Canine heartworm disease is a very common disease in Georgia and the southeastern U.S. It is caused by the filarial (threadlike) worm Dirofilaria immitis, and lives in the heart and pulmonary arteries (blood vessels leading from the heart to the lungs) of infected dogs and cats.

These worms cause damage to the heart and an intense reaction in the blood vessels and lungs. Heartworms are injected into the dog by infected mosquitoes. The most important predisposing factor is failure to receive heartworm preventative medication once monthly. All pets living in Georgia are at risk, even if they live entirely indoors. Indoor pets are frequently infected in our area, and because they tend to be smaller, have a higher complication rate than their larger, outdoor counterparts. In Georgia, about one in three dogs not on preventative will become infected with heartworms at some point in its’ life.

Transmission occurs when a mosquito bites an infected dog and ingests baby heartworms, which live in the dogs’ bloodstream. When the insect bites another dog or cat, some of the larvae are injected under the skin. The larvae grow for 3 to 4 months and eventually make their way into the heart where they develop into adults, and the process is ready to repeat itself. Impact on the pet is variable. Pets can be without symptoms if the infection has occurred recently. In virtually all cases, heartworm disease is eventually fatal if left untreated. Because heartworm disease is easily preventable, it has become uncommon in pets that receive proper veterinary care.

WHAT TO WATCH FOR

Symptoms don’t usually develop until damage has already occurred to the heart. Dogs can have a wide range of symptoms, varying from no symptoms at all early in the course of the disease, to eventual heart failure and death.

• · Coughing

• · Coughing up blood or nosebleeds

• · Heavy breathing, shortness of breath, panting even when cool and resting

• · Unwillingness to exercise

• · Signs of right-sided congestive heart failure, which include fluid build up in the lungs and belly.

DIAGNOSIS

Heartworm tests are run in the clinic with a few drops of blood, and take only eight minutes. They use technology similar to that used in-home pregnancy tests, and check for proteins in the bloodstream of the dog that are produced by the heartworms. These tests are very sensitive and accurate.

Once heartworm disease is diagnosed, many other tests can help determine how far along the disease is, and how much damage has been done. This helps determine the best treatment protocol, and gives additional information that helps determine the prognosis and risk of complications. A physical examination and history, along with carefully listening to the heart and lungs with a stethoscope, is important to determine whether actual heart failure is already present.

Some clinics require additional tests, and they are necessary in patients already showing signs of advanced heart failure. In an ideal world, if money were no object, they would be performed in all patients with heartworm disease. In an effort to make heartworm treatment affordable for our clients, we include the first initial heartworm test and the follow up test in the price of the heartworm treatment.

• Laboratory evaluation. A CBC, biochemical profile and urinalysis may be run as a general health screen, and to assess stability of patient for treatment. Heartworm disease often affects liver function and the ability of the blood to clot.

• Chest x-rays. Looking at the X-rays allows your veterinarian to decide how severe the disease is, and to decide how to best treat the dog, and to warn owners about the individual dogs’ susceptibility to complications with treatment of the heartworms.

• Evaluation of the heart. This specialty examination would include an ultrasound examination of the heart (echocardiogram) to look for enlargement of parts of the heart, or the presence of the heartworms within the heart itself. An electrocardiogram (ECG) maps out the electrical activity of the heart and determines the heart rhythm. An ECG may be recommended if there are signs that the heartworm disease is advanced.

TREATMENT

Killing of the Adult heartworms (Adulticide Therapy)

Many new recommendations and drug combinations are currently underway in the treatment of heartworms.  Our protocols have recently changed a great deal, due to advancements and new recommendations.

1.  (Day One) The first step in treatment is a month long course of once-a-day antibiotics which kill off bacteria that lives inside the heartworms.  The heartworms need these bacteria to thrive and reproduce.  Killing them weakens the worms and prevents reproduction.  Much of the irritation to the heart and lungs when the adult heartworms are killed, are actually a reaction to the bacteria - so pre-treating for the bacteria makes the next stages of treatment easier and safer for the patient. 

2.  (Day 15) Two weeks later, patients will begin monthly treatment with ivermectin (Iverheart Max®).  This begins to kill off the baby heartworms, which again makes the next stages of treatment easier and safer for the patients.  Although Interceptor® is our normal drug of choice for heartworm prevention in dogs, because it protects against a wider range of intestinal parasites, Iverheart Max® is safer for dogs already infected with heartworms.  Dogs will be hospitalized during the day of the first dose, to observe for possible reactions that may require aggressive and immediate medical treatment.  Subsequent monthly doses can be administered at home.

3.  (Day 60) Two months into the treatment, the patient receives the first dose of medication to kill the adult heartworms.  These injections are given on an outpatient basis.

 Melarsomine (Immiticide®): This drug is given by injection deep into the muscles of the back. Immiticide® is currently the only drug available for treatment of adult worms.  Back pain is often noted as a minor complication secondary to the Immiticide® injections into the muscles of the back. About one in three patients will show signs of pain & discomfort, such as limping in the rear leg on the side of the injection, or panting, whining, & restlessness. Since some dogs can experience significant pain without any noticeable symptoms, we routinely place all patients on pain medication for three days. These are strong drugs, and should be kept away from children, depressed individuals, or people with substance abuse problems.

4.  (Day 90 and 91) Three months into the treatment, the patient receives the second and third dose (24 hours apart) of medication to kill the adult heartworms.  These injections are given on an outpatient basis.

5.  (Day 120) Exercise restriction ends.

6.  (Day 210) A heartworm test should be repeated three months after treatment. In rare cases, a patient may not entirely clear the worms on the first treatment. A second round of treatment is then necessary. Tests run sooner than three months may still be positive due to dead worm particles not yet entirely cleared from the system.

BEWARE! Rumors have abounded recently among rescuers, breeders, and on the Internet that patients with heartworm disease can be treated by simply placing them on heartworm preventative. THIS IS ABSOLUTELY NOT TRUE! Extensive research has shown that preventative will clear 94% of experimental infections less than 7 months old.  At 8 months, the clearance rate drops to 56%, and continues to decline with the age of the infection.  A dog must be infected for at least six months before it will show positive on a heartworm test.  By the time of diagnoses, preventative Will often fail to clear the infection.  Irreversible damage is done to the heart and lungs if proper treatment is delayed.

Dogs with advanced heart failure will be referred to larger clinics for treatment. Additional tests and treatment to help stabilize the heart condition will be necessary prior to treatment. This also applies to other high-risk patients, such as very small or elderly patients.

HOME CARE

Strict exercise restriction. THIS IS THE MOST IMPORTANT PART OF THE TREATMENT PROCESS.  This is THE ONE thing owners can do to reduce the risk of serious complications.  Dogs who have been treated for heartworm disease should receive the absolute minimum of exercise for up to 4 months from the beginning of treatment.  Ideally, cage rest should be provided.  In very hyperactive dogs, a sedative may need to be used to help achieve this very important goal.  Dogs should be walked on a leash, not turned loose, for toilet duties.

Exercise restriction is important, because as the drugs are killing the worms in the arteries, the worms can break off and travel to block parts of the blood vessels (pulmonary thromboembolism or PTE). The effect is similar to throwing a blood clot. PTE results in obstruction of the blood flow to parts of the lung (pulmonary infarction). Keeping the dog quiet allows the body time to slowly break down and absorb the dying worms.  Anything that would be good aerobic exercise, getting your heart rate up, increases the risk of embolism.

Any activity that increases blood pressure should be avoided. No running, playing, or dashing about. Outside on a leash only.

Prednisone. Administered pre-treatment only if there is intense lung inflammation and severe coughing. Administered post-treatment only to treat the complications discussed below.

Watching for complications. The major complication to treatment is PTE. PTE is associated with signs of fever, heavy or fast breathing and coughing. Observation of any of these clinical signs would necessitate a visit to your veterinarian or local veterinary emergency center. In its worst form, PTE can result in sudden death.

 Cost of Treatment

PREVENTATIVE CARE

Prevention of heartworm disease is easy and should be undertaken in all pets in Georgia. These include once monthly preventative tablets given orally, or a topical application given monthly.

Milbemycin oxime(Interceptor Flavor Tabs®). This is the drug of choice in our area. While many reliable products are available to prevent heartworms, Interceptor® is the only one that also prevents whipworm infection. Whipworms are a major problem in our area, and can be life threatening. (Although early in the course of treatment, a different preventative will be prescribed, as it is a bit safer for dogs already suffering from heartworms).  Revolution™ is currently the drug of choice for cats.

Year round prevention is absolutely necessary in Georgia. In colder climates, prevention is often skipped during the coldest months of winter, since mosquitoes cannot survive. This does not apply in Georgia. Infected mosquitoes have been found during every month, even January. Sadly, it isn’t unusual for us to diagnose heartworm disease in a dog whose owner skipped preventative during winter. Don’t! The cost of those pills is minimal compared to the cost of treating heartworm disease.

Note - If owners absolutely, positively cannot afford proper treatment, another less expensive option does exist.  However, it is not ideal, not recommended, and is experimental.  Short and long term side effects, complication rates, and success/failure rates are unknown.  This treatment may not work, and the pet could die.  It is however, at least a shot, and is better than doing nothing.  It at least will prevent infected dogs from serving as a source of infections to other dogs.  Signing of an extensive waiver is required.

Please call us for current pricing - or you can e-mail our Office Manager at twbradley@bellsouth.net with any pricing questions.

Again, we do not recommend this course of treatment, and would not take the associated risks with our own pets.  But, it is at least a chance, and far better than doing nothing.  It requires a firm commitment on the part of the owner to follow through.  Exercise restriction is recommended to reduce the risk of potential fatal complications, through the entire course of treatment until a clear test can be obtained.