Heartworms in Dogs: A Comprehensive Guide for Concerned Owners

Heartworms in Dogs
Wyatt Robinson
Written by Wyatt Robinson

Heart worms in dogs can have a devastating effect, therefore understanding what heartworms are and what the disease involves, is essential. The more awareness that is spread about them, the less cases there will be of dogs becoming seriously or even fatally affected by this problem before their owners and veterinarians can even realize what’s wrong.

Heartworm disease is very prevalent partly because many dog owners don’t fully understand what it is or how serious it is, so they don’t take steps to prevent it in time.

Canine heart worms infographic

With the right information it’s something all dog owners can prevent.

What heartworm disease is

Heartworms are a disease that is spread by mosquitoes. When a mosquito bites an infected animal it ingests some of the heartworm larvae that are in the animal’s bloodstream. The larvae then take a couple of weeks to incubate inside of the mosquito and then they’re at the point where they can infect other animals when the mosquito feeds on an animal’s blood. This occurs through the mosquito’s saliva which is infected with the heartworm larvae. When the mosquito feeds, the larvae then travel into the animal’s tissue.

If this animal happens to be a dog then the larvae can migrate from the tissue to the bloodstream and from there to the heart where they will eventually become adult heartworms that are fully capable of breeding and producing offspring that will flow into the bloodstream.

Symptoms of heartworms

Heart worm symptoms in dogs can vary quite a bit from dog to dog so it’s important to be aware of the list of possible symptoms and be able to recognize them easily. Contrary to belief, it’s not obvious when your dog has this problem. Symptoms can be very subtle or, due to the broad range of symptoms, undetectable from other illnesses. In our article on heartworms, an often overlooked disease in dogs, read and find out how you can be more aware of this deadly illness.

Heartworm infection infographic

Even very critical cases are often still treatable when caught in time. Symptoms include:

  • Coughing
  • Fatigue
  • Labored breathing
  • Weight loss
  • Decrease in appetite
  • Uninterested in or reluctant to exercise
  • Exhaustion following normal amounts of exercise
  • Swollen stomach
  • Brown urine
  • Anemia
  • Blockages in blood flow causing caval syndrome
  • Heart failure

Treatment for heartworms

The treatment is expensive and very strenuous for the dog. The first step is a blood test and, if your pooch is positive, there will be other tests involved to determine if the diagnosis is definitely accurate before your veterinarian will proceed to treatment. After the necessary tests are completed you will be advised to restrict all exercise. Restricting all forms of exercise, no matter how cruel it seems, is really important towards your dog’s recovery because exercise can cause more damage to the lungs and heart. Next, the actual treatment depends on the severity of the illness.

Blood test for dogs

In very severe cases where the dog is seriously affected, the only way of saving him may be physically removing the worms through an operation. Mild cases are treated by first killing the immature worms with a preventative product that contains ivermectin. The vet will determine how long your dog needs to be treated before it’s time to tackle the adult worms, based on the severity.

The adult worms are the real threats as the immature ones can’t do any damage but it’s counter-productive to treat the adult worms first because the immature worms are in the process of migrating as they carry out their lifecycle so it’s best if they’re dealt with first before they can finish their lifecycle.

However, if a case is more severe then there won’t be time to wait to kill the adult worms. The vet in that case may decide to treat the immature worms for only a month or so before moving onto killing the adults, or may instead decide that it would be more prudent to kill the adults first even if that means the treatment takes longer.

Heartworm treatment

The adult worms will be killed with Immiticide which is administered through a series of painful injections. The injections often cause reactions at the site of the injection but they are relatively harmless and shouldn’t cause any long-term damage, although some dogs develop a lump at the injection site that never goes away. Be prepared for your dog to be very sore after these injections and possibly in need of pain relief.

Luckily, treating the adult worms usually doesn’t take nearly as long as treating the immature worms. Some dogs may only need two dosages spaced a day apart but other dogs may need more dosages after a few weeks. It’s dangerous to kill too many adult worms at once due to possible circulatory shock so in the more severe cases more dosages will be needed and may need to be spaced far apart. Our piece on medicines to treat heartworms is a must-read, so go check it out.

Myths and facts

There are many myths related to heartworms that are circulated by people who don’t fully understand what they are and how they affect dogs. If you aren’t very knowledgeable on the subject and you read information on a website or two it’s easy to become misinformed. It’s hard to know what to believe on the internet when different websites all seem to contradict each other.

Risk heartworm

Therefore, it’s important to dispel these myths so that no one else is wrongly informed and under the impression that their dog won’t get this disease.

  • Heartworms are only in the south: Many people incorrectly assume that only dogs in the southeastern part of the United States get heartworms, considering that mosquitoes aren’t as widespread in the southwest or northern states. And that might have been true many years ago when heartworms weren’t as common but nowadays they can be contracted in all states.
    True, there are some places, like South Dakota, where heartworms aren’t widespread but they can still be a threat. They just aren’t as strong of a threat as they are in the southeast where mosquitoes are swarming. Furthermore, it’s important to note that in the southeast mosquitoes are so widespread that it’s almost a guarantee that a dog that doesn’t have any protection will get heartworms at some point in its life.
  • Humans cannot get heartworms: We can become infected in very rare cases but we are not compatible hosts for them so they’re unable to complete their lifecycle in us, meaning that we can’t be seriously affected by them.
  • Only dogs can be infected: Heartworms mostly infect dogs, but to a lesser extent they do infect cats and ferrets also. They also infect wild animals like coyotes, wolves and foxes. However, dogs are natural hosts which mean that the worms are capable of going through all of their lifecycle forms in the dog as well as breed and produce offspring. In cats and ferrets the heartworms don’t usually live long enough to breed and therefore they don’t usually have large amounts of worms.
  • Heartworms are similar to the other types of worms that dogs get: Heartworms aren’t like the other species of worms that plague your dog. There are several key factors that are different such as the fact that they don’t live in a dog’s intestinal tract, the eggs aren’t found in soil, they aren’t transmittable through other dogs, and most other species of worms that affect dogs don’t come anywhere close to the dangerous magnitude that heartworms do.
  • Dogs that are indoors don’t get infected by heartworms: Just because your dog doesn’t spend extended periods of time outdoors doesn’t mean he can’t still get bit by an infected mosquito while on a walk, at the park, or even indoors as mosquitoes can and do fly in through open doors and windows.
  • Dogs cannot transmit heartworms to other dogs: A dog infected with heartworms is perfectly safe for dogs and other animals to be around. Heartworms cannot be transmitted in any other way than through the bite of an infected mosquito. It doesn’t matter if a mosquito bites your infected dog and then bites your other dog because heartworms are first incubated in mosquitoes before they can then travel through a mosquito bite into a dog.

Prevention: what you can do

As the old saying goes, prevention is key. While heartworms are treatable, prevention is much preferred due to the seriousness of the disease. It’s cheap and easy to prevent but expensive and grueling for a dog to overcome. Therefore, putting your dog on a heartworm prevention plan is the best thing overall. Preventative methods may cost a bit more than you want to spend, especially if you have a large dog or multiple dogs, but think of it as insurance.

Heartgard for dogs

It costs a bit of money per month and ensures that you don’t have to spend thousands of dollars in the long run. So it is actually cost effective as well, even if it doesn’t feel like it. To help make sure that you’re getting the best preventative for the money there are several tablet and chewable products below in which the pros and cons of each are discussed.

Heartgard: It is invermectin-based and one of the most widely used products for preventing heartworms. It comes in a few different forms such as Heartgard Plus Chewables, Heartgard Chewables and Heartgard Tablets. The chewables are beef flavored while the tablets are not so if you have a dog with a beef allergy, avoid the chewables. Heartgard Chewables and Heartgard Tablets only prevent heartworms but Heartgard Plus also prevents hookworms and roundworms.Interceptor flavor tabs: Its active ingredient is milbemycin oxime so it’s suitable for dogs that are genetically predisposed to have an adverse reaction to ivermectin. Otherwise, it’s quite similar to Heartgard Plus in that it has chewable beef tablets that protect against heartworms, hookworms, and roundworms. Except that Interceptor has the added advantage of protecting against whipworms while Heartgard Plus doesn’t.
Iverhart Plus: This is a generic brand of Heartgard Plus, so aside from the price tag it’s very similar. It’s a chewable tablet that contains invermectin and also pyrantel pamoate in order to control roundworms and hookworms. Although, unlike Heartgard Plus its flavor is pork-liver which fewer dogs are allergic to when compared to beef.Sentinel flavor tabs: A monthly tablet that contains milbemycin oxime and lufenuron which combined control heartworms, hookworms, whipworms, roundworms and fleas. Sentinel also has a range called Sentinel Spectrum Chewables which are exactly like Sentinel Flavor Tabs but have the added active ingredient praziquantel which protects against tapeworms, giving you a 6-in-1 tablet.
Tri-heart plus: This is a beef flavored chewable tablet that is to be administered once a month and it takes care of heartworms, hookworms and roundworms. Its active ingredient is ivermectin, and as with all ivermectin-based products it can cause a bad reaction in some dogs. Fatal reactions have been known to occur in certain breeds of dogs that have the MDR1 gene such as collies, Australian shepherds and border collies. Before use make sure to look at a full list of the breeds that are affected by ivermectin.Trifexis: Its active ingredients are milbemycin oxime and spinosad, and like many others it’s a once a month, beef flavored tablet that kills not only heartworms but hookworms, whipworms and roundworms too. But what is really unique about this product is that it kills fleas as well. It was the first of its kind and is a really appealing option to people that live in the south and have to battle fleas all year long. However, some people have questioned whether it’s safe or not due to the spinosad ingredient and the many adverse reactions it’s caused in dogs over the years.

If you’re unsure as to which preventative you want to use, speak to your vet. They should be able to point you in the right direction. They’re used to helping dog owners find the right preventative for their dog and will have information on the most popular and effective products and they may even be willing to advise you on the best place to purchase them.

Vets of course sell heartworm products themselves but they aren’t always the cheapest place to buy them so you may want to check their prices against other suppliers first. You will probably need your vet to give you a prescription before you’re able to buy heartworm preventatives online so if you plan on doing that than that’s the perfect time to question your vet on other heartworm products. Find out other home remedies for parasites in dogs in our earlier article, go and read it.

Other methods of prevention

Tablets and chewables have their merits but there are also other preventatives that you can consider. Many people use topical applications such as Revolution and Advantage Multi and the nice thing about them is that if you have a dog that’s difficult about taking tablets or chewables than these will eliminate the dreaded monthly battle of forcing the preventative down your dog. Topicals are easy to apply, only takes seconds and your dog won’t find it nearly as objectionable as tablets.

They also protect against other parasites like hookworms, whipworms, intestinal roundworms, fleas and ear mites so it has many different uses all in one topical application. If you already have to regularly treat your dog against some of these parasites than it only makes sense to use one product instead of multiple ones. Here’s a must-read on an article regarding heartworms and other parasite treatment for dogs to give you more options.

Protect your best friend

There’s also an injectable preventative called ProHeart 6. It’s effective against heartworms as well as hookworms but it’s not really recommended for regular use unless you live in an area that is high risk for heartworms.

The main advantage to this product is that you don’t have to reapply it every month; it’s a 6 monthly injection which makes it very convenient to use and you don’t have to worry about accidentally missing a month of prevention. Topical applications aren’t always reliable and can be washed away with frequent baths and swimming so this is a viable alternative.

However, ProHeart 6 is not advisable to use with dogs that are ill, underweight, and younger than 6 months or those that have allergic reactions. To be clear, this includes food allergies, allergies to certain vaccines, flea allergies, atopy, and any other apparent allergic reactions.

Now that you understand the enemy and the various ways in which to fight it, you’re that much more capable of preventing them from infecting your dog. It’s an awful disease that will hopefully become less prevalent in time. With both our advanced medicine and through people spreading awareness of the dangers of leaving your dog unprotected, it can be done.

Education helps a great deal — we’ve already come a long way in the past few decades when people first began taking a more active interest in heartworms and paying more attention to heart worm symptoms in dogs, but we’re always learning more and developing better methods of combating them.

About the author
Wyatt Robinson
Wyatt Robinson

Wyatt Robinson had a great 25-years career as a veterinarian in United Kingdom. He used to be a member of British Veterinary Association and worked in 3 pet hospitals in London and Manchester. He is shining when he sees his pets healthy and full of energy and it is his duty to help other dog owners to keep their best friends full of life.