Question: Dr. Richards-

I appreciate your info about pemphigus. Some followup-”Lexy” responded very well to a brief period of steroids. She is now on weekly gold with the steroids being tapered. All of her skin lesions are gone and she has gotten back to her job as head of the household. I would like to ask an unrelated question. I have seen some references about heartworm in cats. I always thought of this as a dog disease. None of the vets I have been to recently have brought it up, but I have never specifically asked. I live with (not own you understand) six cats.
They are mainly indoors but do have a cat door which allows free access to outside. we now live in southeast Ohio but previously lived in North Carolina. Do you think I should pursue testing and prophylaxis? Thanks for your help. I have multiple other questions but I’ll try to limit them to one every other week or so.

Answer: J.S.-

I am ambivalent about heartworm medication for cats. On the one hand, it is preventable disease and so I think it is a good idea to prevent it. On the other hand, it is much less common in cats than it is in dogs and despite company claims to the contrary, we have a fair number of cats who don’t like the chewable pills and a lot of cat owners who don’t want to administer the pills if the cat won’t take them readily. I am hoping that selamectin (Revolution Rx), which is a topical (applied to the skin) product, will prove to be efficacious and safe. It is supposed to prevent heartworms and kill fleas for a month with once monthly dosing.
That will make it easier to dose all cats. The “expected” rate of heartworm disease in cats is usually about 10% the rate of dogs in an area — so if 80% of dogs not on preventative medications would get heartworms in an area, about 8% of cats will. This is still a guess in reality, though.

At the present time the usual recommendation is just to start preventative medications without doing prior testing. This is different than the recommendations in dogs and is based on the fact that antigen tests (test directly for heartworms) aren’t as accurate in cats as they are in dogs and reactions to microfilaria are theoretically unlikely since very few cats have microfilaria (baby heartworms) in their bloodstream even if they are infected with adult heartworms.

As long as the cost of the heartworm pills doesn’t make other necessary care get pushed aside, I’d recommend using the preventative in areas in which heartworms occur. Especially now that there is more than one choice in preventative medications. I might not rush to be the first one in my neighborhood to try Revolution, though. I like to wait and see if there are going to be unexpected reactions, at least for a couple of months.