Heartworm Dogs & Cats

Heartworm is a parasite that most dog owners and many cat owners have to be concerned about.

Heartworm disease is a serious disease that results in severe lung disease, heart failure, other organ damage, and death in pets, mainly dogs, cats, and ferrets. It is caused by a parasitic worm called Dirofilaria immitis.The worms are spread through the bite of a mosquito.  The dog is the definitive host, meaning that the worms mature into adults, mate, and produce offspring while living inside a dog.  The mosquito is the intermediate host, meaning that the worms live inside a mosquito for a short transition period in order to become infective (able to cause heartworm disease).  The worms are called “heartworms” because the adults live in the heart, lungs, and associated blood vessels of an infected animal.

In the United States, heartworm disease is most common along the Atlantic and Gulf coasts from the Gulf of Mexico to New Jersey and along the Mississippi River and its major tributaries, but it has been reported in dogs in all 50 states.

In an infected dog, adult female heartworms release their offspring, called microfilariae, into the dog’s bloodstream.  When a mosquito bites the infected dog, the mosquito becomes infected with the microfilariae.  Over the next 10 to 14 days and under the right environmental conditions, the microfilariae become infective larvae while living inside the mosquito.  Microfilariae cannot become infective larvae without first passing through a mosquito.  When the infected mosquito bites another dog, the mosquito spreads the infective larvae to the dog through the bite wound.  In the newly infected dog, it takes between six and seven months for the infective larvae to mature into adult heartworms.  The adult heartworms mate and the females release their offspring into the dog’s bloodstream, completing the lifecycle