Heartworms are a parasite carried by mosquitos that can infect dogs (and sometimes cats). As their name implies, the primary site of infection is the heart and lungs. Dogs can become infected from the bite of a single mosquito if it is carrying heartworm microfilaria (larvae). If the dog is not protected by heartworm prevention, these larvae grow into adult worms, breed inside the dog and those adults produce more microfilaria. Mosquitos become carriers of microfilaria when they bite a dog that is infected, and thus the life cycle continues.

Dogs infected with heartworms can have a wide range of symptoms. Those very lightly infected can be asymptomatic, especially early on in the disease. But as the number of heartworms increase in the individual patient or changes occur in the heart and lungs over time, symptoms can range from a mild cough, exercise intolerance and weight loss, to complete cardiovascular collapse from caval syndrome. Caval syndrome is a result of complete blockage of blood flow through the heart and is quickly fatal if the heartworms are not removed surgically.

The treatment of heartworms is a traumatic and costly process. Patients have to be on a month of antibiotics, then injected 3 times with a drug called melarsomine, which is an arsenic derivative. Since the worms break into pieces after they die, dogs with heartworms must have very strict activity restriction to minimize chances of clots as they can lead to sudden death. With appropriate treatment, this rest period is limited to about 12 weeks. However, if a heartworm infection is left untreated, the worms can die at any time, with the potential for clots and sudden death over several years.

The best way to manage heartworms is by preventing infection. There are several excellent preventives available. Most are oral chews that should be given monthly. These monthly medications kill any heartworm larvae that have been injected into the bloodstream by mosquitos. They are only effective against very early stages of microfilaria, so if more than one month of prevention is missed, there is the risk of heartworm infection. We have found that setting a reminder on your phone or giving it on the first of the month is the best way to remember. If you find that you are having trouble remembering to give monthly preventive, there is another option in the form of an injection called Pro-Heart. Pro-Heart is an extended-release injectable heartworm prevention that lasts for 12 months. It eliminates the need to remember to give prevention each month.

It is vital to maintain prevention of heartworms year-round, especially in an urban area like Richmond. Data shows that urban areas are significantly warmer than suburban and rural areas due to asphalt radiation and reduced tree coverage; this extends the transmission season into colder months. Combined with the micro-environments provided by buildings and other aspects of urban areas, dogs here are never safe from heartworms, even in the winter. Don’t leave your dog unprotected!

For more information and all the latest research on heartworms, check out the American Heartworm Society at https://www.heartwormsociety.org/. If you would like to discuss heartworm preventive options, give us a call at 804-424-3600.