Compliments of the Niagara Frontier Veterinary Society 

 Pets owners go to great lengths to ensure their animal companions are happy and healthy. Nutritious diets and routine visits to a veterinarian are two ways to keep pets healthy. Pet owners also can educate themselves about various conditions that can adversely affect their pets’ health, including heartworm. 

 What is heartworm? Heartworm is a potentially fatal disease caused by foot-long worms that can live in the heart, lungs, and associated blood vessels of affected pets. A pet affected by heartworm can develop severe lung disease, heart failure, and organ damage. 

 Are all pets vulnerable to heartworm? The Niagara Frontier Veterinary Society (NFVS) says that heartworm primarily infects dogs, cats, and ferrets. However, wild animals like foxes and wolves also can be infected, as can animals like raccoons and opossums that many people see in their backyards and local parks. Humans also have been infected with heartworm, though the AVMA® notes such instances are rare. 

 Heartworm and dogs. The American Heartworm Society (AHS) notes dogs are a natural host for heartworms. Heartworms that live inside a dog can mature into adults and even mate and produce offspring while inside the dog. Numbers increase if the dog is not treated for heartworm. Even if a dog is treated, the effects of heartworm infection can linger after the worms are gone, contributing to lasting damage to the heart, lungs, and arteries. 

Symptoms of heartworm infection in dogs may not manifest early on. The AHS notes that it’s more likely symptoms will develop the longer the infection persists. Such symptoms may include a mild, persistent cough; reluctance to exercise; fatigue after moderate activity; decreased appetite; and weight loss. 

According to the AHS, active dogs, dogs with heavy heartworm infections or those with additional health problems frequently exhibit pronounced clinical signs. 

 Heartworm and cats 

The NFVS notes diagnosis of heartworm in cats is more difficult than it is with dogs. Unlike dogs, cats are not natural hosts for heartworms, and most worms in cats do not make it to the adult stage. In fact, many cats with heartworm have no adult worms. That contributes to the difficulty of diagnosis, and it does not protect cats against harmful side effects of heartworm, including a condition known as heartworm associated respiratory disease (HARD). Signs of heartworm in cats can be subtle or very dramatic. Sadly, the first sign of heartworm in some cases is the sudden collapse or sudden death of the cat. If cats exhibit symptoms, signs may include coughing, asthma-like attacks, periodic vomiting, lack of appetite, weight loss, difficulty walking, fainting or seizures, and fluid accumulation in the abdomen. 

 Heartworm poses a potentially serious threat to cats and dogs. Pet owners are urged to speak with their veterinarians about heartworm prevention and what to do if a pet becomes infected.   

 The Niagara Frontier Veterinary Society consists of more than 75 small animal hospitals and 200 practitioners in Erie and Niagara counties. Visit to learn more.