Friday, April 26, 2013

Heartworm Disease and Prevention

Canine heartworm disease is a serious and potentially fatal disease that is becoming more common. Heartworms are treatable and preventable. The veterinary community is spending an enormous amount of money to improve the public education level on the disease in hopes of decreasing the high numbers of cases being diagnosed.


Signs & Symptoms of Canine Heartworm Disease

The most common signs of heartworm disease in dogs are the following:
  • Dry chronic cough
  • Lethargy
  • Weakness
  • Loss of appetite
  • Low energy levels
  • Cases have been documented where dogs have died suddenly due to over-excitement

Causes of Canine Heartworm Disease

Heartworms are a species of roundworms and live in the arteries a dog’s lungs and heart, and the blood vessels that surround both. The infected worms are transmitted from mosquito to dog after the mosquito has picked up the parasite from an infected dog. The mosquito is the carrier of the disease and the dog is the host for the disease. The mosquito carries the young immature worm, known as microfilaria; this young worm matures into the infective stage in the mosquito, and then is passed to a dog once the mosquito bites. The deposited microfilaria lands on the skin and begins to migrate through the skin and connective tissue, where it eventually makes it to the dog’s bloodstream. Once in the bloodstream, the worm is transported to the lungs, where it continues maturation and will begin to reproduce offspring. This entire process generally takes six months, while the adult heartworm can live in the dog up to seven years. Dogs of any age or breed are susceptible to heartworm infection.
As the heartworms multiply and take up space in the pulmonary arteries, a tremendous amount of damage is often the result. These worms will also take up residence in the right side of the heart. Once inside the heart, the flow of blood becomes restricted and this reduces the amount of blood to other organs in the body. If there are a large number of heartworms residing in the heart, this disrupts the function of the valves, causing heart damage. Congestive heart failure can be a complication with the more severe cases of heartworm disease. While the worms are lodged in the pulmonary arteries, this causes a decrease in blood flow, and most importantly the amount of oxygen that is getting to vital organs. These are worms that have been measured to be 6 to 20 inches long. Heartworms are NOT contagious from one dog to another by any kind of direct contact..

Diagnosis of Canine Heartworm Disease

Diagnosing heartworms can be done at your veterinarian’s office with a few simple in-house blood and antigen tests. Currently there is a test that requires just a few drops of whole blood from your dog and can be run in about 10 minutes. This test will show a positive if there is enough of the heartworm antigen in the bloodstream. Once it is positive, an additional blood test known as a direct test, a sample again of whole blood, is examined under the microscope and the young heartworms can be seen. The number of baby heartworms that are present under the microscope give an indication of how advanced the disease is. If your veterinarian suspects the positives from the blood tests are correct, he or she will want to do some radiographs and ultrasounds of the heart to determine what condition the organ is in. Once all of this information has been examined, your veterinarian will stage the disease from mild to severe, and this will determine what treatment plan will be best.

Treatment for Canine Heartworm Disease

Heartworm disease is generally a very treatable disease. In the past, treatment was quite dangerous as the medication used to contain a very toxic drug known as arsenic. This caused a fairly high rate of fatalities and some nasty reactions. Your veterinarian will most likely admit your dog to the hospital and proceed with the following phases of treatment to treat ADULT heartworms:
 Phase I:
  • Administer a single injection deep into the muscle around the hip area and observe overnight for any possible complications.
  • Your dog will be sent home the next day with strict orders to REST for at least 30 days. This is not total confinement but very close.
 Phase II:
  • You will return with your dog to the hospital where two more injections will be given 24 hours apart and he/she will again stay at the hospital for observation.
  • Based on pre-treatment testing, there may be some additional blood tests or repeat radiographs and ultrasounds done at this time.
Resting your dog for 30 days is absolutely critical to the success of the treatment. In that time period, the adult worms are dying. They will begin to break up and be carried through the lungs and eventually absorbed by the dog’s body. Any kind of excitement during the period will disrupt this activity and could lead to sudden heart failure and death.
Baby heartworms, or microfilaria, can be killed by giving your dog a dose of heartworm preventive. The active ingredient in this product has shown to be successful with minimal side effects. This will require a stay in the hospital where the technician staff will administer the dose and observe closely for any adverse reactions. An additional blood test is usually done to ensure the baby heartworms have been eliminated.

Prevention of  Heartworm Disease

The American Heartworm Society recommends using a preventative year round, for the life of your Dog or Cat .
Heartworm disease is absolutely preventable. There are currently several once-a-month heartworm preventive drugs that are available through your veterinarian. A heartworm prevention plan is essential for a complete wellness plan for your dog. 
  • If your dog has heartworms and is treated successfully, he/she can get the disease again if you do not follow a monthly heartworm preventive program.
  • Your veterinarian should recommend yearly heartworm testing for your dog.
  • Your veterinarian should recommend the first heartworm test to be done on puppies at six months of age.
  •  Heartworm prevention can be started as early as six weeks of age.

Heartworm Disease in Cats 

Heartworm in cats is caused by infestation of the organism Dirofilaria immitis, a parasitic nematode (roundworm) commonly referred to as the heartworm. The severity of this disease is directly dependent upon the number of worms present in the body, the duration of the infestation, and the response of the host (the infested cat is the host).

The prevalence rate of heartworm disease in unprotected cats that have not received the proper preventative medication, or prophylaxis, is significantly lower than that of  unprotected dogs -- approximately one-tenth the rate of dogs. Additionally, most cats have only a few heartworms present, and the worms infecting cats are physically smaller and have a shorter lifespan than those infecting dogs. Outdoor cats are at increased risk, and are twice as likely to contract heartworm disease as indoor cats.


 There are no specific tests that are able to diagnose heartworm disease in cats. A variety of tests that may be done to aid diagnosis include a urine analysis, heartworm antigen and antibody tests, x-rays which may reveal the enlargement of certain veins or arteries associated with heartworm disease, and an electrocardiograph (ECG), which may allow for identification of worms in the heart or pulmonary artery. An ECG can also exclude or confirm other heart diseases that may exhibit similar symptoms.


 Heartworms are a preventable disease, and there are a number of medicinal preventatives that are highly effective and commonly used.  Dr. Birken can determine which prevention is best for your cat.