What are dog heartworms?
Dog heartworms are actual worms that live in the heart and its major vessels of a dog. They are round, thin and can be 10-12 inches long. It is a common disease that is serious and can be fatal. It causes damage to the heart, lungs, and other organs like the kidney and liver. It infects other canine species such as foxes, coyotes and wolves. These wild species are a constant carrier threat and unfortunately help spread the disease throughout the country.
How does my dog get heartworms?
Heartworms are transmitted through mosquitoes. The dog is the natural host for heartworms. This means that mature worms live in the dog and produce offspring. These “baby” worms are called microfilaria. The microfilaria circulate throughout the bloodstream and are picked up by mosquitoes when they feed. The microfilaria are then deposited into a new dog host when the mosquito feeds again. These transplanted microfilaria then grow to be adult worms in 6 months. They set up camp in the dog’s heart and major vessels and start producing babies of their own! Any dog, inside or out, can be infected wth heartworms. Every state in the United States has heartworm disease. However, states near the coast tend to carry a higher incidence of the disease. According to the American Heartworm Society, research has shown an increase in noncoastal states. It is believed to be due to weather changes that come from hurricanes. Also adopted stray dogs from hurricane diplacement are believed to spread this disease throughout the country.
What are the symptoms of heartworm disease?
It takes 5-7 years for a heartworm to mature and cause problems. Therefore, it can take years for a dog with heartworms to show symptoms. Once the symptoms start, they often relate to heart and respiratory disease. This includes coughing, shortness of breath, dull coat, weight loss, decrease appetite, abdominal distension and lethargy. In serious cases where the is a large amount of worms, passing out and acute death can be seen. Any dog showing some or all of these symptoms should be seen by a veterinarian
How does a veterinarian diagnose heartworm disease?
There are several tests that the veterinarians at Animal Medical Center can use to detect heartworm disease in your dog. Sometimes more than one are used to verify the disease.
- Antigen test-The standard in-clinic testing is an antigen test that checks for antigen from the worm in the dogs blood. An antigen is a foriegn substance detected by the body that often stimulates antibody production to fight the substance. This is a simple 10 minute test. Only adult, female worms produce antigen that is detected by the test. In addition, a worm burden of 5 or more females must be present to produce enough antigen for the test to be positive. With that said, an all male infection would go undetected with this test. Also, an immature infection would not show a positive. When negative anitgen result is produced in a dog with symptoms of heartworm disease, further testing is required.
- Microfilaria test- Sometimes heartworm disease can be diagnosed by seeing microfilaria in the blood. A small drop of the dog’s blood is placed on slide and examined with a microscope. The baby worms are seen in the blood in some cases. This test is often used to verify a positive antigen test.
- Echocardiogram-In rare cases, echocardiogram (heart ultrasound) is used to diagnose heartworms. The adult worms can been seen in the heart and major vessels during this procedure.
How is heartworm disease treated?
In a large amount of cases, heartworm disease is treatable. The first step to ensuring treatment success is to stage the disease. There are many levels of severity in this disease from no clinical changes to severe heart enlargement and renal disease. Chest xrays, bloodwork and a urinalysis may be run to stage your dog’s disease. Once these tests are evaluated, the appropriate treatment schedule is chosen. The main treatment for heartworms is a injection of a drug called Immiticide. The injection is given in the muscles of the back and kills the adult worms. A common treatment schedule includes and injection followed by one month of strict rest. Then a series of two injections are given 24 hours apart. Another month of strict rest follows this series. Strict rest is vital to treatment. When the worms dies, it breaks off in pieces and then is absorbed by the dog’s body. If the dog is too active, large pieces will break off and cause emboli in the vessels that can be fatal. Often, other medications are given during this treatment, including antinflammatories and antibiotics. These are chosen depending on the stage of disease. It is important to remember that Immiticide is a toxin and can have complications. These include painful nodules at injection site, lung congestions, fever, inappetance and vomiting. Worse yet, pulmonary inflammation, edema and death can occur. Once the treatment is completed, an antigen test is performed 6-12 months after to ensure the worms have been cleared. Occasionally, a dog will remain positive and a second round of treatment is needed. Severe cases with a large burden may not be eligible for this treatment protocol. In rare cases, dog’s have to be referred to a cardiologist for surgery to manually remove the worms. These patients are very ill, however, and carry a poor prognosis.
How can I protect my dog from heartworms?
Luckily, there is a way to prevent heartworm disease! Prevention medication can be given to keep your dog healthy. These medications are given monthly or every 6-12 months depending on what type you chose. Prior to starting prevention medication, all dogs over 6 months of age must be tested for heartworms. If your dog is negative, then prevention medication is started. The medications work by destroying certain stages of the immature worms before they reach adulthood. At Animal Medical Center, we have the option of using monthly oral prevention or an injection every 6 or 12 months. These products work very well but are not 100%, even if given perfectly. For this reason, the American Heartworm Society recommends yearly heartworm testing to ensure the health of your dog. What if your are late giving the medication? What if your dog vomits the medication when you are not looking? These yearly heartworm tests also make sure heartworms were not contracted during these times.