Heartworm disease in dogs and cats
Does my dog need heartworm preventative medication year round even if he/she is mostly a house dog? This is one of the most common questions we get in everyday veterinary practice. Heartworm disease is a parasitic disease transmitted by mosquitoes. After being bitten by a heartworm infected mosquito, immature stages of heartworms called heartworm larvae gradually mature over many months and eventually end up at their final place of maturation in the pulmonary arteries of a dog or cat and/or to a lesser extent the heart.
Depending upon the individual susceptibility of a dog or cat, the average ambient temperature in the part of the country a guardian lives, and the number of heartworm carrying mosquitoes in an area, all of these factors affect the risk of infection in a given area. Heartworm positive animals have been documented in all 50 states, and the rate of infection can vary from 2 to 4 percent depending upon the factors mentioned above.
In cats, the risk is somewhat lower; however, heartworm infection in cats and subsequent pathology of the lungs and heart are being increasingly recognized and appreciated by the veterinary community. Symptoms of heartworm infection can range from sub clinical (meaning no symptoms at all), varying degrees of exercise intolerance, coughing and in severe cases abdominal swelling and right sided heart failure.
On occasion, a clot can form as the body attempts to rid itself of the heartworms, which can get into the circulation and potentially lodge in critical organs causing kidney, liver damage, or even sudden death. And while cats are often considered a “dead end” host for heartworms with most cats showing no symptoms, others cats are more sensitive to the presence of even one or two adult heartworms and the larvae, showing varying degrees of respiratory symptoms that are often mistaken as feline asthma, as well as chronic or intermittent digestive symptoms such as vomiting.
Heartworm transmission in the northern two thirds of the country lasts only several months a year, but in the south, transmission can occur year round. However with the increasing recent global warming, as well as the interstate travel that many people are now doing around the country at various points throughout the year, the American Veterinary Heartworm Society is now recommending year- round prevention. Their recommendations also come at a time when there is increasing concern of what are called zoonotic diseases, which are diseases potentially transmitted from animal to human. Most of the current monthly heartworm preventative medications have additional ingredients that also protect against zoonotic diseases, such as roundworms or hookworms.
There are plenty of safe monthly heartworm preventative medications on the market, with a long track record of reliability such as Heartgard Plus and Sentinel. Some of the newer topical flea/tick products also protect against heartworms; however, I remain a proponent of the tried and tested monthly preventatives that have been around for years, rather than the topical medications for heartworm prevention.
Many clients will often ask why their vets require heartworm testing every year. And while medically speaking, giving even a heartworm positive dog any of the newer monthly preventatives is not a problem in most cases, it is still a good idea to have your dog heartworm tested once a year. Although these products are close to 100 percent effective in heartworm prevention, there are still potential individual dogs that are uniquely susceptible to heartworm infection, even with diligent client monthly compliance in administration. If your pet is on heartworm prevention year-round, some veterinarians will allow every other year blood testing. However, if an animal guardian misses a few months of their pet’s heartworm preventative, it is NOT critical that they have them immediately tested before restarting the pills, which many veterinary offices still erroneously tell their clients. This immediate testing was only important when using the old daily heartworm prevention medications that were on the market years ago, because in those cases if one gave a heartworm positive dog one of the old daily pills such as Filaribits, there could be an increased risk of an allergic or life threatening anaphylactic reaction. While reactions to heartworm medications can occasionally occur, most pets tolerate them just fine and enjoy the chewable flavors that they often are packaged with.