Feline heartworm (HW) was first described in the 1920s; awareness has increased greatly since the introduction of heartworm preventative medication for cats in 1997 and the associated marketing campaigns. Feline HW remains difficult to diagnose, yet a fully preventable disease.
Heartworms (Dirofilaria immitis) are small thread-like worms that live in the blood systems and hearts of cats and dogs as well as other species, such as ferrets, wolves, and foxes. The cat is more resistant to heartworm than other animals, but still susceptible. Heartworm is transmitted by mosquitoes, and is found in almost all areas where mosquitoes are found. For example, heartworm has been found in all areas of the United States except Alaska, and in warmer areas of Canada.
How Do Cats Get Heartworm?
Cats are infected with HW in the same way as dogs, but far fewer larvae mature to adulthood (average 15 adult worms in dogs and 1-3 in cats in endemic areas). This doesn’t mean that cats are less affected by heartworm disease however, since the small body size of the cat can be adversely affected by only one or two worms.
It is difficult to estimate prevalence of feline HW for several reasons – there is no perfect test, infections may go unnoticed, and some cats die acutely without a diagnosis. The best available data suggest that feline HW is present at about 5% - 15% of the canine rate in endemic areas. Certainly wherever canine heartworm is found, feline heartworm is present as well.
Some species of mosquitoes will feed on both cats and dogs. Mosquitoes become infected when they bite a dog with immature worms called microfilaria. When the infected mosquito then bites a cat, the microfilaria enter through the bite and develop in tissues under the skin. The immature worms go through several developmental stages, and find their way to a blood vessel. Via the blood vessels, they are carried to the arteries in the lungs, where they cause an intense inflammatory reaction. Many immature worms die at this point, causing even more inflammation. ...... [Read complete article]