How Long Does It Take To Develop Heartworms?

[Guest CleverJason]

Well, I'd better get to posting then, Gryffenne! I have scheduled a heartworm test and general checkup for Baron, and he's going to be back on meds as soon as the results come in. We'll get the shots if we can, if not we'll go back next month.

[3greytjoys]

Other preventatives may be different, but my understanding (from Merial mfg. again today) relating to their Heartgard preventative is that their product effectively kills heartworm larvae (stages L₃ and L₄) in the subcutaneous tissue only.

It is not able to kill heartworm larvae (or adult heartworms) circulating deeper within the bloodstream of a heartworm positive dog. Therefore, if left untreated, heartworm positive dogs could continue to spread heartworms via mosquitoes, even while on Heartgard.

The following is just a guess: Since non-treated adult heartworms actively mate and give birth deeply within the dog's body, I wonder if that contributes to all life stages of the deeper circulating worm burden that may be considered too difficult to kill with a preventative. That might also contribute to a heartworm positive dog continuing to spread the disease via mosquitoes.

Just wanted to add that our previous dogs (indoor only) were on preventative meds. during the warm seasons, but were heartworm infected during a cold winter season (lows in the teens/twenties). Tough, hungry mosquitoes developed ways to overwinter successfully, even in heavier snow regions. Now, year-round heartworm preventative is recommended nationwide, even in places like frigid MN.

CleverJason: Thank you for posting your original excellent question. It's a good opportunity for us to refresh and continue learning as heartworm disease and treatments evolve. Also, a great reminder that preventative meds. are much cheaper and easier to administer vs. facing heartworm disease in our beloved dogs.

Edited June 26, 2014 by 3greytjoys

[JJNg]

Merial is probably not going to comment on how effective Heartgard is at clearing microfilaria because it's not an FDA-approved label claim. There are some older studies that looked at the effect of monthly preventative doses of ivermectin (Heartgard) and milbemycin (Interceptor) on microfilaria (the term microfilaria actually specifically refers to L₁ larva). With both products, most dogs were cleared of microfilaria after 6-8 months, although some took as long as 10-12 months. There were also a smaller number of dogs that still had some circulating microfilaria after being on either preventative, and there is some concern about those being a source of resistant heartworms. This is why "slow kill" with Heartgard alone is no longer recommended as a treatment option. However, when you add doxycycline to the protocol, studies have shown that when the Wolbachia bacteria are eliminated, the microfilaria are no longer infective, so resistance is less of a concern.

[3greytjoys]

JJNG: Thank you for elaborating re: the non-FDA approved label use, plus doxycycline to help control the young microfilaria.

[CharlieRhea]

I agree about the possibility of counterfeit products online. Years ago i ordered Frontline and although my dogs had no problem i won't do that again. I read after the fact that some online meds come from China so i'd never risk it.

 

I have two Vets, one close and one a distance away who is homeopathic and traditional. They suggest every 45 days and that's what i have done for years. My closer vet sells it one at a time or 6 packs, however you want. Don't skimp CleverJason, 30 yrs ago i skipped a couple months of heartguard, i was young and ignorant about how prevalent heartworm was even then. My Afghan got heartworm but luckily came through with arsenic, that's what they used then. So please always get your dog tested once a year and give the heartguard, i'm sure you will.

 

d. There is so much crap/counterfeit products being sold online it's scary. Remember old ole saying--you get what you pay for??? I understand budgets--believe you me but, cutting corners on medications--wouldn't recommend it-esp when giving heartworm preventive. Some folks will say that they never experienced any woes from online medication purchased but, do you really know if they are doing as they say?? I will admit-I'm terrible about applying flea and tick products on my own dogs--I haven't see a tick or flea on any of my dogs in years (hope I'm not jinxing myself)---but, someone could say the same thing after applying online frontline--of course they would say it's working --a great buy--but, is it really working or have you just been lucky like me??
Ok-hopping off of soapbox now :-)