Heartworms are transmitted from dog to dog through mosquito bites. An immature stage of the worm is picked up out of an infected dog's bloodstream by a mosquito. It goes through a developmental stage inside the mosquito and then is injected into another dog’s skin. It then migrates through the skin into the blood stream and eventually ends up in the dog’s heart. The heartworm can grow to be several inches long and live up to four years inside the dog’s heart.
Heartworms can be very dangerous. One mosquito is capable of delivering anywhere from 1-100 of these worms into your dog. A low burden (only a few worms) may not cause your dog any problems. However, a high burden can cause several problems. First, they could cause your dog’s heart to have to work harder than normal due to the resistance to the flow of blood through the heart and vessels. Occasionally, a dog will have such a high burden of worms they will actually block the flow of blood completely causing heart failure. Additionally, these worms can also set up residence inside the lungs or other places in the body and cause allergic reactions.
There are several medications on the market to control heartworms. Most of these medications are designed to prevent heartworms from maturing into adults; therefore, keeping them from setting up housekeeping in your dog's heart. Because they are preventive in nature, these medications need to be taken regularly, with most being recommended monthly. You should consult your veterinarian on the type of preventive medications that he or she recommends.
Heartworm infestations are treatable. However, the treatment can be dangerous. The risk of the treatment depends on several factors including your dog’s age, health, and the potential burden of worms. Unfortunately, the tests for the presence of heartworms don’t tell us if your dog has a few worms or a hundred worms. They only tell us whether or not the worms are present.
When having your dog treated for heartworms, it is imperative that you follow your veterinarian’s advice carefully. Your dog will have to be confined for an extended period of time (possibly several weeks), while the worms are dying. It is essential to keep the dog from getting overly excited because these worms do not just disappear when your dog is given the medication. They are killed, and then it takes time for them to be absorbed and metabolized out of the bloodstream.
Heartworm prevention can be expensive. However, it is safe and very effective. By not giving your dog a prevention, you are taking a big risk with the result being that your dog will develop an infestation and have to undergo an expensive and dangerous treatment.