Offspring can be detected in the bloodstream (pre-patent interval ) about six to seven weeks after the infective larvae in the mosquito enter the dog. The men heartworms (four to six inches in length) and the females (10-12 inches) become completely grown about one year following disease, and their life span in dogs appears to average up to five to seven decades.In experimentally induced infections of heartworms in dogs, the proportion of infective larvae developing to adults is high (40% to 90%). However, the percentage of infected dogs from which mature worms are recovered is almost 100 percent. The amount of worms infecting a dog can be quite large, with the amount of worms in dogs ranging from one to approximately 250.
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