The Mechanism of Heartworm Infection in Dogs

Heartworm disease is a serious and potentially fatal condition that affects dogs worldwide. Although heartworm is preventable, many pet owners are still unaware of how heartworm is transmitted to dogs, the risks associated with it, and how to protect their pets from this dangerous parasite. In this comprehensive guide, we will explore how dogs get heartworm, how it spreads, the symptoms to watch out for, and the best prevention methods to keep your dog safe.

What is Heartworm Disease?

Heartworm disease is caused by a parasitic worm called Dirofilaria immitis, which primarily affects the heart, lungs, and blood vessels of affected dogs. These worms can grow up to 12 inches long and are capable of causing serious damage to the cardiovascular system, leading to complications such as heart failure, lung disease, organ damage, and even death if left untreated.

Heartworm disease is transmitted through the bite of an infected mosquito, which acts as the intermediate host for the parasite. When an infected mosquito bites a dog, it introduces heartworm larvae into the dog’s bloodstream, where they mature into adult worms over time.

Symptoms of Heartworm in Dogs

Symptoms of heartworm disease in dogs can be categorized into two stages: early and late.

1.Early Symptoms

In the early stages of heartworm infection, a dog may not show obvious symptoms. However, as the heartworm population increases, the dog may show the following symptoms.

• Mild cough: This is the most common early symptom and can easily be overlooked or mistaken for a common cold.
• Exercise intolerance: Dogs tire easily after exercise and show reduced endurance.
• Breathing difficulties: Heartworm affects the heart and lung function, leading to breathing difficulties, especially after strenuous exercise.
• Weight loss: As heartworm affects the dog's health, it leads to gradual weight loss.
• Loss of appetite: The dog may eat less because of the discomfort.

2.Late Stage Symptoms

If heartworm disease is not treated in time, the condition will gradually deteriorate and the following serious symptoms will appear.

• Anemia: Heartworms destroy red blood cells, leading to anemia symptoms such as weakness and lethargy.
• Ascites: When heart function is impaired, it can cause body fluids to accumulate in the abdominal cavity, causing the abdomen to swell.
• Heart and lung failure: Heartworm parasitizes the heart and lungs in large numbers, leading to heart and lung failure.
• Jaundice: When liver and kidney function is impaired, symptoms of jaundice, such as yellowing of the skin and sclera of the eyes, can occur.
• Liver and kidney failure: Severe cases of heartworm disease can lead to liver and kidney failure, threatening the dog's life.

How Do Dogs Get Heartworm?

1. Mosquito Bites: The Primary Mode of Transmission

The most common way dogs get heartworm is through mosquito bites. When a mosquito feeds on the blood of a dog already infected with heartworms, it picks up the microscopic heartworm larvae. The larvae then develop inside the mosquito and, after about 10 to 14 days, are ready to be transmitted to another dog. When the infected mosquito bites a healthy dog, the larvae enter the dog’s bloodstream, where they travel to the heart and lungs, eventually maturing into adult heartworms.

2. The Lifecycle of Heartworms in Dogs

Once the larvae enter the dog’s body, they travel to the lungs and the right side of the heart, where they mature into adult worms. The adult heartworms then mate and produce microfilariae, which are microscopic baby worms that circulate in the dog’s bloodstream. When another mosquito bites the infected dog, it picks up these microfilariae, continuing the lifecycle.

Here’s a breakdown of the heartworm lifecycle in dogs:

Step 1: A mosquito bites an infected dog and takes in microfilariae (baby heartworms) from the dog’s blood.

Step 2: The microfilariae mature inside the mosquito into infective larvae over 10 to 14 days.

Step 3: The mosquito bites another dog, injecting the larvae into the dog’s bloodstream.

Step 4: The larvae travel through the dog’s body to the heart and lungs, maturing into adult heartworms.

Step 5: Adult heartworms reproduce, producing more microfilariae that circulate in the dog’s blood and are available to be picked up by other mosquitoes.

Why Are Some Dogs More at Risk for Heartworm?

• Geographical Location

Dogs in certain regions are at a higher risk of heartworm infection. Areas with warm and humid climates are more favorable for mosquito breeding and survival. For example, in the southern United States, where summers are long and hot, the mosquito population is relatively large, increasing the likelihood of heartworm transmission.

• Outdoor Exposure

Dogs that spend a significant amount of time outdoors are more likely to be bitten by mosquitoes. Dogs that like to roam in wooded areas, near bodies of water (where mosquitoes breed), or those that sleep outside without proper protection are at greater risk.

• Lack of Preventive Treatment

Dogs that do not receive regular heartworm preventive medications are highly vulnerable to infection. Even in areas with a relatively low mosquito population, the risk still exists, and preventive treatment is the best way to safeguard against heartworm.

• Age and Health

Young puppies, older dogs, and dogs with weakened immune systems are more susceptible to heartworm disease. Puppies that are not on a heartworm prevention regimen may also be at higher risk if exposed to infected mosquitoes.

How to Treat Heartworm in Dogs?

• Diagnosis

Veterinarians use a variety of methods to diagnose heartworm in dogs. One common test is the antigen test, which detects the presence of adult female heartworms in the dog's blood. Another test, the microfilariae test, looks for the presence of the larval stage of the heartworms in the blood. In some cases, X - rays, ultrasounds, or electrocardiograms may be used to assess the extent of damage to the heart and lungs.

If your dog is diagnosed with heartworm disease, treatment is possible but can be expensive, lengthy, and potentially risky. The treatment typically involves:

• Injections of an adulticide medication to kill the adult heartworms.
• Rest and exercise restrictions to prevent complications while the worms are being killed.
• Supportive care, such as medications to manage symptoms and address any secondary health issues caused by the infection.

In severe cases, surgery may be required to remove the heartworms.

How to Prevent Heartworm in Dogs?

Preventing heartworm is much easier—and cheaper—than treating it. Here are some key ways to keep your dog protected from heartworm disease:

1. Monthly Heartworm Preventatives

One of the most effective ways to prevent heartworm disease is by giving your dog a monthly heartworm preventative. These medications come in several forms, including oral tablets, topical treatments, and injectables. They work by killing any larvae that may have been transmitted by mosquitoes before they have a chance to mature into adult worms.

2. Year-Round Protection

Because mosquitoes are present year-round in many regions, heartworm prevention should continue year-round. Even in cooler months, heartworm prevention is necessary to protect your dog from exposure during warmer months.

3. Regular Vet Check-ups

Annual veterinary check-ups are essential for monitoring your dog’s overall health and for early detection of heartworm infection. During these visits, your veterinarian will perform a blood test to check for heartworm larvae and adult worms.

4. Control Mosquito Exposure

Limit your dog’s exposure to mosquitoes by keeping them indoors during peak mosquito activity (dawn and dusk). If your dog must be outside, use mosquito-repelling sprays and ensure they are in an area free of standing water where mosquitoes breed.

How to Deworm Your Dog?

Dog deworming can be divided into internal deworming and external deworming, the following are some common methods.

I. Internal deworming

Choose the right deworming medicine

• Choose according to your dog's age and weight

Puppies can usually be started on their first deworming at around 2 weeks of age, and then dewormed regularly thereafter according to the dewormer's instructions. For example, for a puppy with a low body weight, you can choose a dewormer that is appropriate for the puppy's dosage. Adult dogs are usually internally dewormed every 3 - 6 months. Different brands of dewormers have different weight ranges, so follow the instructions closely to determine the dosage to be given to your dog.

• Feeding method

In the case of tablets, you can feed the dewormer directly into your dog's mouth and let him swallow it. The tablets can also be crushed and mixed into a small amount of your dog's favorite food (e.g., canned food, jerky, etc.), but make sure that your dog eats all of the food mixed with the tablets. For liquid forms of deworming medication, you can use a syringe or dropper to slowly drop the medication into the corner of your dog's mouth and allow him to swallow it on his own.

• Observation after deworming

After deworming your dog internally, observe your dog's feces closely. If adult worms are discharged or if there are abnormal fecal characteristics (e.g. diarrhea, blood in stool, etc.), it may be necessary to consult your veterinarian whether further examination or treatment is required.

II. In vitro deworming

Choose suitable deworming products

• Drops

These drops generally work by dropping them on your dog's skin, and then the drug will spread throughout the body. For example, drops are applied to the skin on the back of the dog's neck, as dogs are less likely to lick this area. Different brands of drops are suitable for different weight ranges, so choose the right product for your dog's weight.

• Collars

De-worming collars are also a form of in vitro de-worming. The collar contains deworming ingredients that are released slowly and work to repel and kill external parasites. However, the effectiveness of the collar may vary depending on the quality of the product and the activity of the dog.

Usage

• Drops

Before applying the drops, ruffle your dog's fur to expose the skin. Then follow the product instructions and place the appropriate amount of drops exactly on the skin. Avoid bathing your dog immediately after applying the drops to ensure that the medication takes full effect.

• Collar

Choose the right size collar to ensure that it fits comfortably around your dog's neck and is neither too tight to strangle your dog nor too loose to fall off easily. Replace the collar regularly according to the instructions to maintain the deworming effect.

Precautions

After the in vitro deworming, observe whether the dog has any skin allergic reaction, such as itching, redness and swelling. If there is any abnormality, remove the collar or wash off the drops immediately and consult your veterinarian.

FAQs

What does a heartworm cough sound like?

Can heartworm in dogs be cured?

What causes a dog to get heartworm?

Conclusion 

Dogs get heartworm disease through the bite of an infected mosquito, which introduces heartworm larvae into their bloodstream. This parasitic disease can cause severe health problems and even be fatal if not caught early. Preventing heartworm in dogs is much easier than treating it, and routine prevention, regular vet visits, and minimizing mosquito exposure are key to keeping your dog safe. If your dog shows any signs of heartworm disease, seek veterinary care immediately for diagnosis and treatment.

By understanding how dogs get heartworm and taking steps to prevent it, you can ensure your dog lives a long, healthy, and heartworm-free life.