4630 Martin Road Cumming GA 30041

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Heartworm Disease

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. 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 ten 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, which include many rescue groups with limited resources, we do no routinely require these tests in our clinic prior to heartworm treatment. Owners should be aware that in rare cases, waiving these tests may lead to unexpected complications.

• 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)

Melarsomine (Immiticide®): This drug is given by injection deep into the muscles of the back as either a two-day series (one injection per day, two consecutive days); or, in patients with more severe disease, as a split protocol (one injection, followed one month later by two consecutive injections one day apart for a total of three injections). 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.

Killing of the Baby Worms

Milbemycin (Interceptor®) is given six weeks after the adulticide treatment is completed, then monthly for the life of the patient. No other brand or type of heartworm prevention can be substituted, as they will not kill all stages of baby heartworm present.

Follow Up Testing

Heartworm test should be repeated four 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 four 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 by experts at the University of Georgia have shown that while preventative will clear experimental infections after one or two months, they will not clear heartworms present for more than a few months. A dog must be infected for at least six months before it will show positive on a heartworm test. By then, preventative WILL NOT clear the infection.

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. Dogs who have been treated for heartworm disease should receive the absolute minimum of exercise for six weeks following the 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.

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.

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.

PREVENTATIVE CARE

Prevention of heartworm disease is easy and should be undertaken in all pets in Georgia. These include monthly preventative tablets or drugs once every 6 months.

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. 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.

Website maintained by:
Tracy Land, DVM

This page rev: 03/18/07