421 East Fifth, P.O Box 460, Centuria, WI 54824
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Heartworm Dangers


Heartworm infection in dogs is becoming more common in many parts of the United States. Currently, one of the largest concerns is the lack of available Immiticide®, the only currently approved treatment for heartworm infections.  This makes prevention even more important. For the best protection it is essential to understand what it is and how it in contracted.  

Heartworm is, in fact, just as it sounds, a worm, a parasite that lives in the heart. Dirofilaira Immitis is the scientific name of the worms that grow into a 9 -16 inch worm. These worms live in the chambers of the heart (primarily the right ventricle) and the nearby pulmonary artery. Due to their length the bodies extend through the valves prohibiting proper closure as blood is pumped through.  Over time, this action will cause permanent damage to your dog’s heart and possibly lungs.   Symptoms vary from dog to dog but, commonly coughing and shortness of breath are the first to appear. Other organs such as the liver and kidneys can also be affected. Once the symptoms have appeared it may be too late for treatment. If left untreated heartworm disease can be fatal. Each year hundreds of dogs in the United States are confirmed positive. We here at Interstate Veterinary Hospital recommend seasonal disease testing each year. The test we perform includes Heartworm infection, Lyme disease, Anaplasmosis, and Erlichia Canis. Once we confirm your dog is negative a monthly preventative is available. These drugs attack the immature stage of the parasite, and prevent them from maturing to the adult stage.  These medications can cause complications in animals with established heartworm infections, for that reason they are only available by prescription through your veterinarian. The use of these monthly preventatives does not exclude periodic testing. This preventative combination has saved many lives. If your dog is positive for heartworm,  mild cases can usually be treated before symptoms appear.

Now we know what heartworm is but, how does it spread?  Mosquitoes!  In 7 easy steps and 9 short months the lifecycle of heartworm is complete.

Step 1 – A mosquito takes a blood meal from a heartworm infected dog, many microfilaria are taken in with this meal.  

Step 2 – Once in the mosquito, they travel to the digestive tract and spend 2-3 weeks maturing.

Step 3 – Once matured to the next stage the worms move to the mouthparts of the mosquito and wait for the mosquito to take its next blood meal.

Step 4 – While the mosquito feeds on its host, the worms are deposited onto the skin where they burrow into the tissue and continue to mature further.  Heartworms deposited onto non – canine species generally die within a few days.

Step 5 – After the increase in size the worms leave the tissue and enter the blood stream though the wall of a small vein.   They then travel in the blood stream and eventually lodge into the chambers of the heart. 

Step 6 - Once there they continue to grow until they can reproduce and send their own microfilaria into the blood stream for a mosquito to pick up on a blood meal. 

Step 7 - REPEAT

Even though your dog appears healthy, there is no reason to believe they do not have an early infection. We ask all responsible pet owners to not let their dog be responsible for a local outbreak.  

Heartworm life cycle courtesy of Rutgers in New Jersey http://www-rci.rutgers.edu/~insects/hartw.htm