All Pets Veterinary Clinic


It is a very well known fact that dogs can get heartworms and that it is a life threatening
problem/disease. What is not well known is that cats can also contract heartworms and
that heartworms in cats can be just as deadly. This article will focus on the spread,
signs, diagnosis, treatment, and prevention of heartworms in cats.

Spread. The lifecycle of heartworms is virtually the same for dogs and cats. A
mosquito will pick up immature forms of heartworms from an infected animal, usually a dog.
These immature worms will then develop slightly within the mosquito and can be transferred
to a cat when the mosquito bites. The immature worms will then migrate in the body to the
bloodstream. Once in the bloodstream, they will travel to the pulmonary artery, near the
heart, and develop into adults. In some cases, the immature worms may migrate to other
parts of the body, like the central nervous system. The adult heartworms will then
produce immature heartworms that can be picked up by a mosquito. Thus, the cycle

Signs. The signs of heartworm infection in cats can vary greatly. Signs
include: lethargy, weakness, coughing, chronic vomiting that is often unassociated
with feeding, central nervous system disturbances, blindness, and sudden death. In
many cases the cat will appear to be perfectly normal, not having any of the above signs,
and will then die unexpectedly. This does not generally happen in dogs.

Diagnosis. Unfortunately, diagnosing heartworms in cats is not as easy as it is
in dogs. The rapid tests that are available for dogs are generally not very effective for
cats. Thus, when using a test designed for dogs it is possible to get a negative result
and actually have a cat that is positive for heartworms. Finding microfilaria, the
immature heartworms, in the bloodstream will confirm that a cat is positive. However,
in cats, the amount of time in which the immature heartworms are shed into the bloodstream
is a very short. Thus, it is not difficult to miss these immature worms completely when
doing tests that look strictly for young worms. Chest x-rays, echocardiography, and
antibody tests may all be done to help to confirm that a cat is positive for heartworms.

Treatment. Currently, there are no approved treatments for heartworms in cats.
The greatest difficulty in attempting to treat cats with heartworms is that severe,
often deadly, complications occur when the adult worms die. In research institutions
surgery has been done to attempt to remove the adult worms from the pulmonary artery.
This is not a common practice. Treatment using the medications used for dogs is very risky
since these medications have not been tested in cats.

Prevention. Since there is not a cure or treatment for heartworm disease in cats
and because heartworm disease in cats is often fatal, the ideal situation would be to
prevent a heartworm infection from ever occurring. Currently, there are three medications
available for the prevention of heartworms in cats. Heartgard is a monthly chewable
treat that will kill immature heartworms, roundworms, and hookworms. Interceptor is a
monthly chewable pill that will kill immature heartworms, roundworms, hookworms, and
whipworms. Lastly, Revolution is a montly topical medication that will kill immature
heartworms, ear mites, roundworms, hookworms, fleas, and flea eggs. Heartworm preventative
is recommended for outdoor and indoor/outdoor cats. Since mosquitoes can and do come
indoors, monthly prevention should be considered for strictly indoor cats as well.

For our current clients, heartworm medication can be purchased at the clinic or from our
online store. (See link below)

The information provided is for educational purposes only and is not
intended to take the place of your regular veterinarian. Please do not hesitate
to contact your regular veterinarian if you have questions regarding your pet.

Karen Blakeley, DVM, MPH
27 September 2009