Pet Health: Heartworm is a concern for dogs, cats, and even ferrets

Dr. Amber Wolf-Ringwall, Medical Oncology Resident, with her dog "Beauford," Robert H. and Mary G. Flint Animal Cancer Center, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, August 18, 2015

No matter where you live or what time of year it is, your dog, cat or ferret can contract heartworm. April is Heartworm Awareness Month, so it’s a good time to learn about the risks and how to prevent infection.

Heartworms are small parasites that enter your pet’s bloodstream through mosquito bites. The larvae, or immature worms, work their way to the large blood vessels of the lung and into the heart, causing damage and interrupting normal blood flow. The infection can cause severe lung and heart disease.

Any pet is exposed to mosquitoes should be tested. All dogs, no matter their age, sex, or where they live, can become infected with heartworm. Indoor and outdoor cats and ferrets are also at risk for the disease.

New heartworm cases appear across the country every year as society, and pets, become more mobile. Regular use of preventive products is the best way to reduce the risk of heartworm disease and reduce risks of resistant populations of parasites, the Companion Animal Parasite Council advises. An added benefit is that most preventive products also protect against intestinal parasites.

Symptoms of heartworm

The James L. Voss Veterinary Teaching Hospital opens its doors to the public during its annual open house. April 16, 2016
Pets should be tested annually for heartworm, veterinarians advise.

Dogs: Those recently or mildly infected may not appear ill until adult worms have developed in the lungs. As the disease progresses, your dog may cough, become lethargic, lose his appetite, have difficulty breathing, or tire rapidly after moderate exercise. Dogs can develop heart failure and a swollen belly due to excess fluid in the abdomen.

Large numbers of heartworms can cause a blockage of blood flow in the heart, leading to caval syndrome, a life-threatening form of cardiovascular collapse. It is marked by a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine.

Cats: Coughing, respiratory distress, difficulty walking, and vomiting may indicate heartworms in cats. They can faint, have seizures and accumulate fluid in the abdomen. In some cases, a cat may suddenly die from heartworms.

Ferrets: Even indoor ferrets are at risk of heartworm infection. The signs are similar to those seen in dogs, but they develop more rapidly. Just one worm can cause serious disease in a ferret. Your veterinarian can prescribe heartworm medication approved for use in ferrets. The American Heartworm Society recommends year-round prevention for ferrets.

Testing for heartworm

The American Heartworm Society recommends annual testing starting at 7 months of age. The test detects the presence of heartworm proteins in a few drops of blood and can be performed in most veterinary clinics.

If heartworm is detected, chest radiographs (X-rays), a blood profile and an echocardiogram (an ultrasound of the heart) may be necessary to confirm the diagnosis, to evaluate the severity of the disease, and to determine the best treatment plan for your dog.

In cats, diagnosis is more difficult and can require a series of tests. In general, both antigen and antibody tests are recommended for cats to give the best chances of detecting the presence of heartworms.

Preventives do not kill adult heartworms, and will not eliminate heartworm infection or prevent signs of heartworm disease if adult worms are present in the pet’s body. Therefore, a blood test for existing heartworm infection is recommended before beginning a prevention program to assess the pet’s current heartworm status.

Preventing heartworm

Preventive medicine comes as a pill, a topical medication or as an injection. It works by eliminating the immature (larval) stages of the immature heartworms. Because heartworms must be eliminated before they reach this adult stage, it is extremely important that heartworm preventives be administered strictly on schedule – monthly for oral and topical products and every six months for injectables.

Treating heartworm

Rita Yaroush has her ferrets "Riskin" and "Blaze of Glory" evaluated by Colorado State University's Veterinary Teaching Hospital, May 8, 2014 Rita Yaroush has her ferrets "Riskin" and "Blaze of Glory" evaluated by Colorado State University's Veterinary Teaching Hospital, May 8, 2014
Pet ferrets, like dogs and cats, are at risk of heartworm infection.

Dogs: The goal of heartworm treatment is to kill the adult and immature worms as safely as possible. When a dog is being treated, the heartworms are dying inside the dog’s body, so a pet must be much less active than normal. That’s because physical exertion increases heartworm damage in the heart and lungs.

Treatment protocol involves several steps and medications, including antibiotics, pain control, preventive medication and melarsomine, the drug that kills adult heartworms.

Six months after treatment is completed, your veterinarian will perform a heartworm test to confirm that all heartworms have been eliminated. To avoid the possibility of your dog contracting heartworm disease again, your pet will need heartworm prevention year-round for the rest of his life.

Cats: There currently is no effective and safe medical treatment for heartworm infection or heartworm disease in cats. If your cat is diagnosed with heartworms, your veterinarian may recommend medications for pain control; drugs to reduce inflammatory response and resulting heartworm disease; or surgery to remove heartworms.

Heartworm tests should be performed annually to ensure that your pet doesn’t subsequently become infected with the disease and to ensure the appropriate amount of medication is being prescribed and administered.

There have been reports of pets developing heartworm infection despite year-round treatment with a heartworm preventive, so having your pet tested regularly is the best way to keep them protected.

The James L. Voss Veterinary Teaching Hospital, 300 W. Drake Road in Fort Collins, is the largest veterinary hospital in Colorado, with more than 40,000 patient visits each year. It is home base for the university’s renowned DVM Program, which consistently ranks among the top three veterinary schools in North America.

Sources: American Veterinary Medical Association, American Heartworm Society, Companion Animal Parasite Council

James L. Voss Veterinary Teaching Hospital