FACT: Heartworm infection is NOT rapid and will not kill your dog overnight
It takes about three months for microfilaria (baby worms) to grow inside your dog to a larval stage, and even longer for these larva to mature into adult heartworms. If your dog is dosed with a simple Ivermectin treatment at any time during this period before adult worms are present (a period that lasts about three months long), the larvae will never develop into adult worms, and will die.
Read that statement again: a SINGLE dose of Ivermectin (the main ingredient in HeartGard and similar products) will stop heartworm dead up to 3 months after your dog is first infected.
FACT: There is no "preventive" medicine for Heartworm
Despite what your veterinarian may have told you, there is NO "prevention" for heartworm infection; there is only heartworm treatment. ALL heartworm medicines work the same way -- they kill heartworm microfilaria present in the body of the dog.
FACT: You do NOT need a prescription for Heartworm "preventives" nor are tests "required (by law)"
Many vets let you believe that you NEED a prescription for HeartGard or Sentinel or any of the other brands and attach a "required" and usually pricey blood test to the scenario as well. Since the word "required" automatically draws the assumption that it is required by law, many folks don't even bother to ask what the test is really for. If they do the vet most likely will target your conscience as a "good dog owner" and attempts to make you feel bad by simply doubting a simple test to assure your dog's health.
UNLESS your dog is an older dog loaded with years of untreated heartworm (which you will know from the dog's long-term lethargy and chronic coughing), a dose of Ivermectin (the main ingredient in HeartGard and similar products) will not do your dog harm. (More about curing heartworm infection below)
A puppy, under six months of age, of course, will always test negative for heartworm because the microfilaria have not yet had a chance to develop and circulate. Testing a dog under age 6 months for heartworm is a common veterinary scam; do not fall for it!
Logic dicates to test your dog on regular basis and only administer Ivermectin once a test is positive. If you treat your dog monthly anyway, why test at all? There is no reason..
Prescription: It's not necessarily a bad thing to go to a vet for a prescription for Heartgard, especially if you are going to see your vet on another matter anyway, but it is NOT NEEDED. Most vets price-gouge their customers by 100% or more for medicines sold in their offices. In most states a veterinarian cannot charge you more for writing a prescription for a medically necessary medicine as part of an incidental visit, but many do it anyways..
FACT: Humans cannot get heartworm.
Yes, I have heard it before: "I need to get my dog tested first, because a heartworm positive dog can be contagious to my children!"
Let me assure you: Heartworm cannot be passed on to humans -- we are the wrong host animal. Very rarely a heartworm-positive mosquito will bite a human and a small benign cyst may develop in the lung of a human, but this is NOT heartworm, and can be best thought of as a tiny scar showing where a bit of microfilaria attached to the lung wall where it was killed off by the human body.
FACT: Some breeds are more sensitive to Ivermectin
Some lines of collies and collie-crosses have sometimes fatal reactions to ivermectin, the most common heartworm preventative medicine. Though this is not common, and is even rarer today with low-dose Ivermectin such as Heartgard, and seems to only hold true for collies, serious thought needed to be given to dosing any collie, collie-cross, or herding dog with white feet.
For these dogs, the safest heartworm medicine is Interceptor, though in fact the Heartgard box features a Border Collie on it face, and many working Border Collie folks dose their own dogs with a low dose of sheep drench 0.08% Ivermectin.
FACT: You can order Ivermectin online or purchase it at your local feedstore
Remember that, depending on outside temperature, you do not have to dose your dog all year long in large parts of the U.S.
Of course, if you want to dose your dog every month and do so cheaply and without going to a veterinarian for a prescription, there are other ways for a fraction of the price.
I personally use the horse dewormer paste containing Ivermectin 1.87% (the exact same ingredient as HeartGard). A tube is usually for a 1200 lbs horse, so you have to do the math! If your dog lets say weighs 120 lbs, you give him a tenth of the tube once a month.
I rescued a heartworm positive Labrador years ago. I paid less than $5 for the horse dewormer and with the correct dosage she was heartworm negative within 10 months.
FACT: Curing heartworm is neither expensive nor difficult
Any veterinarian who tells you otherwise is not telling you the truth. It turns out that even if your dog has adult heartworms, if the dog otherwise appears healthy (i.e. it is active, not lethargic, and does not have a chronic cough), a monthly dosing of Ivermectin at a dosage normally used to kill roundworms (a dosage that is 3 times higher than that used to simply prevent heartworm), plus a once-a-month 5-day dosing of Doxycycline (sold as Bird Biotic, and the same antibiotic used to treat Lyme disease) will kill all the adult heartworms if it is sustained for a period of 18 months.
Many vets try to tell you that heartworm treatment requires arsenic-based injections to kill the heartworms living in a dog’s lungs and heart.This treatment is expensive (up to $1,000 and often more, depending on the vet) and can be traumatic and risky. It is heartbreaking to watch a dog suffer through this agony of arsenic in the bloodstream knowing it's not necessary whatsoever.
This treatment works better than previous Ivermectin-only treatments because the Doxycline wipes out the Wolbachia microbe that grow in the gut of the adult heartworm, essentially sterilizing all of the female heartworms. A round-worm strength dosing of monthly Ivermectin will not only prevent new heartworm microfilaria from taking hold in your dog, it will also work to dramatically shorten the life of any existing adult worms in your dog. Bottom line: after 18 months of treatment, your dog will be heartworm-free at very little cost compared to other remedies.
A repeated caution, however: if you have border collies or herding dogs with white feet that also appear to have full-blown heartworm, consult a veterinarian, as some lines of collies are very susceptible to Ivermectin toxicity. This is very rare, and the cause is unknown, but it is an area of concern among collies and collie-crosses.
From a vet tech: HW preventative is part of the cure for a full blown case of heartworms, yes there is no full on preventative, just like there is no 'preventative' dewormer. You either deworm an animal or you don't.
For those who may not know, ivermectin works by killing the microfilaria present in the blood stream, preventing them from attaching themselves inside the dog's major vessels and heart and completing the life cycle. Heartguard has been added to the protocol for treatment of patent cases of heartworm infection, as the thinking is that killing off the microfilaria first, before killing off the adult heartworms, is much easier on the dog.
The reason I DO think you should have your dog tested for heartworms before beginning a preventative regimine is because ivermectin won't kill off the adult worms, and you probably want to know if your dog has adult worms in his lungs or heart. Eventually, they will die off and can potentially create issues with pulmonary embolism, or embolism elsewhere in the body.
But, I definitely think requiring testing every year before allowing an owner to have heartworm preventative is overkill. The reason we usually give is that if for some reason your dog winds up HW positive while on preventative, the company will pay for the HW treatment for your dog, but if you refuse the test, the company won't do squat.
And some animal hospitals offer free HW testing during summer months, as well as including it as part of your yearly vax package. Another reason is the snap test most places use for HW testing also tests for at least two other tick borne diseases, such as Lymes, Anaplasmosis, and Erlichiosis. All three of those are something you definitely want to know if your dog friend is suffering from.