Heartworm

Heartworm disease is caused by Dirofilaria immitis, a worm that spreads when a mosquito bites an infected animal and then a cat. Dogs are the natural host, but cats can be infected too. In cats the worms usually number only a few and often die before adulthood, though even immature worms can injure the lungs. Indoor cats can be infected because mosquitoes come inside.

Signs can be subtle or look like other illness. Cats may cough, wheeze, breathe fast, vomit, lose weight or lose appetite, which resembles feline asthma. Some cats show nothing and then collapse or die suddenly. Diagnosis is harder than in dogs, since a single test can miss infection, so vets combine blood tests, X-rays and sometimes heart ultrasound.

There is no approved treatment that kills adult worms in cats. Vets manage the signs, and many infections clear on their own over time. This is why prevention matters. Monthly preventive medicines made for cats are available in areas where heartworm occurs. Ask your vet whether your cat needs one, which product to use, and whether to test before starting. Any cat with a new cough, labored breathing or open-mouth breathing needs prompt veterinary attention.