Heartworm Disease in Cats

Posted by Aaron

Saturday, June 20, 2009

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.


Heartworm Preventatives

Posted by Aaron

Thursday, June 18, 2009

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.


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.


Heartworm Disease Overview

Posted by Aaron

Wednesday, June 17, 2009


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.


Attack of the Face Eating Thing

Posted by Aaron

Saturday, June 13, 2009

Hi Dr. H,

My beautiful, crazy, Grand dog, Ginger, developed the most horrific, runny, itchy, gooey, face eating, thing on her cheek and our local vet called it a Hot Spot. In all my years, I have never seen anything like it. She is on oral antibiotics, and Gentocin Topical Spray. The spray seems to really burn. She is miserable and has convinced Boudreaux and Coco (our other two dogs)to constantly lick it, so I have tried to separate them, but that’s not working out. We started the meds two days ago and it may be a little bit better today, but not much. Are we on the right course?

Mary R.

Yup - sounds like you're on the right course. Hot spots are areas of moist skin infection. They usually come up suddenly. There may be a bite/sting/scratch that starts it. The area gets wet, infection starts to go wild, and within 12 hours they can turn from a small spot to a huge, wet, stinky, sticky, nasty, red, itchy mess. Really impressive. They also hurt like the dickens.

Key to these guys is clipping them up, cleaning, and getting them to air out. At the same time we use antibiotics to control the infection and then usually a steroid - either by mouth or topically. Antihistamines like Benadryl are usually helpful, but not strong enough to help an active hot spot feel better. The more common antibiotics to use are cephalexin or cefpodoxime (Simplicef). Topical medications commonly used include NeoPredef powder, gentamycin/betamethasone (Gentocin, Gentaved), and a newer product called Calm Gel (part of the Douxo line by Sogeval - very nice stuff!). The goal is to get the nasty thing to calm down.

I'll typically have an owner clean them gently with warm soapy water twice daily and then gently blot dry. In the summer time you MUST MUST MUST not let these wounds go untreated and have the dogs outside much - especially when the wounds are fresh. Hot spots are a favorite of flies and you'll get maggots in the wound nearly immediately. Make sure these get clipped up and cleaned right away. Hot spots smell badly enough without being full of maggots.

Good news is that they usually heal up about as fast as they come on. It'll take a week or two to look normal, but the majority of the pain, discharge, moisture should resolve in the first couple of days.

These type of wounds are common in dogs with seasonal allergies. Their skin is already inflamed and is "ripe" for bacterial overgrowth. Additionally, they are usually scratching and chewing. That combination makes a moist dermatitis easy to flair up.


E-mail contact fixed

Posted by Aaron

Thursday, June 11, 2009

Folks have commented that the e-mail me feature hasn't worked. I fixed it. PLEASE PLEASE send me e-mail. I want comments, criticism, critique, and questions. It helps me make sure my blog is helpful and relevant.

E-mails gushing with praise and affection are also appreciated. ;)


Discoid Lupus (aka Crusty Booger Nose)

Posted by Aaron

Also known as Cutaneous Lupus, is an autoimmune disease that occurs when the immune system begins to attack the skin around the nose. Autoimmune means that the bodies own immune system begins to attack “self” instead on only attacking “non-self.” The body usually makes antibodies to attack foreign invaders like bacteria or virus. If the body makes a mistake and begins to make antibodies to itself, the immune system is directed to damage tissues it should normally leave alone.

Discoid lupus (DL) is most common in collie dogs, Shetland sheepdogs, German shepherds, and Alaskan malamutes (and crosses of these breeds). Because there is such a breed predisposition, this probably has a genetic component to its cause. The disease is also heavily influenced by ultraviolet light. Increased exposure to direct sunlight will worsen disease, so these patients need to avoid mid-day sun as much as possible.

Discoid lupus should NOT be confused with systemic lupus erythematosis (SLE) which is the type of “lupus” that most people are familiar with. SLE is much more dangerous and affects the entire body. DL is much more limited in its affect.

Most owners first notice problems along the moist portion of the nose or on the tissues immediately adjacent to the edge of the nose. This area is known as a mucocutaneous junction (an area where moist skin transitions to dry skin). The pigment of the nose or skin starts to fade and turn pink. The same area usually becomes angry, crusted, and often some mucous is seen collecting in the nostril (Thus, my other name for the disease - Crust Booger Nose). The lesions can also extend up the bridge of the nose and along the lips in more severe cases. Some of these guys have ulcerations and are fairly painful, but they are usually more uncomfortable/irritated - like with a cold sore.

Diagnosis is often made based on breed, history, and appearance in mild cases. However, since many different immune conditions can mimic each other, biopsy is required to confirm the diagnosis. If there are lesions found on other portions of the body (ears, feet, prepuce, vulva, anus, eyelids) then other autoimmune conditions are more likely.

We treat all autoimmune diseases by using medications to suppress the immune response. Sometimes these medications have to be used systemically (to effect the entire body), but it is much more desirable if we can use the medication ONLY at the site of disease. Topical steroids are usually our first line treatments. Oral steroids may be necessary if the condition is severe enough. Tacrolimus (Protopic) is amazingly effective in most patients. I love using it, but since it is usualy $90 per bottle, we often start with simple topical steroids. Other medication options include cyclosporine, niacinamide, doxycycline, and prednisone. The choice of one medication over another is made based on severity of disease and what the patient will allow the owner to do.

Topical sunscreen can also be used. Moisturizing products with an SPF of 15 can be used in sparing amounts. I've had owners use Nutrogena or Oil of Olay daily moisturizing creams with SPF and be pretty happy with it. It only takes a small amount, but that additional protection from UV light seems to help tremendously when we have the disease under control and are trying to keep it that way.

Autoimmune diseases are controlled, not cured. You have to keep ahead of the disease. It is always easier to keep it under control than it is to try and get it back under control. With successful response to medications and continuing treatment, most DL patients live long, happy lives.