Heartworms
-- A Year Long Problem By Dr. John Spillman,
This is the time of the year that many people start their pets back on a heartworm preventative. But, heartworm disease is actually a year round problem. Mosquitoes are the vectors (transfer animal) that move the heartworms from dog to dog. In the Louisville area, mosquitoes are present throughout the winter!
Heartworm disease is caused by a parasite that lives in the right side of the heart and in the vessels that take blood from the heart to the lungs, the pulmonary arteries. The worms are up to thirteen inches long and there can be up to 200 worms involved with a single pet. They obstruct blood flow and irritate blood vessel walls. Pulmonary hypertension and increased resistance to blood flow are the outcome. The right side of the heart also becomes irritated and has to work harder to pump blood. This can cause the heart to enlarge and leads eventually to congestive heart failure. The worms can also physically hold one of the heart valves open. The open valve then allows blood to flow backwards and this makes the heart work harder. This backflow can also put pressure on the liver, leading eventually to liver failure.
It's not only the adult worms that cause damage. The adult heartworms have live young called microfilaria. They circulate in the blood and stimulate the immune system to attack. As the body tries to fight the microfilaria, inflammation sets in and damage occurs to the lung tissue and the kidneys. Kidney damage can lead to protein loss in the urine and kidney failure.
These deadly parasites are moved from one animal to another by mosquitoes. When the mosquitoes bites an infected dog, they ingest the microfilaria. Inside the insect, the microfilaria become third-stage larva. When the mosquito bites another animal, the parasites enter the new host's blood. The larva then begin to circulate through the dog and go through two more growth stages. This is when preventatives kill the heartworms -- when they are still migrating through the blood system. If not killed, the larva progress to a fifth state and then on to an adult form. There is a 120 to 180 day period from the time the parasite enters the dog in larval form until it becomes an adult worm. Then the cycle of damage begins again in a new host! The adult heartworm can live up to eight years in a dog. This is over half the average dog's life!
Heartworm disease is expensive to treat and the only drugs that kill the adult parasite are arsenic. The arsenicals have to be carefully administered so that the heartworms are killed while the dog is not poisoned too much. Once the worms are killed, the pet's activity must be restricted for up to 30 days. This exercise restriction protects the pet's body as it works to eliminate the worms' physical remains. In the end, even if the dog is heartworm free after treatment, his health can be permanently impaired because of damage to the heart and blood vessels.
The good news is, your pet does not have to suffer from heartworm disease! A simple preventative, costing between two and ten dollars a month, is available. For the cost of a few treats, you can prevent this disease from being your pet's problem. |