Heartworms are a nasty parasite spread by mosquitoes. These worms can cause terrible consequences for your dog. Knowing the warning signs of a heartworm infection in your pet can save its life. Early detection and treatment are essential. You should also take preventive measures when you can. Heartworm disease is a serious disease that results in severe lung disease, heart failure, other organ damage, and death in pets, mainly dogs, cats, and ferrets. It is caused by a parasitic worm called Dirofilaria immitis.The worms are spread through the bite of a mosquito. The dog is the definitive host, meaning that the worms mature into adults, mate, and produce offspring while living inside a dog. The mosquito is the intermediate host, meaning that the worms live inside a mosquito for a short transition period in order to become infective (able to cause heartworm disease). The worms are called “heartworms” because the adults live in the heart, lungs, and associated blood vessels of an infected animal.
In an infected dog, adult female heartworms release their offspring, called microfilariae, into the dog’s bloodstream. When a mosquito bites the infected dog, the mosquito becomes infected with the microfilariae. Over the next 10 to 14 days and under the right environmental conditions, the microfilariae become infective larvae while living inside the mosquito. Microfilariae cannot become infective larvae without first passing through a mosquito. When the infected mosquito bites another dog, the mosquito spreads the infective larvae to the dog through the bite wound. In the newly infected dog, it takes between six and seven months for the infective larvae to mature into adult heartworms. The adult heartworms mate and the females release their offspring into the dog’s bloodstream, completing the lifecycle. See a graphic of the heartworm lifecycle in dogs. Inside a dog, a heartworm’s lifespan is five to seven years. Adult heartworms look like strands of cooked spaghetti, with males reaching about 4 to 6 inches in length and females reaching about 10 to 12 inches in length. The number of worms living inside an infected dog is called the worm burden. The average worm burden in dogs is 15 worms, but that number can range from 1 to 250 worms.
How Do the Symptoms of Heartworms Present?
The first sign you will notice is your dog tiring more easily. It may have a deep, persistent cough and can no longer tolerate normal activity such as going for a walk. As the infection begins to manifest further, your dog will lose weight and become faint after brief exercise. Its ribs may become more prominent and its chest may bulge.
The severity of heartworm disease is directly related to how many worms are living inside the dog (the worm burden), how long the dog has been infected, and how the dog’s body is responding to the presence of the heartworms. The dog’s activity level also plays a role in the severity of the disease and in when symptoms are first seen. Symptoms of heartworm disease may not be obvious in dogs that have low worm burdens, have been recently infected, or are not very active. Dogs that have heavy worm burdens, have been infected for a long time, or are very active often show obvious symptoms of heartworm disease.
There are four classes, or stages, of heartworm disease. The higher the class, the worse the disease and the more obvious the symptoms.
The severity of heartworm disease is directly related to how many worms are living inside the dog (the worm burden), how long the dog has been infected, and how the dog’s body is responding to the presence of the heartworms. The dog’s activity level also plays a role in the severity of the disease and in when symptoms are first seen. Symptoms of heartworm disease may not be obvious in dogs that have low worm burdens, have been recently infected, or are not very active. Dogs that have heavy worm burdens, have been infected for a long time, or are very active often show obvious symptoms of heartworm disease.
There are four classes, or stages, of heartworm disease. The higher the class, the worse the disease and the more obvious the symptoms.
- Class 1: No symptoms or mild symptoms such as an occasional cough.
- Class 2: Mild to moderate symptoms such as an occasional cough and tiredness after moderate activity.
- Class 3: General loss of body condition, a persistent cough, and tiredness after mild activity. Trouble breathing and signs of heart failure are common. For class 2 and 3 heartworm disease, heart and lung changes are usually seen on chest x-rays.
- Class 4: Also called caval syndrome. There is such a heavy worm burden that blood flowing back to the heart is physically blocked by a large mass of worms. Caval syndrome is life-threatening and quick surgical removal of the heartworms is the only treatment option. The surgery is risky, and even with surgery, most dogs with caval syndrome die.
How Are Heartworms Detected?
Most of the time, your veterinarian will perform a blood test to determine whether your dog has heartworms or not. During this test, the lab will look for the heartworm antigen. An antigen creates antibodies. Sometimes, false negatives occur if the stage of the disease is early and retesting becomes necessary. Your vet will need to administer chest X-rays and ECGs to determine the severity of the infection.
How Are Heartworms Treated?
There are different treatment options depending on the severity of infection. Heartworms can cause major complications including congestive heart failure, liver disease, and kidney issues. These problems can be fatal. If your dog has a non-complicated case of heartworms, the main goal of your vet is to kill the worms. In most cases, your vet will prescribe a medication to accomplish this. The vet will keep your dog in the clinic for a few days for observation. Sometimes, however, the meds used to eradicate heartworms become toxic to the dog and cause dead worms to be flushed into the lungs.
The most common test that a veterinarian uses to check a dog for heartworms is called an antigen test. This blood test detects specific proteins, called antigens, which are released by adult female heartworms into the dog’s bloodstream. In most cases, antigen tests can accurately detect infections with one or more adult female heartworms that are at least seven or eight months old, but the tests generally do not detect infections that are less than five months old.
There are also tests that detect microfilariae in a dog’s bloodstream. Microfilariae in the bloodstream indicate that the dog is infected with adult heartworms (because only adult heartworms can mate and produce microfilariae). Microfilariae can be detected in a dog’s bloodstream about six to seven months after it is bitten by an infected mosquito (because six to seven months is the time it takes the heartworms to develop from infective larvae into adults that mate and produce microfilariae).
There are two drugs approved by the U.S. Food and Drug Administration (FDA) for the treatment of heartworm disease in dogs. Both drugs contain arsenic and are effective at killing adult heartworms. Caparsolate Sodium (arsenamide sodium), the older of the two drugs, is injected into a vein. It is not currently manufactured or marketed in the United States. The newer drug, Immiticide (melarsomine hydrochloride), is given by a deep injection into the back muscles to treat dogs with stabilized class 1, 2, and 3 heartworm disease.
Currently, no drugs are approved to get rid of microfilariae in the bloodstream. However, certain approved monthly heartworm preventives are sometimes used by veterinarians in an extra-label (“off-label”) manner to get rid of the microfilariae.
The treatment for heartworm disease is not easy on the dog or on the owner’s pocket book. Treatment can be potentially toxic to the dog’s body and can cause serious complications, such as life-threatening blood clots to the dog’s lungs. Treatment is expensive because it requires multiple visits to the veterinarian, bloodwork, x-rays, hospitalization, and a series of injections with Immiticide.
The most common test that a veterinarian uses to check a dog for heartworms is called an antigen test. This blood test detects specific proteins, called antigens, which are released by adult female heartworms into the dog’s bloodstream. In most cases, antigen tests can accurately detect infections with one or more adult female heartworms that are at least seven or eight months old, but the tests generally do not detect infections that are less than five months old.
There are also tests that detect microfilariae in a dog’s bloodstream. Microfilariae in the bloodstream indicate that the dog is infected with adult heartworms (because only adult heartworms can mate and produce microfilariae). Microfilariae can be detected in a dog’s bloodstream about six to seven months after it is bitten by an infected mosquito (because six to seven months is the time it takes the heartworms to develop from infective larvae into adults that mate and produce microfilariae).
There are two drugs approved by the U.S. Food and Drug Administration (FDA) for the treatment of heartworm disease in dogs. Both drugs contain arsenic and are effective at killing adult heartworms. Caparsolate Sodium (arsenamide sodium), the older of the two drugs, is injected into a vein. It is not currently manufactured or marketed in the United States. The newer drug, Immiticide (melarsomine hydrochloride), is given by a deep injection into the back muscles to treat dogs with stabilized class 1, 2, and 3 heartworm disease.
Currently, no drugs are approved to get rid of microfilariae in the bloodstream. However, certain approved monthly heartworm preventives are sometimes used by veterinarians in an extra-label (“off-label”) manner to get rid of the microfilariae.
The treatment for heartworm disease is not easy on the dog or on the owner’s pocket book. Treatment can be potentially toxic to the dog’s body and can cause serious complications, such as life-threatening blood clots to the dog’s lungs. Treatment is expensive because it requires multiple visits to the veterinarian, bloodwork, x-rays, hospitalization, and a series of injections with Immiticide.
What Are Some Preventive Measures for Heartworms?
An effective way to prevent a heartworm infection is to prevent mosquitos from biting your dog. There is no way to prevent this completely, but you can limit your dog's exposure. Keep your dog indoors in the early evening and at night when mosquitoes are hungry. Since mosquitos love moisture, keep your dog away from swampy areas and ditches. Provide your dog with preventive medication such as Frontline. You can ask your vet about the pros and cons of this medication and how to start your dog on a program.
Heartworm treatment is dangerous and very hard on your dog. The best thing you can do is be proactive in preventing an infection from occurring in the first place. Protect your dog from heavily populated mosquito areas and provide preventative medications. Know the signs and symptoms of heartworm disease and get your dog to the vet as soon as possible if you suspect infection. Early detection and treatment can and will save your dog's life.
Some information from :
10903 New Hampshire Avenue
Silver Spring, MD 20993
Ph. 1-888-INFO-FDA (1-888-463-6332)
and
Jodi Laycock
Sk, Canada
