Understating how heartworm disease manifests and exploring an alternative in prevention.
Contrary to what we've been told or led to believe, heartworm "preventatives" do not actually prevent infection. They kill the heartworm larvae & microfilariae of an already infected animal and like all medications, come with documented adverse effects.
In better understanding how heartworm disease actually manifests, you'll be provided an informed position when deciding how to approach prevention for your pet.
Here we dive into the heartworm life (and infection) cycle, as well things to consider when testing for heartworms.
Heartworm Life Stages
Before we jump into how heart worm disease manifests, let’s tackle an important detail; the difference between heart worm microfilariae and larvae.
People (and even some vets) often mix up these terms, but they’re not interchangeable. Microfilariae and larvae are both young heartworms, just at different stages of their development. To clarify the differences:
Microfilariae are the heartworm babies.
Larvae are the "toddlers" that grow up from those babies.
When adult heartworms breed inside an animal, they produce microfilariae.
Keep this difference in mind as we discuss how mosquitoes transmit heartworms to your dog. Here’s the sequence of events:
How Heartworm is Transferred:
For starters, Dogs can’t “catch” heart worms from other dogs, mammals, or even from the dog park lawns! And let’s clear up another misconception—puppies can’t “catch” heartworms from their mothers. The bottom line is this: the ONLY way your dog can get heartworms is through a mosquito bite and the below details all of the necessary conditions in order to be infected.
Step 1:
To infect a dog with heartworms a specific FEMALE mosquito of the RIGHT SPECIES is required. There are actually more species of mosquitoes than there are dog breeds: we’re talking about around 3,500 different mosquito species worldwide compared to just about 200 dog breeds. [3] Field studies have identified over 20 species of mosquitoes that can carry the infectious stage of heartworm larvae. [2] Of over 3,500 different mosquito species, ONLY about 20 can incubate and carry heartworm.
Step 2:
In order to transfer heartworm, that specific female mosquito needs to bite a dog and draws blood from a dog that's already infected with mature MALE & FEMALE heartworms that have produced those baby heartworms (microfilariae). Ten to fourteen days later — if the temperature is right (more on those details below), the microfilariae mature inside the mosquito to the infectious larvae stage then the female mosquito transmits the larvae into a dog’s bloodstream with a bite.
Step 3:
If all conditions are right, the larvae develop over the next three to four months to become young adult worms. It takes about six months for those surviving larvae to grow up and reach maturity. At this point, the adult heartworms can start producing babies—but only if there are both males and females present. If the infected animal only has one sex of heartworm, those adults will live several years and then die off without reproducing.
[NOTE: If that same animal gets infected with larvae again the following hot season and now has both sexes, they can start creating microfilariae. This then could lead to more breeding and result in your dog developing heartworm disease.]
Step 4:
This most overlooked fact is a game changer, especially because of where I live, and it could significantly influence your choices moving forward in caring for your pets.
"Laboratory studies show that maturation of the heartworm requires the equivalent of a steady 24-hour daily temperature in excess of 64°F for approximately one month.
In other words, it has to be warm day AND night or development is retarded, even if the average temperature is sufficiently warm. Furthermore, the studies indicated , that 10-14 days of a temperature at/above 80°F, is required for development of microfilariae to the infectious stage.
If the mean monthly temperature is only a few degrees above, 57˚F it can take many more days for infectious larvae to develop that the likelihood of the female mosquito living that long is remote". [3]
The Immune System:
Lastly, heartworms only develop into adulthood if a dog’s immune system doesn’t manage to get rid of them. When a dog's immune system is functioning at its best, it's designed to eliminate those larvae if exposed. This brings us back to an important question: how is your dog's terrain? If your pup is eating a raw dog food diet, soaking up ample sunlight, enjoying grounding walks and hikes, and minimizing exposure to blue light, their immune system can handle that exposure.
In summary, there are a lot of conditions that are required to become susceptible to heart worm disease from a mosquito. But what exactly is the disease that proliferates from a heartworm infection?
What Is Heartworm Disease?
Heartworm disease is no joke; it's a serious and potentially fatal condition that impacts pets across the United States and many other parts of the world. The disease is caused by these foot-long worms that settle in the heart, lungs, and blood vessels of our furry friends. The consequences? Severe lung disease, heart failure, and damage to other vital organs. [1]
While heartworm disease can affect dogs, cats, and ferrets, heart worms aren’t picky; they also hang out in other mammals like wolves, coyotes, foxes, sea lions, and—on rare occasions—humans! Because wild animals like foxes and coyotes often roam near urban areas, they play a role in spreading this disease. [1]
Signs Of Canine Heartworm Disease
In the early stages of heartworm disease, many dogs may not show any symptoms at all—or just a few subtle ones. But as the infection lingers, the chances of symptoms surfacing increase.
Active dogs, those with heavy heartworm infestations, or pets with other health issues often display more noticeable clinical signs, which can include a mild, persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As the disease progresses, it can take a serious turn: pets may develop heart failure and even a swollen belly due to excess fluid in the abdomen.
For dogs with a significant number of heartworms, there’s a real risk of sudden blockages in blood flow within the heart, leading to a life-threatening condition known as caval syndrome. This alarming situation is marked by labored breathing, pale gums, and dark, bloody, or coffee-colored urine. Without immediate surgical removal of the heartworm blockage, survival rates take a nosedive.
The real key to avoiding this dangerous situation is with early testing.
Heartworm Tests Explained:
Catching a heartworm infection early on is the key to significantly improving your pet’s chances of recovery. Unfortunately, there are often few, if any, early signs when your dog is infected with heartworms, making it crucial to get a heartworm test administered by your veterinarian on a yearly or more often basis. There are 3 different types of heartworm tests.
1) Antigen Test
The standard test your vet uses is the antigen test, but it's not without its limitations. Here’s what you need to know:
First off, this test can only identify adult female heartworms. That’s why your vet mentions it takes about six months for heart worms to show up on testing. While heart worm antigens can be present in the blood within five months, most dogs won’t show any antigens until around seven months after infection.
Additionally, these tests might miss a low worm burden. If your dog has only one or two female worms, the test can have a false negative rate of 30-40%. Some dogs may not show any antibodies at all due to “antigen-antibody complexes” in the blood.
This is precisely why your vet may also recommend a microfilariae test to get a clearer picture of your pup's heart worm status.
2) Microfilariae Test
The microfilariae test is designed to check for microfilariae in your dog’s system. And guess what? Official recommendations have changed! In the past, vets would only perform this test if the antigen test came back positive or weakly positive.
Now, the American Heartworm Society (AHS) recommends doing the microfilariae test annually. This proactive approach helps avoid false negatives on the antigen test. If your pup tests positive for microfilariae, it confirms that there are mature heart worms in your dog—and they’re breeding!
These two tests are likely what your vet is familiar with, but there’s actually a little-known third type of test worth exploring.
3) DNA Heart Worm Test
The DNA heart worm test uses advanced PCR (polymerase chain reaction) technology to detect heart worm DNA in your dog’s blood. If you're looking to get this test done, check out HealthGene in Canada. Specifically, you'll want the D319 Canine Heart worm (Dirofilaria immitis) test, which you can find on their website.
What’s great about this test is that it identifies heartworms at all stages of their lifecycle, meaning it can show microfilariae, larvae, and adult heartworms, as opposed to the 6 month period that is required for detection of adult worms. However, you’ll need your vet’s assistance because HealthGene won’t work directly with pet owners. Your vet can order the test kits through HealthGene and then send the sample off to Canada. [4]
The DNA Test by HealthGene—if you can get your vet on board to help you with it--may be worth the extra time and expense depending on where you live and/or your pet's current health status.
This test is more useful because it identifies larvae in your dog’s blood! When an infected mosquito bites your dog, it transmits larvae, which take about 6-7 months to grow into adults. Detecting the larvae instead of adult heartworms makes the infection much easier to treat.
If this test proves to be too challenging (or pricey), or if you can’t find a vet willing to help, the next best thing is the standard antigen test your vet offers. Just keep in mind that you’ll need to do it more frequently than once a year.
Testing: An Alternative For Disease Prevention
Your vet might tell you that there’s no need to test more often than once a year, and that’s mainly because they know the test won’t come back positive until 6 or 7 months after infection. So, they typically test in the spring before prescribing heartworm medications for the upcoming season.
But wouldn’t it be better to know if your dog is positive sooner rather than later? Your vet waits until several months after the end of mosquito season, but if peak mosquito season in your area is during the summer months (June through August), your dog could test positive as early as December or January.
By testing your dog for heartworm more frequently, you'll be able to catch an infection sooner. If your pet happens to get infected in June, it's possible to detect those adult worms as early as January. The sooner you find out about the worms, the easier it is to treat them. This means you can start addressing the issue at an earlier stage!
So, why not think about scheduling heartworm tests for your pets in both January and June? Or even February and July? Don’t let your vet’s reluctance deter you! During those months when mosquitoes are buzzing around and annoying us all, you can use natural supportive products to help keep your furry friend protected. This proactive approach can truly make a world of difference in your dog’s health!
In Summary
With a solid understanding of how heartworm disease manifests, I don't personally administer heartworm drugs due to the toxic ingredients that they contain (we'll cover more on this next week) and that this may actually increase my dogs' chances of getting heartworm disease and other parasites.
Instead, my approach to prevention is regular testing, as it allows you to identify infections earlier, as well as natural repellents (coming in next week's blog) which in combination gives you the best path towards a healthy, happy disease-free pup!
Ultimately, your pup’s health is what matters most, and being informed is the first step toward making the best choices for them.
Consider Adding Everwell Pets To Your Team!
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Citations
If you’d like a visual aid to explain the process, the American Heartworm Society has quite a good diagram.
You can find a holistic veterinarian who uses western herbs in their practice. Search at ahvma.org and select Western Herbs as the Modality.
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