Nooooo. You're misunderstanding because there's so much false information on the Internet. Heartworm tests are done annually to make sure you haven't had a breakthrough infection (or missed a dose) with a dog kept on monthly prevention.
I work with heartworm-positive dogs constantly in dog rescue. It takes 1 month of missed prevention to get it! ONE!!! The HW meds work retroactively to kill the baby larvae, and there's a small window in which they work before the larvae get too big to kill with prevention. So here's what happens if you wait 4 months to test to see what happens:
Mo. 1 -- infection from a mosquito -- W1 worms start growing
Mo. 2 -- more infection W2 worms start growing
Mo. 3-- more infection W3 worms start growing
Mo. 4 --more infection W4 worms start growing
Test Mo. 4 -- It will test negative. It takes 6-7 months before worms growing in the dog are big enough to produce antigen that the test detects. They're there, just not detectable. So you say "yay, negative," and keep skipping prevention, unaware your dog has them but the tests won't pick them up for a few more months.
We continue getting new worms in months 5-8 -- the class of W5-W8 (Where the number tells us the month it started growing).
Now we retest in month 8, on your proposed program.
Dog has been positive since month 1, but now the W1 and W2 worms are finally old enough to produce antibodies that the test can detect, and now maybe they're even breeding inside your dog. If so, then you have microfilariae circulating in the dog's blood, so you're also infecting all the wild canids (coyotes, foxes) and unprotected pet dogs in your neighborhood, anytime a mosquito bites your dog. Arsenic treatment is unfortunately needed. We also have to put the dog on 30 days of a pretty high dose of antibiotics (!) before we can start HW treatment with the arsenic.
In month 8, W3-W7 aren't yet detectable, but they're in there too. W1-W6 are all now too old to kill with prevention. You've also got some juveniles from W7 worms that aren't big enough to kill with arsenic, but can still be killed with prevention.
Now in mo. 9 or 10, we finally start 2 months of very painful shots that hurt so badly the dog may not be able to stand up the next day after each one. And start crate rest -- the dog can't even be let outside to potty except on leash, as an elevated heartrate could kill the dog. So after blasting the dog with 30 days of antibiotics, we now blast it with arsenic.
So to recap: we've damaged the heart and pulmonary arteries, possibly shortened life span, destroyed gut flora with a long course of abx, injected muscles with arsenic, put the dog through a lot of pain, and subjected it to misery of no exercise or fun for 2 months. Oh, and spent around $1,000. All to avoid a little low-dose heartworm prevention? No way. The chemicals you REALLY want to avoid are the long course of antibiotics and the arsenic needed to treat the HW. That stuff is wicked.
Last edited by Magwart; 10-25-2017 at 10:33 PM.