Your Pet's Best Friend

Dog still tests positive after heartworm treatment

Ken writes:

I adopted my dog from a shelter 2 years ago. She was estimated to be 1 year old at the time. She is a mix of Chihuahua and Terrier. She weighs approx. 11 pounds and is 12 inches tall. She tested positive for heartworms but I elected to adopt her anyway.

I had her treated with Immiticide. She was then put on Heartguard and am giving it to her monthly per my Vets instructions. After 2 years she is still testing positive for heartworms (adults) but has been negative for the babies for over a year. The vet has said that she has not previously seen a dog still testing positive for adult heartworms after two years.

The vet has discussed two choices: 1) Second round of treatment of Immiticide, or 2) Continue giving the Heartguard monthly and hope that the adult worms present will die. The vet was not clear on what was the better alternative.

I ask, “What would you do if it were your dog?" and the response was "I guess I would treat it with the Immiticide", but she wasn’t overly convincing.

Overall, Sadie is in good health. She is not experiencing any symptoms consistent with advanced heartworm disease. I am not certain I want to subject Sadie to this procedure unless it is the better alternative. I have read your web pages on this topic and appreciate your thoroughness. I would be interested in your opinion in this matter.

 

Hello, Ken,

 Generally speaking, the best person to advise you is the doctor who is seeing your dog.

 That being said, there are two scenarios that come to mind.

 First, we have to remember that the Heartgard (and other monthly preventives) work to kill the lifestage of the parasite that exists from mosquito bite up to about five or six weeks afterward.

 Second, it takes around six months from the time of the mosquito bite for the adult worms to be developed in the heart. It is only at this stage that they can be detected with the blood test. This is also the stage when the Immiticide works.

 SO, there is roughly a four-month window where the parasites have matured past the point where the monthly preventive can kill them, but they haven't reached the point where they can be detected with a blood test, or killed with Immiticide.

 If your dog was treated with Immiticide in October, for instance, and started on Heartgard at that time, baby heartworms acquired in June, July, August and September will go ahead and mature, and be showing up in the next spring's blood test.  They are too mature for the preventive, and not mature enough for the Immiticide to get them.

 The Immiticide may have killed all the adult worms present at time of treatment, but it didn't keep the partially mature ones from growing up. Thus you have a positive blood test again, even though you were faithful with your preventive.

 The other scenario is the dog where the worms just don't all die with the treatment. Some dogs (rare) will never get a totally clean blood test.

 My bias would generally be to re-treat with Immiticide in early spring (April is not too late, and don't stop your preventive medicine). Any previous parasite exposure will then be in the life-cycle stage where they can be killed. 

 In the case of a dog who had already undergone Immiticide treatment, and started on monthly preventive right away, we would expect very few worms to be present, and we would expect a good result from the treatment.

I hope this is helpful to you.

Heartworm Treatment Decisions

Here's a note from Pat:

I've read so much I am sick. Rescued my shih tzu mix 7 months ago.  He was tested negative for heartworms by agency's vet. My vet did not retest (though he did health exam) until 6 months later, and he is positive.

Vet gave me 2 options, suggesting we start with Heartguard. He has been on Trifexis since I have had him.

I read that the fast kill drug may or may not be available? And that dog has to be crated for up to 9 months.

I work and worry i wont be able to take care of him. And then he may die passing the worm anyhow.  I  cannot afford to leave him at vet for extended time.

Should i just put him to sleep? How do you keep a dog from exercising? Is my dog infectious to other dogs?  Does he need to be kept inside all the time?

I live in South Carolina.  What kind of life is that for a young dog? How do I know what to do?

 

HOLY COW!  So many questions.  It's a complicated disease.  Here we go with some answers.

Hello, Pat,

Be calm. All is not lost.

If the dog tested negative 7 months ago, then you are looking at one summer's mosquito exposure, which probably does NOT equal very many worms.

If there are microfilaria (microscopic baby heartworms) present in the blood, then Heartgard is considered safer than the Trifexis (the active ingredient sometimes causes a reaction with the babies in the bloodstream).

Immiticide (the fast kill drug)is available. There was an older approach of just keeping them on Heargard, sometimes called "slow kill" or "soft kill". Now called "probably no kill", and not recommended. You just don't know if the worms will die any time in the next few years, and you're not going to be watching the dog closely and restricting its exercise for a few years.

After a dog is treated with Immiticide to kill the heartworms, we try to limit their exercise until the body has had time for the white blood cells to dissolve away the heartworm. This takes about 5 weeks. We don't want the dog to have a rapid heart rate and higher blood pressure (from vigorous exercise), as that could shove the dead worms tighter into the artery, and maybe cause a blow-out of the blood vessel.

Most veterinarians are treating dogs in two stages now: a half-treatment of a single Immiticide injection, followed by the full 2-day treatment one month later.

Thus, you would need to restrict the exercise for about 9 weeks, not nine months.

Walking on a leash is fine. Being in the house if fine. Supervised in a fenced yard is okay. No running loose, and you don't encourage him to chase stuff. You do your best to make him a couch potato during this time. He doesn't have to be in a cage.

It is true that he could have bad complications when the worms die after the treatment, but the odds are in his favor, since he likely has very few worms. It is also true that if you don't treat him, there is a remote chance that a worm could damage an artery and cause bleeding into the lungs.

If the dog is not very active, you could elect to just keep him on the Heartgard so that he doesn't get any more worms than he has. He might do okay with that, but I generally prefer to get them treated and cleared out.

The only way that the parasite is transmitted is via mosquito bites. Your dog may be a source of infection, but he's one of hundreds, so don't feel any guilt on that. If you locked him away, there would still be lots of sources of infection. You wouldn't be saving any other dogs.

It is very unlikely that you would need to leave him at your veterinarian for an extended time.

No, you shouldn't just put him to sleep. I'm guessing that everything seemed fine until you got the blood test. So everything is not that bad.

Your veterinarian who is actually seeing your dog is your best source of advice. Do not be ashamed to ask more questions until you feel like you have a good understanding of this complicated disease. If you don't let your doctor know you have questions, he/she thinks everything is hunky-dory.

Horsehair Worms

The horsehair worm is a parasite that lives in water, and its larvae infect insects.   Every year or two,  a panicky client finds one of these in a toilet bowl, water dish, or a bit of pet vomit.  They do not infest the pets, but the crickets or beetles may be eaten by a pet,  and the worm puked up.   If the insect enters the water, the mature parasite will exit to begin its life cycle anew.

There is really no harm in them (unless you’re the unlucky insect).  I’ve kept this specimen in a test tube for years .  If you stretched it out, it would be eight inches long.

 This fall, we have been plagued by an unusually large influx of crickets as the weather cooled off.   They apparently come inside to get warm.  There  have always been a few in the fall, but hardly enough to notice.  This year they have really been annoying.  One of the elementary schools called in an exterminator after finding hundreds of them in a utility room. I have stepped on dozens of them in my clinic in the last month.

I thought they had run their course, but I stepped on yet another cricket yesterday and out popped a horsehair worm, sort of a cricket pinata.

I thought the picture might be interesting to you.  When still alive, they tend to “tie themselves in knots”, hence their other nickname, the Gordian worm.

Here are  a couple of links with more information, if you’re interested.

http://www.marietta.edu/~biol/field_station/field_notes/horsehair.htm

http://www.ca.uky.edu/entomology/entfacts/ef613.asp

Is there a good alternative to Immiticide treatment?

Eric writes:

Thank you for all the information regarding heartworm prevention and treatment. There is a lot of misunderstanding. We are an animal welfare group who took in a dog which tested positive for heartworms. The dog has received ivermectin weekly + doxycyline daily for two weeks, paused a week, and will receive another week of doxycycline.

A few studies conclude doxycyline + ivermectin kill adult heartworm: "Results indicate that the combination of these two drugs causes adult worm death." http://www.ncbi.nlm.nih.gov/pubmed/18433753 There is also internet talk of a "slow kill" method.

Do you have any advice for animal welfare groups or others with a budget that would not involve Immiticide? There are also such frequent shortages of Immiticide, it appears to be an annual event. Thank you.

For some reason, my reply is not posting to the original blog thread, so I am publishing it here.

Hello, Eric,

The American Heartworm Society has withdrawn its endorsement of so-called "slow kill" or "soft kill".

First, while some of the worms may die with long-term (like two years)administration of ivermectin and doxycycline, you cannot be certain of clearing the dog.

Second, the dog's problems with treatment arise from dealing with the death and movement of the worms within the pulmonary arteries.  We want to keep the dog's activity restricted until the dead worms have been dissolved by the body's defenders.

It takes at least five weeks for the dead worms to be cleared from the circulation.  With the Immiticide, we know when the worms will be dying (within a week), and can watch the dog accordingly. 

If you are treating long term with other medications, you would have to keep the dog's activity restricted for years, as you have no idea when (or if) the worms will be dying and moving.

The frustration with Immiticide shortage and expense is something I feel pretty personally.  While I have an adequate supply at present, I had none for several months.

My experience with humane organizations has been that resources are limited and must be allocated where they can do the most good.

When there was no indication that Immiticide would be available, the American Heartworm Society recommended monthly ivermecin (Heartgard, Iverhart, etc.) and 10 mg/kg of doxycycline twice daily for one month.  The doxy inhibits the Wohlbachia (beneficial symbiote of the heartworm)for an additional two months after giving it for one month.  Thus, they recommended repeating this at 3-month intervals.

If I were in a shelter environment, I would follow that protocol.  This is what one would do in the month prior to starting Immiticide treatment anyway.

The adopting owner just has to realize that he/she is taking on a bigger commitment when adopting a pet with heartworms.  There isn't a quick fix.

Thanks for reading and writing.

Pain after Heartworm Treatment

A reader writes in today:

Had our cocker spaniel treated 5 hours ago with his first shot.
For the past 5 hours, he can not get comfortable, fidgets, lays in unusual positions.

When walking, his right rear leg is toeing-in and his walks clumsily, often positioning that right foot too far under his body.
In just the last hour, he has started some toe-dragging with that right foot. Not severe, and he corrects upon moving further into the stepping process.

Also, he has started to drool excessively. Both ears are wet as if he drank from a flat bowl.

Have given him 2.5 mg Diazepam to try to make him more comfortable.

Forgot to mention ... the vet had to stick him twice unsuccessfully and then changed needles and successfully administered on the third try.
Do you think he is just experiencing more pain than usual because of the three 'sticks' at the site, or should we be concerned that something else is going on?

 My Reply:

Please call your veterinarian and let him/her know what is happening.

The medicine in the treatment (Immiticide) can cause a lot of inflammation at the injection site. This can occur no matter how smoothly things go and how little it seems to bother the dog at the time.

This can range from being absolutely undetectable to a dog that is crying constantly with pain. Diazepam helps with anxiety, but has no pain relieving properties to speak of.

Please contact your veterinarian about this, as human 0ver-the-counter products can be harmful to your dog. However, it sounds very much like your dog needs pain medication.

The pain usually subsides in a couple of days, and most dogs don't have this type of reaction, but the ones that do get painful do need some help.

The difficulty in walking may indicate that the inflammation is causing enough swelling to put some pressure on a nerve root.  This can be very temporary, but certainly needs to be addressed.

Call your veterinarian and report this situation.  He/she will decide what anti-inflammatory or pain-controlling measures are needed to help your dog.  He/she can't help if they don't know about it.

What to do now that Immiticide is in short supply.

A reader writes in:

Hi. I have a 12 year old mixed breed who has been on Heartguard preventative most of his life. Unfortunately, he recently tested positive for heartworms. We live in the South, and he is an outside dog.

Anyway, the vet said because of his age and the expense that we should just give him prednisone, doxcycline, and sentinel, and that he would eventually suffer from congestive heart failure.

Will this regimen even help? What exactly will it do? What is the pattern of treatment? The vet mentioned to give him the prednisone alternating months. What do you recommend for the frequency of these meds?

My answer:

Heartworms actually are mostly located in the pulmonary arteries, the blood vessels that take blood from the right side of the heart to the lungs to get oxygen. Their presence in these tubes interferes with the circulation in the lungs, and makes the arteries themselves inflamed. This can cause swelling, which narrows the opening in the artery, further interfering with this blood circulation.

Even when there are no worms in the heart yet, this difficulty in the lung blood vessels makes it more difficult for the heart to do its work. This causes excessive wear and tear on the heart.

Doxycycline inhibits a microorganism called Wohlbachia that benefits the heartworms (much as the "good" bacteria in our intestines help us). When the dog takes doxycycline, the heartworms become weaker and physically smaller. Thus, they cause less interference with the dog's circulation. Doxycycline is also a little bit of an anti-inflammatory medicine.

Prednisone is a form of cortisone, which is a potent anti-inflammatory medicine. If the worms are causing swelling of the blood vessels (making the opening smaller, and more difficult for the heart to work against), the prednisone can open things up again.

There is currently a severe shortage of Immiticide, the drug used to kill adult heartworms. Until it becomes available again, the American Heartworm Society is recommending that dogs be managed in the way that your veterinarian is recommending.

I think that your veterinarian's recommendations are very reasonable, considering your circumstances. If you have more questions, please take the time to let him/her know. Many times we think that we are great communicators. If nobody calls back, we just assume all their questions have been answered. If you have more questions, I'll bet that your veterinarian will be happy to discuss them with you.

AHS offers guidance in face of Immiticide shortage to treat heartworm infection

Aug 11, 2011 DVM NEWSMAGAZINE

National Report -- As a shortage of the heartworm treatment Immiticide® looms, the American Heartworm Society unveiled an interim management plan for veterinarians yesterday.

"With Immiticide unavailable, veterinarians will need to take steps to carefully manage their heartworm-positive patients," says Wallace Graham, DVM, president of AHS in a prepared statement.

Crafted by AHS' Board and Scientific Committee, the management plan calls for veterinarians to:

· Reduce potential pathology from infection

· Maintain the health of the heartworm-positive dog until it can be appropriately treated

· Prevent additional heartworm infection of the dog.

Management steps include:

· Verification of heartworm status

· Pretreatment of heartworm-positive dogs to prevent shock

· Careful administration of a macrocyclic lactone heartworm preventive, followed by clinical observation for at least eight hours

· Continuous administration of a heartworm preventive on the regular dosing schedule

· Administration of doxycycline on a one-month-on/two-months-off schedule

· Restricted activity and exercise of the heartworm-positive dog throughout the management period · Medical treatment of symptomatic heartworm infection to relieve signs of respiratory disease, with surgical options weighed for dogs exhibiting cardiovascular compromise

· Retesting for heartworm status before treatment with adulticide treatment once the product is again available.

The goal, Graham says, is to manage the patient until Immiticide becomes available.

Earlier this week, Merial sent a notification to veterinarians that the drug melarsomine will be in short supply due to technical production problems at a plant. Click here for the AHS Guide to Heartworm Management During Adulticide Unavailability.

From Dr. Mobley:  Now they're telling us we won't even be able to get Immiticide by begging for it.  What's the world coming to?

Demodex Mites live in the hair follicle.

This little guy has localized demodecosis.  He doesn't look bad at all, not like generalized demodecosis (aka, "red mange").

This is the "spot case" type of demodectic mange that almost always is self-limiting, i.e. the dog recovers whether you treat him or not.  Since I've already talked about this at length in previous posts, why bother to bring up this little guy today?

He's got a couple of spots of hair loss, but they really aren't bothering him much.  He came in for his puppy booster vaccinations and the owner hadn't really paid much attention to the spots.  I found them during the physical exam, asked the owner if there were any scratching or chewing, and and there wasn't.

You ALWAYS need to do skin scrapings when you see pets with skin problems, even when you are "sure" that it couldn't be mange mites (because sometimes it is anyway).

The cool thing is what I found on the skin scraping.  In active cases of demodectic mange, you usually find a lot of mites, and in varying life stages: eggs, larvae, nymphs, adults, little family groups, and so forth.  In cases that are recovering, you may find only one or two mites, or none at all.

What you usually don't see is what is in this picture.  I have performed countless skin scrapings in the last 33 years and have never seen this before.  Neither have the parasitologists on Veterinary Information Network.  We know that the mites live deep in the hair follicles, but seeing mites within the hair itself is pretty cool.

Immiticide Shortage Now Under Control... Sort of

Well, I've been remiss in not bringing the Immiticide status report up to date since my last post.  The FDA has granted a provisional approval to the European supplier of the raw materials for melarsomine.  This apparently falls under some sort of "compassionate use" guideline.

The official line now is that we still cannot just buy it from our distributors to keep in stock and have on hand.  That would be too easy.  However, if we call Merial directly, and order product for a specific patient (name, date of birth, weight, serial number, etc.), we can buy as much as we need. 

The thrust of this is that the drug is no longer being rationed for the treatment of sick dogs only.  Now we can go ahead and treat the dogs that missed a pill here and there, or where the preventive simply was not 100% effective.

So, we're working through our backlog of about 15 dogs since the first of the year, plus three more this week.

Heartworm Treatment Drug Shortage Update

You may recall that I posted some time ago on the shortage of Immiticide, the only drug approved to treat dogs for heartworms disease (that is, to kill the adult heartworms).  They were going to have it all fixed by the end of March.

Well, now, last week it was after "March 31st", which was when I had been told previously the shortage would be resolved. I called Merial, and the first layer of staff said, "Not yet; they said late March or early April." The "early April" was new to me. I asked to speak to someone who actually knows what's going on, and she bumped me up to the next tier in the hierarchy.

That person gave me the same story. I said, "Look, I've been a good boy, and I haven't pretended my patients have clinical signs when they don't. I haven't tried to order product for dogs that are apparent lack of efficacy cases. I do have 12 people breathing down my neck wanting their dogs treated. It would help if I could just get a straight answer for them on what the problem actually is. Did you try to move the factory to Pakistan and the Taliban took it over, or what?"

I still didn't get a straight answer, but she asked how many dogs I had and what they weighed, and sold me enough Immiticide to treat them.

Of course, I've got four new dogs to treat since then that weren't on the original list.

If we can get every detail of Tiger Woods' indiscretions, can't we find out what is actually going on at Merial? And where is Osama bin Laden? Does HE have the Immiticide?

Well, here's the news from Veterinary Information Network today... finally:

Merial Statement on availability of IMMITICIDE® (melarsomine dihydrochloride)

Recently, Merial informed veterinarians that our heartworm treatment product, IMMITICIDE® (melarsomine dihydrochloride), was in limited supply because the active ingredient was no longer available from its manufacturer—the only US source of the compound.

Merial has now identified an alternative supplier for melarsomine—one that already produces it for the European and international markets. However, gaining US regulatory approval for the new manufacturer will take time. In the meanwhile, Merial has instituted a temporary measure to extend the supply of IMMITICIDE and continue to make it available to veterinarians.

Through a restricted distribution program initiated in agreement with the FDA’s Center for Veterinary Medicine (CVM), veterinarians who have an immediate need to treat a dog with heartworm disease will be able to purchase IMMITICIDE containing melarsomine manufactured by the alternate supplier. This product must be purchased directly through Merial. It will not be available through Merial’s distributors, nor will it be available for purchase to stock clinic inventories. Veterinarians who wish to purchase IMMITICIDE should call Merial Technical Solutions 

Merial is continuing to work closely with FDA-CVM and the new melarsomine supplier to gain FDA approval for this alternate facility and return to full supply of IMMITICIDE as soon as possible.

Not that this helps me or my patients, much.  I still don't feel like we have the full story.  They sell this stuff like gangbusters.  Why would the supplier of the raw ingredient shut down when they have a guaranteed market?  I still think Osama bin Laden may be involved somehow.