Do dogs need heartworm prevention all year?

Does my dog need heartworm prevention year round?

*Note: I choose to give my dog the minimum amount of heartworm prevention medication I believe is necessary to keep him reasonably safe from heartworm disease. My personal decision should not necessarily be your decision.

To determine whether or not to give your dog a monthly heartworm prevention tablet, I recommend you weigh the risks of the toxic prevention tablet vs. the risk of your dog developing heartworm disease.

For 2013, I have decided to give my dog fewer doses of heartworm prevention medication than I have in the past. In previous years, I gave Ace monthly heartworm prevention in the six warmest months of the year, typically May through October. I’ve never believed year-round treatments are necessary for Midwestern dogs, because heartworm disease is transferred by mosquitoes and those Suckers are dead around here by November.

I live in one of the coldest places on earth. In Fargo, N.D., it’s completely normal for the temperature to remain below zero for days. We are unfazed when the temperature dips below -30. While I tend to be a worrier when it comes to my dog, I’ve never worried about the possibility of Ace getting infected by heartworms in the winter …

Does my dog need heartworm prevention in winter?

While the vets in our area generally recommend monthly heartworm prevention year round, they don’t seem to mind if dog owners choose to treat for just six months as long as they do an annual heartworm test. (This is not a scientific survey, it’s just my observation.)

Before we get to some of the reasons why I believe this is still too aggressive, I’ll go over some brief details about heartworm disease.

What is heartworm disease?

Heartworm disease is transmitted by infected mosquitoes carrying immature heartworm larvae, according to “Dogs Naturally Magazine.” When one of these mosquitoes bites a dog, she could inject the larvae into the dog’s body where they could eventually travel to the dog’s heart. There, the larvae could develop into adult heartworms capable of creating new larvae which could circulate in the dog’s blood. If a mosquito bites the infected dog, she could transfer the larvae to other dogs.

Symptoms of heartworm disease include a loss of appetite and weight loss, coughing, gagging, shortness of breath and a lack of energy, according to “Dog’s Naturally.”

Fear is an effective marketing tool

While heartworm disease can be very serious and deadly, your dog may not face a high risk of contacting the disease in the first place. Let’s remember that fear is an effective and profitable marketing tool.

Is the cost of heartworm prevention a factor?

Heartworm prevention through a monthly medication such as Heartgard is affordable, starting at around $6 per tablet. This is not going to break the bank for most of us. In addition, a heartworm test is around $40 in my area. Obviously if you have to treat your dog for heartworm disease, the cost will be much more than it would have been to prevent the disease.

So what’s the problem? Why don’t I just spend $100 or so on heartworm prevention and call it good?

Because heartworm prevention tablets are toxic chemicals

Heartworm prevention drugs are parasiticides – neurotoxins designed to kill any larvae that your dog may be harboring, wrote Ted Kerasote (author of “Merle’s Door”) in the book “Pukka’s Promise: The Quest for Longer-Lived Dogs.” Just as some veterinarians continue to give dogs unnecessary vaccines every year, some vets also insist on giving dogs a monthly dose of toxic heartworm prevention.

Vets profit from promoting excessive heartworm prevention

Vets are taking advice directly from the American Heartworm Society, a group that studies the disease and recommends year-round chemical preventative treatments for all dogs, regardless of where they live, according to Dr. Karen Becker in the article “Why Haven’t Pet Owners Been Told These Facts About Heartworm?” on the web site The AHS has eight sponsors, and all eight are pharmaceutical manufacturers.

Veterinarians are also permitted to sell the drugs they prescribe (unlike doctors with human patients), so their prescriptions may not always have sound medical justification, Kerasote wrote.

What is a dog’s actual risk of contacting heartworm disease?

Climate matters.

Do dogs need Heartgard year round?

If a mosquito actually bites an infected dog and ingests heartworm larvae, the ambient temperature must remain above 57 degrees Farenheit for about two weeks in order for the larvae to develop into mature infective larvae within the mosquito, wrote Kerasote. Under those ideal circumstances, these could then be injected into another dog, starting a new cycle.

Because of the unique temperature requirements, heartworm disease is only a year-round risk in warm regions such as the southeastern portion of the United States and the Gulf Coast, Kerasote wrote. If the ambient temperature drops below 57 degrees even for a few hours, the heartworm larvae living in the mosquito cannot become infective and the life cycle of the heartworm is broken.

Calculate the temperature in your area to determine actual risk

A healthy way to address the risk of heartworm is to calculate the first date the local temperature consistently stays above 58 degrees and when it once again dips below 58 degrees, Kerasote wrote. “For the mid-Atlantic states and New England, this would mean giving your dog its first monthly heartworm treatment around June and the last one in November – six months of taking a toxic chemical instead of 12.”

For Fargo, it has not yet remained above 58 degrees consistently in 2013. While it has reached 80 and 90 degrees during the day, the temperature has dipped below 58 degrees on all but a few nights so far this spring. We haven’t even gone 48 hours with the temperature above 58 degrees, let alone two weeks. I plan to start my dog’s heartworm prevention if and when the temperature consistently remains about 57 degrees.

Treatment every three months should be effective no matter where you live

Even treating your dog monthly for six months is unnecessary, Kerasote wrote. If your dog gets stung by an infected mosquito on June 1, the larvae will not grow into adult heartworms for a couple of months. You could treat your dog with Heartgard in September and again in December and call it done.

“Even on the Gulf Coast, where the ambient temperature may not ever dip below 57 degrees, dosing your dog with heartworm treatment once every three months should protect it,” he wrote. “For many parts of the United States and Canada, no treatment at all is required.”

He does recommend a yearly heartworm test, just to be sure, especially if you travel to warmer climates with your dog.

While every situation is unique, I hope you consider your dog’s actual risk of developing heartworm disease and make the most appropriate decision for your dog.

What about all those shelter dogs that are heartworm positive?

I know someone is going to attack me, saying how she works at a shelter and sees dozens of heartworm-positive dogs each year and how her shelter spends thousands of dollars to save these dogs.

Yes, this happens, and it is very unfortunate. But let’s remember the majority of these dogs entered the shelter system after being stray or lost. They would’ve been living outdoors and potentially exposed to more infected mosquitoes than an average dog. They would’ve likely had weakened immune systems due to a poor diet and other health problems. Others would’ve come from families that lacked education about any heartworm prevention at all or perhaps lacked the money for heartworm prevention or veterinary care in general.

Animal shelter workers see the worst of the worst, and they tend to make inaccurate generalizations about dogs as a whole based on the tiny group of dogs they actually work with. Most dogs will never end up in a shelter.

Heartgard is probably the most popular heartworm prevention medication in the United States. I was curious what Heartgard had to say about monthly treatments. According to its web site, it recommends monthly treatments for all dogs since it can’t be “determined with certainty when the threat of mosquitoes has passed.”

Um … I’d say the threat of mosquitoes has passed once we reach January in North Dakota. I’d even say so with certainty …

Does my dog need heartworm prevention?

Additional ways to keep your dog healthy

While I do believe heartworm prevention tablets are the most effective way to prevent heartworm disease (if your dog is at risk in the first place), here are some additional ways to keep your dog healthy:

  • Feed your dog a healthy diet. Obviously, I recommend a raw dog diet for dogs, but you could also feed a high-quality kibble.
  • Take your dog in for an annual checkup and heartworm test.
  • Make sure your dog gets out for regular exercise. Fit dogs are generally healthier. Plus, dogs benefit from Vitamin D just like us.
  • Use natural mosquito repellent. “Dogs Naturally Magazine” recommends eucalyptus oil or citronella candles. While dogs supposedly don’t like citronella, we have used citronella candles on our patio while out with our dog and he doesn’t seem to mind the smell. There are also natural bug sprays you can use for yourself and your dog.
  • Limit other toxins your dog is exposed to such as spot-on flea treatments.
  • Only give your dog the minimum amount of vaccines necessary to keep him safe.

What are your thoughts on monthly heartworm prevention tablets?

While I know everyone won’t agree with my decisions, I’d still like to hear your thoughts. As for Ace, I plan to wait until the local temperature consistently remains above 57 degrees (if that even happens) and then give him a heartworm tablet every three months until the temperature once again consistently drops below 57. I will probably still do an annual heartworm test, just to be sure.

I asked Ace if he had an opinion on all this, and he said, “I frickin’ love those beef flavored tablets!”

I guess I’ll have to feed him more steak.

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48 thoughts on “Do dogs need heartworm prevention all year?”

  1. I agree to an extent. My vet recommended I not start my dogs on Heartguard till June this year and I always stop after September. Many dogs over many years and not one heartworm.
    Also, over many years (I’m 60), I have NEVER seen 1 “natural” “organic” remedy or preventative that does a thing and I have tried them all. They were all the rage 30 years ago and that includes Citronella. Talk about marketing……..
    My brother’s dog died last year from heartworm, 50 miles from Fargo. He had never believed in heartworm and his own “heart” was broken. That being said, the dog was a Boxer and spent its entire 7 years of ‘life’ on a chain, in the back yard, year ’round, 50 yards from a river. They don’t ‘believe’ in dogs in the house.

    1. Lindsay Stordahl

      Thanks for sharing your opinion on this. You make some good points about some of the “natural” alternatives.

      Thank you, also, for sharing the example of your brother’s dog. Sorry to hear of his loss.

    2. Thanks for sharing your experience. I appreciatively agree with all your points, that are quite educational to me too.

    3. Wow. No dog, in a warm or cold climate should spend their entire life on a chain. No wonder the dog only lived 7 years. That is a harsh life. Please, if your brother gets another dog, please build that dog a warm ample shelter lined with hay or place him in a heated garage during the cold months….if that’s the only alternative. We need national laws outlawing heavy chain collars or leashes for dogs. How would you like to wear a heavy chain around your neck for life?

  2. Ridiculously appropriate timing, I was just about to schedule a vet appointment to discuss/argue with my vet why annual testing was necessary when 1) I live in a low prevalence area (so low half the vets don’t even push HW prevention) and 2) my dog is on a monthly regimen (accurate to the DAY). She wasn’t even on HW prevention for the first three years of life.

    A little searching on heartworm life cycle and medication + “every other month” is providing a ton of information that, frankly, I’m kicking myself for not thinking to research sooner. Especially since my dog falls in the bottom of the weight range for her meds. (It’s not too much for her but it’s enough for a dog twice her size??)

    Thank you for expanding my horizons. 🙂

    1. Lindsay Stordahl

      Thanks for weighing in with your thoughts. I’ve seen some recommendations (Dr. Karen Becker is one) to give the treatment every six weeks instead of every month. That’s a least a little better, and should still be effective.

  3. Great info, I also only give heartworm prevention(also flea prevention) to my dogs 6 months out of the year and stretch it to every 6 weeks. I bought diluted liquid ivermectin online so that I can give them the exact dose to the pound and don’t have to worry about the wide range dose/weight in the pill form. I have also cut back to vaccines every 3 years. I don’t really trust vets on the issues anymore!

    1. Not quite brave enough to try liquid ivermectin 😉 but I’m with you on the not really trusting vets on the issues. It’s like human doctors who prescribe meds without ever mentioning that changing your diet (or other $0 alternative) will fix the problem.

      1. I can see how it would be intimidating but Norman was already on it for mange when he was a puppy so I knew he would handle it with no issues. The dose is actually much lower than that in heartguard!

      2. Cathy, So true. My dog is nine now and she has not had booster shots since she was three, except for 3-year rabies shots. She is wonderfully healthy and goes on 20 block walks with me each day. Even the rabies shots–I follow a protocol to reduce the effects, using holistic homeopathic rabies formulas after the shots and prepping her before with a special diet and vitamins.
        I started out giving her heartworm prevention –Interceptor–when I lived in the Southeast but when I moved back East, I placed her on a six month plan–stretching doses out to 45 days with testing once per year.
        I’ve also stopped using Frontline Plus and other chemical flea control–unless fleas are really bad. I only used it once last year. If you read the fine print–you only need to use it once every three months for flea control. It is only needed every month if you are using it for tick control–so I use it in July. The rest of the year, it’s all about bathing, natural flea spray and washing and vacuuming.

  4. Thank you again for sharing the link to this article, because I learned much more than what I found. There’s something about learning from a fellow dog parent that helps me more than just reading online.

    Our dogs just started a raw diet in April and I’m excited to see the changes in their diet. They don’t take heart worm medication and I use a natural product for fleas and ticks; what I don’t know is if I should consider using something more serious, because we had such a mild winter in the PNW. Mild = no snow fall and our temps don’t drop below 30 degrees.

    Spring started early this year and it’s 70 degrees today. Looks like I have more homework to do!

    ~ Kim

    1. Lindsay Stordahl

      Good question. I think each situation is unique, and each dog owner needs to make the best decision based on that situation.

      For my dog, I typically give him one dose of spot on flea/tick prevention in July or so. I check him for ticks if we have been in the woods or tall grass. I prefer to use natural brands but my husband is very allergic to the ingredients in those, so frontline it is. One dose in the middle of summer is plenty of protection for my comfort level. I vacuum often and wash my dogs bedding often, too.

      Again, I’m in a colder climate and my dog is very much an indoor, suburban boy.

      What’s your opinion?

  5. When I lived in Texas, I would say that regular preventative against heartworms is necessary. In Kansas, where we’ve had winter weather all the way into May, I would say it is not needed all year around. However, after trying to adopt a Border Collie last year and having the adoption process delayed because I didn’t give my dogs treatment all year around, I now treat my dogs monthly. I’ve heard that heartworm treatment for Border Collies can sometimes be deadly, and since Pierson is possibly a Border Collie mix, I don’t want to take any chances. So what are the risks of giving your dog monthly heartworm prevention?

    1. Lindsay Stordahl

      I will have to write another post on the actual risks of heartworm prevention tablets.

      For me, it’s about avoiding extra toxins. A high percentage of dogs die of lymphoma and other cancers each year. While much of this is related to genetics, there are also environmental links. While it’s impossible to avoid all toxic chemicals, I do what I can to limit what myself, my husband and my pets are exposed to. Chemical flea and tick treatments as well as toxic heartworm preventatives are just a few examples. We also use very few cosmetic chemicals, cleaning chemicals and so on.

      It’s all a personal choice and finding your own comfort level. I am more concerned about the toxins my dog is exposed to vs. his potential risk for heartworms. That will not be the same for everyone. The point is you have a choice.

  6. Thanks for this article. I am really torn. I am in montreal and it gets really hot here early. I started his treatment in may and all his fur where I applied advantage fell out. The doctor suggested giving the pills from now on but if it did that to his fur topically I wonder what would happen if he ingested it.

  7. Great article! I had no idea that the temperature was a factor in developing larvae. Thanks again 🙂 Now I can tell the vet to go “Fly A Kite” until the temps remain steady for a while 🙂

  8. I’m so glad I came across this post because I was feeling worried about not being on top of preventative care for heartworm in my dogs. We live in Michigan, and last year we had an extremely low amount of mosquitoes due to a really late frost that pretty much knocked them out for the summer. We’ve only recently started noticing an increase in the mosquitoes within the past month or so, and my dogs pretty much go outside just to go to the bathroom…otherwise they are chilling in the house laying on my furniture and my kids. I’m not saying my dogs are at zero risk, but I think their risk is low. You make alot of sense with respect to the vets interest in making money off the drugs. And the temperature thing is something I’ve never heard about. Thank you!

  9. I spent about 1/3 of my life in ND, including Fargo (still my favourite place), but now live in NW BC (and moving to northern Ontario.) The vets in ND always prescribed HW meds year round. My vet here doesn’t recommend them at all, in fact, I think our vaccines are every three years…and my seniors don’t need them. All are inside dogs. Of course, we are about three hours away from Alaska.! LOL however, we are only 1 1/2 hours from the coast & live in a boreal rainforest – read: LOTS OF FRIGGIN SKEETERS! That said, apparently there has not been an originating case of HW here (only from southern transfers). However, the pharm companies still recommend it. LOL I volunteer with a rescue and all of my dogs are rescue/shelter dogs. We haven’t had a case either, though, testing isn’t a normal practice. We are travelling through ND this spring/summer & so I was thinking of giving them a treatment…now, I’m thinking that probably won’t be necessary. Thanks for the article! Re the post about the boxer living outside year round in ND, sorry, but short hair breeds like that never belong as outside dogs (if any do).. Always breaks my heart to see that, well for any dog, but especially for short hair breeds. Those elbow calluses of neglect always anger me. My lab X is 12 & the vet marvels at how healthy she is, something he attributes to good food, appropriate environment & of course GREAT vet care! LOL

    1. Lindsay Stordahl

      I really enjoy hearing everyone’s opinions on this, so I’m so glad you shared yours. Yay North Dakota! 🙂 So glad to hear heartworm disease is not an issue where you live now.

  10. I am so appreciative of your article. It answered every one of my questions. I have never given my dos protection from heartworms. Shame on me! I lost a nine year old healthy Golden unexpectedly. I hope he was not infected with heartworms. The vet said he died from a heart issue. I to hate giving my dogs toxins. That is how I found your advice.
    Thank you, Linda

  11. Thank you for sharing this. I live in Michigan and as you probably know the weather has been horribly cold since…I think October lol! My vet is really pushing the heartworm test and I feel that my dog is at low risk since whe was a puppy last year and had heartworm medication from May – October, and now will start them today after her visit to the vet. I’m glad I found this so that I have some knowledge to back up what I already felt was unecessary! Thanks again 🙂

  12. I have two 80 lb dogs and we live in central, IL. I don’t give my dogs heartworm or flea prevention once the ground freezes, which is anywhere between Nov-Dec, and then I start back up with protection when the ground is not longer frozen. I think this year I started back up with prevention late April the beginning of May. My dogs don’t live outside but we do live close to farms and wildlife. They are tested every year and I have never had a problem. It doesn’t make sense to give them protection when the temps are below freezing.

  13. Thanks for sharing your thoughts! We just moved to the midwest from CA and “heartworm pill” popped up on my calendar today. I looked outside at the snow covered ground and thought…”geez…there is NO way there is a single mosquito living out there.”

    Some eye opening info here – I will be sure to connect w my vet on this but it’s true as you say…there’s just no way those bugs are alive out there right now 🙂

  14. I want to avoid toxins (heartworm pills) when possible. However I know that heartgard-plus also prevents against roundworms and hookworms. Do I need to worry about those if my dog gos off the pills in the winter?? (I live in NYC)

    1. Lindsay Stordahl

      If you think your dog is at risk for hookworms or roundworms, then you may want to keep him on the prevention medication for that. Just depends on your area, what the risk is, your comfort level, etc.

  15. I agree with you, but did you know private rescues in a city don’t give a damn how many dogs you adopt. I have 9 dogs and I have just decided I will NEVER again vaccinate my dogs, and that includes rabies. Check out what the top Chief and professor for Vaccination research says about vaccines. They can harm, disable and even kill your pet at an early age. I don’t give a damn what the law is. The Rabies shot is good for a life time and they have proven 7 to 12 years. But the Government says, “Well we’ll make it every three years so the pharmaceutical companies and Vets can make money. Yeah, off the death of your pet. I began searching this after one of my dogs, after her Rabie shot developed fluid filled lumps all inside her body. Adult dogs do no need to be re-vaccinated. Check out this
    There is a lot of study showing re-vaccinating your dog or pets is harmful and can kill or shorten their life. Many studies have proven the facts and it is the pharmaceutical companies and vets making money off the death of your animals. Example, a dogs immune system is mature about 4 to 5 months old and does not need to be vaccinated ever again. This includes rabies which the vaccine is a killer.
    Please listen and watch Dr. Beck and the Top Doctor & Chief , Dr. Schlutze Vaccine expert who is involved in the research of vaccines.

  16. I totally see the logic here and would like to avoid monthly doses if possible. I’m concerned about the length of time my dog spends in temperatures below 57 degrees. I mean, sure, it could be 50 degrees outside, but if he is only outside for a half hour at a time and spending the majority indoors at 68-70 degrees, then does the outside temperature matter? The way I understand it, the dog would have to be bit by an infected mosquito, and then not be exposed to temperatures lower than 57 degrees for about 2 months after the bite in order to become heartworm positive.

    So, let’s say I give my dog a dose on March 15, then he gets bit by an infected mosquito on April 1. He spends 20-30 minutes in 50 degree temperatures 4 or 5 times over the following 4 weeks, but stays in 68-70 degree environments the reminder of the time, is it safe to wait until May 15 to give the next dose? I guess what I’m asking is, does a lower temperature outdoors really play a role if the dog is not outside for extended periods of time?

    1. Its not what temp your dog is in, its the temp the infected mosquito was in outside that matters. If the mosquito is in 57 or below for a few hours it will kill the heartworm larvae inside it.

  17. My last vet visit and the vet said we needed to test for heart worms and they needed to do an examination before getting the 3-year rabies shot. I asked the vet why the test for heart worms when I had been religious giving the heart guard? She said it might not be working. Right. Rip off! And then an examination to get the 3-year rabies shot? Why. Again, rip off.

    I think vets are the reason so many people are turning in their dogs. My son’s cute little spaniel has a benign growth on her chest and the vets want $800 to remove it. Rip off. I have a weird feeling when I visit the vet, because like dentists I hear ca-ching, ca-ching and don’t trust them.

  18. Loved this article! so informative….I live in neighbor has the cutest rescue Pitt who I have grown to love dearly..they are a young couple with 3 children who adopted this pup about a year ago (prior owner kept him in a basement..poor diet and care….)..anyway, I dog sat while they vacationed this summer..and continue to walk dog few times a week while they work……I asked them if they gave him his heartworm and flea/tick meds..they did not have a clue what I spoke of..i explained heartworm..they told me they would inquire about it… now winter months are here..i am not going to push issue….but was just curious about need for meds..i gave my dog monthly meds on time for 15 years..but always had in back of my this necessary?hummm”thanks again..glad conversation continued for these years……

  19. Your article has given me so much comfort and new insight. While I am very interested in health and nutrition, it had never occurred to me that my dogs were possibly being endangered by the very meds we are instructed to administer to protect them! While I live in the south, we begin getting temperatures below 57 degrees by late October. I will be giving a lot of thought about giving them anything not required by law in my state. Please tell me what flea and tick preventions you feel are most safe — that is a real problem here, though neither of my dogs have ever had a flea and only one tick that I know of. Of course, I have been using the topical application between their shoulder blades — yikes!! Thank you so much for your excellent information.

    1. Lindsay Stordahl

      Unfortunately, now that I live in San Diego where fleas are a big problem, the only products that seem to work are the chemical products vs. natural. I don’t know that there is a brand that is “safer” than the others. I would just say use as sparingly as you can but sometimes in order to prevent fleas you don’t have a choice. I give a dose every 5-6 weeks for my dog year-round these days and my cats every 6-7 weeks. When I lived in North Dakota it was thankfully not needed at all. We have to do the best we can.

      If your dog is on the end of the spectrum for the dose one way or the other, I’d go with the smaller dose. That’s what I do with my cats. They get the dose for “small cat” 5 to 9 pounds when they are more like 10 and 13 pounds.

  20. Thank you for your article. I live in San Francisco and go up north to Mount Shasta each summer for camping and am concerned about my dog contracting heart worm disease. Just wanted to be clear about what I’ve read in your article and so am asking if this would be correct: test my dog for heart worms. If she is negative, I can begin giving a preventative such as Trifexis once every 6 – 8 weeks during the warm months (april – november). Is it also just as effective and safe to give her the dose once ever 3 months (the first of april, july, oct) instead without having to do bloodwork before dosing each of those dosing? Why then do companies like Trifexis say to dose monthly rather than every 3 months? Thank you

    1. Lindsay Stordahl

      I suppose they say this to make things easier for people (once a month, regular schedule) and also just to be “safe” and also to make money. Yes, you had it right in your summary. I choose to test my dog every spring and then give prevention every 6 weeks April through October or so. I live in San Diego and also travel to Mt Shasta area!

  21. Hello! I am very excited to have found your informative article. I also live in San Diego and am looking to lessen the drugs given to my dog. Seems as though every two or three months will be our regimens for heartworm medication.

    I was wondering your opinion on Comfortis however. We are very active and definitely need flea protection. What I’m trying to find out is if we can get away with a dose every other month since it kills eggs and adults within hours.

    I am curious to know your thoughts on this. Thank you very much!

    Brooke L

  22. We live up in Michigan and we give it June through December.
    Ivermectin is an extremely safe drug. It is also used world wide in humans to kill worms as well. Within 36 hrs the body will have flushed at least half of it (50%) by excreting it in the feces – Ivermectin does NOT stay active in the system like flea preventative does for a month.
    Ivermectin is a Anthelmintic. Which means they kill helminths. Helminths are worm-like parasites such as flukes, roundworms, heartworm, and tapeworms. It is important that anthelmintics are selectively toxic to the parasite and not the host. Some work by inhibiting metabolic processes that are vital to the parasite but absent or not vital in the host. Other anthelmintics are poorly absorbed through the gut, which means the parasite is exposed to much higher concentrations of the anthelmintic than the host. Starvation or paralysis of the parasite result, followed by subsequent expulsion or digestion.
    Ivermectin is barely metabolized at all which means it gets excreted almost the same as it went in.

    Now there are breeds such as collies that are sensitive to the amount of Ivermectin. If given ivermectin they must be on a more exact amount so usually to prevent a problem those dogs are just on another preventative like Intercepter. So Ivermectin isn’t the drug you should be worried about. It’s the flea and tick preventative that is often sold with it in the same pill that is so toxic. I always strongly suggest people do not give combo heartgard and flea preventative together to our puppies. We have had some puppies end up in the ER who’s owners were given a sample of Trifexis.
    Secondly, ivermectin is a clean up preventative. Not a real preventative in the sense that it stops microfilaria from entering the body. So if an infected mosquito bites a dog and transfers the microfilaria then that microfilaria will stay in the system and developing until you give the next dose of Ivermectin. Yes, it takes 5-6 months for the worm to be mature and to produce more microfilaria but by waiting 3 months, it’s now a half mature worm. Killing the microfilaria early is key. I know dogs who’ve gone through treatment. The treatment is extremely toxic not to mention extremely costly as well. So toxic that the two dogs I’ve seen go through it were never the same after. They both went mental and had to be euthanized. Both dogs were sweet and loving pets that became neurotic dogs. One becoming chronically restless and at times aggressive to its owners and the other also becoming restless and irritable and turning on the other family dog who was her best buddy from puppyhood. Those two dogs were inseparable they loved each other so much. That dog was a well taken care of house dog who’s owner just didn’t get her dog in early enough to start preventative in the summer here in Michigan.
    I’ve seen mosquitos below 57 especially if it warms back up during the day. In fact we don’t consider Michigan to be mosquito free until it dips below freezing for several days during the day. Some mosquitos can hide on things like firewood and a person can bring them in during the fall and early winter. Your house will warm them up and make them active.
    So personally telling people they shouldn’t give heartworm preventative every month, especially in areas that are heavily laden with it like the gulf coast etc is horrible advice. The treatment side effects and the cost far outweigh the price of preventative and Ivermectin is extremely safe. Plus if their dog is infected to the point that it is detectable on a test then they can’t get more heartgard from the vet.
    My advice always is: definitely give heartworm preventative. It’s extremely safe and has been used for decades now in domesticated animals and widely used in humans too.
    Only use flea and tick treatment if you are in an area that is highly infested with fleas and ticks. Not every area needs flea and tick preventative. Flea and tick preventative IS toxic. It’s far more dangerous than ivermectin.

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