One of the more common deadly diseases of dogs is heartworm disease, which can be prevented. Heartworm disease is also possible in cats, but can occur in cats with about the frequency of winning the lottery.
The adult worms live inside the dog’s heart. They will cause heart disease, including failure of the valves to close completely, and taking up so much space in the heart that congestive heart failure results, but also they’ll drift into the lungs, where they may cause respiratory disorders. The adult worms produce microscopic larvae (babies) called microfilaria. These circulate in the dog’s bloodstream and can also cause organ damage.
The disease is transmitted by mosquitos. If a mosquito bites a microfilaria-positive dog, it will ingest some of these microfilaria along with a blood meal. When the mosquito bites the next dog, it injects some of these infective larvae into the dog’s blood stream. They will migrate to the heart and grow into adult heartworms, and the cycle begins again.
Heartworm prevention is very, very good. But, even under direct challenge in laboratory conditions, there are failures. (Perhaps as many as 1-2% of test dogs ON HEARTWORM PREVENTION injected with microfilarii still get heartworm disease.) Knowing that the prevention is not 100% effective, manufacturers usually offer (except generic and online products) to pay for treatment if a dog receiving heartworm prevention gets the disease anyway.
Heartworm disease is a treatable disease, however the treatment carries risks, mostly due to the tissue damage and organ damage already present in the dog. Delayed treatment may result in heart failure and/or permanent damage to the liver, lungs, and kidneys – possibly causing eventual death. Unfortunately, the signs of heartworm disease, such as coughing, lethargy, and weight loss occur after the disease process is well underway, perhaps as many as three years after the dog becomes infected. In my practice, signs seem to show up in the second year of infection and look like congestive heart failure and a non productive cough.
It is therefore important to have your dog’s blood tested yearly. The earlier this disease is detected, the greater the chances are of your dog surviving the treatment. Also, some infected dogs will have reactions if given the preventative while carrying the disease, which can be fatal, and this would be prevented by checking for the presence of adult worms. There are two basic preventive programs provided by our clinic. Your choice between the two types depends on what program is more practical and convenient for you.
- Monthly pill/chewable
Our office does not recommend or endorse Revolution, or any of the cheap knock-off heartworm preventatives being made available these days. There are two now, that are supposed to give me “wider profit margins” to quote the drug-representative, however I do not trust the products. Nor do they present ANY warranty of fitness. They’re selling on price, not quality or reliability. No, not for MY clients.
In the Southeastern United States, I recommend that medication be given all year long since our mosquito season is variable. Also, stopping in the Fall permits maturation of the last mosquito’s microfilarial inoculation.
Basic Facts on Heartworm Disease
1. It’s treatable
2. It’s preventable
3. It’s carried by Mosquitoes
4. Costs less than 100$ per year to prevent
5. Costs over 600$ to treat
6. Usually fatal within 3 years of contraction.
Starting the preventative before the pups are 6 months old saves you the expense of a heartworm test before starting the preventative. Then a test each year will ensure that no adults are surviving the medication.
Dr Erik Johnson
