Heartworms: Disease and Prevention

Published 10:00 pm Tuesday, April 5, 2016

Heartworm disease is a common, yet preventable, disease of which most pet owners should be aware.  Heartworms can infect both dogs and cats, and may not cause noticeable symptoms until they have caused significant damage. The disease is treatable, although lasting damage may occur. Prevention, however, is easy and very successful.

Heartworms are large worms that live in blood vessels in the lungs, around the heart. They can be up to 14 inches long! Adult dogs can host several hundred worms. Infections in cats usually result in fewer worms, but the consequences of feline infection can be sudden and severe.

Transmission of heartworms occurs via mosquitoes. The life cycle occurs when a mosquito bites a heartworm-infected animal that has young heartworms, called microfilariae, in its bloodstream. Within two weeks, the microfilariae in the mosquito develop into larvae. The mosquito bites a dog or cat, which becomes infected with the larvae. The larvae circulate in the pet’s bloodstream for three months, and then migrate to the blood vessels in the lungs, where they mature for another three months. There, the worms reach adulthood, and begin producing microfilariae, which infect mosquitoes and start the cycle over again.

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Adult worms live for five to seven years in dogs and a few years in cats. Worms cause severe damage to the lungs and heart, and can obstruct blood flow, resulting in emergent complications.

Symptoms of heartworm disease may not be noticeable until the infection has been present for quite some time. Symptoms in dogs include coughing, lethargy, and weight loss. Symptoms in cats are usually less noticeable than in dogs until the disease is severe, and include difficulty breathing, vomiting, coughing, and sudden collapse.

The best way to diagnose heartworm disease is with a blood test  Heartworm tests in dogs are very accurate for diagnosing infections that have been present longer than six months. Diagnosing heartworms in cats is more complicated, and may involve a combination of tests. If a test result is positive, additional diagnostics, such as x-rays, may be recommended to determine the severity of the disease. All pets with exposure to mosquitoes should be tested for heartworm disease. This includes pets that live indoors, because mosquitoes can exist indoors.

There is an FDA-approved medication to treat heartworm disease in dogs. It requires significant exercise restriction, and takes months to complete. No treatment is approved for cats, so management is usually intended to reduce associated inflammation rather than to kill the actual worms.

It is much easier, and healthier for your pet, to prevent heartworm infection than to treat it. There are many heartworm preventatives on the market. The American Heartworm Society recommends testing pets prior to starting on prevention, and using prevention year-round.

Annual heartworm testing is recommended for dogs to ensure that heartworm prevention has been effective. Heartworm testing is recommended for cats before starting them on a preventative, and then as deemed necessary by your veterinarian.

For more information on heartworm disease and heartworm prevention, please visit www.heartwormsociety.org.

Dr. Kelly Sulik owns and operates Animobile Mobile Veterinary Services in Tryon, N.C. She can be reached at animobiledvm@gmail.com.