Heartworms are a parasite that is transmitted from infected mosquitoes to dogs (and cats and other animals.) Heartworms are not contagious or transmitted to other animals. The infected mosquito bites and draws blood from one heartworm infected dog and then when it bite a dog that is not on regular monthly preventative, that dog is infected with heartworms. It takes approximately six months for a dog to test positive after they have been bitten.
When we accept a dog in to our rescue we very seldom know they are heartworm positive until we have confirmed on the dog, the shelter has done a work up which includes neutering the dog, giving the dog its vaccinations and a heartworm test. We find out when we go pick the dog up if the dog is negative or positive. On average, we treat 1-2 dogs per month for heartworms. The average cost for heartworm treatment is $100-150 for every 10 pounds the dog weighs.