How Do Dogs Get Heartworms?

Joanne Keenan
how do dogs get heartworms

There’s a lot of misunderstanding about heartworm in dogs … including about how do dogs get heartworms. Your dog can't get heartworms from another dog ... only from a mosquito bite. But a lot of things have to happen before a mosquito bite can transmit heartworms.  

So … how do dogs get heartworms? We'll explain the whole process in this article. First, here are some heartworm basics.

What Is Heartworm In Dogs?

Heartworm in dogs can be a serious and potentially fatal condition. It’s caused by a worm called Dirofilaria immitis. When it’s at the larval stage, it can infect a dog and then mature into adult worms that can continue to grow and reproduce to clog the heart, arteries and lungs. This can block blood flow and cause severe organ damage. 

What Does Heartworm Look Like?

Adult female heartworms can range from 10 to 12 inches in length, while adult males are typically smaller, measuring around 6 to 8 inches. They are thin and thread-like, which allows them to inhabit the heart, lungs and blood vessels of host animals.

Can A Dog Die Of Heartworm?

Untreated heartworm disease can lead to suffering and death. Adult worms multiply and block blood flow, which causes strain on the heart and lungs. Dogs will have symptoms such as coughing, difficulty breathing, fatigue and weight loss. In advanced cases, heart failure, organ damage and death can occur.

How Do Dogs Get Heartworm?

First of all … not all mosquitoes are infected with heartworms. Secondly, even in mosquitoes that are infected, heartworm must be at the larval stage to infect an animal.

Here’s some heartworm biology:

  • Microfilariae and larvae are both young heartworms … but in different stages of development.
  • Microfilariae are heartworm babies
  • Larvae are the next stage of growth ... immature heartworms.  
  • Larvae mature into adult heartworms that reproduce, creating microfilariae.

Here’s what needs to happen for a dog to get heartworm:

  1. The mosquito has to first bite an infected animal ... one that has circulating microfilariae.
  2. A mosquito that bites the infected animal picks up heartworm microfilariae from the animal's bloodstream. 
  3. Once inside the mosquito, the microfilariae grow into larvae over the next 2 months.
  4. A mosquito with heartworm at the larval stage bites your dog … and leaves the larvae in his bloodstream.
  5. In 6-7 months, the larvae grow into adult heartworms in your dog.
  6. Adult heartworms start breeding and produce microfilariae. An adult female heartworm can produce several hundred to over a thousand microfilariae per day.   
  7. If not detected and treated, adult heartworms can grow and block arteries in and around the heart and lungs, and continue to produce offspring microfilariae.

Here’s a diagram from the American Heartworm Society that shows the stages of the heartworm process quite clearly.

How Often Do Dogs Get Heartworm?

Dogs aren't immune from getting heartworm a second time. A dog can be bitten by mosquitoes multiple times … but again, it is only mosquitoes carrying heartworm larvae that can infect a dog.  

The incidence of heartworm depends on geographic location, climate and mosquito prevalence. Dogs living in areas with high mosquito populations and warm climates are more susceptible. 

The American Heartworm Society provides regular maps showing recent incidence of heartworm disease. The southern US states have the highest number of reported cases. But there are many parts of the US that average less than 1 reported case per veterinary clinic annually, with many other areas reporting 5 or less cases per clinic. 

How Do You Detect Heartworm in Dogs?

Veterinarians advise testing annually in spring in colder climates, before mosquito season begins, or semiannually in warmer areas. As explained, it takes 6-7 months for microfilariae to grow into adult heartworms that lead to heartworm infection. If the test is positive, you can begin treatment knowing the infestation is minor. 

You'll see images of worm-engorged hearts used to market preventive drugs … but these images are after long term infestation. If you are testing once or twice a year and treat heartworms right away, it will never reach this severe state.

In addition to blood tests, veterinarians can use X-rays, ultrasounds, and blood tests to determine the severity of an infection.

Antigen Test

The most common testing method is the antigen test. This detects specific proteins produced by adult female heartworms. Heartworm may be present for as much as 5-6 months before heartworm antigen becomes noticeable in the blood. However, in most cases, dogs may not test positive until 7 months post-infection. 

This test may not identify a low worm burden, so there’s a 30-40% false negative rate if the dog carries only a few female worms. So that’s why your vet may also do a microfilariae test. 

Microfilariae Test

This test detects the presence of microfilariae in the dog's system. Now the American Heartworm Society (AHS) advises performing the microfilariae test annually to prevent false negatives on the antigen test. A positive microfilariae test is confirmation that mature heartworms are present and reproducing in the dog's body.

There’s also a less-known third option.

DNA Heartworm Test

This uses PCR (polymerase chain reaction) technology to examine heartworm DNA in the dog's blood. HealthGene, situated in Canada, offers the D319 Canine Heartworm (Dirofilaria immitis) test, which covers heartworm identification at all life stages, including microfilariae, larvae and adult heartworms. HealthGene only works with veterinarians for test kit orders and testing, so you’ll need to ask your vet to help you.

How Do You Get Rid Of Heartworms In Dogs?

There are veterinary methods that use medications and long terms of rest, and natural methods that involve building the immune system for a preventative approach. 

Veterinary Method To Get Rid of Heartworm in Dogs

Veterinary methods use a combination of medications that kill both adult worms and larvae. Depending on the severity, treatment may also require hospitalization and close monitoring. The dead heartworms must be eliminated from the dog’s body so dogs are placed on restricted activity for several weeks to avoid excitement that might stress the heart and cause further problems.

Conventional Heartworm Treatment

Because heartworm is a scary and potentially fatal disease, many dog owners opt for conventional treatments. Conventional heartworm treatment involves several stages.

  1. First, they give regular monthly “preventive” meds to kill immature heartworms and stop new infections. These drugs continue through the whole treatment period.
  2. At the same time, your dog will get one month of the antibiotic doxycycline f. This is to treat any Wolbachiabacteria that may be present. Wolbachia live in the heartworms, so the antibiotics are to minimize the risk of complications.
  3. Then your dog will get several intramuscular injections of the adulticide drug called immiticide (merlarsomine), at 60 days, 90 days and 91 days/ This is the risky stage of treatment and your vet may want your dog to be hospitalized to avoid complications. Some vets will add steroids (prednisone) to lower side effects.
  4. 120 days into treatment, the vet will test for microfilariae. If your dog still has microfilariae, they may give another drug and retest at day 150. If there are no microfilariae, your dog can usually resume activity. 
  5. There’s usually another test after 1 year to confirm your dog is heartworm free.

How Long Does Veterinary Method Take To Get Rid Of Heartworm In Dogs

The duration of treatment depends on the severity of the infection as well as the method used. The full treatment (as shown above) can take several months and up to a year to completely remove all heartworms. Strict rest and exercise restrictions are imposed during the treatment period. 

Heartworm Slow-Kill Method

There’s also a “slow-kill” method using heartworm meds for a year or more, often with the antibiotic doxycycline. This method is controversial as the American Heartworm Society discourages it … but studies show it can be effective. 

Natural Methods To Get Rid Of Heartworm In Dogs

Heartworm treatment is a situation where you should always work with a holistic veterinarian or herbalist. Don’t try to treat heartworm on your own.

A professional holistic vet or herbalist can prescribe a protocol that may include herbs like wormwood, hawthorn, ginger, thyme, garlic, peppermint, cinnamon, dan shen, medicinal mushrooms and CoQ10. 

RELATED: Find alternative methods to get rid of heartworms … 

Natural Heartworm Prevention For Dogs

Harnessing your dog's immune system can serve as the strongest defense against heartworm disease. Because of the slow growing nature of heartworms, a healthy immune system can kill the larvae before they mature.  

How To Support Your Dog’s Immune System

  • Provide a whole food, raw meat-based diet instead of kibble
  • Minimize vaccines
  • Opt for natural remedies over pharmaceutical drugs
  • Use natural flea and tick prevention
  • Eliminate chemical use in the home and yard
  • Supply fresh spring or filtered water
  • Give your dog plenty  of exercise

Avoid Mosquito Bites

It’s important to control mosquito exposure, especially in high risk areas for mosquitoes and heartworm.

Here are things you can do:

  • Get rid of standing water in your yard
  • Keep away from standing water or swampy areas on walks or hikes
  • Limit outdoor activities at dawn or dusk, to avoid peak mosquito activity
  • Use natural mosquito repellents
  • Add fresh garlic to your dog's diet, to help discourage mosquito bites
  • Add herbal supplements, immune-boosting foods, and natural detoxification protocols. 

It’s never too late to begin any of these practices to support your dog’s health and establish a robust immune system.

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© 2024, Four Leaf Rover - The content on this website is not meant to replace veterinary advice. Please support the hard working holistic vets who make this information possible. To find a holistic or homeopathic vet near you or to find one who will do phone consultations, visit The Academy Of Veterinary Homeopathy.