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What is Heartworm Disease?

One of the best things you can do for the health of your pet cat or dog is to make sure that he is tested annually for heartworm disease. In addition, the American Heartworm Society is recommending that preventive medication is given regularly.

Heartworm disease is what it sounds like: worms that invade the arteries of the lungs and in the ventricles of the heart, causing illness and even death. These parasitic worms are passed onto our pets from mosquitoes that are found throughout the U.S.

First, a mosquito will bite an animal (dogs, cats, and other mammals such as wolves, foxes, and raccoons) to feed on its blood. If the animal is infected with what’s called microfilariae, or the young produced by adult female roundworms, the mosquito will become infected with the microfilariae.
Passing through the mosquito like this is the only way the heartworm microfilariae can mature into larvae. This is typically a 10- to 14-day process, and longer in colder climates. When a mosquito carrying larvae bites an animal, it releases the larvae, which mature into the dangerous roundworm that can potentially kill an animal.
In dogs, it takes only about six months for the larvae to mature into worms. In cats, it can take a month or two longer. Eventually, the worms can make their way into the arteries of the lungs and heart. Adult heartworms can grow to a length of up to 12 inches and will live up to seven years in dogs and about 3 years in cats.
Dogs are more susceptible to heartworm. Cats seem better able to fight off microfilariae and even larvae. If they get infected with heartworms, the number and longevity of adult worms are smaller in cats than in dogs. If, however, the cat is unable to fight off the infection, it’s bad news because treatment options for cats is limited. And for cats, just a few adult worms can cause sudden death.

What are the Symptoms of Heartworm Infection?

It’s important to know that in the earlier stages of infection, dogs and cats may not exhibit any symptoms. Your pet’s bloodstream can be carrying the microfilariae, which won’t develop into the adult worms until after it goes through the mosquito again for maturation into the larval stage. Even if your pet is carrying adult worms, if it’s a small number of worms, there may not be any obvious symptoms.
In cats, symptoms can be mistaken for asthma or other illnesses. Unfortunately, more obvious symptoms develop after there is a larger number of heartworms inside your pet.
Some symptoms of infected dogs:
  • difficulty breathing
  • coughing
  • lethargy
  • weight loss

Some symptoms of infected cats:

  • difficulty breathing
  • coughing
  • gagging
  • vomiting
  • lethargy
  • weight loss
As the number of worms increase, the severity of symptoms will also increase. When there is a large number of worms disrupting the proper functioning of the lungs and heart, the animal can faint, collapse, and go into shock.

How Can I Prevent Heartworm Disease?

It’s fairly easy and painless for you to take steps to prevent heartworm. First, you should have your veterinarian check to see if your pet has been infected. There is a blood test available to check for the heartworm antigen, which is
produced by a mature female worm that is producing microfilariae. The body recognizes antigens as foreign and fights to rid itself of them.
The test might not pick up the infection if there are only a few worms. Another blood test checks for microfilariae, and a third test checks for antibodies produced by the larvae of the heartworm. This third test can only determine if the pet was exposed to the heartworm larvae at some point in time, but not necessarily that it is currently infected because the antibodies can be detected even after the heartworms have died and the animal is no longer infected.
X-rays, Ultrasonography or echocardiography can also be performed to determine if there are adult worms in the lungs or heart. If there is no infection, preventive medicine is available from the veterinarian. There are several oral, topical, and injectable medications available. Consult with your veterinarian to get your pet tested and then start him on a heartworm preventive plan.

How Can Heartworm be Treated?

If it turns out that your dog has heartworm, there is treatment available. However, the treatment can be harsh and difficult. The medicine used to kill the heartworm is usually a derivative of arsenic and is very hard on the dog. Some doctors will keep the dogs in the hospital so they can most effectively confined them and restrict their movements.
First, the adult worms are killed, then the microfilariae and larvae are killed. The worst side effects come when the adult worms die off and start to decompose, releasing substances that the dog’s body must fight off. This causes inflammation. In addition, the dead worms can block the arteries and veins even more, causing loss of blood flow.
Sometimes the worms can be surgically removed. Unfortunately, the treatment for cats is limited to supportive care and monitoring the cat’s condition. In some cases where the cat is not responding the supportive care, medication aimed at killing the adult worms can be administered, but then the cat suffers side effects of the decomposing worms inside their bodies.
More uncommonly, surgery may be performed to remove the worms. In the end, the best thing you can do for your pets is to make sure you communicate with your veterinarian and provide the most appropriate detection and prevention methods. Also consult with your vet about any new medications and treatment methods that are being used to combat this deadly infection and disease.
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