Dirofilaria immitis lives primarily in the right ventricle of its host’s heart.  Since it feeds on its hosts blood, the heard and blood vessels are ideal places for the heartworm to live.  Bacteria and occasionally other parasites live in this same habitat.  The microfilaria of Dirofilaria immitis also spends the first couple molting periods inside of a mosquito.

On a geographic level, Dirofilaria immitis occurs all over the world.  Basically, wherever mosquitoes live Dirofilaria immits also has a presence.  Mosquitoes thrive in warm and wet conditions, therefore tropical countries and regions that are closer to the equator have a greater presence of Dirofilaria immitis.  It is also important to look at the prevalence of the parasitic worm from an economical standpoint.  Third world and other developing countries are not able to medicate host’s invaded with this parasite because the medication is expensive and there are not very man veterinarians to administer the medications. 

It would be very helpful if there was some way to predict the climate in a certain area and then make predictions about the prevalence of Dirofilaria immitis in that particular region.  According to Vazzani and Carbajo, the help is already available.  Geographic information systems (GIS) can predict disease occurrence based on climate or environmental characteristics of a particular area.  They can use these predictions so compare them to the climate or environmental requirements of a certain species.  These predictions are useful in disease mapping and prevention (Vezzani 2006).

Above: A table showing the incidence of Heartworm disease in the U.S. in 2005.  It is hard to see the writing, but the dark colors indicate a greater average number of cases reported per clinic in that particular region.