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ARF is a 501(c)3 non-profit dedicated to rescuing homeless dogs and cats in Mobile! Be a part of this lifesaving effort!

Heartworm Disease

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the

arteries of the lungs and occasionally in the right side of the heart of dogs. Heartworms are rarely seen in cats but it is possible for a cat to have heartworms.


The parasite is spread through infected mosquitoes and exist, first, in a larval stage in the dog's

bloodstream. From there, the juvenile worms (or microfilaria) can live for up to 6 months before lodging in

the heart and lungs of a pet. There they mature into adult worms.  The male worms are a few inches long

and look like angel hair spaghetti. The female worms are much larger and cause most of the damage.




There are various treatment options for heartworms depending on how advanced the disease is, size

and overall health of the dog.  The most effective method is the use of melarsomine dihydrochloride.  It

is marketed as Immiticide and contains arsenic. The drug can result in numerous side-effects and even

death in advanced heartworm disease.


Before Immiticide is given, Doxycycline, an oral antibiotic, is given for 30 days.  This drug has been

proven to render adult female heartworms sterile while also killing the Wolbachia (an organism that

lives inside of heartworms).  Some veterinary professionals now believe that Wolbachia is responsible

for some of the blood clots and malaise that occur during treatment. Because of this, more and more

veterinarians are pre-treating dogs with doxycyclene to destroy Wolbachia prior to administering



Once the Immiticide injections are given, the heartworms immediately die and begin breaking apart. This

is a several week process with the first six weeks being the most dangerous.  As the medication breaks

apart and dissolves the worms, they may then become lodged in blood vessels or the lungs.  Dogs may

suffer embolism, stroke, suffocation or other serious conditions.  With time, the body absorbs them but

until then the dog's body must deal with all the dead heartworms in its circulation.


During this time, it is absolutely critical to keep the dog as calm and inactive as possible.  This requires

strict cage rest in a cool, isolated, quiet area.




At ARF and under a vet’s care, all dogs are given a monthly preventative regardless of their heartworm

status.  This is necessary to prevent further population in heartworm positive dogs.  And because

heartworm disease is so prevelant in our are (see map) it’s just as important in keeping our remaining dogs heartworm free.


Monthly heartworm preventative is a requirement for all pet owners living on the Gulf Coast.  The disease

is very easy to prevent but just as hard to treat.




Unfortunately, many of the dogs at ARF come to us heartworm positive. This poses a significant challenge because these dogs need quiet kennel rest to undergo heartworm treatment. This kind of treatment just isn't possible in a shelter environment, therefore, we rely heavily on foster homes while our dogs undergo treatment. If you're interested in fostering a dog for 6-8 weeks during heartworm treatment, please submit a foster application.  And, check out some of our dogs that are waiting for heartworm treatment on our ARFans in Need page.


In addition to the challenge of finding a foster home, heartworm treatment is expensive. Even after extremely generous discounts from local veterinarians, heartworm treatment costs us $250-300 per animal.

Donate to the heartworm treatment fund


Tinker bell was successfully treated for heartworm disease by ARF and now enjoys a happy, healthy life including weekend hiking with her family.