Dr. Mark is a veterinarian. He works mostly with dogs and exotic animals.
What Is Heartworm, and Why Is My Dog Tested?
Heartworm is a large internal parasite (worm) that is spread through the mosquito when young and as an adult lives in the heart. Dogs with a case of heartworm disease start out with mild symptoms like coughing and exercise intolerance but later develop full-blown heart disease (cardiomyopathy and congestive heart failure, with swelling in the limbs, fluid buildup in the lungs, and reluctance to move as the dog becomes quickly exhausted).
Dogs are tested so that they can be treated and the adult heartworms killed before they cause heart disease. Testing dogs from the shelter, older dogs that have never been on preventative, and dogs that have been off of preventative for a long time is really needed. Annual testing of dogs that are on heartworm preventative is not necessary, however. Testing that often is not harmful to the dog, only to your wallet, so unless you feel the need to test, you should just keep your dog on the preventative.
Why Do Dogs Need to Be Tested Yearly?
Throughout my years in practice, including several years in some of the areas with the highest endemic heartworm populations in the US (Mississippi valley), I never saw one dog test positive that was already on monthly heartworm preventative. I have never met a colleague who found a positive heartworm dog that was being treated with preventative. (Which is why the companies that sell heartworm preventative will guarantee their product.)
So is heartworm testing a scam? Why are dogs already on preventative required to be tested? Several of the sites I found on a web search made the sort of recommendation we always gave in small animal practice: Dogs were required to be tested each year before their heartworm medication could be refilled.
(The stated reason for this was that dogs who received a dose of preventative while infected with heartworms could suffer a severe and potentially fatal reaction. This was the case when older preventatives were used, medications that were popular in the 1970s. If anyone has ever seen and documented a case like that, I would like him to leave a comment.)
Vets make a profit on each test, certainly a lot more than in just dispensing the medicine. It does not harm the dog, just the owner, so there has been no outcry to stop the procedure.
Can I Keep My Dog on Preventative Without Testing?
Looking to avoid this issue and get a prescription so you can get your medication online? Dogs that did not have a current test could not receive a prescription from the vet. Most dog owners (at least those who do not own a pack) will find they are better off buying ivermectin tablets online. There are several sources of nonprescription medications available. Nuheart and Valuheart are generic ivermectin and when purchased through Canada do not need a prescription.
If you do own a lot of dogs and want to use the ivermectin available in feed stores, I have to warn you that it is concentrated for use in cattle and a dog dose for heartworm prevention is very low. A product sold for sheep is much safer.
Ivermectin Preventative Doses
Several sources on the internet give doses for ivermectin preventative that are absurd, but the label on a common heartworm preventative is only 0.006 mg/kg, so a 20 kg dog will only be receiving 0.32mg. Since Ivomec is sold at 1%, or 10mg/cc, the 20 kg dog only needs less than 0.05cc.
The only way to get close to this dose is by using an insulin syringe—preferably one sold that holds only 0.5cc. For smaller dogs, there is really no way to dose that low.
(One of my professors recommended diluting that tiny dose with sterile water and then putting it onto a biscuit before giving it to the dog—that way, you are sure he is going to consume the medication)
That being said, ivermectin is used at a much higher dose when treating demodectic mange (0.3-0.6 mg/kg) and for a long time, an average of 3–8 months. It is quite safe even at those levels.
Can Ivermectin Cause Problems?
Collies, Shelties, OES, Aussies, and some other mixed breed dogs might be sensitive to ivermectin. If you are concerned in any way, you can test for the mutation on the MDR1 gene that causes sensitivity. Testing is available through the Washington State University College of Veterinary Medicine. Of course, these dogs can be given heartworm preventatives that do not utilize ivermectin (Revolution (selamectin) and Advantage multi (moxidectin) are both topical, so they treat fleas as well as preventing heartworm disease).
The drug companies who marketed the preventatives also recommended we tell clients not to buy a large dog dose and split it, as the medication might not be adequately mixed in the tablet and one of the dogs would not be medicated. (If this were the case, it would be dangerous to prescribe one-half tablets of any medication.)
Is Heartworm The Most Important Health Issue?
Dogs that do not have an annual heartworm test still need a physical exam.
If you choose not to go in for a heartworm test each year, do not forget about your dog's teeth. Many dogs die each year from the secondary effects of periodontal disease.
If you live in an area where heartworms are a danger to your dog, and you do not have the income to spend on annual testing, at least spend what is necessary to prevent this disease in your dog.
Prevention is simple and inexpensive, and untreated cases are terrible to observe.
More About Heartworm . .
- Safe Herbal Heartworm Treatment
Among the alternatives for heartworm treatment, herbal therapy is available. It may not be as good as slow kill treatment but it is a lot safer and less painful than the Immiticide injections. This article will discuss what is involved in the therapy
- Safe Heartworm Treatment for Your Dog
Safe heartworm treatment for your dog is possible but it is not always the best option. This article will give you details on how you can treat your dog safely if he contracts this disease.
- How to Avoid and Prevent Resistant Heartworm in Dogs
There is a new strain of heartworm disease that does not respond to the traditional prevention. Find out how to prevent it and how to protect your dog from this terrible disease.
Questions & Answers
Question: Is annual heartworm testing mandatory to purchase heartworm meds?
Answer: Some vets will not give you a prescription for heartworm preventative until you have a test done. It is not mandatory in any state. If your vet does not want to give you a prescription, you can purchase the preventative online.
Question: Is an annual vet visit (yearly exam) required by law to prescribe heartworm prevention? I am not referring to the yearly heartworm test, but a separate vet exam. I live in Florida and was told that by law, all dogs need a yearly exam plus heartworm test to obtain heartworm preventative.
Answer: Some dishonest vet or vet tech is telling you a lie. If there is such a law, tell them to prove it. Of course, they cannot.
The ONLY thing required by law is that you vaccinate your dog for rabies, once every one to three years (depending on the state). Heartworm is not a zoonotic problem, so no legislature is going to create a law for something like this.
It is just a vet's office telling you that story. That person should be reported to the state veterinary license bureau and have his license suspended.
At the very least call around and talk to some reporters in your area.
Question: Isn't the rule about dogs getting a heartworm test every year based on the requirements of a state's board of veterinary medicine, and don't the laws differ by state?
Answer: The state board of veterinary medicine does not set laws. Laws are only put in place by state and national congresses.
Laws about pets are only put in place when the disease in question, like rabies, is a public health issue to humans. Heartworm does not spread to humans.
Question: My five-year-old dog has been on Heartgard for years. I missed a few months of treatment, and his vet said it’s too dangerous to refill without testing. That could make worms resistant, apparently. My last vet vehemently disagrees with this assertion. Is it dangerous?
Answer: Heartworms will not become resistant because you missed a few months. The dog may have become infected in that time, but it depends on how long the dog was off preventative and how long it has been since he stopped taking the meds. It takes about six months from the time is bitten by a positive mosquito until there are adult heartworms in the heart. The best thing to do would be to continue heartworm preventative and then test the dog later, at least six months after the time that he was off the preventative.
Question: Is there an actual law that requires vets to do a yearly checkup before they can refill a heartworm prescription or do they just tell us that so they get more money?
Answer: Laws are put in place to protect the human population, as well as to stop animal cruelty. Heartworm is not a disease that affects humans, so no law exists.
I do not think most vets are doing the test because they are making money on it. Most of them do so because they think it is in the best interest of the dog. If you tested dogs every week, you might even find one positive every 20 or 30 million. Of course, doing the test that often is not in the best interest of the dogs or the owners.
Question: My puppy has been on Heartgard since she was four-months-old. My vet wants to do a heartworm test. Is this necessary?
Answer: If this is her first spring, then there is virtually no chance that she is going to have heartworm disease.
Unless you are living in an area where Heartgard resistant heartworms are found, I do not think it is necessary to have your dog tested at this time. (If you do live in an area where Ivermectin resistant heartworms are present, why was your puppy prescribed Heartgard?)
Question: My 4 year old Chihuahua has never been tested or treated for heart worms. No symptoms shown. My vet recommends a test now and again in 6 month before treating him. The problem is he's too feisty for blood work without being sedated. Is it worth testing him twice? Or should I just start treating him now?
Answer: Do you mean give a preventative? (Treatment is for dogs that are already infected with heartworm.) If you mean preventative, then you can test just once.
If you mean treatment, how has your Chi been diagnosed?
Question: If I give my dog the ivermectin medicine and he has heartworms will he get sick and die?
Answer: Preventative medication will kill the immature heartworms (microfilaria) in the blood, but it will not kill the adults. If the preventative is not given, the microfilaria will develop into adults and invade the heart. No, giving this preventative will not make him sick and die.
Question: My puppy has been tested for heartworm twice in eight months. Does he need another test this same year?
Answer: I am not quite sure why your puppy was tested twice in eight months, but if you are in an area that is heavily infested with heartworm, like the Mississippi Valley, and you stopped giving preventative for several months, a new test is a good idea. If your dog belonged to me, I would not choose to have another test.
Question: If a dog dies because of heartworm diseases what will it look like?
Answer: They usually die from congestive heart failure. The most common symptom is coughing because of fluid buildup in the lungs, but it is also common to see swelling in the legs and edema in other parts of the body.
Dennis C Rathsam on June 09, 2020:
I just spent 598.00 dollars at my vet for an ear infection & check up. When I asked for my yearly heartworm pill I was denied because they wanred to test her again. Ive done this evey year, but Im stopping now. Vets are rippoffs, every artical Ive read says you dont need a test done every year, its a moeny maker for the vet. Ill get my pills from Canada
Dr Mark (author) from The Atlantic Rain Forest, Brazil on July 22, 2019:
Here is a link to the Auburn study
and if you are interested here is another Auburn study that is very interesting: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC56884...
As for your other comment: I cannot see the use of another test at this time for your dog. You are not in a very heavily infested area and the temps may have been a little warm but there was still most likely a die-off.
Nirvi on July 21, 2019:
Hi Dr. Mark,
Thanks for such a great write up (along with your other article on how to buy the ivermectin sheep drench). I was curious if you could provide a link to the study by Auburn about increasing ivermectin dosage - I HAVE heard through the grapevine that many veterinary research schools were recommending an increase due to developed immunity (and my hubs graduated from Auburn, so we're a bit nuts over anything Auburn researches).
I also have a question; my pup was tested (4DX) in October 2018 and was HW negative. She was on monthly preventatives until January, and we'd like to start again (we live in Virginia - in the western mountains - and are following the "treat for 6 months" recommendation of a lot of holistic vets). Would you recommend we get her blood tested in the chance she did develop HW during the winter (our low temps are below 50deg beginning in October, so almost impossible for HW to properly mature), before beginning her dose of ivermectin drench? Our temps have been generally above 50deg since mid-June, and am a bit nervous about microfilariae die-off if we do dose her (or am I overworrying, since I also read ivermectin does it gradually?).
Thanks so much!
genajolly on March 28, 2019:
Friends are the gift of God and the most important part of life. We can live happily with them and share our problems with them. I was researching all about the Heartworm Test for Dogs and other health issues related to pets and my good friend pointed me to this one. I am thankful and this is great info.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on January 30, 2019:
Hi Shirley, yes, Revolution is effective. The main reason that the article refers to the oral product is that I am referring to ivermectin, which is commonly available as Hartgard.
Shirley on January 30, 2019:
In reading your article posted above, I note only reference to oral or injectable products. Do you also consider Revolution an effective heartworm preventative?
Dr Mark (author) from The Atlantic Rain Forest, Brazil on August 29, 2018:
Hey Ticked Off Tech, I do not know if you will be intelligent enough to find this site a second time and read this, but I will reply anyway. Yes, this comment applies to Michigan too. No law states that a dog has to have a yearly heartworm test. It appears you and your ilk are using that law to justify overcharging your clients. You are wrong, and your comment is both incorrect and not helpful to clients. Thank goodness I do not need to rely on the poor services provided by you and your business.
Ticked Off Tech on August 29, 2018:
"Some dishonest vet or vet tech is telling you a lie. That person should be reported to the state veterinary license bureau and have his license suspended.
At the very least call around and talk to some reporters in your area"
Perhaps you ought to look into the law again, "Dr. Mark", or at least make it clear you can't speak for Michigan. Please reference Michigan Law For Veterinary Professionals, R 338.4922, Rule 22, section (b) “A veterinarian shall have sufficient knowledge of the patient to initiate at least a general or preliminary diagnosis of the medical condition of the patient. "Sufficient knowledge," as used in this subrule, means that the veterinarian has recently seen and is personally acquainted with the keeping and care of the patient by virtue of an examination of the patient, or by medically appropriate and timely professional visits to where the patient is kept.”
And R 338.4923, Rule 23, section (2) “Without a veterinarian-client-patient relationship, a veterinarian's merchandising or use of veterinary prescription drugs, including the extra-label use of any pharmaceutical, may be considered unprofessional conduct in violation of section 16221 of the code.”
So please stop providing the general population with poorly researched, incorrect advice.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on July 02, 2018:
According to the sales rep from the companies that sell the heartworm preventative, it is not a good idea to cut the pill in half because the medication is distributed unevenly. This goes against everything I and other vets learned, since we routinely split larger pills when dealing with tiny dogs. It is up to you whether to believe Big Pharm or your vet.
A tiny dog that is inside the house 95% of the time will probably never get exposed to heartworm. If he does, however, there will be serious medical consequences, perhaps even heart failure, from very few worms. (Their hearts are very small and the worms are large enough to block the vessels and lead to heart failure and death;) No one can make you get a heartworm test but in your case it is a good idea to have it done. It will probably be a waste of time but it might save your dogs.
LJElrod on July 02, 2018:
I have two dogs (4 and 5 lb). I am concerned regarding giving heartworm prevention to such small dogs. Can I cut the pill in half? Also, my dogs are inside 95% of the time and I watch very carefully for mosquitoes. Must I get a heartworm test before giving ivermecxtin? Thanks very much.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on May 24, 2018:
Maryanne, it is not a good idea to rely on the previous owners, even if they did say that the dog was vaccinated. Since you are not sure, your Chiweenie would be a lot better off if you had at least one series of vaccines. After that it is your call. I do not vaccinate yearly because adult dogs have long term immunity after being vaccinated. Some vets do not agree with this and continue to vaccinate yearly, as we were taught 40 years ago.
As far as a heartworm test, it is a good idea to get your dog tested as soon as possible. You do not HAVE to get her tested before starting the preventative, but her heart is so small that even a few worms can lead to congestive heart failure. Get it taken care of as soon as you can.
I hope you two have a great time together! Congrats.
Maryanne on May 23, 2018:
I recently got a chiweenie she is four years old and I'm not sure of her medical history.My question is can I just start her on heartworm prevention or do I need to get her tested first and also I'm not sure when her last vaccinations were so what do you recommend.Thank you!
Dr Mark (author) from The Atlantic Rain Forest, Brazil on February 01, 2018:
Ryan, fecal exams are not mandatory, but if your dog is exposed to parasites a great deal (like running a lot in a dog park) you can take a stool sample in twice a year to have it checked. Take it in--you do not have to pay an office call just to have the stool checked for worm eggs.
Ryan on February 01, 2018:
What about Fecal O&P tests every year?
Dr Mark (author) from The Atlantic Rain Forest, Brazil on January 20, 2018:
DVM, I kind of doubt that you have zero financial gain from the sale of prevention and testing. Are you really selling tests at cost?
DVM on January 20, 2018:
I have several patients that have tested positive despite being on prevention. Testing allows us to catch those cases and treat appropriately. Even if adulticide treatment is not the best option for that pet and client, there are other options. Prevention for a HW positive dog is not a recommended course of treatment without concurrent use of doxycycline or similar. There are resistant strains of HW and testing is how we catch that. You are doing pets a disservice. And I’m a dvm but have zero financial gain from sale of prevention or testing. I recommend what is in my patients’ best interests.
Avalon1000 on June 10, 2017:
We live in San Diego and just performed a heartworm test in April 2017. We went back to the vet on June 09, 2017 due to an ear infection and they said we need to have a heartworm test again because we did not give heartworm preventive medicine since April. We have a Terrier mix and she stays in the house 99% of the time, is this correct or are they just bilking us?
Nuus on April 11, 2017:
Testing every year when Ivermectin has been given on the same day of the month for the past 12 months is silly, and illogical:
12 doses dispensed after the last test didn't hurt the dog, but the next dose might? Why not test between each dose if the medication given in the proper dose at the proper interval isn't sure to be effective? Why use the medicine if it doesn't actually work? Why has my dog's heartworm test been negative all these years of annual testing, but now it might not be?
Dr Mark (author) from The Atlantic Rain Forest, Brazil on March 07, 2017:
KNW, you sound like a rep from a heartworm testing company trying to sell us all on testing. If you really did have your dog on year round preventative he would not be dead, since that is the slow kill method of preventing a buildup of adult worms in the heart.
You are not putting your dog at risk by not getting them tested every year.
KNW on March 07, 2017:
My husband and I never once missed giving our dog his heartworm preventative. He turned up heartworm positive. My vet at the time did not test on an annual basis. We just happened to go to a different vet and the heartworms were found. Had we not, our dog would be dead by now. Your dog needs to be weighed and checked for heartworms every year. It is NOT a scam. You are putting your pet at risk by not getting them tested every year. It DOES happen.
Jenny on February 27, 2017:
Thank you, Dr. Mark, for this informative post. I have four Chihuahuas, and recently moved to the East Coast (where I've been advised to use a heartworm preventative) from Los Angeles (where heartworm wasn't an issue at all). I've been purchasing Valuheart from a Canadian pet products website, per your recommendation, and find it to be easy and cost efficient. I'm glad to know I don't need to take my pack in for an annual heartworm test -- that's more money that can be spent on their annual dentals instead!
Dr Mark (author) from The Atlantic Rain Forest, Brazil on September 21, 2016:
Thanks for reading, other DVM. As you are probably aware, the major funders for heartwormsociety.org are the big pharmas that manufacture and sell the heartworm preventatives (Merial, for example.) I am sure you can see the danger in that.
Many of the families I have come across in practice over the years cannot afford yearly testing and medications. They may be spending their money on children, rent, food, and other things, and I do not think they have to give up their pets because they cannot afford everything they are told to do. If they cannot afford yearly testing, they probably can afford to buy heartworm preventative from an online pharmacy,or maybe ivermectin sheep drench, which does not need to be diluted and can treat many dogs for less than a box of heartworm tablets.
Thank you again for taking the time to share your views.
otherdvm on September 20, 2016:
I encourage everyone who owns a dog or cat and also reads my comments to visit heartwormsociety.org.
Heartworm disease is one of the most studied diseases in veterinary medicine, one of only a handful with a dedicated society of professionals and for which detailed guidelines for prevention, diagnosis, and treatment are available to the public.
As a veterinarian, I have seen dogs who are on prevention test positive for Heartworm disease. Should you be one of the unfortunate few, testing annually allows you to catch it early in it's course, when treatment is much safer and the heart, arteries, and lungs have not been damaged. When your dog begins to show signs of illness due to Heartworm disease, it is in an advanced stage.
Also, if you choose to purchase your own ivermectin and make your own solution, ivermectin does not mix with water, necessitating an alternate diluent, such as propylene glycol.
I wish Dr. Mark the best in his professional endeavors, including this forum, just speaking out as one professional having a different perspective on educating the public regarding Heartworm disease.
Buster's mom on September 09, 2016:
Hi My vet also charged for an office visi of $22 on top of the heart worm test! My dog has been going there for 3 years. Does anyone else's vets do this?
Doug S. on August 25, 2016:
An important issue here is owner compliance. I will often ask if the patient has been on preventatives. We had a client recently who admitted they gave it once years ago, it didn't work, so they haven't given it since. Usually, they aren't as upfront. We also look at the Owner's body language when we ask. If they avert their eyes, hang their head, etc. can be signs of lying.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on March 26, 2016:
dawnmha--your dog is more at risk because of where you live. Yes, the links are valid, but you should read the link about "How to avoid and prevent resistant heartworm" and consider another preventative instead of ivermectin. Leave me a not if you have any questions I can help you with.
Dawnmha on March 25, 2016:
Hi, I do live in the Mississippi Valley. My vet is trying to do that to me and my prior vet did not. The link you provide for heartworm meds is legit right? I believe everything you say, but of course I am concerned about the safety of buying these pills for my dogs. Hope you can confirm their safety and effectiveness. Thanks
tara on March 20, 2016:
I didn't bother reading the entire post, however I just feel it's obvious when a non medical person posts these types of things. Of course hw likely won't happen on prevention, but there are a lot of "what ifs".
The medical profession - human and animal - has developed unfortunately out of need - necessity- and things have evolved because mistakes have been made.
Medicine is more of a rule OUT things until you're left with the only outcome.
By saying if you're on prevention therefore your dog doesn't need a test is not in the vein of good medicine. Likely you are right. But animals throw up, people think they dosed an animal and didn't. Hell, I have to use a pill caddy to give my cat his daily meds - I forget all the time!
There are many known factors - vomiting, missed doses, late doses, incomplete doses etc. There are also other "unknown" factors as well.
The big thing is that prevention can be damaging if you do have a heart worm infection. So yes, vets suggest testing yearly; not because they want money - trust me I've worked in the industry for 20 years and we are all not well off! Medical stuff is expensive.
We want you to test because it's the best thing for your pet; and while we sample for Heart worm - tick and mosquito borne diseases - blood parasites - we also encourage other blood testing. We don't make money on this - the lab maybe. We suggest this because it's the best medicine. And I offer my pets what I'd want for myself or my children.
Prevention is great - and necessary. Testing is too. Unfortunatley medicine is full of abnormal things - unheard of anomolies... as a medical person I know I'm tested until....until they figure stuff out. There is not a huge change of being infected with heartworm, but the testing also tests for tick born diseases as well - lyme, erlichia and others.
Don't minimize the role medicine plays in maintaining good health.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on March 04, 2015:
I appreciate your sharing this info on your Facebook. Ivermectin has been used since the 1980s, and is safe at the doses listed above. It is no change for most people since it is the active ingredient in heartgard, just a lot cheaper than the product sold through veterinary clinics. Here is some more info on ivermectin if you want to read more:
Trena on March 04, 2015:
Thanks for this info! It would be helpful if you could provide references, though...for example, where can the factual info be found to support how ivermectin works etc. I don't disbelieve you, but I like to check out facts before making major changes affecting my pets' or family's health and it would save us a LOT of time if you already had the info referenced at the bottom of your articles. I posted to Facebook for you, as either way it's good information to provoke thought and inquiry rather than blindly trusting healthcare professionals who may not stay on top of the latest/best studies, and conversely get much of their information from drug reps! Thanks again!! :)
Dr Mark (author) from The Atlantic Rain Forest, Brazil on January 11, 2015:
Nicole, I do not want to pay Merial hundreds of dollars a year so that my dog can suffer through a painful heartworm treatment.
No, testing is not necessary before starting ivermectin. Most of the vets and techs that tell you that your dog will die without testing are using the example of Filaribits. Those old scare tactics are morally reprehensible.
Any drug can be fatal if given in the wrong amount. The proper doses are given, and people can administer it without worrying about paying a drug company for advertising.
Yes, heartworm prevention is safe and affordable. Just not purchased from big Pharma.
Nicole on January 11, 2015:
Actually the reason for the testing is the makers of the product. If an animal test positive and the owners have been using the product as directed than they will pay for the treatment. There is also an issue of compliance, owners may have purchased the heart worm prevention but that doesn't mean they are giving it correctly. Also there are some products if they are used and the animal is heart worm positive they can potentially kill the animal. Oral ivermectin can be fatal if not given the right amount, or if not given enough you are not doing any good. Heart worm prevention is actually very affordable and safe. If you are consistent with you giving your dog heart worm prevention, ask you veterinarian if you can do a heart worm test every 3 years, most are willing.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on June 08, 2014:
Health Reports--your dogs are probably totally safe in Georgia, because as far as I know the resistant strain has only been found there one time. That being said, no one can guarantee your dogs will not become infected with the resistant strain since you live down south.
If you want to use an alternative product, and can afford the extra cost, you should go ahead, but this is really your decision.
I hope your dogs stay healthy! Let me know if I can be of any other assistance, but you should really read the Auburn info on the internet about this too.
Jane Wilson from Geogia on June 08, 2014:
Ah - we are in Georgia - I'll go find your other article. Thanks for the response!
Dr Mark (author) from The Atlantic Rain Forest, Brazil on June 08, 2014:
Yes, there have been a few reports in isolated areas of the US--lower Mississippi and Louisiana, and a case from Georgia. (There are details in an article I wrote on "How to Avoid and Prevent Resistant Heartworm in Dogs".) If you live anywhere else, I really do not think it is even worth worrying about.
As you pointed out in your article on HP, there are a lot of advantages to giving ivermectin year round as a slow kill method anyway. If you are treating with the slow kill method, and preventing Heartworm year round, the test is always going to be negative.
Most people have limited money, and we spend what we can on our pets. I think the best thing to do is spend a little on sheep drench (ivermectin) and give it year round.
Thanks for taking the time to read this.
Jane Wilson from Geogia on June 08, 2014:
Great article - thanks for posting it. My last vet tried to insist on a test before selling me the Heartgaurd. Her reasoning was that the FDA had recently detected that heartworms were becoming immune to preventatives. This was a couple of years ago, and I still have not heard of immunity becoming a problem in protecting dogs from heartworms. Have you heard anything like that?
Dr Mark (author) from The Atlantic Rain Forest, Brazil on May 29, 2014:
Hi bodylevive, since rabies shots are required by law you still have to take them in at the recommended time (1 or 3 years, depending on your state). The vax actually last a lot longer than that but if one of your dogs bit someone you could get in a lot of trouble if the rabies vax were not current.
BODYLEVIVE from Alabama, USA on May 29, 2014:
Thank you for all this information, I find it to be useful because I have two dogs that really put a dent into our pockets when we take them to the vet. We will be following your advice on some of the fixes for our dogs. I do agree that some preventative measures through the vet is really a rip off and I appreciate your honesty in what can be done at home. We still have to take them for rabbies shots?
Gail Louise Stevenson from Mason City on January 08, 2013:
Heartworm is a terrible disease. My mother went with someone who'se dog had heartworm and the dog had to be put to sleep. The dog had wolf in him and he died a long time ago. I thought that the dog was on preventative medication, but he got the disease anyway and it was too late for him. I voted up.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on September 23, 2012:
Thanks for leaving that comment! I was worried about that high dose!!! I just read a study from Auburn and they recommend slightly higher ivermectin doses, due to the development of some resistance. 0.4 cc would still be safe and provide an addittional 80micrograms of ivermectin.
Thank you again for the comment. I appreciate your visit.
Shelly on September 23, 2012:
Thanks for catching my typo on the dosage for Ivermectin for my Aussie, Dr. Mark. (One of the perils of my iPad) I should have typed .03ml dose:-(. I purchased a syringe without needle that will deliver that dose so don't worry about my middle aged eyesight tripping me up when my first purchase of sheep drench arrives this week!
I am going to read your article about teeth brushing next since my guy has some issues.
Shelly and Akilah's Sweetheart Porter aka Mr. P
Dr Mark (author) from The Atlantic Rain Forest, Brazil on September 20, 2012:
Yes, it is really unfortuante that veterinary practices feel the need to take advantage of those people who take the time to learn about the disease. Since heartworm preventative (ivermectin) works as a treatment, anyway, that refusal to refil the meds has absolutely no medical basis.
Your Australian Shepherd only needs 0.3-0.4 ml of sheep drench, which is 240-320 micrograms. I put the doses in my article "heartworm prevention for less than 10 dollars a year"; it is so cheap that it is easy to keep a dog on year-round and never worry about this disease. 3.0 is a lot of ivermectin! I found a lot of recommendations on the internet forums but most of them were a lot higher than the amount of ivermectin contained in Heartgard.
As long as the 3.0 ml dose is not hurting him, though, there is nothing wrong with it except that he is taking in a lot of insecticide each month. If he has any symptoms of ivermectin toxicity, like incoordination, you should give him less. Thanks you for your great comment. I apprectiate your visit.
Shelly on September 20, 2012:
Hi Dr. Mark,
Thanks for the information. I wanted to point out that you can buy .08% (diluted) Ivermectin (Sheep Drench) from several places on the internet including amazon.com. My 51 - 100 lb Australian Shepherd dog then needs a 3ml dose according to other forums. Yes, I did have him tested for sensitivity a few years ago. I am just very angry and disappointed with the vet for flat out refusing to re-fill the meds unless I have him tested (we live in Southern California - not a hotbed for heartworm) even though I have been buying the Heartgard (at a 100% mark-up) from them. For information, I went to the FDA's site for a neutral perspective. Since the test will only reveal the presence of adult heartworm, which takes 7 to 8 months to achieve, isn't it true that the "preventative" which is actually a poison that kills the larvae when already present, should keep a dog free of heartworm?
Dr Mark (author) from The Atlantic Rain Forest, Brazil on June 16, 2012:
Thank you all for taking the time to read and be concerned!
Dr Mark (author) from The Atlantic Rain Forest, Brazil on June 16, 2012:
According to the Heartworm society, yes. If there are any mosquitoes in your area it is theoretically possible, although it may be unlikely.
Daughter of Maat, for safety sake she should be tested before starting the meds again, but the preventative should be started anyway, no matter what the test results show
Shasta Matova from USA on June 16, 2012:
This is handy advice. Thanks! My vet doesn't require the test, but we don't live in the Mississippi valley. Should I still be giving her the heartworm treatment?
Melissa Flagg COA OSC from Rural Central Florida on June 15, 2012:
Fantastic hub. This is probably a stupid question, but should you give heartworm medication to a dog who has not been tested and who has been off heartworm medication for about a year and a half especially if the dog lives in Florida?
Voted up and Shared all over!
Angela Brummer from Lincoln, Nebraska on June 15, 2012:
I am going to share this again with all the sources!
Dr Mark (author) from The Atlantic Rain Forest, Brazil on June 12, 2012:
Im glad it is useful for everyone. Just some more info--that bottle from Amazon will last about 3 years for a medium sized dog, so for anyone that needs it that is less than 10 dollars a year for heartworm protection
catgypsy from the South on June 11, 2012:
Very interesting article. I have wondered why the testing was necessary too. Thanks for the information!
Rebecca Mealey from Northeastern Georgia, USA on June 10, 2012:
Thanks so much for that website for the heart worm meds w/o a prescription.This is so useful for so many people, including me. Voted very useful and shared!
Angela Brummer from Lincoln, Nebraska on June 10, 2012:
This is really an amazing hub. I looks very professional. I have gotten this shared. Also, you should comment to the others and share their hubs and leave the ones you would like shared.
Ireno Alcala from Bicol, Philippines on May 16, 2012:
Here in the Philippines, the military officials with the help of health department administer such kind of dog treatment.
In the farflung barangays or counties, stray dogs outnumber handful vet doctors in the nearest city.
Although, animal rights is extensively promoted here and responsible pet ownership as well, still, the scenario on pet health care is not fully implemented yet.
Dog treatment is always a case-to-case basis and it's for the owner who can afford such medication.
Dr Mark (author) from The Atlantic Rain Forest, Brazil on May 15, 2012:
That is somewhat akin to guaranteeing that your home in Iowa will never be struck by a tsunami.
Dragonrain on May 15, 2012:
Interesting hub. I know someone who buys Heartgard online from Australia and has never had any issues doing so. I'm too paranoid to do anything like that myself. Plus, most heartworm preventative companies will refund your vet costs if your pet gets heartworm while on their product, but they apparently only do so if you bought your preventative meds directly from a vet.
Some animal shelters and low cost clinics will offer heartworm testing for a fraction of the cost that you'd pay going to a regular vet. That way you can save some money, but still get a prescription for heartworm meds so that you can buy them from a vet.
Does my dog really need a Heartworm test?
June 1 st is the start of Heartworm season in southern Ontario, although it seems the mosquitos have been biting for months.
This is the time by which we have had enough warm days for the Heartworm larvae to develop to an infective stage and be carried by the mosquitos to our dogs. Traditionally, a Heartworm preventative is given once monthly throughout the summer months to kill off any Heartworm larvae that might have been transmitted from a mosquito bite into your dog’s blood, before the larvae can form into the stringy white worms that live and breed in the blood vessels around the heart. Any dog that is bitten by a mosquito is at risk and so it is generally recommended that all dogs who spend any amount of time outside be put on preventative medication throughout the summer months as part of a Heartworm prevention plan. The other part of that prevention plan is testing. It is recommended by most veterinarians and by the manufacturers of the Heartworm medications that each dog have a test prior to receiving the medications each year, to ensure that the pet is free from Heartworm disease.
But hold on, Doc you just told me that medication prevented infection. Why do I need a test? This question is asked of veterinarians a lot, and so I thought I would address it here.
Like most tests in medicine, the testing for Heartworm disease is designed to let us know what is going on inside your dog before we see outward signs of the disease. You go to get your cholesterol level checked so that you can find out if it is high and do something about it before plaques build up in your blood vessels and stop blood flow. The same is true of the testing for Heartworm disease- we test to find out before signs develop. Although in severe infections we see dogs who are lethargic, coughing or having difficulty breathing, for the most part, dogs with early Heartworm infections don’t show outward signs.
The testing is aimed at pre-clinical infections. Also for dogs who have high numbers of Heartworm larvae in their bloodstreams, taking preventative medications can be dangerous as killing off large numbers of larvae can cause allergic type reactions in some pets. But the medications are (in the vast majority of cases) very safe and effective, even for heartworm positive dogs.
So why do testing then?
The real reason is that dogs with Heartworm disease need special treatment. The monthly preventatives do not kill adult Heartworms. If your dog has an infection, then he needs a different course of medication and some further diagnostics and monitoring. If we don’t ever test a dog, and simply keep giving preventatives every year assuming that they are doing their job, then it is very possible that worms are growing in the heart of a dog receiving his medication every month. These are the dogs we are looking to catch with our testing. We also see some variation in the start and end dates of Heartworm season as well as the dosing of medication in pets. If a spring is particularly early or hot, or if it stays warm late into the fall, this can change the Heartworm transmission risks. And even a single missed or delayed dose of medication can put a pet at risk of contracting this disease. For these reasons we suggest that at least once yearly we check your pet for exposure even if they have been receiving their medication. If you don’t think that any of these risk factors apply to you or your pet, discuss testing with your veterinary team and see if it is right for you.
One last point Although it is Heartworm season, we also like to focus on whole-body wellness for your pets. If we are taking a blood sample, we also have the opportunity to check for tick-borne diseases like Lyme disease, and have a look at your pet’s organ function and blood cell counts with the same sample. Often we combine these tests with Heartworm testing in a Wellness panel and this can add value to the testing by giving us a picture of what is going on inside your pet and helping identify problems before they cause illness. For all of these reasons, we think that Heartworm testing is valuable to pets and their owners, but ultimately the question of whether you need to do a Heartworm test is up to you. We are always here to help.
How To Get Titers
Titers used to be more expensive, but now there are two types of economical in-clinic titer tests that may be available at your vet.
- TiterCHEK offers testing for canine distemper and canine parvovirus with results shown as positive or negative.
- VacciCheck offers testing for canine adenovirus, canine distemper, canine parvovirus, with results shown as negative, low positive, significant positive or high positive.
If your clinic doesn’t have these in-house tests, you can still ask your vet for titers from an outside laboratory.
But some vets don’t like offering titers, or will charge a ridiculous amount of money for them (we’ve heard reports of as much as $200 to $300!). This is usually done to tempt dog owners to make the risky decision to save money by just getting the vaccinations instead.
So what can you do then? You can get titers yourself for the most important tests – distemper and parvovirus. Here’s what to do.
- Ask your vet to draw the blood for a titer. That’s a simple procedure that should cost about $15 to $20.
- Go online to Hemopet, check Distemper & Parvo Vaccine Titers on the form, and submit the form along with your payment (currently $52).
- Mail the blood sample (wrap it in some packing paper or bubble wrap and ship it in a US Postal Service Small Flat Rate Box works quite well for about $6) to Hemopet.
- Hemopet will send the results to you and your vet and they’ll advise you whether your dog needs to be revaccinated or not.
So, are annual dog vaccines necessary? When it comes to protecting your dog, don’t just take your vet’s word for what your dog needs. Do your research before you take him to the clinic, and be prepared to stand your ground if your vet recommends giving unnecessary vaccinations. Your dog’s health depends on it.