Basics of Heartworm Disease in Dogs

Basics of Heartworm Disease in Dogs

Heartworm disease is a serious and life-threatening disease for pets in the United States and around the world. It is caused by foot-long worms that reside in the heart, lungs and associated blood vessels of affected pets, causing heart failure, severe lung disease and other organ damage. Heartworm disease can affect dogs of all different types and breeds. For this reason, prevention is the best option, and treatment – if needed – should be administered as early as possible during the course of the disease.

How Dogs Get Heartworms

Heartworms are incredibly serious (even deadly) parasites that are only transmitted by mosquitoes. They spread rapidly and often carry subtle symptoms, meaning if dogs aren’t tested, you may very well never know they’re present.

Dogs can only get heartworms if they are bitten by mosquitoes that are infected with the parasite. That is the only way the condition is transmitted. An infected dog can not give heartworms to another dog or animal, not can they give it to you. A big problem is that we can’t test mosquitoes to see if they have the parasite. We only know about outbreaks and infections after the point of infection, so preventative treatments are crucial to keeping your dog safe.

All dogs are in danger of being infected with heartworm disease. Even if your dogs are mostly indoors, they can still get infected. All it takes is a bite from an infected mosquito to transfer a parasitic worm. Symptoms appear only in very advanced stages and resemble those of congestive heart failure. In severe cases, dogs have difficulty breathing and coughing, become intolerant of exercise, and have a decreased appetite.

How Are Heartworms Transmitted?

The mosquito plays a vital role in the life cycle of heartworms. Adult female heartworms living in an infected dog, coyote, fox, or wolf produce microfilaria, which are microscopic baby worms that move through the bloodstream. When a mosquito bites and transports blood from an infected animal, it picks up the baby worms, which grow and mature into “infective stage” larvae over a period of 10 to 14 days. If an infected mosquito bites your dog, the larvae are dropped onto the surface of the dog’s skin and enter the dog through the mosquito’s bite wound. Once inside, the larvae will then mature into adult heartworms in about 6 months.

Rate of Infection

Veterinarians believe that just about 100 percent of dogs who have been bitten by an infected mosquito will develop heartworms. That’s a staggering statistic. If you have cats, you should know that they, too, can also have heartworms. Their likelihood of developing them after exposure ranges from 60 percent to 90 percent.

The Development of the Infection

It takes a long time for a dog that has been exposed to heartworms to show symptoms. When an uninfected mosquito bites a dog that is infected, it picks up microfilariae.

Over the next two weeks, the microfilariae turn into larvae inside of the mosquito. If the mosquito bites another dog in that time, it transfers the larvae to that dog. In about six or seven months, the larvae will mature and turn into adult heartworms. Once matured, they begin releasing their own microfilariae (offspring) into the dog’s blood, allowing the cycle to continue.

What Are the Signs & Symptoms of Heartworm Disease?

Most dogs show few or no symptoms in the disease’s early stages. The longer the infection persists, the more likely your dog will develop symptoms. Signs may include fatigue after moderate activity, reluctance to exercise, a mild persistent cough, decreased appetite and weight loss. As the disease progresses, your dog may develop a swollen belly due to excess fluid in the abdomen or heart failure.

Heartworm disease diagnoses are documented in all 50 states. And because infected mosquitoes can come inside, your dog is at risk whether it is outdoors or indoors. As a preventative measure, you should have your dog tested once every 12 months for heartworms along with giving your dog a heartworm preventive every month.

Dogs with Class 1 and Class 2 heartworms have very few symptoms, sometimes developing a cough or signs of fatigue as the disease progresses. As a dog progresses to Class 3, they begin to look ill, have a more persistent cough, fatigue far more easily, and start to show signs of breathing trouble. If left untreated, your dog’s organs will eventually become damaged.

Some dogs progress to Class 4, or caval syndrome, where the heartworms have progressed to the point where they are choking off blood flow through the heart.

Treatment for Heartworms

Treating heartworms is incredibly expensive and is considered dangerous, but if your dog has an infection, not treating it is no longer an option. One medication requires injections; the other is just a topical medication applied to the skin.

Treatment isn’t particularly pleasant for anyone, especially your dog, and the amount of vet visits, exams, x-rays, blood workups, and treatments can be financially devastating. Worse yet,  treatments can also cause complications, including toxicity and canine blood clots. If your dog is diagnosed, you will need to keep him calm and quiet at all times; this can be extremely difficult. It’s critical to prevent side effects like heart attacks and strokes.

As the worms die, they will actually begin to break up and enter the bloodstream in small pieces. Exertion and barking can promote the spread throughout the body and ultimately contribute to organ damage or blockages. You may end up needing to crate your dog for a while to keep him calm when you are not around. The truth, though, is that the horror stories you may have heard about dogs dying from treatment are more likely tied to dogs who were allowed to exercise during treatment than not.

Treatment Options

Veterinary treatment is available but is costly, and not all dogs can withstand the treatment. The medicine that kills the worms is an extremely toxic and deadly poison. Aftercare treatment instructions include:

  • Restricting exercise during the first month following heartworm treatment. After the first month, you can gradually resume normal exercise and play.
  • Continuing care. It is crucial that your dog stays on year round heartworm prevention for maintaining optimal health.
  • Veterinary care. Dogs who endure heartworm treatment can test positive for the first six months following treatment because some larvae may remain in their bloodstream. Nevertheless, it is extremely probable that the result is a false positive.
  • After treatment. Make sure to monitor closely your dog after treatment for listlessness, lack of appetite, coughing, labored or troubled breathing, diarrhea, fever, vomiting, pale gums, difficulty walking, and nosebleeds. If you see any of these warning signs, contact a veterinary emergency clinic immediately.

As a dog owner, it is better to prevent heartworms before they have a serious chance of affecting your dog. For that reason, focusing on keeping your dog healthy begins by maintaining a diligent heartworm prevention program.

How to Prevent Heartworm Disease

Heartworm prevention medications aren’t like vaccinations. If your dog is bitten by an infected mosquito, the microfilariae will enter the bloodstream. Preventatives attack the parasite so that it can’t develop into larvae and then develop into adult heartworms.

Many American states experience a reduced risk of mosquito exposure in the late fall, it’s important to keep your dog on preventative medications year round just in case the climate stays warm and there is exposure. Moreover, heartworms can incubate for up to six months in your dog’s body. It takes just one bite to result in infection during an off month.

Your Vet Wants to Prevent Heartworms

A lot of people go to the vet and are astounded by the tests and treatments recommended for heartworms. Don’t scoff at the heartworm preventatives or the blood work at your annual well visit. They could very well save your dog’s life. The complications noted above are unpleasant – and sometimes, even deadly. Your vet does not want to end up treating your dog for heartworms.

They also know that just about 50 percent of dogs who are not on preventative treatments will develop heartworms at some point. The warmer the climate you live in, the higher the risk.

Heartworm Preventatives May Prevent Other Worms, Too

Heartworm preventatives don’t just treat heartworms; they prevent other parasites like roundworms and hookworms  at the same time. While these parasites aren’t as dangerous to your dog, they can still be really uncomfortable and cause significant health problems. That makes preventative treatment a double win.

Preventatives Don’t Treat

There is a myth that preventative treatments are sufficient to treat developed infections. This isn’t exactly true.

Your dog’s preventative medications will kill off the heartworms over time, but it could take two to three years for the infection to completely clear your dog’s system. In the meantime, the parasite will continue to move through your dog’s system, causing more damage to his heart and lungs. Your dog will likely remain uncomfortable and symptomatic, and your risk of him developing complications will definitely increase. It’s a risky endeavor that’s just not worth betting on.

Be Proactive About Heartworm Prevention

The best treatment to ensure that your dog stays healthy and parasite free is prevention. Heartworms are preventable with daily or monthly chewable tablets and monthly topicals. The medications work by interrupting heartworm development before the adult worms reach the lungs. Ensuring that your dog tests negative for the infection includes:

  • Annual blood tests to check for exposure from the previous year.
  • Preventative medication that works backward by a month.

Dogs Don’t Outgrow Heartworms

The average heartworm lives for about seven years, but that doesn’t mean you can just hope for the best after seven years of infection. Heartworms persistently reproduce, replicating over and over. Your dog will not outlive the lifespan of the heartworm and get rid of it naturally. Opting to not treat your dog will likely result in his death.

Dogs Don’t Develop Immunity

Dogs who have had heartworms once can get them again. They do not develop immunity, nor do they become better capable at fighting off heartworms in the future. You need to get your dog onto a preventative treatment as soon as his disease treatment is complete – and keep him on it for the rest of his life.

Heartworms are incredibly serious and can cause your dog a lot of discomfort.  If you have concerns about this devastating disease, take your vet seriously and explore your options, then choose a preventative that works. Your dog’s life might depend on it.

Heartworms Are Everywhere in the U.S.

Veterinarians have detected heartworms in all 50 states. In the past, there were some areas where veterinarians never saw the disease, but that’s no longer true. Now, even drier areas like California and Arizona have enough irrigation and development to create environments mosquitoes can live in. In fact, even just standing water in a bucket or puddle is enough to harbor harmful mosquito larvae.

The good news is that there are things you can do to prevent heartworms and to treat them if your dog should become a victim. We want to help you better understand heartworms so you’ll be better equipped to protect your dog, but preventatively and reactively.