Heartworm Disease in Cats

http://www.knowheartworms.org/

Checkout this link. It has good information.

Here's the scoop - we always knew that cats could develop heartworms. We knew that occasional cats would develop an adult worm in the heart and that those cats were in a pretty dangerous position. If you tried to treat the adult worm, about 33% died outright, 33% were so sick they wished they were dead and 33% did great. Thankfully, the incidence of this disease was fairly low in cats and so prevention was recommended, but not encouraged as much as it should have been.



Guess what - we were wrong! Research completed at North Carolina State in 2005 confirmed that although true that few cats develop adult worms, the real story is that MOST cats kill the worm before it turns into an adult. That's great except that when this happens, these kitties often develop wicked asthma. I've treated dozens of cats for asthma. Feline asthma is considered a fairly common disease. We now know that many (most?) of those cats are heartworm disease!



Diagnosis of these kitties is difficult because of when they kill the heartworm larva. There is a very narrow window of time that a cat would be 'positive' on a test. By the time we see a sick kitty, it is quite likely that we will not be able to prove the presence of heatworm as the cause. Worse yet - our treatment at this point is supportive. I can't reverse the disease, I can only control it. There is now a name for this condition - HARD - Heartworm Associated Respiratory Disease. Heartworm is a misnomer in cats - lung disease is the primary problem, not heart disease.



So the major change in our thinking has been that PREVENTION is critical in cats. Many more cats are at risk that we ever though. Prevention is now seen as just as important in cats as it has always been seen in dogs.



But my cat is indoors. Heartworm disease is transmitted by mosquitoes, so how could my indoor cat be at risk?

There's the other shocking finding. In that same NC State study, roughly 30% of those cats diagnosed with heartworm disease (usually after death) were reported by their owners to be 100% INDOOR cats. So 1 in 3 cats dead of heartworms never left the house (according to their owners). We all know mosquitoes will get into the house. Now we have proof that they bring problems indoors with them.



Moral of the story?

Cat's get heartworm disease. Most frequently they get respiratory disease. Heartworm disease is often fatal in cats. It's hard to diagnose. It's hard to treat. It's also VERY PREVENTABLE if you use a monthly preventative prescribed by your veterinarian. Prevention, Prevention, Prevention, Prevention. My personal favorite is Revolution for cats. There are other excellent products like Heartguard, Iverheart, Advantage Multi, and Interceptor. Each of these have the added bonus of also controlling intestinal parasites.



AMH

Heartworm Preventatives

Now that I've talked about heartworm disease, here's the skinny on heartworm preventatives:

You now know that mosquitoes are the carrier for heartworm. Exposure to mosquitoes is therefore required. Risk is highest for dogs outdoors at the hours of dusk and dawn when the little buggars are out feeding.

HOWEVER...

Mosquitoes come indoors! Dogs go out to pee or at the very least poo (usually). Although your risk is lower as an indoor only cat - about 1 in 4 SICK cats are considered 100% indoor by their owner. There is no such thing as a dog that doesn't need preventative.

Preventatives are critical. One common misconception is that heartworm preventatives work for the NEXT month after they are given. What's happening is that the preventatives are killing off any larva that the pet has been infected with over the LAST month. In other words, we assume that the pet has been infected and the preventative is killing them before they grow to adults.

There are many different heartworm preventatives out there. They all do the same thing - they kill the larva. All of the preventatives you should be able to get today are in the same class of drugs. Some people are still using Filaribits (DEC) but if you are - STOP. Some preventatives have activities against other parasites - some kill intestinal parasites or fleas in addition to heartworm larvae.

Common products you'll find are:

• Heartguard (plus)
• Interceptor (or Sentinel)
• Advantage Multi
• Revolution
• Iverheart (plus)

They each have really pretty literature that shows how they are the best product on the market and all of their competition sucks. The truth is somewhere in the middle. They all have their ups and downs. Go with your veterinarian's recommendation. I'm a Heartguard man. Always have been. Always will be. All of these products are effective. All of these companies support their product claims. It's really a matter of your situation, what you think is easiest, and what your veterinarian recommends for your area.

The most important concept is that they are all intended to be given once a month. You have to use them once a month. The one exception out there is ProHeart. This is an injectable heartworm preventative that is given every 6 months.

AMH

Heartworm Disease Overview

http://www.heartwormsociety.org/

The link above will give you lots and lots of good information on this subject. The pictures above are small, I know. I don't have any larger pictures. Maybe someday I'll get a good heart to get pictures of.

I'm going to post a separate blog on preventative choices, feline heartworm disease, and heartworm treatment.


Here are a few common myths and answers. There's discussion below.

Myth: Heartworms are found in the stool. Your dog gets heartworms by coming in contact with another dog's stool.

Fact: Heartworms are exactly that - they are found in the heart. The larvae are found in the blood stream and they are transmitted by mosquitoes.

Myth: Only dogs get heartowrm.
Fact: We used to think so. We were WRONG. Cat's do get heartworm. So do people.

Myth: My dog is indoors, so I don't need preventative. Same argument for cats.
Fact: Turns out this is absolutely false as well.

Myth: Preventatives are over the counter. My vet is just being a pain in the butt about requiring me to come in.

Fact: See my previous posts on the importance of regular physical exams. Preventatives are all PRESCRIPTION products. This means we can't just sell it over the counter or we get huge fines and risk loosing our license. We're not being a PItA. We're following federal drug law.

Here's the skinny on heartworm disease.

These worms start out as baby larva in an infected dog. These larva are referred to as L1 larva. A mosquito comes along, takes a blood meal that includes the L1 larva and flies away. The larva grow and develop into L2 and then L3 larva. Same mosquito bites another dog and those little L3 larva come down the mosquito's mouth and climb into that tiny hole and into the dog (cat, human, wolf, fox, etc). The larva then continue to devlop into L4, L5, then adult worms. As L5 and adults they take up residence in the right side of the heart and the pulmonary artery leaving the right side of the heart and into the lungs. You must have both males and females to reproduce, but once you do - the life cycle begins over again. Adults live for about 5 years in the dog.

The canid is the definitive host - meaning they are the host the parasite is intended for. Dogs, fox, coyote, wolf are all routinely infected. Other species can be infected with the parasite, but the body kills it off before it can become an adult. In people, it's usually killed off in the skin but it is possible for it to migrate to the lung and form a little granuloma before it's dead.

We used to think that cats were an uncommon host for the parasite - we were incorrect. See my companion post about cats and heartworm disease.

It takes about 4 or 5 months for a worm to go from larva to adult. The preventatives only work during the first 30-45 days of this period. Tests used by your veterinarian are only positive when there are adult female heartworms present. It is therefore possible to have worms in the heart and a negative test if either 1) they are only 4 months old or 2) you have all males or less than 3 females. 100 males, 1 female = NEGATIVE test! (This is uncommon, but it happens!)

The timing on this is important because this means there is a period of time between when a larva can be killed and when the test would become positive. For this reason, a pet that has been off preventative cannot be considered negative until a repeat test is done 5-6 months later.

What happens if I don't treat or prevent heartworm disease? Honestly, a dog can probably tolerate a small worm burden (1 or 2 worms) for a lifetime. The will have changes in the blood vessels in the lungs and will have chronic bronchitis-type problems. Most dogs with the disease don't just have one or two worms and therefore get progressively get sicker and sicker with hearts that fail and lungs that don't work. They may develop clots in the lungs and can suffer sudden death. Untreated heartworm disease kills. It's pretty nasty.

Next posts will be on prevention, treatment, and feline heartworm disease.

AMH