 Dengue fever is an acute febrile illness transmitted by mosquitoes, which affects half the worlds population. There are 96 million symptomatic infections, 500,0000 hospitalisations and 25,000 deaths per year attributed to the disease. The economic burden is 12 billion. In Singapore, as elsewhere, the incidence of the disease continues to increase despite aggressive control measures. At present there are no approved medicines for treating dengue fever. Only supportive fluid replacement therapy is used to treat vascular leakage in patients with severe illness. Therefore there is an urgent need to find alternative treatments. Experiments in the laboratory have shown that Celgosivir and modipafant inhibit dengue virus and improve mouse survival. Both drugs have previously been used in humans with good safety records, so investigators are taking this one step further to find out how well it works in dengue patients. Investigators plan to enroll dengue patients within 48 hours of fever onset and assign them to one of four treatment groups over five days. Together with the support from the industry partner, 60Pharmaceuticals PLC, the investigators will determine the safety and effectiveness of these drugs on acute dengue patients and pave the way forward for dengue antiviral medicines to reach patients. 