The Latin name for the heartworm parasite is Dirofilaria immitis and the adult worm can be quite large, some as much as 35 centimetres in length.
The adult worm makes its home in the heart which is how it gets its name but in actual fact, it prefers to live in the pulmonary arteries where they get their nourishment from the blood as it pumps past on the way to the lungs.
The presence of worms in the arteries causes inflammation which, in turn can cause the blood to clot and cause secondary problems.
There can be as many as one hundred worms living in an infected dog but the infection load is medically termed as heavy in a smaller dog of around 40 pounds in weight if only twenty-five worms are present. At this point major problems start to occur as there are too many to fit into the arteries and they start to fill up the chamber in the heart which pumps blood into the dog’s lungs. This chamber is called the right ventricle and the problem for the dog at this point is that the heart cannot pump properly at this point and so there is less blood being pumped to the lung and it follows that there is less oxygenated blood to be pumped around the dog’s body. There is an amazing video on the heartworm treatment for dogs page which shows a successful operation on a dog that had 86 heartworms removed!
If the infection gets so bad that more than fifty worms are present this chamber of the heart is completely full and so the worms start filling up the chamber which receives blood from the dog’s body. This chamber is called the atrium. Untreated, the worm infestation keeps getting worse until the point is reached where almost no blood can be pumped by the heart.
The actual point at which this happens, depends to a degree on the size of the dog but either way, once this point is reached, unfortunately most dogs die from the infestation.
Effective heartworm prevention for dogs is available and an annual blood test to find out if juvenile worms (microfiliariae) will help your vet to advise you on the best course of treatment so that heartworm infection never gets to this heartbreaking stage.
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