A Banner Year for Heartworm Disease

Photo Credit: Flicker CC, KatleneNiven,cat and dogIf ever there was a year to be vigilant about heartworm prevention, this is it. The number of dogs and cats diagnosed with heartworm disease within the United States is expected to increase this year because of above-average precipitation and temperatures, ideal conditions for the propagation of mosquitoes that transmit heartworms to our pets.

The nonprofit organization, Companion Animal Parasite Council (CAPC), tracks trends for various infectious diseases within the United States including heartworm disease, Lyme disease, anaplasmosis, and ehrlichiosis. A CAPC announcement released earlier this year states, “Given the ongoing trend toward above average temperatures and rainfall, CAPC is forecasting high levels of heartworm disease activity in 2017 for most of the country, with an especially active year for the Western United States.”Geography of heartworm disease

According to an American Heartworm Society survey, the number of cases of heartworm disease seen per veterinary clinic was 22 percent higher in 2016 than in 2013.  The five states with the highest incidence of heartworm infections in 2016 were, in order, Mississippi, Louisiana, Arkansas, Texas, and Tennessee.

The CAPC is predicting more heartworm disease this year in the lower Mississippi Valley as well as in the Rockies and westward. The incidence is also expected to be higher than usual in the Upper Midwest, the Ohio River Valley, New England, and the Atlantic Coast States. Interestingly, the CAPC predicts that West Texas, from Amarillo to Laredo is expected to have no increase and may have a decline in heartworm disease cases. (Texas readers, please do not take this is an invitation to back off on giving heartworm prevention!)

What this means for you and your pets

Don’t get caught with your pants down when it comes to giving heartworm prevention medication to your dogs and cats. Heartworm infection is a “poster disease” for the old adage, “An ounce of prevention is worth a pound of cure.” Treatment of heartworm disease is risky, pricey, and quite miserable for both pet and pet caretaker. And, the animal who isn’t treated for heartworm disease experiences some pretty darned awful symptoms along with a significantly decreased life expectancy.

There used to be areas within the United States considered to be “safe zones” where heartworm disease didn’t exist and prevention wasn’t necessary. This is no longer the case. Heartworm disease has been diagnosed in all 50 states.

If you aren’t already giving heartworm prevention medication to your dog or cat, consult with your veterinarian right away to get the ball rolling. The first thing your pet will need is a heartworm test to make sure that infection hasn’t already occurred. Keep in mind that animals typically show no symptoms of this disease for the first six months or more following infection.

If you’ve been giving preventive medication to your pet, but not on a regular basis, it’s time to create a reminder system that results in better compliance. Talk with your veterinarian about whether or not heartworm testing is warranted to make sure that a heartworm-carrying mosquito didn’t sneak up on your pet during a lapse in medication.

The American Heartworm Society website provides a great resource should you want to learn more about heartworm disease.

Have you ever treated a pet for heartworm disease? If so, how did it go?

Best wishes,

Nancy Kay, DVM

Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
Become a Fan of Speaking for Spot on Facebook

Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health.   There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at http://www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.


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5 Comments on “A Banner Year for Heartworm Disease

  1. I wanted to comment on just a few things that Jane posted.

    Recommended dosage of doxycycline is 10 mg/kg twice a day (not once a day) for four weeks according to the American Heartworm Society.

    The higher dosage given for ivermectin should be safe for most dogs, but more than just collies and herding dogs can be affected by the MDR1 gene that makes high doses of ivermectin dangerous. More info here:

    I don’t know of any studies showing that the high dose of ivermectin would be more effective than just giving the much lower heartworm preventative dose (6 mcg/kg, which comes to 164 mcg for a 60-lb dog), but it’s possible. I also know of no studies showing that daily treatment is more effective (the studies I’ve seen used weekly treatment), but again, it is possible.

    Advantage Multi (moxidectin) has been found to be more effective than ivermectin at killing adult worms. A study published in 2015 showed that Advantage Multi (topical heartworm preventive medication using moxidectin) eliminated adult worms in 8 of 11 heartworm-infected dogs in just six months, using just the normal monthly heartworm preventative dose. In contrast, studies using weekly ivermectin (standard heartworm preventative dosing) combined with doxycylcine found that after 36 weeks (about 9 months), the use of doxycycline and ivermectin combined reduced the adult heartworms by 78.3%.

    It is the death of the worms themselves, not the medication, that is so dangerous when treating dogs who are infected with heartworms. Anything that increases the heart rate also increases the risk of pulmonary embolism caused by worms dying. While doxycycline reduces this risk, and worms dying gradually is less risky than the heavier die-off that happens with melarsomine (Immiticide) injections, there is still some risk to all dogs as long as heartworms are present in their bodies. It is not accurate to just say that “no restricted activity” is needed.

    The American Heartworm Society says, “In cases where arsenical therapy is not possible or is contraindicated, the use of a monthly heartworm preventive along with doxycycline at 10 mg/kg BID for a 4-week period might be considered. An antigen test should be performed every 6 months and the dog not considered cleared until two consecutive NAD (no antigen detected) heartworm antigen tests, 6 months apart, have been obtained. If the dog is still antigen positive after one year, repeat the doxycycline therapy. Exercise should be rigidly restricted for the duration of the treatment process.”

  2. I have treated a couple of foster dogs for heartworms. It is pretty brutal: it is a series of shots that are very painful for the dog. Then the dog must be kept quiet with very little exercise or excitement for a few months, because as the heartworms die, theoretically they drift out of the heart and eventually end up in the intestines to be excreted. But if the dogs’s heart beats too fast, they can throw a clot of heartworms that can kill them. It’s a scary and painful process.
    I live in the San Francisco north bay; although we get freezes, I keep my dogs and indoor cat on preventative year-round.
    There is now an alternative protocol for heartworm treatment and prevention that has had excellent success, is easier on the dog, and costs a fraction of the traditional treatment. I know several people who have used it to great benefit, and I use this as a preventative for my dogs and cat:
    This costs a fraction of traditional heartworm treatment. I hope this will be shared with as many rescue organizations as possible; I know that before this, we sometimes had to pass on saving a dog with heartworms because we just couldn’t afford the treatment ($500-$800 for the HW dogs I personally have fostered) A bottle of bovine injectable Ivermectin (although for our purposes, it is not injected, but given orally) cost me $50 at a farm supply store and would see a dog through the entire treatment, I believe. As a preventative, for my 60-70 pound dogs monthly I put 1/3cc of Ivermectin on a piece of bread and when it has soaked in, I put a smidge of butter on it, so it is eaten immediately.

    The idea here is that heartworms have a symbiotic relationship with some bacteria. By beginning treatment with doxycycline, the bacteria is killed, which weakens the heartworms. Then you hit them with the Ivermectin, daily. This way the HWs die in small amounts and the dog does not have to be kept quiet! As more HWs die, the dose is increased, killing the stronger HWs, until they are all dead and slowly pass out of the dogs system.
    I had considerable trouble getting the propylene glycol; I finally ordered it through the local CVS pharmacy; others have gotten it at farm supply places; although for larger dogs, I would skip it; its only purpose is to make the dose easier to measure.

    no painful shots of poison for the dogs
    no restricted activity
    rescues don’t have to let dogs die because they can’t afford the HW treatment!

    Negative: the person in care of the dog must be not only willing, but capable of not missing doses! THIS IS CRUCIAL.

    0.82 cc of Ivermectin with 1 oz. propylene glycol (total 30cc) = 272mg/cc

    Monthly dose:
    1cc = dose for 51-100lbs.
    ½ cc = dose for 26-50 lbs.
    ¼ cc = dose for up to 25 lbs

    1cc concentrate in 9cc propylene glycol =1,000mg/cc
    Dog gets dosed EVERY DAY for at least 6 months. After 6 months, re-test for HW; if still positive, continue to administer Ivermectin at highest dose for another 3 months; then re-test. Keep re-testing until the heartworms are gone. This usually takes 6 months; but may on occasion take longer.
    for 60 pound dog (average weight of huskies; adjust dosages as necessary)
    1st 2 weeks: give 3 tablets doxycycline (300mg) once a day (42 tablets)

    Then give 200 micrograms Ivermectin once a day for one month (.02 cc concentrate) or .2cc at 1:10 dilution

    Then give 400 micrograms Ivermectin daily for one month.

    Then give 800 micrograms once a day until cleared; may take 6 months total

    After 6 months, retest.

    ******The only dogs of concern in ivermectin sensitivity are collie breeds/herding breeds. There is testing but it would be needed on a case by case basis when herding breed is suspected.******
    Ivermectin reactions
    Side effects are not a concern with the extremely low doses used in commercially marketed heartworm preventives.
    Problems may arise when higher doses, such as those used against skin mites, are employed but even then, side effects generally do not occur with any anti-mange doses of ivermectin except in animals with genetic sensitivity. Such individuals are usually Collies, Shetland sheepdogs, Australian shepherds, and Old English sheepdogs, although some individual animals that are not members of these sensitive breeds may also be prone to side effects. Very low test doses are often recommended to identify these individuals regardless of their breed. Alternatively, a blood test is available to test for genetic sensitivity (see below).
    Collies with ivermectin sensitivity have been found to have a mutant gene for what is called the P-glycoprotein. The P-glycoprotein has been studied largely because overexpression of this protein (i.e. having more of it than normal) results in poor function of chemotherapy drugs during cancer treatment. The P-glycoprotein appears to be involved in keeping drugs out of certain body tissues. Having excess P-glycoprotein keeps chemotherapy drugs from reaching the tumor. When it comes to ivermectin sensitivity, the problem is the opposite: mutant or non-functional P-glycoprotein leads to failure to keep certain drugs out of the central nervous system, allowing them access to sensitive tissue. Side effects stem from ivermectin entering the central nervous system.
    Approximately 35% of Collies have a genetic mutation creating a non-functional P-glycoprotein. This allows for ivermectin doses that would normally be blocked from the central nervous system to gain access to it. Other herding breeds as listed above also tend to express this mutation. There is now a test for P-glycoprotein mutation so that ivermectin-sensitive dogs can be identified. This is a DNA test using an oral swab. Test kits can be ordered directly from the Washington State University Veterinary School.
    Heartworm preventive doses are so low that side effects are not produced even in ivermectin sensitive individuals.
    Side effects of concern are: dilated pupils and drunken gait that can progress to respiratory paralysis and death if medication is not withdrawn and supportive care is not initiated.

  3. We have a 6 year old male Leonberger we got him as an 8 week old puppy. Since almost day one he has been taking a 1000mg capsule of processed Garlic oil.
    We are outside everyday walking in parks, grassy areas etc. Insects do not bother him at all, not fleas, ticks, mosquitos, black flies, nothing. In the six years he has been with us I have found only 3-4 ticks on him and No fleas.
    I take the same capsule and I too have no problems.
    There is absolutely no perceptible garlic odor to humans.

  4. I adopted a dog in Central America that was heartworm positive. The local vet used the “slow kill method” whereby ivermectin was used long term. Most dogs she saw in her practice had heartworm and were in a weakened state. She swore by the slow kill method and said she’d seen it work even in severe cases. And in fact, a year later, my dog tested negative on heartworms. This was 15 years ago and it may be that slow kill using ivermectin is no longer as effective if the parasite is developing resistance to this drug. I was so grateful though and my dog lived 10 more years.

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