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Canine heart worm disease is a serious parasitic disease caused by a long, thin worm that lives in the blood vessels and heart of infected dogs. The disease is spread from dog to dog (and to cat) by mosquitoes. The mosquito bites a dog with heart worm infection, collects some of the microscopic heart worm offspring and then, after a couple of weeks, passes these on to another dog or cat.

Inside the dog, the microscopic heart worm can grow into a parasite exceeding a foot in length. The life cycle is somewhat complicated. The important thing is to prevent worm development using safe and effective preventative drugs.

Many pet owners ask – does my dog really need heart worm prevention. In most areas of the country – the answer is yes!

Heart worms are present (endemic) in most parts of the United States and in many parts of North America. Mosquitoes are the key – without them the disease cannot spread. The highest rates of infections are found in subtropical climates like those of the southeastern United States, the Gulf States and Hawaii. However, heart worms are also found throughout the central and eastern United States, particularly near oceans, lakes, wetlands and rivers.

Heart worm disease injures the lungs, the arteries of the lungs and the heart.

What are Symptoms of Heart worm Disease?

Symptoms include tiring, coughing, weight loss and heart failure. Heart worm infection in dogs is usually diagnosed by a blood test. Talk to your vet immediately if you have concerns about heart worms in your pet. Early detection makes the difference between life and death.

How do You Prevent Heart worm Disease?

Prevention of heart worm disease is simple. In most cases, a once-monthly prescription tablet or topical treatment is all that is needed to effectively protect your pet. These products include milbemycin oxime (Interceptor Flavor Tabs® and Sentinel Flavor Tabs®), ivermectin (Heartgard® for Dogs), and topical selamectin (Revolution®).

These preventatives are only available from your veterinarian, who must first make certain that your dog is not heart worm positive.

These "preventatives" kill microscopic larvae that are left behind by mosquitoes when they bite a dog. Before beginning heart worm prevention, any dog over 7 months of age should first have a heart worm test. Preventatives in heart worm positive dogs can cause severe reactions. Be safe, and make sure you and your vet are on the same page before starting or stopping any medications.

Repeated heart worm blood testing every year is recommended even for dogs taking heart worm preventative year round. Previous recommendations were for every 1 – 3 year testing but this changed with the 2005 American Heart worm Society (AHS) recommendations to yearly testing. This is due to concern with breaks of pets on preventatives that still contracted heart worms. Annual testing will ensure that an infection is caught in plenty of time to effectively manage it. Testing is also recommended when a pet owner switches between preventative medications.

What are the Official Recommendations Regarding Heart worm Prevention?

The AHS recommends that all dogs in areas endemic for heart worms should take a year-round preventative. If you are not certain about the danger of heart worms in your area, call your veterinarian.

Most veterinarians follow the guidelines published by the American Heart worm Society, a group of concerned veterinarians and scientists. They will be able to give you accurate advice on how to treat your pet.

As noted above, dogs over 7 months of age should first have a heart worm test.

The recommended heart worm prevention is a once-monthly pill (milbemycin oxime sold as Interceptor Flavor Tabs® and lufenuron/milbemycin oxime sold as Sentinel Flavor Tabs®, ivermectin sold as Heartgard® or Heartgard Plus® or a topical treatment selamectin (sold as Revolution®). Speak to your veterinarian about administration guidelines.

Some heart worm preventatives also control intestinal or external parasites. The wide range of excellent and safe heart worm prescription products can be explained by your veterinarian.

For more information about the most recent recommendations on heart worm prevention, visit the guidelines posted on the Society's web site at www.heartwormsociety.org.