The heartworm is caused by a parasite called Dirofilaria immitis, which completes part of its life cycle first in an intermediate host (mosquitoes), which also acts as a biological vector, and then in a definitive host (an animal such as a dog or cat).
In the absence of timely treatment, the heartworm causes difficulty in breathing up to the death of the infested animal.
For further information: Filaria or Filariasis: What is it? the animal does not seem to have much influence. of the heartworm reach sexual maturity and settle in the heart (heart) and pulmonary arteries, several months pass.
Then, before the adult parasites reach enough numbers to cause obvious symptoms in the dog, a further period of time passes.
Therefore, when the owner notices signs of disease in their pet, it has already been infested for several months or even years.
Dogs affected by filariasis are usually divided into four symptomatic classes (based on the signs they show), according to the severity of the infestation (which corresponds to the number of adult parasites present in the pulmonary arteries and in the heart, therefore at the time of the invasion of the Heartworm in the animal):
- Class 1 (subclinical or mild form): the dog has no changes in the state of health, looks good, does not show signs and symptoms of disease, but in laboratory tests it is however positive on the antigen search test (elements of the parasite that are searched to identify it) of the heartworm ( in practice, parasites are present but still do not cause damage so great as to compromise the health of the dog);
- Class 2 (moderate form): inside the pulmonary arteries and the right heart (that part of the heart that receives venous blood and "pumps" it to the lungs), the parasites of the heartworm have reached a size and number such as to cause symptoms such as dog fatigue, occasional cough , poor performance with dyspnoea (difficulty in breathing) under exertion (for example after a run or after playing), possible heart murmurs (changes in the function of the heart valves) and possible weight loss;
- Class 3 (severe form): the heartworm has parasitized the animal for so long that it has reached a size and number such as to cause numerous damage to the heart and pulmonary arteries, which can manifest itself with: a poor physical condition of the dog (which also appears thin ), dyspnoea or tachypnea (increased breathing rate), cough, anemia (decrease in red blood cells, as the heartworm parasite feeds on blood cells), enlargement of the abdomen, right heart failure (poor function ), epistaxis (loss of blood from the nose), pulmonary changes and thromboembolic phenomena (fragments of parasites, together with thrombi - or blood clots caused by the parasites themselves - can cause sudden blockages of blood vessels);
- Class 4 (vena cava syndrome" animal.
Dogs should also be kept indoors (especially at night when mosquitoes start to appear) and, if possible, use mosquito nets.
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