How are heartworms transmitted to a cat?
Heartworms are transmitted by mosquitoes. When an infected mosquito bites a cat, it deposits baby heartworms (larvae). The larvae migrate and mature for several months, ending up in the right side of the heart and the pulmonary arteries. They mature into adult heartworms about six months from the time they enter the cat. Shortly thereafter, they begin to release immature heartworms, known as microfilaria. Microfilariae live in the cat’s blood for about one month. They are ingested by mosquitoes feeding on the cat. However, most mosquitoes acquire microfilaria by feeding on heartworm-infected dogs. Because of their life cycle, it is necessary for a cat to be bitten by a mosquito to be infected with heartworms. Heartworms are not transmitted directly from one cat to another or from a dog directly to a cat.
Is there a way to prevent heartworms?
It is strongly recommended that all dogs receive year-round monthly heartworm preventative. It is well accepted that even dogs in very cold climates should be on heartworm prevention at least part of the year. There are excellent feline heartworm preventatives now available. Prevention of heartworm disease in cats is safe and easy. The reasons that heartworm prevention should be considered for your cat are:
- Diagnostic Difficulty. Diagnosing heartworms is not as easy in cats as in dogs. A simple and reliable in-hospital blood test is not yet available, and the tests that are most reliable must be sent to an outside laboratory. Often, radiographs or ultrasound studies are needed to confirm the diagnosis. Many cats are diagnosed with an autopsy following sudden death.
- Unknown Incidence. Heartworms are not nearly as common in cats as they are in dogs. However, they are probably more common than we realize. As we look more aggressively for heartworms in cats with better and better tests, we expect to find that the incidence is greater than previously thought.
- No Good Treatment. There is no good treatment for heartworm-infected cats. Effective drugs are not available, and cats that seem to be doing well may die suddenly. Treating heartworm infections in cats is risky, and not treating these cats is just as risky. If they are cured of the disease, it takes about two years.
- Prevention Is Easy. Cats given heartworm prevention drugs have not shown signs of toxicity. There is a wide margin of safety, even in kittens as young as six weeks of age.
- Indoor Cats Get Heartworms, Too. Exposure to mosquitoes is required for transmission. Cats do not have to be exposed to cats or dogs infected with heartworms. Obviously, cats that go outdoors are more likely to be exposed; however, about 25% of cats that are diagnosed with heartworms are reported by their owners to be indoor only. This simply means that mosquitoes that come into the house are just as dangerous as the ones outdoors.