Dogs are a natural host for heartworms. A single dog may harbor hundreds of them, which can cause lasting damage to the heart, lungs, and arteries if the heartworm disease is left untreated. Therein lies the rub. The drug used to combat heartworm disease in dogs cannot be used in cats. In felines, the disease must be left untreated by default. Only supportive care is available to manage symptoms without getting to the root cause.
Granted, cats are not as susceptible to heartworm disease as dogs. And a cat who ends up with the illness might typically harbor only one to three adult worms; thus, a cat’s immune system can often eliminate the infection on its own. But not always.
Even immature worms in a cat that have not grown to adult size can cause a serious condition known as heartworm associated respiratory disease (HARD). Symptoms of infection in cats may include coughing, asthma-like attacks, periodic vomiting, lack of appetite, or weight loss, reports the American Heartworm Society (heartworm society.org). Because those signs are often not specific to that particular illness, time may be lost in getting at a diagnosis.
Occasionally, an infected cat may have difficulty walking, experience fainting or seizures, or suffer from fluid accumulation in the abdomen. In particularly rare instances, the first sign is sudden collapse of the cat, or even sudden death; there’s no buildup of symptoms. That’s why prevention for every pet cat is critical.
Effective prevention strategies
Fortunately, while there is no medicine that can cure heartworm disease in a cat — you just have to wait it out with drugs that ameliorate the symptoms and hope for the best — preventive medicine is virtually 100 percent effective.
Obtained with a prescription from a veterinarian, it can be in the form of a tablet (ivermectin or milbemycin) or a topical liquid that you apply to your cat’s back (Revolution, Advantage Multi, or Bravecto Plus). The drug will kill worm larvae, which infect cats via mosquito bites. When a mosquito carrier sucks blood from a feline, it leaves the larvae behind.
The medicine should be given once a month, including to cats who live entirely indoors, since mosquitoes can make their way inside a home. It should also be administered every single month of the year, advises the American Heartworm Society. While those who live where the temperature typically becomes too cold to support mosquito life during the winter may feel that’s unnecessary, the society points out that mosquitoes can be blown great distances by the wind. And they do survive cold weather for at least a little while. Furthermore, climate is becoming more unpredictable, with northern cities such as Boston experiencing temperatures in the 50s here and there during the winter months. And mosquito species keep changing to adapt to cold weather.
Testing, testing…
While it is recommended that dogs get tested for heartworm disease once a year, for cats the advice is not so cut-and-dry. It’s not a bad idea to have your cat tested before starting on a monthly heartworm preventative regimen and then retested as your veterinarian deems appropriate. Testing involves a blood draw that will check for an antigen specific to the illness and, if symptoms are present that could potentially indicate the presence of heartworm disease, perhaps x-rays or ultrasound.
