Heartworm Disease in Cats

Cats can get heartworm, too — and in cats, it's mainly a lung disease rather than a heart disease. The same mosquito bite that infects dogs can infect cats, but cats are unusual hosts: infections are usually just a few worms (often one to three), and most cats eventually clear the infection on their own. That doesn't make it harmless. When young worms reach the lungs and die, the cat's immune system overreacts, causing a condition called Heartworm-Associated Respiratory Disease (HARD). It looks just like feline asthma on X-rays, with coughing, wheezing, and difficulty breathing. Infected cats may also vomit, and 10–20 percent die suddenly when worms die and block blood vessels. There is no safe heartworm treatment for cats — the injections used in dogs can be fatal to cats — so vets usually manage symptoms with anti-inflammatory medicine and monitor the cat while the worms die off naturally (a process that takes two to four years). Prevention is everything: monthly heartworm preventive is recommended for all cats in mosquito-prone areas, and that includes indoor cats — studies show a quarter or more of infected cats never went outside. Call your vet if your cat coughs, wheezes, breathes with effort, or vomits repeatedly, and ask about starting heartworm prevention even if your cat stays indoors.