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Stafford

Heartworm and the Pacific Northwest

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Our vet is recommending a heartworm screening, and if negative, heartworm preventative for Grace.

According to the vet, we have had only a couple of cases of heartworm in the Portland, OR area recently. However, she said there were a large number of heartworm-positive dogs in Eugene, OR in the past year, which is about 100 miles South of us. Heartworm _may_ be spreading towards us, and she thinks better safe than sorry.

I'll ask on a local canine-activities list if people in Portland are putting their dogs on heartworm preventative at this time, but I'd like to hear from the general border collie community if there are any special caveats for BCs and heartworm preventatives. Any brands/formulations to avoid? Any that are better/cheaper/what not?

Thanks,

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All heartworm meds are in the same class of drugs and can have the same side affects at the dosage prescribed for heartworm prevention.

Choose a monthly preventive that you find cost effective and convenient. I believe there is a generic version of HeartGard and this is likely the least expensive.

Mark

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That's interesting. I live near Eugene and use 3 vets in the area and none have ever mentioned heartworm being in this area - but they do say there is a lot in Medford. I test yearly and don't use monthly preventative.

Marie

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Hmmmm...is the climate in Eugene that different from the climate in Medford that mosquitoes could thrive (and carry HW) in the one area and not the other? (Genuine question as I am from the east coast and though I can see that Medford is south of Eugene I would expect both climates to be similar given their relative proximity to the coast....).

J.

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For what it's worth, I live in Salt Lake City and every vet we have ever used has recommended heartworm screening and medication.

Our rescue told me that if we use heartworm medication (they are in Casper, Wyoming and apparently is too cold for heartworm there) we should use a medication that does not contain the ingredient [b]ivermectin[/b] as there is concern that it may cause toxicosis in Border Collies. Heartgard contains ivermectin. My vet recommended that we use a monthly dose of Interceptor, which uses milbemycin as its active ingredient.

I think a lot of the folks on this board use Heartgard with no problem though. I got spooked by the comments by our rescue and from what I read, so I use Interceptor for my BC.

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Just as a BTW for any who don't know, when testing for heartworm, at least in AK you're testing to find out if your dog already HAS this disease. If yes, then you're trying to get rid of it, which is kind of expensive - or it was last time I did it; in AK we don't have heartworm, and won't unless either the worm mutates to handle cold, or global warming starts accelerating. Hence it has been several years since I had to treat a heartworm positive dog, for which I am grateful. Dogs can and do die during treatment for heartworm, and the treatment isn't all that fun for them. If it was me, I wouldn't take the chance (the risk and expense of prevention being less that of treatment once the disease occurs). This is just my opinion, but I'm stating it in case there's any confusion as to what it means to be testing for heartworm. Bear in mind also that it takes about 6 months from the time of first exposure until you have adult worms living in the heart, so you can have a negative test and have a dog who will in the next few months actually HAVE heartworm disease. It's a confusing life cycle, so if it hasn't been properly explained, it's easy to misunderstand it. Just FYI.

FWIW, I personally have yet to see a BC have trouble on either milbemycin or selamectin (the only 2 we use at our clinic, since we are HW negative up here - we send it for travel or people moving to new environments.)

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Allie Oop,
See Mark's post above. He's a research chemist so ought to know of what he speaks with regard to the chemical properties of the various HW preventives. Many of us use ivermectin as a preventive. I believe that the dose used is well below the threshold at which you would see a toxic response. There is a genetic test available if you really worry your border collie might be sensitive. Google the American Working Collie Association and visit their website. Since collies are at a much higher risk of carrying the mutation that causes ivermectin sensitivity, the web site has tons of good information.

AK Dog Doc,
Have you seen problems in border collies being given ivermectin? Maybe I should qualify that since your clinic doesn't offer ivermectin and ask: have you in your professional reading/conference attendence/schooling heard or seen that ivermectin sensitivity is a big problem in border collies?

J.

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Hmmm. My reading of AK Dog Doc's post was that he was in favor of prevention, rather than trying to cure HW after the fact. He expressed no opinion about ivermectin, only mentioned that he'd seen no problems in treating BCs with milbemycin or selamectin meds as a HW preventative.

I am very interested in AK Dog Doc's opinion as a veterinary specialist. I did some of my own research and was also advised by my own vet to avoid the use of ivermectin. So we do.

You're right, the dosage in the HW preventatives is very low and a lot of folks use the ivermectin without any problems. However, Stafford's post asked [quote]. . . if there are any special caveats for BCs and heartworm preventatives. Any brands/formulations to avoid? Any that are better/cheaper/what not?[/quote]There may not be a big problem with using it, but there have been some incidences. Both products cost about the same. So, Stafford and the vet can decide what prevention, if any, they want to use.

[url="http://www.bcrescue.org/ivermectin.html"]Border Collie Rescue - Ivermectin[/url]

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Julie, I have not personally seen any problems with BCs and Ivermectin (and I should say we don't carry any HWP products that use it, not that we don't use Ivermectin at all.... just that we use it for other things.) My recollection is that the gene that causes Ivermectin sensitivity is not highly represented in BCs; however, if there's a possibility of it, and a safer alternative exists, I generally avoid the risk. For that reason, I can't pull the numbers out of my head (haven't had to know them for too many years, so now I can't recall them anymore.) :rolleyes: Maybe Mark remembers, though...?

[quote]My reading of AK Dog Doc's post was that he was in favor of prevention[/quote]- "She". :D (Not that it matters on the 'net, really, and it's not a mistake likely to be made in person....)

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My apologies, Doc! It's hard to be gender correct on a bulletin board and as I am new, I don't know much about any of the folks who post. (My vet is a "she" also.)

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This issue comes up frequently on these boards. I'm posting a previous reply (by me):

Important points to remember

1) The normal dose of ivermectin used for prevention of heartworm in products such as Heartguard (6 micrograms/kg) is not documented to cause the toxicity associated with this mrd1 mutation in collies or any other dog. It is only when higher doses are used, often by people mistakenly thinking the cattle/sheep dose is appropriate for dogs, that toxic symptoms appear in susceptible dogs.

2) Any of the avermectins, the class of chemicals ivermectin belongs to, are capable of producing the same toxicity in affected dogs when used at high doses. The commonly held belief that heartworm preventives such as Interceptor are safer than Heartguard is incorrect. Both products are safe at the low dose used. However, there are confirmed reports that moxidectin, which is used in the six month injectable for heartworm prevention, has caused neurotoxicosis in susceptible collies.

3) Any breed of dog can suffer from toxicity and death from ivermectin and the related class of drugs if they consume high enough levels to penetrate the blood-brain barrier. Levels of ivermectin shown to cause toxicity in beagles, a breed that does not have the mdr1 mutation are 2.5 - 40 mg/kg which is greater than 200 times the therapeutic dose.

Special considerations for farm dogs

An important consideration not everyone is aware of is that farm dogs often consume ivermectin or other avermectins in the manure from recently treated stock. Merck reports an apparent half-life for ivermectin of 1-1.5 weeks in sheep manure from sheep wormed with the standard drench dose of 200 micrograms/kg. They also estimate typical soil incorporation rates for manure from treated sheep to range from 0.16 ppb to 5.1 ppb. (From [url="http://www.fda.gov/cvm/FOI/131-392FONSI.pdf"]http://www.fda.gov/cvm/FOI/131-392FONSI.pdf[/url] ) Therefore, it?s possible for collies and other breeds known to have the mdr1 mutation to consume a toxic dose of ivermectin from eating the manure of recently wormed stock. The timing of worming stock with avermectins should also be taken into account when giving farm dogs heartworm preventative to prevent accidental overdose.

Partial list of drugs known or suspected to cause problems in dogs with the mdr-1 mutation

Ivermectin (antiparasitic agent)
Loperamide (Imodium?; over-the-counter antidiarrheal agent)
Doxorubicin (anticancer agent)
Vincristine (anticancer agent)
Vinblastine (anticancer agent)
Cyclosporin A (immunosuppressive agent)
Digoxin (heart drug)
Acepromazine (tranquilizer)
Butorphanol (pain control)

Partial list of drugs thought to have the potential to cause problems with the mdr-1 mutation

Ondansetron
Domperidone
Paclitaxel
Mitoxantrone
Etoposide
Rifampicin
Quinidine
Morphine

Reference: Neff, et al, 2004


As far as the internet reports on cases of ivermectin sensitivity in border collies, as I said, I contacted the people who do the gene test and they said no border collies had been confirmed to have the mutation. I asked specifically about the unconfirmed reports and they are still unconfirmed. The number of border collies that've had the test is now over 300.

C Denise Wall, PhD

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Thanks Denise.

Here's a little more detail on Denise's point #2.

[quote]So-called "ivermectin" sensitivity is actually sensitivity to a broad class of compounds due to a basic defect in the blood-brain barrier. Normal dogs are protected from acute and often fatal neurotoxicoses when these compounds are administered as pharmaceuticals (including ivermectin) by P-glycoprotein, an ATP-dependent drug transporter that moves a broad spectrum of substrates across several tissue borders throughout the body. The normal gene encoding for P-glycoprotein is MDR1.

Anti-helminthic pharameuticals that are P-glycoprotein substrates include the family of compounds known as macrocyclic lactones. These compounds exert their anti-helminthic properties by causing neurotoxicosis in a number of invertebrates (including helminths and arthropods) by potentiating ligand-gated chloride ion channels in the peripheral nervous system. Generations of macrocyclic lactones known as avermectins have been developed for veterinary use, decreasing their toxic side effects to normal animals (without the mdr1-1Δ mutation).

These compounds include: ivermectin (HeartGard), milbemycin oxime (Interceptor and Sentinel), moxidectin (Proheart), selamectin (Revolution), and doramectin (Decomax).

Given the mechanism for toxcity, there is no reason to consider milbemycin oxime safer for dogs with the mdr1-1Δ mutation than ivermectin. The monthly oral dose of both ivermectin and milbemycin oxime has been administered for heartworm prophylaxis to Collies homozygous for mdr1-1Δ without incident and both have been shown to have similar pharmaceutical margins of safety in sensitive Collies (Tranquilli et al. 1991). (source [url="http://www.awca.net/drug.htm"]American Working Collie Association[/url])[/quote]Mark

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If you'd like to read more on the mutation here is the link to the scientific study on the multidrug sensitivity mutation in various breeds.
[url="http://www.pnas.org/cgi/reprint/101/32/11725"]Breed distribution and history of canine mdr1-1 delta, a pharmacogenetic mutation that marks the emergence of breeds from the collie lineage[/url]

A group at the Washington State University Vet school was part of the study and this is a link to their webpage.
[url="http://www.vetmed.wsu.edu/depts-vcpl/index.asp"]Multidrug Sensitivity (e.g. ivermectin)[/url]

If you would like to get you dog tested for this mutation, WSU is performing the DNA test and this is a link to that information.
[url="http://www.vetmed.wsu.edu/depts-vcpl/test.asp"]Testing your dog for the mutation[/url]

Mark

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Thanks for all the info, folks. This is a good community.

While most of our travel for flyball, agility, and herding has been northward to Washington and in the future British Columbia, it's quite conceivable that we could head south.

Provided that she tests negative for heartworms, I'm inclined to start her on preventative.

We guesstimate that Grace turns a very healthy two years old this month. We plan on keeping her healthy...

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[quote]Originally posted by Stafford:
[b]...While most of our travel for flyball, agility, and herding has been northward to Washington and in the future British Columbia, it's quite conceivable that we could head south.
[/b][/quote]Are you coming up in February for the Flying Squad tourney in Abbotsford?

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We have a very bad problem with heartworm in Hawaii and I have had both my dogs on preventitive since day 1. They also get tested every year just in case.

Many, many of the shelter dogs die from it because there isn't enough money to treat it or it's gone on for too long.

When we rescued Buddy at 22 months he had not been on preventitive at all. He was on Heartguard for about a year, then we switched to Interceptor because it also prevents certain worms (which we have a lot of here as well.)

I'm not one for drugging my dogs at every chance, but I think it's best to do what you can if there is any risk you could get it. Some folks only use preventitve during the mosquito season (on the mainland - every season is mosquito season here!) so that may be an option. You'd have to ask your vet.

D

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For what it's worth, here's the way it was explained to me when I lived in the Seattle area, and it's not a matter of whether heartworm is in the area or "moving that way" -- but a matter of whether or not it can threaten your dog. I was told that in order to infect a dog, the heartworm must go through a developmental stage within the mosquito, and it can only do that if the temperature NEVER drops below 67 degrees for 2 weeks straight; and since that is never the case west of the Cascades, heartworm was not something I needed to worry about in that area.

I would of course want to know if this information is not accurate, as I'm sure everyone would. But I think this is also why many don't worry as much about heartworm during winter.

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Kristi - probably not going to make it up to BC in February. Seems to be a busy time for the team members in other activities. We'll make it up there sometime this season though, I'm pretty confident.

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PairDogx1.5, that's why we don't have heartworm in AK (though I generally tell people 70 degrees or greater, 24/7, for 2 weeks in a row. Doesn't happen up here either). Two of the larval instars take place in the mosquito's mouth parts; the L5 (if I recall correctly) is the infective stage, and without the mosquito, the worm can't make it to the L5 stage.

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Okay, now I have a question. Does the DOG need to be someplace 24/7 for two weeks while the temp stays over 70 deg to get infected, or does the dog just need to visit someplace, say for a couple of days, where is has been over 70 deg 24/7 for the two preceeding weeks to get infected?

My dog lives in Alaska (yay), but we are forever jetting off to the lower 48 for meetings or to go backpacking, generally for stays of two weeks or less. So do I need to worry about heartworm?

Many, many thanks to AK dog doc for reappearing in our midst! I'm sure you know how much we appreciate you, but I just wanted to say so anyway

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Thanks, Alaska!

To answer you question, no, the dog does NOT have to be in 70+ temps 24/7 to be at risk. That refers to the conditions applying to the MOSQUITO. Technically, if your dog went to a heartworm-positive state and was there for 5 seconds, and a heartworm-bearing mosquito with mature L5's bit your dog, your dog would then be growing heartworms - even if the dog immediately hopped a plane back to cooler weather. Six months down the road they'd be adult worms, living in your dog's heart, and producing baby heartworms of their own. However, if your dog had returned to cooler climes after the exposure, those worms would NOT transmit to other dogs, because it would be too cold for them ot develop to L5's in the mosquito. So, despite our - um - "vigorous" mosquito population up here, we're safe so long as we stay here - unless the worm mutates to handle cold temps, and/or global warming takes a rapid turn for the worse. Knock on wood that neither of these things should occur.

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For the record... when heartworm was first a problem in my area - about 20 years ago - I was advised to use the ivomec sheep drench - about 1cc for a 50 to 60 pound dog. This was done monthly for the 6 warmest months. I have had collies and border collies and many friends with these breeds also, and we have had no fears of having problems at that dose. It is criminal to have to pay 100 times more for a pill with the measurements made, and packaging. I have since moved to a slightly cooler area, and we do no preventative. Many around this area are the same and don`t give preventative because we don`t seem to have reports of positive cases (as long as we stay home). Now a stray mosquito on travels could be a problem.

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