaced over a period of four weeks. This is done because heartworm treatment is dangerous in itself. The worms are adhered to the blood vessels and heart, and when the drug begins weakening them and killing them, they detach from the blood vessel walls. They then break up into pieces which, flowing through the bloodstream, can be dangerous for your dog. If your dog becomes overly excited or exercises during this time, the heartworm fragments can become lodged inside the terminal branches of arteries in the lung, causing a pulmonary embolism. This is science-speak for a blockage of the blood vessel, making breathing difficult or impossible. It is an emergency condition that can be fatal.

However, this is preventable. To reduce the risk of this happening, your veterinarian will ask you to strictly confine the dog for a period lasting about six weeks. Strict rest is absolutely necessary, so you will have to keep your dog in a crate or small room. Bathroom breaks on leash are allowed about 3 times per day. You can’t let your dog run, romp, or play during this time. Doing so could cause an embolism and result in death, or at the very least a stressful medical emergency.

Despite the harshness of the treatment, if your dog tests positive for heartworm it is his only chance for survival. If you follow the rules, your dog will survive the treatment and go on to live a happy, normal life. That being said, one thing that this condition should make clear is that prevention is the best thing you can do for your dog, so that he can avoid going through this horrible experience.

DISCLAIMER: The information on this site is not intended to replace the advice of your own veterinarian or doctor. Should you think that your pet needs medical attention, please contact your local veterinarian.  
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