Nibbles and Bits — August 2011

They call these the “dog days of summer,” and believe me, I am dog-tired with all this heat, but cats also have their days in summer and some concerns that go along with that. Most people are aware of the dangers of heartworm disease in dogs, but did you know that our feline friends are also susceptible to this ailment?

Cats are not the natural host for heartworms so the disease manifests differently in them. They are infected the same way as dogs — from the bite of a mosquito carrying the larval stage, called microfilariae. The insect injects the microfilariae into the skin and the worms then travel through the body, eventually ending up in the heart and the blood vessels leading into the lungs. Since cats are not the animal heartworms prefer, they do not grow as large or are present in as high a number as in dogs. They also do not live as long as they do in dogs — two to three years as opposed to four to seven years. However, when you consider that a cat’s heart is about the size of a walnut, even two or three heartworms a couple of inches long can cause significant issues. Cats infected with heartworms can show a variety of signs included periodic vomiting and trouble breathing, often confused with asthma. Unfortunately, one of the most common signs is sudden death. They can deteriorate so quickly that there is no time to even diagnose the disease.

Diagnosing heartworm disease in cats can be very frustrating. Unlike dogs, which will show up positive on the in-house heartworm tests quite reliably, those tests are not as dependable in cats. Antigen tests, which are run in the office, need at least one or two female heartworms to turn positive. Antibody tests, which we send to our outside laboratory, will turn positive even if there was an old infection from which the cat recovered. You cannot see heartworms on an x-ray, although there are sometimes changes in the lungs that can be compatible with heartworm disease.

There is no effective treatment to rid a cat of heartworms. Immiticide, the drug we use for dogs, is toxic to cats and cannot be used in them. We concentrate on controlling the signs with the use of steroids and monitoring chest x-rays until the heartworms die on their own.

You may think that only outdoor cats get heartworm, but the surprising truth is that almost half of the cases of heartworm disease in cats are diagnosed in indoor cats. We have been seeing a rise in cases of canine heartworm disease in recent years. This is at least partially due to in influx of dogs coming up from the south, where heartworm disease is rampant. Therefore, we are also more concerned about in increase in cats as well. Cats very rarely are contagious themselves — they almost never have microfilariae.

The good news is there are preventatives for heartworm disease in cats, just like in dogs. Revolution is a topical product applied monthly which protects cats against heartworms, fleas, ear mites, roundworms and hookworms. There are also oral monthly tablets as there are in dogs. We are strongly encouraging our cat owners to test their cats annually and use heartworm preventative. Please feel free to contact our office with any questions you may have and stay cool this summer!