Methods of treating viral infections. At least one example embodiment is a method including: measuring a core temperature of a human patient; testing the human for the presence of a virus that causes disease; responsive to the human having both fever and presence of the virus, submerging at least a trunk and legs of the human in water comprising a surfactant, the human at least partially submerged in the water for a treatment period of at least three hours; and controlling a temperature of the water during the treatment period.