April is Heartworm Awareness Month and everyone should be remembering to give their heartworm preventatives every 30 days. Heartworms are spread by mosquitoes by taking a blood meal from a heartworm positive animal, and passing it through the mosquitoes’ saliva to the next animal that the mosquito feeds on. The immature heartworm circulates in the bloodstream, matures, and stays in the heart (in the dog). This spaghetti-like mass of worms causes obstruction of blood flow through the heart and lung vessels, causing heart and lung disease or failure. Typically when we talk about heartworms, most people are worried about their canine friends. Heartworms also infect our feline friends. Heartworms are not just a dog disease, cat and other wild canids (coyotes and wolves) can also be affected by this blood parasite.
In cats, heartworms have a different disease process than dogs. Cats are infected by the same mosquito bites as a dog, but their immune system reacts stronger to the immature worms. Usually only 1 or 2 heartworms develop into adulthood in cats. Most canine infections can involve 50-100 worms or more (depending on the mosquito population and carrier animals). Unfortunately it only takes one or two heartworms to kill a cat. In cats, the immature heartworms migrate through the body, with some of them ending up places outside of the circulatory system. This migration can cause a variety of problems depending on where the heartworm stops migrating. The heartworms that make it to the heart usually end up living in the large blood vessels of the lungs. In the lungs, the immune system continues to attack the heartworm, causing asthma-like signs. When the heartworm finally dies, this can trigger a huge allergic reaction that sends the cat into respiratory failure- a fatal asthma attack.
Testing and treatment for heartworms in cats is not as straightforward as dogs. Blood testing in dogs detects almost all cases- a positive result means there are heartworms present. Blood smears can also show immature heartworms (microfilaria). In cats, since they usually only have one or two heartworms, the same tests may not pick up the parasite. And since the feline immune system is so reactive to the immature worms, there usually is no microfilaria in the blood smears. We treat adult heartworm infections with Immiticide in dogs. Unfortunately this same treatment given to cats can cause the same fatal reaction when the heartworms die, so it is not recommended.
Since there is no treatment for adult heartworms in cats, prevention of infection is crucial to stop heartworm infections in cats. Monthly preventative medication in cats and dogs kills the immature heartworms, stopping heartworm migration around the body, and stops immature worms from reaching the heart and lungs. The Peoria Area Veterinary Group (Chillicothe Veterinary Clinic, Dunlap Veterinary Clinic and Dunlap Veterinary Clinic II in Peoria) carry a monthly preventative for cats called Revolution. Revolution must be applied to the skin every 30 days to be effective in preventing heartworm infections. Revolution also prevents fleas and ear mites, and some intestinal worm infestations. This topical product is very easy to use, and dosing is based on the cat’s weight. Please contact our offices to get your cat started on heartworm prevention today.
By: Dr. Lora Deckert