Heartworms are large worms that live in the hearts of dogs and cats. Dogs are the most common hosts for this parasite. Heartworms are also known as Dirofilaria Immitus. The adult heartworm lives in the right chamber of the heart and pulmonary artery which routes blood through the lungs where carbon dioxide is removed and oxygen is added to the red blood cells. Heartworms can cause significant damage and even death.
Heartworms are transmitted when a mosquito bites an infected dog and picks up microscopic versions of the heartworm called microfilariae. These microfilariae live in the salivary glands of the mosquito for about two weeks. When the mosquito bites another dog or cat, some microfilariae finds it’s way into the wound where it migrates through the tissue, following veins to the heart. This process usually takes between 70 and 90 days.
As the larvae migrate, they molt and continue to grow in size. If both sexes are present, they will begin producing their own microfilariae within 6 to 7 months after the mosquito bite occurs. The more times a dog or cat are bitten by infected mosquitos, the more heartworms they can acquire. The signs of heartworm disease will vary according to the number of worms present, stage of the worm’s life cycle and the age and species of the host.
Acute Disease—There are usually no clinical signs at this stage, the dog has just acquired the disease.
Mild to Moderate—cough, resistance or inability to exercise.
Severe—coughing, fainting episodes, fever, marked shortness of breath, weight loss, abdominal swelling and even death.
Possible Signs of Heartworms in Cats:
The signs of heartworm disease are different in cats than in dogs. The cat can live with the disease without exhibiting any clicical signs. The most common signs in cats mimic feline asthma—coughing and difficulty breathing. Vomiting can be a sign of heart worm disease in cats but vomiting is also a sign of many other feline diseases.
Prevention is the best treatment for heartworm disease. It is much less risky and less expensive than treatment for the disease. There are two main types of prevention: oral and topical. The most common oral preventative medication is ivermectin. Ivermectin is very effective in killing microfilariae. Common brands containing ivermectin are: Tri-Heart Plus, Ivehart Plus and Heartgard. Some dog breeds, especially collies, have a sensitivity to ivermectin and their owners may want to consider milbemycin medications, which include Sentinel and Interceptor.
Topical preventions are usually either moxidectin or selamectin medications. Both of these medications work to prevent the development of the microfilariae into mature heartworms and they slowly clear the bloodstream of the microfilariae. Revolution (selamectin) and Advantage Multi(moxidectin) are the most common brands of topical preventive medications.
Diagnosis of heartworm disease is most commonly done by a blood test in a veterinary office. Ultrasound, x-ray and other tests may also be performed. When a dog develops heartworm disease, treatment is essential for long-term survival. Most cases are treated with an injectable medication to kill the adult heartworms. The worms are killed slowly to prevent a sudden blockage in the heart or lungs and the patient must be kept quiet. At the present time, the only FDA approved injectable treatment for heartworm disease is Immiticide, which is an arsenic-based drug. Once the adult heart worms are killed, the microfilariae are killed using one of the preventative methods listed above.
If you have any questions about heartworm disease or about the preventative medications that are right for your pet be sure to consult your pet’s veterinarian.