Vets: Is a heartworm Test Really Necessary?

I only ask this for one reason:
Every year we take our 6 dogs in for their yearly check-ups, and all the required shots, and last weeks visit got me thinking; is this test really necessary?

After looking through my bill, I see that each test cost $43, ok no problem, this part I understand, and this is required every 2 years, but on the next line of the bill, I see an amount of $81.25 for “heartworm Advantage 20”

So I ask my vet, “Why do I need the Heartworm Advantage if we don’t have the test results back”, to which he explains this is a preventative maintenance in case the dogs do have heartworm.

So if they are given the advantage anyway (wether they have heartworm or not), why bother with the test at all, and just put them on the advantage (seeing as they get it anyway)
I figure this would save me the $43 x 6 fee (less my 20% multi-dog discount)

I’m not trying to be a cheap ass here, but when you add these fees to the $44. physical exam fee, as well as the various shots (lyme disease, DHPP, Bord, kennel cough treatment) you can see how the fees can add up relativly quickly for 6 dogs, and if that money could be better spent somewhere else, then why not?

I’d rather put that money towards kibble and treats if it isnt really necessary.

I don’t mean to offend anyone with my question, I know you vets go through a shitload of schooling and you deserve everything you make, but I just want to make sure this isnt just a money grab that can be avoided.
We only feed our critters Fromm ;s 4-star and give them the best care possible.

I never really noticed the $$ part when we had 2 or dogs, but with 6, I definitly notice it now. (4 of our 6 our rescued dogs)


I’m not a vet, but the way it’s always been explained to me is that you need the heartworm test because if the dogs indeed have heartworm, the preventative medication will cause a bad reaction. My vet told me to not start the dogs on the medication until we got the test results back.

The medication itself keeps dogs from getting heartworm if they don’t already have it.

That’s the part I don’t understand, why start them on the advantage before the results are even back?

If your dog has heartworms, starting them on meds can kill them.

I’m not sure why you think the test results “haven’t come back”. Most heartworm tests are in-office procedures that can be completed during the visit.

Do you keep your dog on heartworm preventative year-round? If so, they shouldn’t need testing every year. If you only give the Advantage seasonally, they’ll need to be tested first each year. If you miss a month of meds, especially in season, the vet may require a re-test before starting the preventative again.

I think I’ve read that some vets want period testing (even on dogs taking the meds year-round) just in case the dog has picked up an infection despite the preventative meds.

On the other hand, I’ve known one vet that IMO just tested every year because he could charge more that way.

I’d clarify that with your vet. Mine was very careful to tell me NOT to start them on the medication until we got a call with the test results.

Mine too. It was, “We’re giving you the pills now, so you don’t have to make an extra trip to come pick them up, but don’t start giving them to Daisy until you hear back from us on the test results.”

I just took my two (newish) dogs in to get their first shots. They were both tested for heartworms. One of them came back positive for both adult and baby heartworms. The heartworm preventative kills the heartworms, and the resultant dead heartworms can make a dog very sick. So they kept Lucy for about 12 hours while they monitored her on a very low dose. She tolerated it well, and we were given three more low doses to give three days apart. Then three days after that, start her on the monthly dose. It could take almost two years to get rid of the heartworms, but they are not reproducing.

If she had reacted adversely, we would have had the option of doing a “massive” dose to kill them all at once, which would have to be monitored extremely closely.

The other option would be to do nothing, and let the heartworms eventually kill her by strangling her heart causing congestive heart failure.

I feel so bad that I waited so long, but thankfully she is doing just fine.

I’ve got a funny feeling this might be what happened, and I didn’t pay attention. I’ll give a call to the office tomorrow and clarify.

Thanks folks.

I don’t have anything to add even though I am a vet. The standard monthly heartworm products kill the infective juvenile worms but don’t get rid of adults. The idea being if Fido is bitten by a mosquito, the juvenile worms in the mosquito are killed before they can develop into an adult…

So you need to know if your dog has adult worms (and then treat them) separately from slapping them on the preventative.

In large animal practice, samples are frequently pooled to save money. You could ask if the vet. wouldn’t pool all your dogs blood samples into 1 tube and test that. If it’s negative they’re all negative - and you’ve only paid for one test. If it’s positive, you’ll need to test indiviudally.

Wait, unless the vet is doing the Knott’s test (looking under the microscope for evidence of the microfilaria in the blood), every other heartworm test is a relatively simple, done in 15 minutes or less (probably less) in-house snap test. Perhaps the vet chooses not to run any in-house blood diagnostics and sends that off? Otherwise, I don’t see why they would take long in get the results. Heck, even the Knott’s test is not THAT time intensive.

My take is that they probably did the test, got a negative result while you were still in the clinic, and gave you the preventive. Of course, the vet should have told you the results were negative, or something like that.

Once again, if they did any of the common tests, they probably had the results by the time you left the clinic.

Even among veterinarians, there is not universal agreement on these topics. Much hinges on where you and your dogs are located. Is the area endemic for heartworm? In my area, heartworm is relatively uncommon. Deadly, but uncommon. With my dog, I give a preventative year round. Not for the purpose of heartworm prevention, but rather for the other benefits of the products (other enteroparasites are reduced/prevented).

Talk to your veterinarian. Heartworm testing can be used as a revenue generator, and IMHO that is inappropriate.

Spam reported.

You may want to have another conversation with your Vet. Advantage II (aka Advantage 20 for dogs weighing between 11 and 20 lbs) contains imidacloprid and only treats fleas.

You guys better read this. There is no such thing as “preventative medicine” for heartworm. Only treatment after the nematode is inside the dog. Also be aware of the constant temperature required to even get your dog infected. No wonder it’s called a scam.

Even zombie heartworms can kill!11!!

Very interesting article and website, though. Thanks!

Also incorrect in many points. Oh wrong, oh so wrong… I’ll try to break it down as much as I can in later posts…

This is the homepage for the American Heartworm Society. Here is its mission statement. This is a credible, evidence-based website. It even has a whole area dedicated for pet owners, where they explain what you want to know about the disease, prevention, and treatment.

Also, treatment recommendations change a lot. What was standard treatment 20 years ago is definitely not what is standard now, and even what is recommended now is not what was recommended five years ago, when I graduated veterinary school.

Here is the most recent incidence map for canine heartworm, 2010. This gives a better breakdown on case incidence.

Vets often recommend and charge for unnecessary tests. It is part of their office policy. Mine is known as one, but I stick with the facility for the quality of the vets, they’re 24-hr, nearby, etc.

You are particularly vulnerable when you are a new dog (or whatever) owner. Later on you get a sense when, eg, after some vomiting a fecal test could be held in abeyance and $$ saved.

Ok, an attempt at debunking…

This starts off the main problem with most of the claims. They have some kernel of truth, but it is mixed with blatant misinformation.

Yes, there are areas of the country where heartworm is rare. There are plenty others where it is incredibly common. I don’t understand what the author means by “pretty rare in much of the country”. I mean, the completely white areas are less than half the mainland US area, and many of the areas with high incidence of heartworm are also densely populated areas in the US, meaning that finding a dog with heartworm there will be more common than in the deserted areas.

And of course, this goes without mentioning, but most likely, the incidence is what it is because people use preventive treatment with their dogs. The survey is done on reporting clinics, and the clinics report about the patient they get. If the clinic makes a good job in having a good part of their patients taking preventive medicine, their incidence is going to be lower than what it would otherwise be. So the map is the incidence (which is alarming in many places), even with the use of prevention by part of the population. It would be worse if no dog was taking preventive medicine.

OK, this is true, in and of itself. For one single microfilaria to reach full adulthood in a non-medicated dog, it will take 5-6 months before it can cause clinical signs. There are many holes, though, in this part:

  1. Heartworm is not just a one-time thing. Mosquitoes transmit heartworm, and they inject many stage L3 larvae each time they bite a dog. So your dog is bombarded with potential L3 larvae each time a mosquito bites. And mosquitoes come unannounced! Therefore, you dose every month so that the protection against the mosquito bites for the next month remains.

  2. While most preventive drugs do and can last a bit longer than one month recommended daily dose, the long-term accumulative effects take time. In other words, in order to get months of protection from a single dose of preventive, the dog must have been on continuous, on schedule treatment for a while.

  3. It used to be a bigger problem with older drugs, but if you wait a while, in a zone known for having a high incidence, you carry the risk of, when skipping months and giving the pill just once in a while, cause a massive die-off of larvae. Unlike zombie threads (heh), zombie heartworm parasites can and do kill, by causing anaphylactic (hypersensitivity) reactions.

OK, first of all, the life cycle is not broken, it is just extended. The larvae cannot develop to the next stage, but they don’t necessarily die, and they’ll reenter the cycle once the conditions are met. How else would it make it through winter, otherwise? And yet each year we get new ones!

Also, the data is from 1998. That’s 15 years ago. Do YOU accept all medical recommendations that were present 15 years ago? Do YOU trust an incidence map from 15 years ago to be actual now?

Seasonal treatment can be a sensible idea in many parts, but this is something best discussed with the dog’s regular veterinarian, not assuming that an article off the internet citing epidemiology and date from more than a decade ago is still valid in their region and for this year.

And personally, I’ve lived in a region where it gets way warmer than the minimum temperatures way before June.

Bwahahahahaa… OK, they all work by killing the microfilaria through L3. Hint: microfilaria is the L1. The baby heartworm are microfilaria, the L1. What your dog gets when it is bitten by a mosquito is the L3.

The idea of prevention comes because they kill the parasite before it can cause disease. The disease is really caused by L4 and L5, so killing the parasite before it can cause disease is a preventive measure. Similar as to how people that are going to malaria-infested regions take anti-malarial drugs before the travel.

Well… d’uh! Most medicine are toxic poisons to the organisms they are attacking. In the case of most heartworm preventive medicines, they have been found to be effective at killing the pre-L4 parasite without affecting the animal (with rare occasions, see below). They are macrocyclic lactones and macrolides, part of a range of drugs.

Unless the animal has continuously been taking them, unfortunately, no, these preventives are not effective against killing the adult parasite. Continuous (as in, monthly) use of the preventive can, though, render the adult female sterile, which can decrease the burden and eventually the worm will die (because they are not immortal). But this can take years.

Also, I’m getting tired of the author calling all life stages microfilarial. They are not! Stop it!

I don’t deal with human medicine, but I seem to remember rare cases of human infections with Dirofilaria immitis (the nematode). Since humans are not the right host, the diseases (while very very rare) where also very very severe.

OTOH, do you know what other species can also rarely get them, but then it is lehtal? CATS!!! Cats can and do get heartworm, and their clinical sign is “found dead”. Unlike dogs, which can handle quite a load of parasites before dying, kittycats keel over with as little as 3-4 adult worms found at necropy.

This is true. But not all collies are affected, and there are several other drugs on the market that have been found to be collie-safe.

Perhaps in the rare clinic, although I see more plastic models now. Easier to handle, slightly less gross. But I can tell you, I’ve seen enough of them throughout my training and career, which spans… Oh, about 15 years since I started working at vet clinics until my current position. I’ve also seen them in cats. I’ve also seen them in cases my coworkers have had. It is not uncommon for me, although granted, I’ve always lived in high-incidence area. The idea that they need to go to Mexico for that is… absurd.

One benefit of going to the veterinarian is that, in case there is a problem with dosage, as can happen with the compounding doses mentioned there, or if there is a product recall or a bad lot or a breakthrough infection… If you have the paper trail through your vet that any of that happened to you, the drug company WILL pay for most if not all the “real” heartworm treatment (the adulticides are expensive). I’ve seen this happen a couple of times.

Microfilaria (the L1) can be produced by the adults (L5) living in the dog when they have not yet caused clinical signs. As mentioned earlier, a massive die-off of these baby heartworm can cause a hypersensitivity reaction and kill the dog. This is why they do the testing. The other one is to check for breathrough infection. No drug is ever 100% safe, and in the case of heartworm, better to treat the infection early, before clinical signs have had a chance to really develop, than to wait for coughing and respiratory problems to occur.

The author has not kept up with the literature either, and that is 3 years old, anyways…

Here are the latest canine treatment guidelines, as of 2012. The drug melorsamine is the expensive drug.

I’ll repeat again… Macrocyclic lactones ARE NOT considered to be effective at killing adult parasites, which are the main cause of disease.

I think that is it for now. Any questions?

That first sentence is obviously too sweeping. Some do, and at worst it is part of their business policy.