Since 1949 the veterinary staff at La Jolla Veterinary Hospital has made heartworm prevention for dogs an important part of our approach to preventive care. A heartworm infection can lead to numerous health problems up to and including early death. Therefore, heartworm prevention cannot be ignored. Our team is here to educate you and protect your dog from this terrible disease.
While outdoor playtime certainly offers numerous benefits for dogs, it also increases the risk of exposure to heartworm. This does not mean that dogs are completely safe indoors. It simply means that potential exposure to heartworm infection increases with more exposure to the outdoors.
Heartworm is spread through dogs via bites from infected mosquitoes. Living in CA, the presence of mosquitoes throughout the spring, summer, and early fall months mean greater chances for your dog to contract heartworms. Once a heartworm infestation occurs, it will become life-threatening. Therefore, our goal is to implement a preventive program before your dog is exposed.
What is Heartworm Disease?
Heartworm disease in dogs is a blood-borne parasitic nematode (roundworm) known as Dirofilaria immitis that is transmitted by mosquitoes.
Upwards of 30 species of mosquitoes can act as heartworm transmitters. Mosquitoes ingest immature heartworm larvae, called microfilariae, by feeding on either an infected cat or dog. The microfilariae develop further for 10 to 30 days in the mosquito's gut and then enters parts of the mosquito's mouth.
When an infected mosquito bites a dog, it injects larvae into the dog. The larvae then mature over a period of several months, eventually ending up in the right side of the heart and the pulmonary arteries. Once this occurs, they mature into adult heartworms in dogs and can reproduce about six months from the time of the invasion. At approximately eight months after the invasion, heartworms in dogs begin to produce a new crop of microfilariae, which will live in the dog's blood for about one month. By the time this occurs, most dogs are showing significant heartworm symptoms, and their lives are in danger.
Heartworm Symptoms - The Four Stages of Heartworms in Dogs
Heartworm symptoms in dogs are divided into four stages. It is important to understand that individual stages are not always clearly identifiable, and some stages can overlap, but the following information will help educate you about the four major stages as well as their accompanying heartworm symptoms. The four clinical stages of heartworm begin when your dog has already become infected and the heartworms are present in the dog's heart:
Stage 1: In dogs, the first stage of heartworm will typically be symptom-free. In this stage, the heartworms are present and settling into the heart. However, in stage one the disease has not yet progressed to the point where the heartworms will have produced a new generation of microfilariae, and the dog's body will not yet have produced antigens in an amount sufficient for detection.
Stage 2: Stage two of heartworm in dogs is accompanied by moderate symptoms, including intolerance for exercise and a lingering cough. The heartworms have been present in the body long enough for antibody production and probable microfilariae production. During this phase, heartworm disease may be detected with blood tests.
Stage 3: By stage three of heartworm in dogs, the symptoms of the disease will be very noticeable and have a big impact on your dog's health. Dogs who continue to cough and experience fatigue after exercise may be reluctant to exercise at all and can have trouble breathing. During this stage, dogs may also cough up blood. By stage three, the disease is quite evident, and the worms in the heart and large vessels will be obvious on X-rays.
Stage 4: Dogs in stage four of heartworm disease have very visible heartworm disease symptoms. These symptoms are accompanied by long-term implications for the dog's health. These dogs are very ill. The symptoms are similar to those in Stage 3 but more severe. Dogs will be reluctant to exercise, tired after exercising, and will exhibit a cough. They will probably experience trouble breathing as well. Testing may reveal the impact of the disease in the form of abnormal sounds within the dog’s heart and lungs and an enlarged liver. Even with treatment, this stage of the disease carries a high risk of long-term debilitation and possible death.
The severity of heartworm disease in dogs is directly dependent upon:
- The number of worms present in a dog's body
- The duration of the incubation
- The response of the infected dog in fighting off the infestation
As heartworm disease progresses through each stage, the treatment methods become increasingly invasive. This is a big reason why early detection plays a major role in the options and ability of your dog to recover. Remain aware of any changes in your dog's behavior. Keep an eye out for any changes in behavior that align with the symptoms of heartworm, and if your dog is displaying symptoms that could be indicative of heartworm, it is important to make a veterinary appointment right away.
Other heartworm symptoms include:
- Fainting Spells
- Right-Side Chronic Heart Failure
- High Blood Pressure
- Rapid Heart Beat
It is important to understand that the symptoms listed above are indicative of advanced-stage heartworm disease. Unlike medications that are used to prevent heartworm in dogs, the medications that are used to kill an advanced stage heartworm infection carry a higher rate of potential side effects can be painful for the dog and are costly to the owner. In addition, the treatment will require considerable downtime from your dog's normal exercise routine while the dog recovers from the infection.
Heartworm Prevention for Dogs
Heartworm prevention is given in the form of a monthly chewable, which is readily accepted by most dogs as a treat. It is very important that the chewable be given once a month on the same day of the month to make sure that your dog is adequately protected. Side effects of chewable medication are rare. However, as with any medication, please call if you notice any changes in your dog's health or behavior.
What You Need to Know about Heartworm Treatments
The first thing to understand is that there is a significant difference between heartworm prevention and heartworm treatment. Prevention is simple to do and is effective in protecting your dog from heartworm disease. Treatment options are used for dogs that are already sick because they have become infected.
The first step in heartworm treatments is obtaining a diagnosis. Most veterinarians use a battery of tests to determine the presence of heartworms in dogs. The first step in the diagnosis of heartworm in dogs is to perform a blood test.
A positive heartworm blood test is the first step in the diagnosis. If the blood test comes back positive, then the following tests will also be performed to determine the stage and severity of the disease in order to determine the most appropriate treatment plan:
- A urinalysis, or the testing of the dog's urine.
- An antigen test determines the presence of adult female heartworms.
- Radiographs, or X-rays, to view the size and shape of the dog's heart. This is helpful because many dogs with heartworm develop enlarged pulmonary arteries or have obstructions in the arteries leading to the lungs.
- Ultrasound allows us directly view the internal structures of the heart and surrounding vessels in order to assess the condition and function of the heart
During initial heartworm treatments, most dogs are hospitalized to receive an adulticide, which is a medication that kills adult heartworms. The microfilariae in the body can be eliminated through monthly prevention, which can be administered at home.
For more severe cases, such as dogs experiencing thromboembolic complications (in which a blood clot that has formed breaks loose and travels through the bloodstream to clot another vessel), hospitalization may be necessary for a longer period of time while heartworm treatments are administered. In some extreme cases, a surgical procedure may be necessary to remove adult worms from the right heart and pulmonary artery by way of the jugular vein. This procedure is recommended if the infestation consists of a high number of adult worms.
Ask Your Veterinarian about Heartworm Medicine for Dogs
It is important to consult your veterinarian when making preventive care decisions for your dog. This is true for a variety of reasons. There are many over-the-counter products on the market today, which range from ineffective to outright dangerous. Our veterinarians are trained and qualified to help you make the best decisions regarding preventive care and treatment of any health conditions your dog may develop, especially when it comes to parasitic infections.
Heartworm is an easily preventable disease. If your dog is not currently using a veterinarian-recommended heartworm prevention medication, please schedule an appointment right away. There is no reason for your dog to be exposed to heartworm disease when prevention is so simple.