contributed by Anne McGuire
Houston, TX

(Note: Anne wrote this article for the Greater Houston Golden Retriever Club. You will therefore see references to GHGRC throughout the document). For additional information on heartworm and heartworm treatment, please consult with your veterinarian.

Heartworm Test

Each GHGRC rescue dog must receive a heartworm test, unless we have reliable information about recent (within the past month) test results for the dog and/or have reliable information that the dog is currently on heartworm preventative. It is imperative that we have a reliable heartworm test result. If a dog has heartworms and is given heartworm prevention medication (particularly the daily type), there is potential for a life- threatening reaction.

There are 2 types of heartworm test. The Difil test is easily and inexpensively done in most vet offices and animal shelters; this test checks for the presence of Diofilaria microfilaria in the dog's blood. Microfilaria are "baby" heartworms that are produced by adult heartworms in the dog's heart, and their presence confirms the existence of adult heartworms. The problem is that adult heartworms do not constantly produce microfilaria so that a dog may test Negative on the Difil test yet still have heartworms. A Difil test may also detect the presence of Dipetalonema. These are another type of microfilaria, not heartworm. They are harmless. The Occult heartworm test tests for the presence in the dog's blood of antigens of adult heartworms. This is generally considered the more reliable test, but it is more expensive and many vets must send blood samples to outside labs for this test. False positive readings are possible, though unusual, for this test, and dogs that have been treated for heartworm may test Occult positive for at least 6-9 months after treatment, some for years after treatment. For the GHGRC rescue dogs, we need an Occult test, unless a Difil test is done first and shows a heartworm-positive result. If your fosterling shows a negative result on the Occult test, then he should receive a dose of heartworm preventative immediately, and should then continue on a program of regular prevention, hopefully for the rest of his life. We prefer to use the monthly heartworm preventative ivermectin (brand name Heartguard), as this drug is less likely to produce problems if the dog did have heartworms. GHGRC has a supply of ivermectin and the In- Care Coordinator can get you a dose for your fosterling. The liquid ivermectin we use is administered by drawing the appropriate amount up into a syringe and squirting it down the dog's throat. This is simple and easy for you to do at home. You will need to note the day that the preventative is given, and remember to give preventative in 30 days, if the dog is still with you. If your fosterling has a positive heartworm test result, you should notify the In-Care Coordinator and discuss plans to arrange treatment for the dog. GHGRC rescue tries to provide heartworm treatment to all rescued Goldens that need it. Read the section below to learn more about what is involved in the treatment and follow-up care of the dog.

Heartworm Treatment

Heartworm treatment is a serious veterinary procedure. The drugs used to kill adult heartworms are very strong and toxic (an arsenic compound is used). The dog's kidney and liver will work hard to rid the dog's body of the by-products from these drugs and from the resorption of dead heartworms. Serious complications may result from either the dog's body reacting to the drugs, or newly-killed heartworms may break lose from the heart, travel into the blood vessels or lungs, and may form a life-threatening clot. There is a real risk to the dog's life. The good news is that GHGRC rescue has had many dogs treated, and only a very few have had complications. Before beginning heartworm treatment, your fosterling should be in good health and condition. If he was underweight when he came to you, he should have a chance to gain weight before treatment. Usually getting rid of intestinal worms and a few weeks on puppy or performance diet will get a dog in good shape for the treatment. The dog should be spay/neutered and should have had sufficient time to recover from that before heartworm treatment. Since the recovery phase involves a lot of time in a crate, it helps to get the dog used to being crated. The actual treatment involves the dog spending about 3 days boarding with the vet. The dog is given twice daily injections of the drug to kill the adult heartworms. Occasionally a dog becomes very ill during the injection phase and treatment must be stopped. In this case, the dog will come back to you to recover its health and strength for a few weeks, and then treatment is tried again. Usually everything goes fine the second time! Following the injection series, the dog will come home to you for 3-4 weeks of recovery. The drugs used in the injections frequently cause nausea. Expect that the dog will not want to eat and may vomit. This is a normal side effect and usually passes after a few days. There may be some coughing, and coughing up occasional small specks of blood is common. If the dog vomits blood or coughs up large amounts of blood, call the vet immediately. It is important to try to keep the dog's strength up during this time. If he doesn't want to eat, try tempting him with delicacies such as canned food or some boiled chicken. Be sure he has clean water available at all times. Because his kidneys and liver are working overtime during this phase, a food with lower protein and sodium content (adult or senior diet) may help the dog. During the recovery phase the adult heartworms are dying and being resorbed into the dog's blood stream. The greatest danger of complication is that dead worms will break lose and form an embolism or a clot blocking blood circulation and causing rapid death. To prevent this, it is absolutely necessary that the dog be kept still and quiet. This means being kept crated AT ALL TIMES, except when going out on leash to relieve himself. For potty purposes, the dog should be kept on leash and taken outside to do its business and be brought back into the crate immediately. NO WALKS. NO PLAY. NO EXERCISE of any sort. Right after treatment your fosterling will probably not be feeling well and will be content to sleep in his crate. However, as he feels better, he will want to run and play -- it is up to you to resist his pleading eyes and keep him confined! This is particularly important for the first full two weeks. If the dog is doing well, and his veterinarian approves, he may take short, slow walks beginning in the 4th week following treatment. It is common for the dog to shed coat heavily following heartworm treatment; groom him regularly to remove dead hair. As his health recovers, his coat will recover also. Signs of serious complications are:

  1. Excessive coughing
  2. Abdominal breathing
  3. Blue, white, or brick red gums
  4. Collapse

If you see [1] or [2] , excessive coughing or abdominal breathing, call the vet immediately for advice. If you see [3] or [4], blue, white, or red gums, or collapse, you have a medical emergency on your hands and you should get the dog to the nearest vet IMMEDIATELY. Do NOT call the vet, or call a GHGRC rescue person, or call anyone else -- there is NO time. You may have only a few minutes to get the dog to treatment to save its life, and the treatment will require equipment and drugs not available in your home. Take the dog to the NEAREST open clinic and tell them you have a medical EMERGENCY. Once the dog's condition has been stabilized, he can then be transferred to his regular vet. In general, if we expect at dog to be at high risk for complications, we will place it in foster care with one of our members who is experienced in emergency vet care. We hope that you will not have to deal with this situation, but you should know the symptoms and be prepared to take action fast. When your foster dog begins his heartworm treatment, you should make sure you know the location of the nearest vet clinic to your house and the location of the nearest 24-hour emergency vet clinic, in case an emergency occurs after normal office hours. A "follow-up" treatment is administered 3-4 weeks following the injection series. The injections killed off the adult heartworms, but there may still be microfilaria in the dog's blood that will ultimately develop into adult heartworms if not killed. At 3-4 weeks post- injections, the dog should receive a dose of ivermectin to kill off any remaining microfilaria. There is a slight risk of reaction to the ivermectin dose. It can be administered at home (it is given orally, not a shot), using ivermectin from the GHGRC rescue supply. Ideally this should be done during a week day when your vet will be in his office and available in case you need emergency care for the dog. If it occurs, the severe reaction is anaphylactic shock and circulatory collapse. Symptoms usually begin 3-4 hours after the ivermectin is given, and are depression and respiratory failure (stops breathing). If you see these symptoms, get the dog to your vet IMMEDIATELY. Dog's who may be at greater risk should be boarded at the vet the day this treatment is done so that they may remain under veterinary observation. If the dog is fine 24 hours after the follow-up ivermectin, then he should have no further problems!

He is now ready to be adopted! About 2 weeks after the ivermectin dose, the dog may be given a Difil test to be certain all microfilaria were killed. If microfilaria are detected, another ivermectin dose should be given. One month after the ivermectin dose, the dog will be due for monthly heartworm preventative, and should stay on regular heartworm prevention for the rest of his life. We recommend using ivermectin (Heartguard); Interceptor may be used if the dog is testing Difil negative (clear of microfilaria). The daily heartworm preventative (Filaribits) should NOT be used, at least until about a year after treatment and the dog has tested negative on an Occult heartworm test. If the dog were to still have heartworms, there is a greater danger of severe, life-threatening reaction if taking the daily heartworm preventative. It is important that the dog's new adoptive owner understand that, in Texas, dogs MUST receive regular heartworm prevention year-round for their entire lives. Heartworm treated dogs should receive an Occult test about 9-12 months after treatment. Any sooner than that is useless because the dog may still be carrying antigens from the pre-treatment heartworms. About 9-12 months following treatment, most treated dogs should be testing Occult negative. For older dogs, sometimes the best procedure is not the direct treatment. Instead we may use a "soft" treatment: The dog is started on heartworm preventative, ivermectin (Heartguard) is preferred. This prevents the dog from developing new heartworms. Over a course of months to several years, the adult heartworms in the dog's heart will die naturally, of old age, and eventually the dog will be free of heartworm. This treatment is not preferred for young dogs because significant, irreversible heart and lung damage can occur from the adult heartworms before they die off. For an older dog, or dog that for any other reason, may not be able to survive the traditional, direct treatment, this "soft" treatment offers the dog a chance at life, albeit with some potential risks. As mentioned before, there is a risk of serious reaction for some dogs given heartworm preventative when they have heartworms already. For this reason, dogs given the soft treatment probably should remain in foster care for several weeks following their first dose of ivermectin to be certain they are not likely to react. When this type of treatment is used, it is imperative that potential adopters clearly understand the dog's condition and the risks involved, before committing to adopt the dog.

Heartworm Treatment

contributed by Doug McGuire
Note: Doug McGuire gave the following information in answer to how heartworm is treated.

We routinely treat our rescue Goldens for heartworm - it's unusual to find one without it here in Houston. The treatment you describe is like nothing I've ever seen or heard described here and, as I obliquely suggested, all the vets in this area have a LOT of experience with treating dogs for heartworms. The foster dog that Anne and I have at home now is almost through his post- injection rest period - he had some rough times but is doing well.

Typical treatment is an initial injection series over a period of 3-4 days. We dropped Clyde (our foster dog) off at the vet's Monday morning and picked him up Thursday mid-afternoon. The drugs used to kill the worms are pretty nasty (arsenic-based?), and adverse reactions are not unheard of, which is why the vets like to keep them in the office during the injections. For the next 3 days, Clyde seemed fine, except for a spot on his leg where some of the drug had gotten on his skin. We pretty much treated that like a hot spot and it's cleared up now. After 3 days, the coughing started: awful, honking coughing triggered by the slightest exertion, sometimes accompanied by bits of blood. Clyde clearly felt pretty awful, but his appetite remained O.K. and he eventually, over a period of about 9 days, stopped the coughing. He's pretty much back to normal now, but we'll keep him quiet for another week at least. Three to four weeks is normal for the quiet phase.

After that stage is complete, we'll do a difil test to make sure all larval worms were killed, at which point he'll get a substantial ivermectin dose. And that's it - all done. Regular heartworm preventative prophylaxis is then followed, and the dog is retested (difil AND occult) six months after treatment. It's not unusual for the occult test to register a weak positive, as the antibodies may not have completely gone away. In such cases, an antibody titer is recomended.

We've treated maybe 40-50 rescue dogs for heartworms, and only seen bad reactions in 3 or 4 dogs. I know of two cases where the treatment was not 100% successful, and the dog had to be re-treated later. These second rounds are easier on the dog, both because their condition is generally much better than when they come to us and because they're carrying a much smaller load of worms. [We had to delay Clyde's treatment for more than a month just so we could put some weight on him and build up some strength (he was in awful shape when we got him) so that he could cope with the treatment.]

All in all, heartworm treatment is not pleasant but is generally successful. It's infinitely preferable to the alternative.

Doug McGuire