Dog Heartworm Disease - Causes, Treatments, and Preventions

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Dog heartworm disease in dog outside in a field

Dog heartworm disease in dog outside in a field

What is heartworm Disease in dogs?

Heartworm infection is a potentially very dangerous disease that is caused by heartworm called Dirofilaria immitis, which is transmitted by mosquitoes. Adult heartworms are usually found in the heart or pulmonary arteries, but they can also be found in other blood vessels. Female heartworms measure 15 to 36 cm long and 3 mm thick, while males are about half the size of females. An adult heartworm can live for up to five years, during which time the female lays millions of heartworm larvae (microfilaria) that live inside the tiny blood vessels of an infected pet.

Heartworms can damage and destroy organs such as the heart, kidneys, lungs, and liver. Fortunately, newer drugs can treat heartworm, and it can be successfully resolved in over 95% of cases. Because prevention is possible through regular preventives, it is necessary to implement periodic management to prevent the disease.

What are the main causes of heartworm disease in dogs?

Heartworm disease is caused by heartworms that are transmitted through mosquito bites. When a dog with heartworms is bitten by a mosquito, the heartworm larvae enter the mosquito and grow into infective stage larvae for 10 to 14 days. When this mosquito bites another dog, the larvae enter the dog's bloodstream and develop into adult heartworms, causing heartworm disease. The incidence of heartworm is higher during mosquito season because the transmission of the disease becomes more prevalent. 

What are the common symptoms of heartworm disease found in dogs?

Heartworm disease is a condition that affects the cardiovascular system and can cause a range of clinical symptoms. In the early stages of infection, there may be no or only mild symptoms, but as the infection progresses, more severe symptoms may occur.

The following is a list of some commonly occurring symptoms of heartworm disease:

  • Coughing

    Heartworm affects the heart and lungs and causes frequent coughing.

  • Refusal to exercise, fatigue
  • Loss of appetite and weight loss
  • Bloating

    Heartworm disease can cause right heart failure and result in ascites. If ascites build up in the abdominal cavity, the abdomen may become distended.

  • Canine caval syndrome

    Heartworms can accumulate in the right atrium, right ventricle, pulmonary artery, and vena cava, obstructing blood flow. As a result, they interfere with the function of the tricuspid valve between the right atrium and right ventricle, obstructing the flow of blood to the pulmonary artery and causing damage to various organs. This can lead to clinical symptoms such as difficulty breathing, pale gums, hematuria, and fainting. It is a serious phenomenon that can suddenly interfere with life.

Dog heartworm disease in dog outside in a field

Classification according to the course of heartworm disease

The severity of heartworm disease depends on the number of worms living inside the dog, the duration of their infestation, and the dog's body's reaction to the infection. Symptoms may not be apparent if the dog has recently been infected or is less active.

  • Stage 1: Asymptomatic or mild symptoms such as occasional coughing

  • Stage 2: Mild to moderate symptoms such as intermittent coughing and fatigue

  • Stage 3: Severe coughing, shortness of breath, and fatigue even after light activity

  • Stage 4: Also known as canine caval syndrome, symptoms of ascites and abdominal distension may occur, and surgery may be required as an emergency.

What is the risk of heartworm disease in dogs?

Heartworm disease initially causes only mild symptoms, but it can become life-threatening as the infection persists and adult heartworms build up. Caval syndrome, in particular, can be dangerous and cause sudden death. Therefore, preventing heartworm disease is crucial, and if suspected, you should seek medical attention. Since heartworm is transmitted by mosquitoes, it is more common during mosquito season or in areas with a high mosquito population.

If your dog experiences any of the following symptoms, you should contact a veterinarian right away.

  • When coughing and fainting symptoms become frequent
  • When the gums become pale and the tongue turns blue
  • When hematuria (blood in urine) occurs

Can I treat heartworm disease in my dog at home?

Heartworm disease requires a visit to the hospital, as it is difficult to treat at home. If you suspect that your dog may have heartworms, it is recommended to stabilize and limit movement until you can visit the hospital. It is important to limit physical activity, as it can increase the rate at which heartworms damage the heart and lungs until a diagnosis has been confirmed.

How is heartworm disease diagnosed?

To diagnose heartworm, your veterinarian will first ask you a few questions to help decide which tests to perform to confirm heartworms.

Questions your veterinarian may ask include:

  • Do you get regular monthly heartworm preventives?
  • When did coughing begin to appear?
  • Does your dog refuse to go for a walk or stay in bed at home?
  • Has your dog had any recent symptoms of fainting?
  • Did you change the type of preventive?
  • Have you and your dog recently traveled to another country?

Based on the answers to these questions, several tests are performed to diagnose heartworm disease.

  • Heartworm antigen test

    The heartworm antigen test is used to detect substances produced by mature female heartworms. However, this test can only be conducted five months after a dog has been bitten by a heartworm-carrying mosquito.

  • Blood tests

    Certain blood tests can be performed to check for heartworm protein. Another blood test, called the Microfilaria test, can confirm the presence of microfilaria. If this test returns a positive result, it means that adult worms are present in the body. This test can only be performed six months after a mosquito bite.

  • Echocardiography

    Echocardiography is a technique that can detect the presence of heartworms in the right ventricle, right atrium, or pulmonary artery, as well as evaluate the overall function of the heart.

  • Chest radiation

    Chest radiation is not a test for diagnosing heartworms, but it can be used to check for other issues with the heart or lungs when heartworms are strongly suspected.

What is the treatment process like for heartworm disease in dogs?

In the past, heartworm medications had many side effects and were difficult to use, but recently, drugs with a cure rate of 95% or more have been developed. Dogs with severe heartworm disease may need antibiotics, pain relievers, a special diet, diuretics to remove fluid that has accumulated in the lungs, and drugs to improve heart function before treatment can begin.

  • Removal of adult parasites through drug treatment

    The treatment for adult worms involves the use of a drug called melarsomine, which is given as an injection. After the first infusion, there is a 30-day washout period. After that, the dog will receive two injections, once a day. Antibiotics may also be prescribed during this process. The week following the first injection is very important, as the injection will kill most of the adult worms and the resulting debris can cause problems. Therefore, during this first week, close monitoring and restricted movement are necessary to stabilize the dog. In severely infected puppies, coughing may persist for up to 7 to 8 weeks after treatment. After about 6 months of treatment, a re-examination is performed to confirm that the heartworms have been completely removed.

  • Medication to remove microfilaria

    Imidacloprid or moxidectin is used to remove microfilaria. This will be prescribed while removing the adult worms, and at the same time, a vaccine will be prescribed.

  • Medication for long-term management

    Dogs that have had heartworm disease for a long time can develop heart disease even after treatment. As a result, medications for heart disease management may be administered.

  • Surgical removal

    Surgical intervention may be necessary if canine caval syndrome, the fourth stage of heartworm disease, occurs. However, the success rate of surgery is not high and death may occur during the procedure.

How to prevent heartworm disease in dogs

Heartworm can be prevented through the periodic use of preventives. There are various FDA-approved products for this purpose, including edible products, skin applications, and injectable vaccines. These products can prevent not only heartworm but also other internal parasites such as roundworms and hookworms and external parasites such as fleas and ticks. It is advisable to consult with a veterinarian to create a prevention plan specific to your pet, especially during the summertime when there are more mosquitoes.

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