Did you know that heartworm disease can start well before any recognizable clinical signs appear? Even worse, the disease can cause irreversible lung damage before you have the chance to diagnose it with standard antigen tests.¹ Let’s dig into the science to explore exactly how that can happen and why it’s essential to protect all your canine patients from heartworm disease. 

Once heartworms reach their adult length (10 to 12 inches) and heartworm infection progresses, they can cause chronic inflammation that leads to scarring and narrowing of the pulmonary arteries as well as thickening (fibrosis) of the surrounding lung tissue.¹ Lung pathology can occur within 4-5 months of a dog being infected, but antigen tests only start showing positives after 6-7 months. Thus, irreparable damage to the lungs can occur before heartworm disease is clinically diagnosed. 

The severity of the disease is influenced by factors such as the quantity of heartworms present, the duration of the infection, and the activity level of the dog.¹ Over time, heartworm infection results in notable thickening of the pulmonary arteries, obstructive disease, perivascular inflammation, and fibrosis. Additionally, natural, sporadic death of worms can trigger intense embolic and inflammatory reactions, leading to significant acute and long-term consequences. Worms can also interfere with heart valves, further worsening workload on the heart. This will ultimately lead to heart failure. Heartworms may also affect the kidneys or the liver through damaging effects of the body’s reaction to them being in other vessels in the body (caudal vena cava). 

“In my necropsy work, I have never seen a dog with a heartworm infection that didn’t have heartworm disease,” says Stephen Jones, DVM and American Heartworm Society board member and a past President of the American Heartworm Society. “And I have never necropsied a dog treated for heartworms that did not have permanent damage, even when the infection occurred many years before.” 

The ultimate goal of heartworm treatment is to slow down or stop the progression of the disease and to substantially resolve the acute disease over time. The takeaway should be that year-round, lifelong prevention is one of the most important recommendations veterinarians can give to protect the lifelong health of their patients. Stay ahead of lung damage and heartworm disease. Prioritize the heartworm disease prevention conversation with every dog owner during every visit. #ProtectMoreDogs 

Reference: 

1. Jones S. Heartworm disease causes lifelong damage. American Heartworm Society, Quarterly Update Summer 2019.