Monday, July 29, 2013

Monday Medical: Heartworm in Cats

Two summers ago, we had quite a scare: Allie developed a croupy, dry cough and when examined, our veterinarian advised us to get her tested for heartworms. It was the first we'd ever heard that a cat might be susceptible to this parasite.

Allie gave us quote a scare a few years ago!
Not only that, but we were informed that their practice treated more cats with heartworms in 2011-2012 than they did dogs.

Each summer since, we've felt this to be a critical message to pass along - especially here in the midwest.

And if my experience outside yesterday evening was any indication, we're in for another mosquito-infested summer in our neck of the woods.

So we decided to ask Dr. Sara Huber of Leawood Plaza Animal Hospital to help us understand the symptoms, risks and preventive care for heartworms in cats.

Heartworm in Cats, Part 1

Dr. Sara Huber of
Leawood Plaza Animal Hospital
A Tonk's Tale: Hasn't heartworm traditionally been a dog disease?

Dr. Sara Huber: Yes. But though we typically think of dogs as the host of heartworms, the life cycle also can be completed in cats. Infection rates are usually 10-20% that of dogs in endemic regions.

Several studies have shown that heartworm infection rate in cats is actually greater than that for FIV and FeLV!

ATT: That is one scary statistic. We heard that it can take a while for heartworms to manifest in a cat...?

Dr. Huber: That's true. Here's how it works: an infected mosquito bites a cat and larvae migrate through the subcutaneous and vascular tissue.
Once they enter the bloodstream, the larvae are brought to the pulmonary arteries and into the lungs (3-4 months post infection). Only a small amount of heartworms mature to the adult stage. These are able to reproduce around 7-8 months post infection (1-2 months longer than in dogs).

The disease in cats is split into three stages. The first stage is associated with the arrival of the juvenile worms in the pulmonary arteries and they develop an acute inflammatory reaction. This stage is followed by a symptom free period where the host immune response is suppressed and the worms are maturing.

When the worms die, an intense inflammatory response develops with sudden death reported in 10-20% of cats (stage 2). If they survive this stage, they go onto stage 3 which is permanent lung injury and chronic respiratory disease.

ATT: This is something we did not know about - but it makes such sense, given that the parasite takes up residency in the cat - sometimes for years. Are there any signs we can watch for?

Dr. Huber: Sometimes yes, sometimes no. Owners may notice a variety of clinical signs including chronic cough, sudden difficulty breathing, vomiting, lethargy, etc. Vomiting and coughing are common clinical signs in heartworm infected cats and when seen together should be a red flag for the veterinarian.

Asthmatic-like signs are common 3-4 months after infection. But unfortunately, sometimes the only clinical sign the owners see is severe respiratory distress or sudden death. (I know this is scary to hear, but don't worry! Its preventable!!)

ATT: Is there a conclusive test that exists to diagnose this?

Dr. Huber: Confirming a diagnosis often requires a combination of tests. The testing is hard to explain in non-veterinary language. Tests for antigen and antibody, when used together, improves the probability of making a correct diagnosis. Simply put, talk to your veterinarian about which blood test(s) are best to confirm the disease if it is suspected.

Thoracic radiography and/or echocardiography are very useful in conjunction with blood tests, though radiographic changes consistent with heartworm disease are only seen in about half the cats suspected to have the disease.

Echocardiography can be very useful in determining the severity of damage from the disease but is very operator dependent and should be done by a specialist skilled in this trade.

We thank Dr. Huber for her time and insight into this scary but preventable disease!

Next week:
Treatment and Complications
for Heartworm in Cats


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  1. Interesting that your vet treated more cats than dogs for heartworm. And scary, too. Sounds like another one of those things that need a lot more public outreach and education!

  2. I used to let my cats outside in an enclosure, but as heart worm became more prevalent around here I stopped (that and a gopher dug a hole into the cage for some odd reason) I don't think they get enough benefit from it to risk it nor do I feel inclined to give them medications (heart worm preventative) so they can..

    If all seven of them loved it, that would be one thing, but only two or three kinda like it..

  3. Coincidentally I have just been reading about this, being concerned about sweet Abby of Manxmnews who has CHF. So I wondered if Heartworm might be part of what is going on with her. Our state is "low" incidence but still something to think about.

  4. Wow we never knew cats could get them. Good on you to put out the word. Have a marvellous Monday.
    Best wishes Molly

  5. This is all news to us...
    I'm going to ask Katie's Vet about it ...she's going in soon for a check up. Although I don't think it's heartworm related, she occasionally will breathe loudly when sleeping or resting. ...and she's been tossing up more hair lately. ...probably Waffles-related, but it's worth a conversation.

    Thanks for the heads up.
    : ) GG

  6. Mom didn't know that cats could get heart worm until we had our annual round-up vet visit in April. We had always used Advantage, but she suggested changing to Revolution as it kills these parasites as well. The one thing she didn't mention was the incubation period before any symptoms might occur. That makes this parasite seem even scarier. We'll look forward to next week's post. Purrs and hugs, Lily Olivia, Mauricio, Misty May, Giulietta, Fiona, Astrid, Lisbeth and Calista Jo

  7. Mosquitoes thrive in our country, year round. Heartworm prevention for dogs can be found easily. When I first heard about heartworms in cats, I asked several vets if there was any prevention for cats and was told there wasn't, contrary to what I read. It seems no one brings in heartworm prevention for cats because it's not common. After reading this article, I'm not sure about that...

  8. Thank you for sharing about heartworms in cats! We've heard they are increasingly prevalent in our area (lots of mosquitoes, unfortunately), and it's good to know all of this...

  9. We thought it was just dogs, thanks for making us aware xx00xx

    Mollie and Alfie

  10. Hade no idea that cat´s could get heartworm´s !
    Maybe because we don´t have this in Sweden at all.
    Me and my humans have seen woffies with heartworms on Animal Planet.
    Good thing that you tell us all about it !

  11. Since Mario does get outside with a leash and harness, guess we'd better talk to the vet about this. Either D or myself are always out there with him, and we haven't swatted one misq so far this year. I'm sure they are out there. We just haven't noticed them yet.

  12. I did write about Feline Heartworm Disease a while back. I think many cat parents are surprised to hear about it. A couple of years ago, I heard that the amount of cats who have heartworms was actually larger than what doctors thought. I guess because it can be hard to diagnose. I've also heard that it's misdiagnosed as asthma a lot.


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