by Rhonda Pierce, DVM
Dirofilariasis (heartworm disease) is caused by a parasitic roundworm called Dirofilaria immitis. This parasite is spread by mosquitoes. Female mosquitoes ingest the first stage larvae (L1) which are called microfilariae from an infected host (usually domestic dogs or wild canids such a coyotes, foxes and wolves). The first stage larvae will then mature in two stages to the third stage infective larvae (L3) in 10-18 days. The mosquito will then inject the L3 larvae during a blood meal into a susceptible host (dogs, cats, ferrets and other canids). The larvae then will develop in multiple stages over about 5-7 months into adult worms that produce microfilariae (the first stage larvae).
Heartworms primarily like to live in the pulmonary arteries; which carry deoxygenated blood from the right side of the heart to the lungs; but can also be found in other locations such as the eyes, systemic vasculature, peritoneal cavity and intramuscular or subcutaneous cysts/abscesses.
In our pets, the physical exam will usually be normal unless there is severe disease. Dogs with severe disease usually have weight loss, increased respiratory rates, and/or difficulty breathing. Cats with heartworm disease can vary from acting normally to having an asthma-like attack, periodic vomiting, decreased to no appetite, and/or weight loss.
Diagnosis of heartworm disease is usually via lab work and/or chest x-rays. At Ridge Lake Animal Hospital we utilize in-house and outside laboratories to test for heartworm disease. We will gently draw a blood sample from your pets and we may also need to collect a urine sample. We also have a digital x-ray unit for chest radiographs. Electrocardiograms (ECG) can be helpful and we have this diagnostic tool at our hospital as well.
Heartworm disease is characterized and treated based on the severity of the infection. Treating heartworm disease is a painful and potentially dangerous process. Therefore, as pet owners, preventing an infection in the first place is the best option. At Ridge Lake Animal Hospital we have multiple options to prevent Dirofilaria from ever infecting your pet. Please see one of our veterinarians to discuss which preventative is the best option for your dog or cat.
A great website for more detailed information is from the American Heartworm Society. See www.heartwormsociety.org.