“The Good Word” by Dr. Carol Good – Rockford Animal Hospital
*Why does my dog need a heartworm and tick disease test every year?*
This is a very good question that has several good answers. In order to understand the reasons, I need to tell you a little more about the disease that heartworms cause in dogs and the medications that we use to prevent heartworm infection. (Next blog I’ll talk about heartworms in cats, so stay tuned!)
Heartworms really are worms that make their home inside the right chamber of the heart and the pulmonary veins where the blood flows. The adult worms live and breed there and pregnant females give birth to baby worms, called microfilaria, right into the blood stream. The babies swim and travel around with the blood inside the blood vessels just like fish swims in a river.
If a mosquito feeds on the blood of a dog infected with heartworms, they ingest the microfilaria along with the blood meal. Over two weeks, the microfilaria develop and migrate to the salivary glands of the mosquito.
When that mosquito feeds on another dog, a drop of saliva containing the microfilaria is left on the skin. These baby worms are small enough to travel through the tiny hole left by the mosquito bite and enter the dog’s body. Over the next 6 to 9 months, the microfilaria grow and mature and finally enter a blood vessel where they travel to the heart and become breeding adults.
In dogs, the disease caused by the adult worms is to the heart itself. As the worms bang around against the walls of the heart, heart valves and blood vessels, the heart is damaged. It leaks, enlarges and eventually the heart fails to pump blood properly and symptoms of congestive heart failure appear. Dogs will cough, not be able to exercise, have breathing problems and eventually die.
Baby heartworms are like sludge in the blood and clog up tiny blood vessels in organs like the liver and kidney. The resulting inflammation causes damage to these vital organs and they sicken as well.
There is no early warning sign that a dog has heartworm disease. Once outward signs of disease appear, serious, permanent damage is already done to the heart, lungs, liver and kidney. Even if a dog is treated to get rid of the worms, this damage persists.
What about tick disease? Is it really necessary to test for tick borne, bacterial infections every year? The answer is yes. The public health department confirms that Lyme disease is present in West Michigan and increasing. We are also seeing other tick borne infections like Ehrlichia and Anaplama more often.
These bacterial diseases are the great imitators. They can mimic other diseases or even hide out and be difficult to diagnose. By the time the infection is noticed, permanent infection and damage can be done to a dog’s body even if antibiotic treatment is given. In addition, every one of these bacteria can infect people. So, if your dog is getting exposed, so are you.
But why do you need a test every year if you are giving the heartworm/tick disease preventative medication? Doesn’t it work? Well, yes it does work, but it has limitations. Let me ask you a question. Have you ever heard of a person who was taking birth control medication but got pregnant anyway? I have.
Things happen. Maybe you think that your dog can’t get infected in the winter (they can!) so you stop giving preventative year round. What if you forget and are late giving your dog the heartworm preventative, miss a dose completely, or your dog vomits the pill up before it is absorbed? He can get infected! There is a “window of opportunity” that your dog must get the medication. This is the only time that the medication can kill the immature microfilaria growing up inside your dog. Once they mature beyond this point, the medicine will no longer kill them and the heartworms will complete their life cycle even if you continue to give the medication from then on.
It is very important that we find infections both of heartworms and tick borne diseases before they cause permanent damage or kill your dog. If we test annually we will have the best chance to find these parasite and bacterial infections before this happens. This is why annual testing is the best. Now, help out your dog and call us to schedule an appointment for a heartworm test if it’s been 12 months since this was last done. You will be doing both yourself and your dog a big favor.