What you should know about heartworm in cats and the updated AHS guidelines

This content is sponsored by Antech Diagnostics.

In this episode of The Vet Blast Podcast, presented by dvm360, our host Adam Christman, DVM, MBA, welcomes special guest Kelly Mitchell, DVM, DVSc, Bsc, DACVIM (SAIM), to discuss all things feline heartworm. Throughout the episode, Mitchell highlights the need for a multimodal approach to testing, limitations of microfilaria testing in feline patients, treatment focusing on managing clinical signs and support care, and why prevention is crucial.

Below is a partial transcript, edited lightly for clarity.

Adam Christman, DVM, MBA: The presentation that cats present for heartworm is definitely different [from] that of dogs. So at a practical level, how is heartworm's clinical presentation different in cats vs dogs?

Kelly Mitchell, DVM, DVSc, Bsc, DACVIM (SAIM): Cats are not the natural definitive host for heartworm, and that results in a few differences in the pathophysiology of their disease, and a few...important differences when we compare them [with] dogs. Infection intensity in cats is often lower, so maybe only 1 to 2 worms and single-sex infections are thought to be more common in cats as compared [with] dogs. Now, considering cats [have a] generally smaller body size, the American Heartworm Society guidelines emphasize that even 1 to 2 [worms are] going to represent a significant infection burden in a cat. But to your point...the clinical signs of infection in cats are also very different than dogs, and I think in part, it leads to how this is a more elusive or difficult diagnosis in cats. So the clinical signs [in] cats [are] going to range from the obvious and the significant to the more subtle and nonspecific.

While we certainly want to be cognizant of the obvious and the significant—those are going to include sudden death or a per-acute syndrome of severe respiratory or neurological signs, and sometimes cats will show clinical signs related to aberrant worm migration. Those are the obvious and the significant, but what we don't want to forget about are the subtle and the nonspecific. So, signs of chronic respiratory disease are most common, [such as] cough [and] increased respiratory effort or rate. Cats may also show nonspecific signs, [such as] lethargy, anorexia, vomiting, weight loss—clinical signs that can also be intermittent, right?

Thinking about it from that big picture, we do want to make sure that we're cognizant of these more subtle clinical signs and the differences between cats and dogs, just so that it's always on our list.... If we're not thinking about it, then we're going to miss that opportunity to diagnose it.