Problems with Heartworm Treatment

The perfect treatment for a disease needs to satisfy several requirements:  the treatment should be 100% effective and it should be completely safe for the patient.  If it were also easy to do, and inexpensive, that would be perfect.  When the standard treatment for a disease fails to satisfy all four of those requirements, people begin to look for alternatives.  Sometimes this results in better treatments.  Sometimes it results in the patient receiving no effective treatment because he's busy getting some quack remedy that does nothing at all (or kills him.  Remember Laetrile?).

Treating a dog to clear him of heartworms is a situation where the state of the art is not perfect.  Prevention of the disease with monthly preventive medicine has been effective most of the time.  Treating the dog who has adult, foot-long worms in his heart -- that's a different story.

The conventional view is that the worms are in the right ventricle of the heart, and the big pulmonary artery trunk.  If you do a post-mortem on a dog who has died from heartworms, you'll find a lot of them there.  In a dog with a lower worm burden, there are not so many worms in the heart.

Most of the worms will actually be in the pulmonary arteries (taking blood from the right side of the heart to the lungs to get oxygen).  There may not be any worms in the heart.  If you open this dog at post-mortem, even though there may not be huge numbers of worms, you can cut the lung way out at the edge and find worms in the blood vessels.

The worms don't eat the heart or arteries, they just float.  When there are so many worms present that they clog the outflow from the heart (like roots in a pipe), the heart wears out (prematurely) from the constant overwork of pushing blood through the clog. 

Actually the worms don't just float -- they swim upstream. If they just floated, the pressure in the artery would force them downstream until they hit a branch too small to pass.  This would clog the artery either partially or completely, resulting in poor circulation to the downstream area of lung.  The dog might get a secondary pneumonia in this damaged area.  If he ran hard, increasing heart rate and blood pressure, the damaged artery could blow out, hemorrhaging into the lungs.  Indeed this does happen in some dogs, though most infected dogs develop the less dramatic signs of congestive heart failure: weight loss, coughing (especially after exercise), labored breathing, fainting spells and so forth.

This is ALWAYS what happens when the dog is treated to kill the heartworms.  Worms who have been swimming upstream, keeping the artery open, float downstream and clog up the works.  Unlike an intestinal worm infection (hookworms, roundworms, tapeworms, etc.), there's no exit here.  With intestinal worms, you kill the worms and they leave the body with the next bowel movement.  With heartworms, they clog up the works like a blood clot would (except that few blood clots are a foot long).  You've heard that you shouldn't get an air-bubble injected -- how about a handful of foot-long worms?  The only way to get rid of them is to let the body's microscopic white blood cell defenders eat them.  They'll do it, but it's a slow process, like termites eating your house.  It takes weeks after the death of the worms before the body dissolves them out of the circulation and opens all those clogs.

This is the unsatisfactory part of the heartworm treatment.  It's why dogs feel bad a week or so after they are treated.  That's when the worms die and shift position.  The dog may have a fever, cough, lose appetite, have trouble breathing, or cough up blood.  Sometimes you don't see any of those things, but you can just tell that your dog doesn't feel good.  You know your dog, and even though he may not have specific signs, you can tell when he doesn't feel well.  This is the reason we ask you to restrict the dog's activity for several weeks after treatment -- no hard running for a while.

Most complications of treatment are minor and very treatable.  Severe problems like blood-vessel  rupture or allergic-shock-like reactions are extremely rare.  It could happen, but most dogs have years added to their lifespan when the heartworms are destroyed.

Here's the crux of the matter, and the reason I'm writing today.  Ill effects during the heartworm treatment are related almost exclusively to the dead worms clogging up the pulmonary arteries.  The drug that's used (Immiticide TM - melarsomine dihydrochloride) is unlikely to cause anything worse than some temporary soreness at the injection site.  It takes those little worms five days to die and they're taking a  bath in it.  There just isn't enough drug to bother the dog (unless he has some pre-existing severe liver disease).  That's why it doesn't matter whether your alternative remedy is a better chemical, a cheaper chemical, organic, holistic, homeopathic, herbal or black magic.  If it kills the worms, the arterial blood pressure is going to shoot them downstream and clog up the works.   

I've seen people use D-con rat poison, gunpowder, and levamisole (a sheep-wormer that is VERY hard on the dog's liver).  Today a client brought in some misinformation he'd downloaded from some "Natural" website (with many products for sale).  Their nostrum is alleged to be superior because "There seems to be no risks of the parasites dislodging and creating vessel blockage."  Yeah?  Do the worms die or don't they?  If they die, they're going to move.  You may not have seen an artery pumping, but a two-millimeter artery will shoot three feet in the air if your clamp slips off before you get it tied.  Dead worms don't swim - they go scooting downstream.

I wish that our standard heartworm treatment was 100% effective, safe, easy and inexpensive.  It doesn't totally satisfy any of those criteria.  It is usually effective in eliminating all the worms, most dogs have no complications (or very minor and easily treatable ones), and it just takes two injections, 24 hours apart.  But, it's not cheap.  And you have to let the body deal with those dead worms.  There's just no way around that, no matter how you kill them.

P.S. Don't forget to give your dog his heartworm preventive.

Comments

[joanne]

I was wondering which brand/type of heartworm treatment you recommend?

[Dr. Mobley]

Dear Joanne,

Thanks for reading. We really only have one option to treat adult heartworm infestations: Immiticide, made by Merial.

For regular monthly prevention, there is milbemycin oxime and the avermectin family. Milbemycin is in Interceptor and Sentinel, made by Novartis. Ivermectin is in Heartgard 30 (made by Merial) and various generics, such as Iverhart. Selamectin is in Revolution, made by Pfizer, and applied topically.

There are other products. These are the ones that I use to provide a variety to my clients. There is no one product that is best for everyone. Some give intestinal parasite control as well, so give flea control as well. Some are easier to administer for one dog, others for another. I believe them to be equally effective, so it's a matter of what works best for you and your dog.

[Gina]

Have you ever heard of heartworm treatment affecting a dog's behavior? We adopted a rescue dog a couple of months after he was treated for heartworm (he ended up losing an eye because the second dose wasn't administered in the right timeframe) and we're having some severe behavioral problems. Just wondering if this could be part of it.

[Doc]

Heartworm treatment generally causes problems in the lungs, via the damage to the blood vessels that supply them (the pulmonary arteries). The period of recovery while the worms are being dissolved can certainly be stressful for the dog. Generally speaking, I have not seen any changes in the dog's personality and behavior after recovery.

I would not be surprised if the dog were having trouble adjusting to the loss of an eye, but I am puzzled as to how this occurred. I have never heard (nor can I find in a search of Veterinary Information Network) of a similar situation. Ivermectin is generally used at the end of treatment to clear the baby heartworms from the bloodstream, and ivermectin toxicity is known to cause blindness, but this is usually in both eyes and is usually temporary. I have never seen this myself, but it is reported as a consequence of overdosing (or in a dog that is exceptionally sensitive to the drug).

I would be interested in more information as to how the blindness developed.

[Mary Lee]

I have a 3 year old great dane that I recently rescued from a family that "didn't have time to take care of him." He is heartworm positive and I took him in to start his "Immiticide" treatment this past Monday 2/7/08, and was told if everything went well he should be able to come home on that Wednesday 2/9/08. Long story short: He is still not able to come home as of today 2/14/08. He has had a "very severe reaction to the injection" as in the injection site itself. My veterinarian says that he has never seen a dog react this severely before from the actual injection. His whole pelvic area is completely inflamed, his white blood cell count is extremely elevated, he is in sever pain and cannot even get up to go to the bathroom. I can't even type this without crying. I feel like they are doing everything they know how to help him. They have him on an IV for fluids, a strong antibiotic they started today, and "tramadol" for pain. Any suggestions?

[Mary Lee]

Correction to recent post. My dates are messed up. I brought him in for treatment on Monday 2/4/08 and was supposed to be able to pick him up on 2/6/08. Today is 2/11/08.

If they're is any advice you may be able to give, I would greatly appreciate it. It seems that since it is uncommon for a dog to have such a severe reaction there is in turn limited info on it. This great dane named Duke is the most precious dog I have ever met. I am a huge dog lover in general but there is something extra special about him and I will do anything I can to help him. I love him very much.

[Doc]

Hello, Mary,

I am sure that your veterinarian has already called Merial (the maker of Immiticide) to report the reaction and ask for their advice.

When Immiticide first became available in the U.S., Merial sent out mailings, including an instructional video on giving the injections. The injections are given deep in the epaxial muscles (the long loin muscles on either side of the spine), using a 1&1/2-inch long needle to deposit the medication deep in the tissues.

I had been using the product for about a year when I had a similar experience to yours. A Rottweiler patient developed an open sore the size of a golf-ball at her injection site. When I called Merial, they asked if I had kept firm pressure on the injection site for two minutes. I had not. They then said, "You need to do that."

The medication is very caustic and needs to be distributed deep in the muscle fibers for absorption. There's really no "place" for it to go -- it just spreads between the muscle fibers to be picked up by the bloodstream. The easiest place for it to spread would be back up the needle track, allowing it to pool under the skin. This produced the bad reaction in my Rottweiler patient. The two minutes of pressure is to try to prevent this creep back up the needle track.

I noted that there was no mention of this "pressure for two minutes thing" in their literature or video [and there STILL is not, and I have spoken personally with several veterinarians who have never heard of this]. They replied, "Yeah, we know, but you still need to do it." Thus, all of my heartworm treatment patients since then have also received a "laying on of hands", and I've had no further problems.

That being said, everything may have been done as well as humanly possible and the dog is having an idiosyncratic reaction, like someone who just can't take aspirin or something. It's not the drug, it's just him. As far as treating the problem is concerned, at this point the care is going to be mostly supportive, as it would be for a brown-recluse spider-bite that causes tissue to die and slough.

Your doctor's approach of Tramadol (a mild narcotic which is usually very helpful and well tolerated) and antibiotics (so that bacteria don't get a chance to complicate the situation by invading the damaged tissue), both sound very appropriate. The only other thing I might be doing would be hot compresses three times daily to increase circulation to the area and speed healing. You might also ask about Lidocaine patches. These can be applied to the skin on either side and give a constant slow release of local anesthetic into the area to help control pain. NSAIDs like Rimadyl can be combined with Tramadol for additional pain relief. NSAIDs should not be used if the patient is already on some form of cortisone for inflammation.

It sounds to me like your veterinarian is doing a good job in a difficult situation.

I hope this information is helpful to you. Good luck and thanks for reading and writing.

[Liz]

Butch is a rescued Malamute and golden lab. mix.He tested positive for heartworms and I was told if the worms were not stage 5 he could be treated. The tests were done and Butch was treated. He ended up with his salivary glands infected and severe pain. He went back for a stay at the vet and was sent home again and now we are being told that he has a blood clot and he is dying and the vet said we should put him down? Why would he have us go through with the treatment to tell us that? The dog has lost alot of weightand his equilibrium seems to be very bad, he can only walk so far without coughing and falling over. Help us Please.

[Doc]

As I mentioned in my posting, there is always a risk involved when you treat dogs for heartworms. There is simply is no way to guarantee success when you have foot-long worms clogging up the works. Most dogs do well, or survive minor complications, but some do not.

I must confess that I cannot imagine how there could be any relationship between the heartworms and the salivary glands. There must be something lost in the translation here.

I am sorry that things have gotten so bad, but I feel that your veterinarian acted in good faith to do what he felt was in the best interests of your dog and for you. Sometimes things just don't work out the way we would wish for them to.

Thanks for reading and writing.

[Cindy O'Neal]

My Golden has been on the heart prevenative medication "Heartgard" I have never missed a dose and she goes to the vet and is very well taken care of. Today, I took her and the other golden that I adopted to the vet. Red, checkup...and Maggies the adoptee to be spayed. An hour after dropping them off, they called to tell me that maggie had heartworms, and cancelled the spayed. We went to the vets office and then told that Red also was positive...and she has always been on heartgard. Then they told me that we would have to pay for Maggies the adoptee, but Red...Meril would pay for it since we have records of her being on heartgard monthly. What do we do now...these dogs are the world to us. Any advice please

[Doc]

I sympathize with your situation -- more than you know. I'm going to have to post on this one at last, so look in on the blog pretty soon.

The failure of the preventive medicines (ALL of them, not just Heartgard 30) to be 100% effective is becoming a problem. I am told it is primarily in the Mississippi valley, and gets worse as you go farther south.

In the last two years, we have seen a ten-fold increase in this situation. The good news is that we are still seeing just a small percentage of dogs affected, and almost all are large breed, outside dogs. The other good news is that these dogs have very few heartworms present, as evidenced by the fact that none of them have had any significant side-effects of treatment.

While there is no guarantee, the odds are overwhelmingly in your favor that your dogs will do well. Get them treated, send the bill to Merial, and get them spayed afterwards.

Good luck, and thanks for reading and writing.

[Sam]

I am fostering (to adopt) a sweet little girl dog who was heartworm positive and has received the initial treatment (on the 21 and 23 of February). She and her 3 pups were deposited in a drop box in S. Carolina. The treatment was given at a clinic in N. Carolina, and the Vet's guesstimate on her age is 1, I think maybe a little older, lots of tartar, but maybe that's just a poor diet? Anyway she is young and probably had the pups about 8(?) weeks ago. She is definitely underweight, at about 20lbs. She seems happy enough and alert and not without energy, but is not hyperactive. I am trying to figure out how "quiet" she should be kept. Walks? Playing in the house? No activity? And for how long? I want to keep her mind engaged with training, etc... but don't want to get her over-excited. Also, she is sneezing a lot. (not boogery sneezes, just dainty little ones, but a lot, usually after she's been lying down) Does this mean anything re the heartworm, or is it more likely that it's something in my house (she's only been here for two days)? So glad I found your blog!

[Doc]

Hello, Sam,

The sneezing is probably not related to the heartworm treatment. Consider feeding a good quality puppy food while you are trying to help her recuperate from poor nutrition and nursing babies.

Activity should stop short of any prolonged aerobic exercise. Relaxed walking on a leash is okay, any normal mild play in the house is okay. We want to avoid any dramatic or sustained rise in heart rate and blood pressure. This would be more likely to shove chunks of dead worm farther into the arteries, creating a more complete blockage, increased pressure, and potential blow-out, bleeding into the lungs.

It is not possible (nor desirable) for the dog to lie still for six weeks. Just make your best effort to avoid strenuous activity. Call your veterinarian if your dog shows signs of difficulty: coughing, difficulty breathing, poor appetite, fever, or just generally feeling bad.

Thanks for reading and writing.

[paula b]

My foster dog who had heartworms was treated with Immitcide and was finally retested for heartworm and thankfully it was negative.
She was adopted, the adopter was told of her HW treatments and that she still had a cough and wheezing if she got excited or ran while playing...My vet put her on prednizone 5 mg bid...and now says to up it to 10 mg. bid....the person who adopted her took her to his own vet...who told him to bring her back to us because she would have problems if not now..but down the road....he did no tests or anything...just from hearing that she had been treated for heartworms and was still coughing and wheezing some. I understand that it takes several weeks sometimes for the fluid and inflamation to go away and that is why you give them pred. I have to take her back because this guy's vet scared him. Whose vet do you think is right? Mine or the adopter's? I am so upset about all of this. I would appreciate an answer or advice asap.
Thank you, Paula B

[Doc]

Hello, Paula,

I would have to say that, generally speaking, the doctor who has actually examined the dog is in a better position to give an accurate assessment of the dog's health.

It is certainly true that the dog's pulmonary arteries and lungs suffer damage from the presence of the worms, both while they are alive, and when they are killed and being phagocytized (dissolved away by the white blood cells). There may very well be permanent problems, in that the damage may prevent the dog from being athletic. However, even so, he may be able to lead a perfectly good quality of life.

I would say it is possible for the dog to be chronically ill after recovering from heartworm treatment, but I would also say that it is not very common for that to be the case. Most dogs lead a good quality of life (even if not "100%"), and are NOT "perpetual patients".

For a more objective evaluation, one could radiograph the dog's chest now and repeat the films in 30 days to see how the condition of the lungs progresses. I believe it is too soon to say what the dog's eventual outcome will be.

I hope this is helpful to you. Thanks for reading and writing.

[paula b]

Hello, thank you for such a quick answer. I do appreciate that.
I picked Shyanne up today and have her back. She is happy acting...lively...certainly not depressed but is wheezing a lot. I am not sure if the adopter was giving her the pred like he was told or not. I just gave her 10 mg. of pred. Would your advice be to keep her on that twice a day until the wheezing stopped? Also, I have read about Doxycycline and she did not have that prior to the hw treatments nor during them...would it be a good idea in your opinion to start her on that?
My vet, gets a little irritated with clients who get on the internet to read up on things like this. I guess she feels like if a client does this..that they don't trust her judgement as a vet. I just want to educate myself as much as possible. I do realize though...that sometimes people who are not trained and have degrees in medicine can easily get confused and maybe even panic reading too much into something or not understanding it right.
I read somewhere that if the dog's gums are dark red there could be a secondary infection...so of course as soon as I got her back tonight...I looked at her gums...they do seem to look darkish red...not pink. Am I reading too much into this and starting to panic or should I be concerned? My vet is out of town until monday. I have doxycycline here but it is 100 mg.
One more question...until her wheezing stops altogether or at least for the most part...should I try to keep her in a crate or confined area like I did mostly during her actual treatment period. I am sure those worms are still trying to get out of there. Or is it fluid and inflamation making her wheeze?
I will ask my vet for a lung xray next week...is that what I should ask for first?
Thank you so much for your time.
Paula B

[JAYNE GLENN]

Our 5 year old australian shepherd is showing no signs of illness after his his heartworm treament - 2 injections , 24 hours apart. He is home. Nothing more that a little bit of coughing at times. He is doing remarkably well! I thought he was going to be really sick after the injections, such as coughing a lot. Not so! Just after 2 weeks of his treatment he already has more energy. Thanks to an excellent Dr. who put him on all the needed drugs for heart worm treatment:
DENOSYL, DOXYCYCLE, AND PREDNISONE DAILY, ALONG WITH REST , LOTS OF TLC!! AND A GOOD HEALTHY DIET OF PROTEIN. LOTS OF CHICKEN AND EGGS. WE CALL HIM THE MIRACLE DOG, OUR BABY SHEP WAS AT DEATH'S DOOR BEFORE HIS TREATMENT. THE TREATMENT IS VERY , VERY EXPENSIVE. IT INVOLVES BLOOD TESTs EACH VISIT..
OUR DOG WAS WORTH THE 3,OOO TO SAVE HIM. HE IS PART OF OUR FAMILY. I WOULD RATHER HAVE HIM STILL BE MY SIDE THAN THE 3,OOO I COULD HAVE SPENT ON A VACATION. HE WAS WORTH EVERY BIT OF THE TIME INVOLVED TAKING HIM BACK AND FORTH FOR CHECK UPS, BLOOD WORK. IF YOU REALLY LOVE YOUR COMPANION, YOU WILL NOT THINK TWICE ABOUT THE EXPENSE , TIME AND CARE THAT HAS TO GO INTO SAVING YOUR DOG FROM HEARTWORMS.
NOW A HAPPY OWNER OF A HEALTHIER SHEPHERD! He is already showing better quality of life, and it has only been 2 weeks after his injections. Best wishes to you and your companion. They can be saved! Ours was. -jayne

[paula b]

Hi Doc! I had shyanne's lungs and heart xrayed today..my vet says it looks what she would expect after having heartworm...still thinks she should stay on 10 mg. pred bid for another month because she is still breathing hard..sort of wheezing a bit when she gets excited or runs. She thinks Shyanne should heal some though...anything to add to this? Paula B

[Doc]

I think that the doctor "on the ground" is in the best position to judge the situation. Your veterinarian has probably already told you that you will have to taper off slowly after taking that much pred for that long a time. Good luck!