Monday Medical: Heartworm Treatment for Cats

As we mentioned last week, 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!

In last week's Medical Monday, Dr. Sara Huber of Leawood Plaza Animal Hospital talked to us about what heartworm disease in cats is and what symptoms you might see if your cat is infected.

Today, we continue our discussion with her, as she discusses treatment, possible complications, and the good news - it's completely preventable.


Click here to read
Heartworm in Cats, Part 1

Dr. Sara Huber of
Leawood Plaza Animal Hospital

A Tonk's Tale: So we learned one very scary statistic last week: there are more incidents of heartworm in cats than there are cats infected with FIV and FeLV. That was shocking to us - and made us even more determined to get the word out about it.

What can you tell us about heartworm treatment in cats?

Dr. Sara Huber:  To be honest, treatment for the disease can be frustrating. Studies suggest that 10-20% of infected cats die secondary to the death of the worm. Treatment to kill the adult worms is also, in and of itself, risky.

Infected cats are usually managed with supportive care for the pulmonary disease secondary to the infection (with drugs such as steroids, bronchodilators, ivermectin, etc.).

To make things even more confusing, heartworms can be infected with a bacteria called Wolbachia. Cats have a strong immune response to this bacteria and it is thought that the bacteria could play a role in the strong inflammatory response to infection.

ATT: So if the shock to a cat's system when the worm dies isn't enough, now we have to worry about a more pronounced reaction in our cats, because the heartworms may have this bacteria as well?

Dr. Huber: Yes. And for this reason, veterinarians will frequently treat infected cats with an antibiotic called Doxycycline.  Now I need to point something out here real quick: the use of Doxycyline tablets in cats has been associated with esophageal stricture - a narrowing or tightening of the esophagus which causes swallowing difficulties - and for this reason, the medication should be compounded to a liquid.

(Note: If you haven't read about the positive impact a compound pharmacy can have on your pet's health - and the danger we're in of losing this vital resource here in the U.S. please click here and add your voice to the petition!)

ATT: So what can we as cat owners do?

Dr. Huber: Prevention is key! It is very important for cats living in heartworm endemic areas to be on a preventative year round.

My favorite product (and I am in no way affiliated with the company that makes it, nor do I profit from recommending it!) is Revolution topical. In addition to preventing heartworm infection, it prevents several intestinal parasites, can treat ear mites, and prevents and treats fleas. It is a small volume of liquid that goes between the shoulder blades. Very easy to administer and based on what we previously talked about, worlds easier and safer than managing an infection.

Take a look at this map of the 2010 prevalence of heartworm infection in the US.

 
Keep in mind, this is only reported cases. I am confident that a number of cases go unreported every year. Also bear in mind, this is an older map. The mosquitoes that carry the disease are beginning to show up in many areas previously thought to be a low risk area.

As I said before...prevention is key!!!

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We thank Dr. Huber for helping us spread the word about the very preventable dangers of heartworm infection in cats. For more information, you can visit the American Heartworm Society at http://www.heartwormsociety.org.

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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