Dengue fever can be caused by any one of four types of dengue virus: DEN-1, DEN-2, DEN-3, and DEN-4. You can be infected by at least two if not all four types at different times during your lifetime, but only once by the same type.
NIAID Research on Viral Infections
Dengue and hemorrhagic fever: A potential threat to public health in the United States
Modified Skeeters Could Save People from Dengue Fever