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Heartworm Disease and Prevention in dogs

Heartworm disease is becoming more common in many parts of the United States.  It is caused by the heartworm.  This parasite lives in the right side of the dog's heart and in the large vessels (pulmonary arteries).  The female heartworm produces large numbers of microscopic, immature heartworms that circulate in the blood.  These immature worms (microfilariae) are taken up with the blood by a mosquito feeding on an infected dog.  After living in the mosquito for 10 to 14 days, the microfilariae can infect another dog that the mosquito feeds on.  The feeding mosquito deposits infective microfilariae into the skin of another dog, and these enter the body through the mosquito bite wound.  The microfilariae eventually travel to the heart where they develop into adult heartworms.  The adult heartworms produce new microfilariae within 3 months.  It takes at least 190 days from the time the dog is bitten by an infected mosquito until the dog becomes a new source of infective microfilariae.

Most cases of heartworms are diagnosed by finding microfilariae in the blood.  Sometimes, however, no microfilariae are found in the blood.  These cases are diagnosed by a combination of blood tests and chest x-rays.

Failure to treat heartworm disease may result in heart failure and/or serious disease to the liver and kidneys.  Untreated heartworm disease is usually fatal.


There are highly effective medications available to prevent heartworm disease. Mosquito control is certainly helpful but should never be your only means of prevention.

Heartworm preventives must NOT be given to dogs harboring microfilariae. Your dog must be blood tested before starting the preventive medication.

Weigh your dog monthly and if the weight changes a dosage change may be required.

If you give the prevention in your dog's food, mix the medication in a small amount of food and give that first. If you mix the medication in a whole bowl of food, your dog may not eat everything and you will not know if the proper dose was given.

The medication must be given on schedule to be effective. You must not skip any doses.


Heartworm Disease and Prevention in cats

Heartworm disease in cats does have a lot in common with heartworm disease in dogs, but there is the potential for more severe rections and even sudden death in cats. And yes even indoor cats are at risk for heartworm disease.

Infected cats usually have low heartworm counts. But, even these low counts are very dangerous.

The most common signs of heartworm disease in cats - coughing , vomiting, breathing difficulties, weight loss, and lethargy - are often mistaken for other conditions such as asthma, pneumonia and digestive problems. In fact, most common clinical signs of heartworm disease in cats resembles bronchial asthma.

There is no single diagnostic test as there is with canine heartworm infection. Clinical signs (if any) are non-specific and could include but are not limited to: coughing, vomiting, difficulty breathing, sluggishness or even sudden death. Other possible diagnostics include: chest x-rays, blood tests for occult heartworm antigen and clinical signs.

Once a cat is diagnosed with heartworm disease it can become a difficult and hazardous to your cat's health. Treatment, as well as non-treatment, is very risky, because there's currently no approved product for treating adult heartworms. Even if the disease is treated, your cat may experience severe complications or even death when the worms die.


As for dogs, cats also have effective preventive medications available.

Please don't think that just because you keep your cat 100% indoors that he/she is safe from heartworm disease. According to a recent survey, 55% of the cats that tested positive for heartworm disease were "indoor cats". Remember there is no approved treatment for removal of adult heartworms in cats.

Prevention is the best medicine!


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