The Truth About Heartworm Disease
by Melissa Rotella, DVM

HW-heartAndrew is a sweet ten year old Golden Retriever who came into Route 516 Animal Hospital for his annual wellness exam and vaccinations. Andrew was an apparently healthy senior who did occasionally cough and had suffered from arthritis in his hind legs. A heartworm test was performed on Andrew, as it is recommended to test annually in our office. This test is performed using a small amount of blood and the results are obtained within minutes. The test will also notify the doctors of any exposure to Lyme’s disease and two other tick born diseases. This year, Andrew was found to be positive for Heartworm disease.
Heartworm disease is actually an infection from the parasite Dirofilaria immitis which is transmitted to dogs and cats from mosquitoes. Heartworm disease is most prevalent in warm areas, especially along the Gulf of Mexico, Atlantic coastline, and along the Mississippi River. Many people falsely assume that NJ is not a risk factor area. Andrew is proof that this assumption is not true, having never left the state.

The immature heartworm parasite, or larva stage, is transmitted through a bite of a female mosquito. The parasite then makes its way through the bloodstream to the heart where it develops into an adult worm. This process can take up to seven months to complete. It is the presence of the worms in the heart that causes inflammation and damage to the pulmonary arteries. A number of factors contribute to the severity of the disease including the duration of infection, number of heartworms present, the animals response to the worms, and how active the dog is. There is a wide range of clinical signs ranging from no outward signs, cough, weight loss, exercise intolerance, collapse, heart failure, and death.

HW-Life-Cycle-2012comparedogIt is possible to treat an active heartworm infection but it is also expensive and sometimes dangerous. It can take weeks for an infected animal to recover. Patients must be on strict cage rest following treatment for 4 to 6 weeks and reactions to the drug are possible. After a thorough work up, Andrew was started on a medication called Immiticide and was able to make a full recovery.
Heartworm disease is 100% preventable. There are a number of effective products on the market that will prevent infection. Medications such as Heartgard or Interceptor will kill the immature state of the parasite so that it can never develop into an adult worm. The American Heartworm Society ( recommends year round preventative.