Why Your Dog Does Not Need a Heartworm Test Every Year
What Is Heartworm, and Why Is My Dog Tested?
Heartworm is a large internal parasite (worm) that is spread through the mosquito and 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 cardiomyopathy (with swelling in the limbs, fluid buildup in the lungs, and reluctance to move as the dog becomes quickly exhausted).
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. It 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.
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 with large animals and a dog dose for heartworm prevention is very low.
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 . . .
- Buy Heartworm Prevention Cheap
Heartworm disease is an internal parasite that can cause death in dogs and cats. This article gives dog owners a less expensive option for buying heartworm preventative.
- 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.
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
Questions & Answers
Is annual heartworm testing mandatory to purchase heartworm meds?
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.Helpful 40
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?
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.Helpful 34
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.
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.Helpful 25
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?
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.Helpful 23
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?
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.Helpful 17