Here at Towne South Animal Hospital we recommend year round Heartworm preventative for every dog. If for some reason your dog has been diagnosed with Heartworms, then in most cases we recommend treatment for the elimination of the Heartworms. This is a multistep process that takes several months to complete. Each case is evaluated individually and a treatment plan is determined for your dog. Simply call our office 318-797-8489 or e-mail us; we will be glad to prepare a written estimate for you.
What Happens in Heartworm Disease
By Wendy C. Brooks DVM, DABVP
Heartworm Disease vs. Heartworm Infection
Before reviewing the clinical signs seen in heartworm disease, an important distinction must be made between heartworm disease and heartworm infection. Heartworm infection by definition means the host animal (generally a dog) is parasitized by at least one life stage of the heartworm (Dirofilaria immitis). Dogs with heartworms in their bodies do not necessarily have adult worms in their hearts; they may have larval heartworms only in their skin. Dogs with heartworms in their bodies are not necessarily sick, either. Dogs with only larvae of one stage or another are not sick and it is controversial how dangerous it is for a dog to have only one or two adult heartworms. These dogs are certainly infected but they do not have heartworm disease.
On the other hand, dogs with heartworm disease are sick. They not only have the infection but they have any of the problems listed below because of it. Fortunately, heartworm disease is both treatable and preventable. We will now discuss the damage heartworms can do to a dog's body.
Damage to the Pulmonary Arteries
Arteries do not do well with worms living inside them. The lining of the artery becomes damaged within days of the worm's arrival. Cells of the immune system are called into the area, but the worm is far too big for these tiny cells to destroy. The resulting inflammation; however, continues to damage the artery. The arteries dilate and become tortuous, which may be visible on a radiograph. Aneurysms and abnormal blood clotting called embolism results. Blood is shunted to other arteries that are not plugged up by worms, and fluid begins to accumulate in the lung around the worm-filled arteries. Blood being sent to the lung is not efficiently oxygenated and areas of lung become consolidated and unable to participate in providing oxygen to the blood.
- Coughing and exercise intolerance result as areas of the lung are affected.
- Nose bleeds may occur due to abnormal blood clotting in the lung.
- A form of non-infectious pneumonia (pulmonary eosinophilic granulomatosis) can result from excessive infiltration of inflammatory cells into the lung in response to the parasite.
Heart Failure
Blood normally is pumped with ease through the arteries of the lung. With the arteries plugged with worms, the heart must pump harder against the pressure of the plugged arteries. This condition is called pulmonary hypertension and the right side of the heart must drastically increase its ability for the heart to work. It may be strong enough and it may not be.
If worms begin backing up into the heart, there will be less space in the pumping chamber for blood to be pumped. The heart must pump through the high pressure system of the plugged arteries using less blood then normal. In order to meet the body's oxygen demand, the heart must pump faster and stronger still. There may come a point when the heart simply is not strong enough.
- When the heart muscle begins to thicken (as any over-worked muscle will), it may not conduct electrical impulses normally. This means that the pumping/filling rhythm can be disrupted and an arrhythmia may result.
In any heart disease, arrhythmia is a possibility;
when arrhythmia is a possibility, so is sudden death
If the right side of the heart becomes too weak to keep up, fluid may accumulate in the chest and abdominal cavities, leading to a pot-bellied appearance and/or difficulty breathing.
Chronic Immune Stimulation
When a dog goes without treatment for heartworm disease, its immune system becomes chronically stimulated. Antibodies, which are not only important tools of the immune system but are also inflammatory proteins, are produced in high amounts all the time. These antibodies can cause a lot of trouble by settling in the delicate membranes of the eye, kidney, blood vessels, and joints. Antibodies that are stuck in these areas call in inflammatory cells and damage these delicate membranes, thus setting up tremendous tissue damage and pain.
Caval Syndrome
Caval syndrome represents an especially disastrous form of heartworm disease. Here, there are so many worms at one time (around 100) that the entire right side of the heart is filled with worms and they are backing out into the large veins that feed the right side of the heart. Usually there have been no signs of heart disease prior to the collapse, shock, and red blood cell destruction associated with this syndrome. Death usually occurs within 1 to 2 days and the only effective treatment is to open the dog's jugular vein and physically remove the worms with a special clamp. If enough worms can be removed to re-establish blood flow, the dog may survive.
Heartworm disease is a highly significant problem and must be managed both by dealing with the worms and by dealing with the heart disease.
Heartworm in Cats
Heartworm disease in cats is quite a bit different from dogs. Cats are so small that only one adult worm can be enough to cause heart failure, plus in cats there is much more inflammation involved with the immature worms. See details on infection, disease, treatment, and prevention of heartworm in cats.
Heartworm Disease and Treatment
The following is a general outline of our treatment protocol. In each case we will go over all steps in detail with you to determine a plan for your individual pet’s needs. We will be happy to answer any questions or concerns you may have concerning this serious disease.
Our treatment protocol consists of 3 steps.
Step 1:
- A complete physical exam is performed and your dog is evaluated to determine how advanced the infection or the disease has become.
- A blood test is performed to determine if microfilaria are present in the bloodstream.
- Your dog will then be started on heartworm preventative (if not already on a preventative) for several months and prescribed medication to be given for 30 days prior to the first adulticide injection.
It is very important that your dog be restricted in its activity at this point.
Step 2:
- An examination is performed to re-evaluate your dog’s condition.
- Your dog will be hospitalized for 1 night.
- Possible bloodwork, chest x-rays and/or cardiac ultrasound are performed, depending on your dog’s needs. This will be determined by your pet’s doctor.
- The first adulticide injection is given and medication is dispensed for you to give at home.
It is necessary at this point that you severely restrict your dog’s activity.
Step 3:
- A medical progress exam is performed to again re-evaluate your dog’s condition.
- You dog will be hospitalized for 2 nights.
- Two adulticide injections will be given and medication will be dispensed for you to give at home.
- A follow up visit will be scheduled for 10 days later.
It is important that you continue to severely restrict your dog’s activity for 6 more weeks following discharge from the hospital.
You will be sent a reminder for a heartworm test 6 months following the completion of heartworm treatment.
