Heartworm is a preventable disease that could become fatal if left untreated. In this article, we’ll discuss all you need to know, including how your dog could become infected. There is no need to worry, these cannot affect humans. 

What is Heartworm Disease

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Heartworm disease is a serious disease that can result in death in pets such as dogs, cats, and ferrets. The results of heartworm disease are severe lung disease, heart failure, and other organ damage. A parasitic worm called Dirofilaria immitis is the cause of this, and it is spread through mosquito bites. A dog is often considered the most definitive host, as the worms can mature into adults, mate, and produce offspring whilst living inside of a dog. The intermediate host is the mosquito. This means that the worms live inside the mosquito for a short period of time in order to become infective and cause this disease. These worms are known as heartworms because the adults live in the heart, lungs, and blood vessels of the host. 

The Life Cycle of Heartworm in Dogs

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When a dog has been infected, the adult female will release her offspring, called microfilariae, into the bloodstream of the infected dog. If a mosquito comes to bite the dog, the microfilariae then infect the mosquito. Under the right environmental conditions, the microfilariae become infective larvae within 10 to 14 days while still living inside the mosquito. Microfilariae cannot be infectious unless it has passed through a mosquito. If another dog is bitten by the infected mosquito, the larvae are spread to the dog through the bite wound. It will then take 6 – 7 months for the infective larvae to mature into adult heartworms in the newly infected dog. Afterward, the adult will mate and release their offspring into the host’s bloodstream, as mentioned above. 

Heartworm disease is not contagious. This means that the dog or pup will not become infected with the disease if they have been in contact with another dog that has been infected. This disease can only be spread through mosquito bites. 

Heartworm can live anywhere from 5 to 7 years inside of a dog. Adult heartworm resembles a strand of cooked spaghetti. Male heartworms, in this case, can reach 4 to 6 inches in length, and females can reach 10 to 12 inches in length. A large amount of worms living inside of an infected dog is called a worm burden. For example, 15 worms are the average worm burden in dogs but can range anything from 1 to 250 worms. 

How are Dogs Tested for Heartworm

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In order to check for heartworms, the vet will make use of blood tests. An antigen test is used that detects specific heartworm proteins. These proteins are called antigens and are released by female heartworms into the dog’s bloodstream. Antigen tests can often accurately detect infections with one or more female heartworms. Heartworm proteins can be detected in a dog’s bloodstream at the earliest 5 months after being bitten by an infected mosquito.

There is another test that is able to detect microfilariae in the dog’s bloodstream. If a dog has microfilariae in the bloodstream, it is an indication that the dog is infected with adult heartworms. This is because only adult heartworms are able to mate and produce microfilariae. Microfilariae can only be detected in a dog’s bloodstream at the earliest 6 months after being bitten by an infectious mosquito. 

When Should Dogs be Tested for Heartworm

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When you should test your dog for heartworm as well as the frequency of the testing is dependent on many factors. 

These factors include:

  • Your dog’s age at which heartworm prevention has started.
  • If you have forgotten to give heartworm prevention and for how long.
  • If you have recently switched your dog from one heartworm prevention to another. 
  • If your dog has recently traveled to an area in which heartworm disease is more common.
  • The length of heartworm season within the region where you and your dog live.

Before starting heartworm prevention, dogs that are 7 months and older should be tested for heartworms first. It’s possible for dogs to appear healthy on the outside, whilst heartworms are living their best lives on the inside. If prevention has begun before a heartworm-positive dog has been tested for heartworms, the dog will remain infected with heartworms until it gets sick enough for symptoms to arise. Heartworm preventatives are unable to kill adult heartworms. It may even be harmful or deadly to give an infected dog heartworm prevention. If a dog has microfilariae in its bloodstream, a heartworm preventative could cause sudden death. This could trigger a shock-like reaction in your dog and result in death. 

It is recommended that your dog gets tested for heartworm annually. The local vet should be able to advise you on the best time for your dog’s annual heartworm test. 

What are the Symptoms of Heartworm Disease

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How severe the symptoms of heartworm disease are will depend on the number of worms living inside of the dog, how long the dog has been infected, as well as how the response of the dog’s body to the presence of the heartworms. The activity level of the dog plays a large role in how severe the disease can become as well as when symptoms will arise. If a dog has a low worm burden, the symptoms of heartworm might not be obvious. This counts for dogs who have been recently infected or are very inactive as well. Obvious symptoms of heartworm disease can be seen in dogs with heavy worm burdens, dogs that have been infected for an extended period of time, or dogs that are very active. 

There are four classes of heartworm disease. The higher the class tier is ranked, the more dangerous the disease and the more obvious the symptoms.

The classes are:

Class 1: There are no symptoms or only occasional symptoms, such as a cough

Class 2: Symptoms are mild to moderate such as an occasional cough as well as tiredness after doing a moderate activity.

Class 3: There are more severe symptoms, such as a sickly appearance, a cough that is persistent, and tiredness after any mild activity. Common signs are trouble breathing and signs of heart failure. Changes in the heart and lungs are often seen on chest x-rays for class 2 and 3 heartworm disease.

Class 4: This is also known as caval syndrome. This is when there is such a heavy worm burden present that the blood that needs to flow back to the heart is unable to do so due to a large number of worms. This is a life-threatening condition, and the only treatment option is to surgically remove the worms. It is a high-risk surgery, and often even after surgery has been done, dogs who have been diagnosed with caval syndrome pass away. 

Caval syndrome doesn’t affect all dogs with this disease. It is still advised not to leave it untreated as it can progress and damage the dog’s heart, lungs, liver, and kidneys which eventually causes death. 

Are There Treatments Available

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In order to treat adult heartworm in dogs, the vet will need to prescribe your dog a medication called Diroban or Immiticide. This medication is administered by deep injection into the back muscle to treat stabilized class 1, 2, and 3 heartworm disease. Your vet may also give your dog something to get rid of any microfilariae in the bloodstream. 

Treating heartworm disease is not cheap. The treatments can be potentially toxic to the dog and could cause other serious complications, including life-threatening blood clots in the lungs. Therefore preventing heartworm disease is a better option. Treatment often includes X-rays, blood tests, hospitalization, and a series of injections, making several vet visits undeniable. 

Prevention is the Best Possible Treatment

Heartworm disease all begins with a mosquito bite. To prevent your dog from getting heartworm, your vet could administer preventative. Curing heartworm is extremely expensive and could be life-threatening for your dog.