5 Facts on Heartworm Disease in Dogs

5 Facts on Heartworm Disease in Dogs
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vet verified PetCareRx Staff Veterinarian DVM

Heartworm infections can and will turn into heartworm disease if left untreated and can be potentially fatal to your dog. Keep these five facts in mind when dealing with this condition.

Parasites are gross and uncomfortable, but more than that, your pet’s parasites can cause them physical harm. Heartworm infections, which are spread by mosquitoes, can morph over several months into heartworm disease. If untreated, this disease can have an extremely severe impact on a dog’s health and may potentially be fatal. As you think about how you can handle and prevent this disease, keep these five facts in mind:

1. Prevention is good for your dog…and all dogs

There’s a lot of conversation about the importance of heartworm prevention when it comes to tackling the problem of heartworms. The monthly dosage of a heartworm preventative works by attacking the larval heartworms that dogs get after mosquito bites. 

This stops the infection in its tracks for your dog. But this also means that mosquitoes that bite your dog cannot get the larva and pass them on to other dogs. Using heartworm prevention for dogs has a ripple effect: Not only will you help your dog, but you’ll lessen the spread of the disease and help prevent other nearby dogs from being exposed to the infection.

2. Prevention tops treatment

This probably won’t be a surprise, but as with most things in life, prevention is easier than treatment. Where treatment is expensive, uncomfortable, and lengthy, preventative treatments are generally just a monthly chewable tablet. Giving a dog the preventative drug is easy. The hardest part is probably remembering the monthly task and making the initial appointment at the vet to get a prescription. Also, it helps to have some understanding of what you can expect from heartworm pills for dogs.

3. Can I catch it from my dog?

No. Heartworms spread through mosquito bites. And, if you have two dogs, and one has heartworm disease, the second dog will not catch it from the first. This is true even if both dogs are bit by the same mosquito bite in short succession since the heartworm larvae need an incubation period within the mosquito before they can be transmitted to another dog. Note that while humans can get heartworms, it’s very, very rare.

4. From Arizona to Alaska

Since mosquito bites are so vital to the spread of heartworm infections, the disease is most likely to spread in hot, humid states, which are comfortable environments for mosquitoes. That said, heartworms have been detected in states as dry as Arizona and as chilly as Alaska. Bottom line: All dogs should be given preventive treatment, regardless of where they live. This will also help if you take your dog on a road trip, and wind up in a state where mosquitoes are more likely to thrive.

5. Growing and growing and growing

It’s the female heartworms that get long, and those female heartworms get quite long, growing up to a foot in length. The male heartworms are shorter, reaching about four to six inches.

Don't Let Heartworm Get Your Pet's Heart

Heartworms, or Dirofilaria immitis, are worm-like parasites that can reach up to a foot in length. While many warm-blooded mammals, including ferrets and cats, can get heartworms, dogs are the main target of heartworms. Heartworms are transmitted by mosquitoes, who leave a larval form of them behind after bites. Adult heartworms travel to the pet's lungs. If untreated, these heartworms cause extreme health issues, which may lead to death.

Heartworm Causes

When a mosquito bites a dog with heartworm, it ingests the microfilaria, or baby heartworms, along with the dog’s blood. These microfilariae mature over about a week within the mosquito, transforming into a larval form of the heartworm. After the larval form is achieved, the mosquito passes it along to other dogs that it bites.

Without the intermediary step of the mosquito, heartworm disease would not spread. Because the parasite relies on mosquitoes, the disease spreads particularly rapidly during the summertime, when temperatures are warmer.  

How to Prevent Heartworm in Dogs

The best way to handle heartworms is to give your dog a monthly preventative treatment like Tri-Heart Plus, Heartgard Plus, and Sentinel Spectrum. The American Heartworm Society recommends that preventatives be given year-round. This treatment helps stop your dog from getting heartworm disease, but it also helps stop other dogs from getting heartworm.

The preventative treatments do not prevent mosquitoes from biting and transmitting the heartworms; rather, the dog heartworm med destroys the microfilariae within the dog's bloodstream.

Heartworm Tests Explained

In addition to year-round preventatives, dogs should be given an annual heartworm test, which serves to double-check that the preventatives are working. The heartworm test checks to see if your dog got heartworm disease the previous year. The tests cannot detect heartworms until they have reached maturity and given birth to microfilaria.

During a heartworm test, vets will take a sample of the dog’s blood and look for either sign of microfilaria or antigens that the heartworms give off.  A heartworm test is also generally required before starting your dog on a preventative or switching preventative heartworm medicine like Drontal Plus for dogs.

Heartworm Symptoms

In the early stages of heartworm disease, there are virtually no symptoms. Heartworm disease has four stages, and as it progresses, the symptoms become more noticeable and disruptive. Some signs of the disease are a cough, a reluctance to exercise, and lethargy. As the disease progresses, dogs may start to bleed from their lungs.

How to Treat Heartworm in Dogs

During treatment of heartworm disease, vets will need to destroy the microfilaria, as well as the adult heartworms. Two different courses of treatment are necessary for the different stages of heartworms. For young heartworm, ivermectin-based preventatives can be given. Adult heartworms will require treatment with an adulticide, to kill them off. Since killing off the adult heartworm is a traumatic experience for a dog, a month-long rest period is required after the first treatment, which is an injection of heartworm meds for dogs, usually given in a hospital. During the rest period, dogs need to abstain from all activity. Although trying and expensive, treatment is generally successful.

Female Heartworms 

Female heartworms live in dogs' hearts and major blood vessels near the heart. They grow to be as long as 12 inches long.

Male heartworms do not live in the bloodstream, but instead, tend to move from the lungs into a dog's heart and then travel out through the pulmonary artery and into other parts of a dog's body. This is why male dogs are more likely than females to develop symptoms even if they don't have female worms in their blood vessels.

They Can Live For Five to Seven Years

After they mature, heartworms can live for five to seven years. This means that if your dog has adult heartworms, it's possible that the infection could be present and active for a long time before symptoms become evident.

When a dog dies, the worms die with it. That's why heartworm infection can also happen in areas where mosquito activity is low or when there are few mosquitoes around during the summer months. The life span of an infected mosquito cannot exceed one month unless its internal environment is kept cool or humid enough to prevent desiccation. This means that a dead infected mosquito wouldn't be able to transmit heartworm larvae into another host animal, even if it were outdoors during wintertime.

Heartworm Disease Is a Potentially Deadly Condition

Heartworm disease is a serious, potentially deadly condition. Heartworm is a parasitic infection that affects the heart and lungs of dogs and other mammals. The worms are transmitted to dogs by mosquito bites and live in their hearts and lungs for years, causing significant damage to the organ systems of infected animals.

While there are preventatives available to help prevent your dog from contracting heartworm disease, it’s important to understand what this illness looks like so you can better recognize if your pet may be suffering from it.

Heartworm disease is a parasitic infection that is spread by mosquitoes. Dogs are the only animal affected by heartworms, which live in their heart and major blood vessels near their hearts. If left untreated, this can be fatal. The good news? There is heartworm medicine for dogs available to fight off these little invaders!

Related Content:

Heartworm Medicine
How to Prevent Heartworm in Dogs
Heartworm Tests Explained

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis, or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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