Several parasites tend to infect our furry friends more so than others. It’s important to know how to properly protect your pet against parasites so he or she can live a happy, healthy, parasite-free life for as long as possible. Chances are you have probably heard about the nuisance of flea and tick infestations, but you may not be as familiar with another important parasite-derived illness: heartworm disease. A heartworm infection can lead to a life-threatening number of worms that colonize the heart and nearby vessels, possibly leading to heart failure and death. Additionally, though very rare, heartworm can lead to nodular inflammation of the lungs in humans and is therefore a public health risk. So, you’re probably wondering: how can pets get heartworm disease, is my pet at risk, and what can I do to prevent it?


The Basics

Heartworm disease is caused by an organism known as Dirofilaria immitis, which is transmitted by mosquitoes. A mosquito acquires Dirofilaria immitis by feeding on an infected animal, and then deposits microfilariae (larval stages of Dirofilaria immitis) in an animal which it feeds on. The microfilariae enter the host animal through bite wounds and mature over the next 2 months to become adults.

The development of microfilariae in the mosquito is associated with temperature: development increases at higher temperatures, can be slower at cooler temperatures, and stops at temperatures below 57F. Because temperatures have been higher than normal this year, it is likely your pet could be affected by parasites early in the year, not just the summer months! Once mature, adult heartworms enter the blood supply, travel to the heart and pulmonary arteries, and replicate in the pulmonary vasculature. Male adult heartworms can be up to 5-6 inches long, female adult worms can be up to 10-12 inches long, and adult heartworms can live for 5-7 YEARS in a dog and 2-4 YEARS in a cat!

Besides taking up vital space in the heart and blood vessels, a heartworm infection damages blood vessels and causes an inflammatory response. Because of the worm load and associated damage, an infected animal’s heart may have trouble pumping normally, potentially leading to right heart failure. This is a serious, life-threatening infection, and there are several symptoms you should be aware of.


Signs and Symptoms

Common signs of heartworm disease in a dog include coughing, trouble breathing normally, weight loss, exercise intolerance, bulging of the external jugular vein on the neck (known as jugular venous distension), and fluid in the abdomen (known as ascites). Cats with heartworm disease frequently have a cough, trouble breathing normally and/or wheezing. Sudden death can occur in 10-20% of cats with heartworm disease. The severity of symptoms is influenced by worm numbers, the infected animals’ immune response, and duration of infection.

Dogs and cats that live outdoors are at highest risk of developing heartworm disease due to the increased risk of mosquito exposure, though any dog or cat, indoor or outdoor, can develop heartworm disease. There are a high number of heartworm infection cases in the Southeastern United States, Mississippi River Valley, and Northern California. Although it can be a terrible disease, there are very reliable ways to detect, treat, and prevent against heartworm infection.


What to do

The Companion Animal Parasite Council recommends annually testing all dogs, even those on preventive medication, for heartworm and using preventive heartworm medication for all dogs year-round. Annual heartworm testing should only be performed on dogs at least 6 months old, and requires a blood sample.

Dogs should receive monthly heartworm preventives consistently to avoid infection. Luckily, there are a wide variety of options available, including topical and oral medications. Many preventive medications are also formulated to work against other common parasites such as fleas, ticks and intestinal parasites.

Should a dog test positive for heartworm, a variety of medications will be used to eliminate adult heartworms and microfilariae. Microfilariae can carry bacteria known as Wolbachia, so antibiotic therapy is often used in treating heartworm positive dogs as well.

The Companion Animal Parasite Council recommends testing cats for heartworm prior to starting them on preventive medication, and maintaining all cats on preventive medication year-round. Testing cats for heartworm requires a blood sample.

Unfortunately, there are currently limited treatment options for feline heartworm disease. Because of the limited treatment options available for cats, it is very important to consistently give cats heartworm preventive medications. Anti-inflammatory medications and bronchodilators may be useful in managing coughing, wheezing, and breathing issues in heartworm positive cats.

With so many options in heartworm prevention and control, it is important to discuss options with your veterinarian, as he or she will create a treatment plan specifically for your pet’s needs. We hope this has been a helpful resource. Should you have any questions about testing your pet for heartworm or starting your pet on preventive medication, please do not hesitate to schedule an appointment with us today!