Heartworm has been diagnosed in dogs in all 50 states. It is very common and has a virtual 100% prevalence rate in unprotected dogs living in highly endemic areas. Mosquitoes transmit heartworms. The mosquito injects microscopic larvae, which grow into adult worms six to eighteen inches long within 6 months. These worms reside inside the heart and pulmonary vessels of affected dogs.
The heartworms can initially cause mild symptoms, such as coughing. With time, however, more severe symptoms such as weight loss, fluid build up in the abdomen, fainting spells, anemia, congestive heart failure, collapse, and death can occur.
Luckily, we have several excellent medications which can prevent heartworms, if given as directed. There are oral medications which are given monthly and also help protect against many intestinal parasites. There is also a monthly topical medication that helps to prevent flea infestation, too. An injectable medication, that is administered every six months, is back on the market after being withdrawn for several years. However, there are so many precautions with the product that we do not feel comfortable using it at this time.
The American Heartworm Society says it is important to check all dogs yearly for heartworms by doing a blood test–even dogs that have been on preventative. Many people are not totally compliant about giving the medication on time, and no medication is perfect. If a dog has heartworms and it is given a dose of preventative, they can have a serious reaction that is detrimental or even deadly.
The treatment for adult heartworms in dogs is expensive and can have significant side effects. This is why it is much better to just prevent the disease in the first place.
Heartworms were once thought to be rare in cats. But, the disease in cats is different than in dogs. Cats usually test negative on the routine blood test done in the hospital, the worms are smaller and usually do not produce microfilaria (which are like baby heartworms) that circulate in the bloodstream. Veterinarians have to do different tests, sometimes more than one, to diagnose heartworms in cats, and even then the disease can be hard to detect.
The symptoms in cats are different also. Cats usually have asthma-like signs, including coughing and vomiting.
There is not a treatment for adult heartworms in cats, at this time. Some veterinarians are now recommending monthly heartworm preventative in cats also.