Achy Breaky Heart

Written by: Karen Drummond, Ph.D

When Billy Ray Cyrus sang his well-known song, he wasn’t referring to Beardies, but our Beardies certainly are prone to having their hearts be achy and break due to Heartworm disease. Most of us realize that in the deep south it’s more a matter of WHEN — not IF — a dog is going to present with heartworm disease if they are left unprotected. Unfortunately, a lot of the rescues that we attempt to help are heartworm positive, as they haven’t been protected with the monthly treatments.

The reality is, you should have your vet check for heartworms yearly, even if you have been religious about prevention. Leaving them unchecked can be deadly. Heartworm is carried by infected mosquitoes. The disease is unique to animals, but is not a threat to humans. Mosquitoes that carry heartworm are now in all 50 states, and there is no area that is totally free from the possibility of infection. Even arid areas like Arizona that used to be free of the problem now have incidents due to irrigation (mosquitoes breed in standing water).

The key to understanding the disease is to understand how it develops. Once a mosquito bites an infected host, the mosquito acquires the disease microfilaria. Once inside the mosquito, the microfilaria go through three stages, called molting, in 14 days. When the third one occurs, the microfilaria migrate to the mosquito’s salivary glands, which then allows them to infect Fido or Fifi when they bite them. Once a dog is bitten by an infected mosquito, it generally takes about 7 months for the larvae to mature into adult worms, which is when they can be detected by blood tests. At that point, they start their paths of destruction by lodging in the heart, lungs and surrounding blood vessels. These worms then start to reproduce within these organs, and continue to grow. At maturity they can be 12 inches or more long, and actually can live between 5 to 7 years inside of the dog. It is estimated that dogs can harbor around 250 worms in their systems. These worms begin to block ventricles of the heart or blood vessels that feed the heart, and eventually can cause a blockage that ultimately results in death.

So, how do you know if your dog has heartworms? When he or she is first infected, neither you nor your vet will not be able to diagnose it. You will not see any symptoms until the worms mature, when a blood test will be positive. When it reaches that stage, they hungrily arrive at the right ventricle and neighboring arteries and begin damaging them. The dog’s body responds with infammation to try to repair the damage, but the heartworms cause damage faster than the body can repair itself. The artery becomes severely damaged and dilated. Blood clots can form, and aneurysms are common. Also, a complete blockage can occur. When this artery gets blocked the blood re-routes to other arteries, but then blocks more vessels, causing fluid in the lungs, which reduces the lungs’ ability to oxygenate the blood. Over time the worms continue to grow, mature and reproduce, finally filling the heart and vessels and eventually causing heart failure. In these later stages, your dog may experience coughing, wheezing, a change in activity level, loss of appetite and weight, or even jaundice.