TheOldBroad, a regular reader of Fully Vetted, commented on last week’s post about canine distemper with a question about feline distemper. Here's my take on this disease, which is deadly, but thankfully relatively uncommon — at least in well-vaccinated domestic cats.

First of all, despite their names, canine and feline distemper have little in common. I don’t know how the two diseases ended up both being called "distemper," but this unfortunate happenstance has resulted in no end of confusion for pet owners. Canine distemper is caused by a morbillivirus, while a parvovirus is responsible for feline distemper, which explains why feline distemper in fact has far more in common with parvo in dogs than with canine distemper. In fact, the relationship between parvoviruses is close enough that cats can become infected with some types of canine parvoviruses, although the clinical significance of this remains unclear. On the other hand, dogs do not appear susceptible to feline parvovirus.

Some people actually call feline distemper feline parvo, but I prefer the term panleukopenia. It’s a good description of the condition and prevents all the distemper/parvo confusion; so from here on out I’ll call the disease panleukopenia.

As I said, panleukopenia is caused by a virus, a particularly nasty one. It is ubiquitous, meaning that it is essentially found everywhere because it is so cussedly tough. It can survive for years in the environment and massive quantities of the virus are shed in the bodily secretions of infected cats. Therefore, almost every cat comes into contact with the virus early in its life. In some ways this is a positive, since kittens usually get some immunity from their mothers. If they are then exposed to low levels of the virus in the environment, they can develop their own protective immunity as they get older.

Problems arise when cats with no or only partial immunity are exposed to massive amounts of the virus. This typically occurs when young or inadequately vaccinated cats are grouped together; in shelters, pet stores, or feral cat colonies, for example. When the virus overwhelms the immune system, cats become desperately ill.

The most common visible symptoms of panleukopenia are vomiting, diarrhea, loss of appetite, and lethargy — symptoms which are obviously not unique to this disease. What is unique, however, is the way the virus obliterates a cat’s ability to make white blood cells, thereby explaining its name:

pan- all + -leuk- leukocyte, or white blood cell + -penia deficiency

"All white blood cell deficiency.” Now that makes a lot more sense than “distemper.” (Sorry, but I love this type of stuff. I did write a dictionary after all.)

A practical diagnosis of panleukopenia can be made in a cat with typical symptoms and a poor vaccination history when a veterinarian finds extremely low numbers of white blood cells on a complete cell count (CBC) or blood smear — there isn’t much else out there that will do this. If questions persist, a stool sample can be tested using a canine parvovirus snap test (they aren’t approved for use in cats but they work well) as long as the cat hasn’t been vaccinated for panleukopenia within the last week or so. Recent vaccination can cause false positive test results, and cats may still get sick since the vaccine hasn’t had enough time to stimulate the immune system. Other laboratory tests are available in complicated cases.

That’s enough for today. Tomorrow I’ll talk a little more about what panleukopenia does to a cat’s body and what, if anything, can be done to treat and, more importantly, prevent the disease.

Dr. Jennifer Coates

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