Which of the 50 states has not documented a case of heartworm disease?

A: Alaska is the only state or U.S. territory that has not experienced a single documented case of heartworm disease in either a dog or cat. The American Heartworm Society does not expect the disease to spread to Alaska, even as dogs that may be infected move to the state, because the cold environment does not promote the larvae to mature to spread the infection. For more information about heartworm disease and new treatment guidelines visit the Top Story.