Parasitic worms, heartworms in dog
The disease is spread from one dog to another by mosquitoes, therefore it coincides with the mosquito season.
One untreated heartworm positive dog can be the source of infection to a vast number of other dogs in a wide area for many years.
Heartworms in dogs are about six inches long. They live mostly in the heart and the large blood vessel that bring oxygen-rich blood from the lungs to the heart.
Adult male and female worms living in the heart produce thousands of microscopic baby worms (larvals) which circulate throughout the body. These larval dog heartworms do not grow to adulthood in the dog where they were born. (If they did, the dog would quickly die and that would be bad for both the dog and the heartworms.)
In order to mature, the larvae of heartworms must spend time inside a mosquito. Therefore, mosquitoes are absolutely necessary for the spread and development of heartworm disease.
The first stage of the heartworm’s development occurs when an adult female worm releases microfilariae into the blood stream.
The next stage happens after a female mosquito bites the dog and takes in some microfilariae. These microfilariae continue developing inside the female mosquito (and can only grow to the next stage in the mosquito).
They reach the infective larval stage in about 2 - 2 ½ weeks. If the mosquito then bites another dog, it will infect the dog.
The infective larvae enter the dog through the bite wound. The larvae migrate through the body tissues and continue developing for the next 100 days.
Then the heartworms in dog as young adult worms enter the vascular system. About 3 months after that time, microfilariae are released by the fully mature, adult female worms and the cycle begins again.
Every dog should be placed on a Heartworm preventive at 3 to 4 months of age. All dogs should have a Heartworm test performed every year.
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