Wormsheild from Banfield

[Mark Billadeau]

Here is an abstract from JW McCall that describes the well established method for infecting dogs with HW and then testing preventatives.

 

Evaluation of ivermectin and milbemycin oxime efficacy against Dirofilaria immitis infections of three and four months' duration in dogs.

 

The important part is the dose used to create the infection.

 

Each of 21 dogs was given 50 infective larvae of Dirofilaria immitis by SC inoculation.

 

The study linked by Maralynn (What's new and what we thought we knew about canine heartworm slides 20 & 21) theorizes that the L3 exposure/month could range from 288 to 10,000. This would support the hypothesis that the minimum effective dose may not be effective with the current levels of exposure in some regions. A hypothesis that could be tested.

[Mark Billadeau]

Here is an early study on minimum effective dose of ivermectin where about 100 infective larvae were used.

 

Jpn J. Sci 49, 115-120, 1987

[Debbie Meier]

Reading the past posts reminds me why we never rely solely on the monthly preventative. I guess we have used it as the line of defense in case the dog becomes infected. I think that we lean more on mosquito control and utilizing repellents when the dogs are in areas where the mosquito population is high and doing things around the farm/house to keep the mosquitos at bay both for us and the dogs. Never really thought of our dogs as being "safe" when on preventative.

 

Deb

[diane allen]

Curiously...within the hour that I posted my question, I got my current issue of Whole Dog Journal, and an article there explained the shortage issue. I still do not understand why the CHEWABLE is still available...unless they just have a larger supply of it on hand most of the time. I totally understand "rationing" what they have left for dogs who have been infected. But it sounds like this will continue through 2010 at a minimum. Guess I'll look into something else (though I too don't totally believe 100% protection...nor, as much as I would like to, believe in any "natural" preventative....).

Thanks, Mary.

 

diane

[timberviewfarm]

I would just like to reiterate that while people may "buy" 12 doeses the 12 doses do not always make it through the dogs system. As my vet explained to me when I had a dog who had to be treated for heartworms, there are many ways a dog can avoid their heartworm meds, I.e. throwing it up within an hour, getting it stuck in throat and coughing it back up, spitting parts of it out, etc....how many of us really sit with our dogs for a few hours and watch them like hawks after giving them their heartworm meds? Even I, the queen of OCD behavior, can't say that I watch them closely enough!

 

For as long as I can remember (at least 15 years), heartworm companies have covered the cost of heartworm treatment if you purchase your heartworm meds from a vet every month. They didn't used to cover the treatment if you ordered treatments online or purchased from more than one vet.

[PennyT]

My vet said most of what he told me comes from other vets on the vetinfo website board. I don't have access to that board because it is subscription based. Someone here is bound to have access.

 

He also mentioned the annual HW Society symposium is being held this weekend in Memphis and that when he gets a run down on the presentations he will let me know the gist.

 

Penny

[AK dog doc]

My vet said most of what he told me comes from other vets on the vetinfo website board. I don't have access to that board because it is subscription based. Someone here is bound to have access.

 

He also mentioned the annual HW Society symposium is being held this weekend in Memphis and that when he gets a run down on the presentations he will let me know the gist.

 

Penny

 

Well, I have access to one such professional board. AK is not a big HW area (lowest incidence in the U.S.), so it's less of an issue for us (although I have treated 2 HW positive dogs in the last year, and another doc at our clinic has treated one.) In ALL of the above cases, the infestations occurred in dogs who were NOT on appropriate HW prevantative. One was a stray found by clients who were vacationing in AR; the other two were compliance failures. I don't have followup on all of them as not all of them are my own patients, but where I do have followup, treatment has been effective (as in, patient doing well, with no further evidence of infestation.)

 

There are a couple of threads about "resistance" of heartworms, both to preventatives and to treatment in HW positive dogs... but if you read the threads in question, it is NOT clear that there is resistance actually occurring. There are several issues being brought up, including compliance failures in dosing the prophylactics, differences between various treatment protocols for adult HW, differences in type of testing used to determine if the dog is HW positive, differences in the FDA reporting guidelines since 2003, and the fact that exposure may be significantly different recently than it has been in the past (in part due to the number of hurricanes and the resultant shift in mosquito populations and associated epidemiology.) What that indicates to me - and several of the boarded experts responding to the thread - is that more reporting is going on, which may be part of the PERCEIVED increase in cases; and that patient exposure to HW is different (and increased) in recent years, in effect "overburdening" the meds as normally given in the standard protocol. This is not proof of "superworms" that are resistant to the meds (to prove that, specific studies would have to be done; in one thread on HW, a study was said to be underway at Auburn, but no results were posted, and it will probably be another year before publication).

 

One point to bear in mind: If you have a drug that is 99% effective, there are ALWAYS going to be the 1%-ers who fail the protocol. Even if the drug is STILL 99% effective, if you have higher exposure rates and parasite burdens (because of a change in mosquito population dynamics), there is going to be a larger total # of animals who are not cleared of the entire parasite burden. This has nothing to do with drug resistance. It has to do with parasite burden and exposure.

 

As a BTW, the threads on this subject are from early to mid-2009 or before. I found nothing in 2010. I will not be attending the sympsium in Memphis (I know! Shocking!) - but I'll be interested to see what the final data are when the dust settles.

[M.L.]

The quotes Mark provided did ansnwer this question. Not all dogs absorb the drug from their GI tract at the same rate. The dogs becoming infected may be absorbing a lower dose. If a dog is sick (ex: diarrhea) the drug may pass through their system too quickly to be absorbed.

 

The last time I gave the HG chewable to the dogs, Bailey threw up the next day and the HG chewable was still a huge chunk in his puke. It was the last one I had so I had to dig it out of his puke, rinse it off and give it back to him. Disgusting, I know.

 

So how long does it take to get absorbed if it sat in his gut for a day? It hadn't softened up at all. Doesn't seem very absorbable.

 

Should I break up the chewable before giving it to the dogs? Would that make a difference?

[Mark Billadeau]

More to the point; if dogs do not chew the chewables and it takes longer to digest whole chewables than chewed chewables (slower and longer adsorption) will the level of HW preventative in the blood stream get high enough to meet the minimum effective dose? I would hope that the drug companies took into account variation in adsorption due to not chewing when they formulated the chewables.

[juliepoudrier]

I agree Mark. Very few of my dogs actually chew chewable meds (the ones that will actually take a chewable); they just swallow them whole. And of course the ones who won't chew a chewable have it put down the hatch by me, so those aren't chewed either.

 

J.

[PennyT]

"I found nothing in 2010. I will not be attending the sympsium in Memphis (I know! Shocking!) - but I'll be interested to see what the final data are when the dust settles."

 

There are a dozen or so too short interviews from the symposium up on You Tube.

 

AK, will you go look on Vetinfo and see if any abstracts of papers or digests of presentations are available?

 

Penny