Westbury Animal Hospital
713.723.3666 · 4917 S. Willow Dr. Houston, Texas 77035 

One Worm Can Kill a Cat

L.D. Eckermann, DVM

Wow!  That sounds horrible, almost shocking, but it is so true.  This does not happen often, but when it is your cat, percentages are not important.

What I am writing about is heartworm disease in the cat.  The disease is similar to dogs, but manifests itself in a much different way.  We must remember that cats are not small dogs!  The heartworm does not belong in the cat, but it occurs and can be deadly.

Heartworms primarily live in the pulmonary artery but can migrate into a portion of the heart, and other organs of the body. What is interesting, a trivial point, but the primary vector is the aedes species (Asian Tiger mosquito) which was introduced into the Port of Houston in 1985. The mosquito will take a blood meal from a cat and then inject infective larvae into its skin.  The larvae then migrate to pulmonary arteries and the heart over a 4 to 6 month period.  The life cycle usually takes 6 months.  Heartworms can live for about 2 – 3 years in the cat; 5 – 7 years in a dog.

In dogs, the disease manifests itself in the right side of the heart. Cats tend to have more disease in the lungs which is termed HARD (heartworm associated respiratory disease).  Again, cat lungs are not dog lungs.  For instance, it is not unusual to have asthma in cats, but rare in dogs.  When one heartworm dies in a cat lung, there is a severe inflammatory response, which often leads to a fatal acute lung injury.

A few points on symptoms of heartworms in cats

  1. Coughing
  2. Wheezing
  3. Vomiting- remember, if you think a cat has a hairball, make sure you see the actual “big waddy” hairball, and not just clear liquid with hair.  The clear liquid with hair is not a hairball.

Diagnosing heartworms in cats can be much more difficult due to the smaller number of worms in the cat (cat 1-5, dogs 15-60).  Your veterinarian will do blood tests, chest x-rays and sometimes an ultrasound of the chest.  The one test that we do in dogs is often not enough information to diagnoses heartworms in cats.

What can I do if my cat is diagnosed with heartworms?  The treatment for dogs is not used in cats. There could be an anaphylactic reaction.  It is recommended to use steroids to reduce the inflammation in the lung and hope with time, the disease will subside.

After discussing all this, what is most important is that feline heartworm disease can be prevented. Every cat that resides in Houston should be on a preventative, inside and outside cats. 

There are many different products on the market for cats for preventing heartworm disease that are monthly applications. Please note that you should never put a dog preventative on a cat as many canine products are toxic to cats.

Remember, heartworm disease in cats as in a dog, is a preventable disease.  All cats, inside and outside, should be on a preventative. 


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