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 that is spread through the mosquito. 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 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.
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?
Owners of 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 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?
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 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.
Questions & Answers
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.
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.
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.
If I give my dog the ivermectin medicine and he has heartworms will he get sick and die?
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.
My puppy has been on Heartgard since she was four-months-old. My vet wants to do a heartworm test. Is this necessary?
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?)