1) Dengue fever is caused by the dengue virus and transmitted by Aedes mosquitoes. It presents with fever, rash, and thrombocytopenia. 2) Dengue hemorrhagic fever is a severe form characterized by bleeding, low platelets, and fluid leakage causing shock. 3) Diagnosis is based on fever, thrombocytopenia, bleeding, and fluid shifts seen on hematocrit levels. Severe cases are classified as dengue shock syndrome.