A 23-year-old man presents to your clinic with a 24-hour history of high fever, headache, muscle aches, vomiting and diarrhoea. He recently spent four months travelling through Thailand, Laos, Vietnam, Cambodia and Singapore. On returning to the UK he spent one week in the company of family and friends before commencing work. He is ten days into his new job. What questions would you ask this patient? Is he likely to be suffering from dengue fever? What other diseases might you consider? Would you treat this as an urgent case?