Yellow fever
Yellow fever causes fever, chills, loss of appetite, nausea, muscle pains particularly in the back, and headaches, but it typically only lasts for a few days. For about 15% of patients, after a few days of improvement, the fever comes back, abdominal pain occurs, and jaundice sets in, causing liver damage and the skin to turn yellow. When this happens the risk of bleeding and kidney problems increases. 20-50% of those who develop jaundice die, with about a 5% total mortality rate. Those who survive, though, develop a lifelong immunity.
No reliable treatments for yellow fever exist. Some healers swear by the benefits of the oil of white leadtree seeds, and some believe that an essential oil of lemon beebrush can help, but the efficacy of these medicines remains unproven. Healers often rely instead on providing patients with plenty of water and rest, as well as some analgesics. This inability to treat the disease makes yellow fever one of the most feared diseases in the Fifth World.
The climate of the Fifth World increased the range of the mosquitoes that spread yellow fever to the entire globe, year-round, so the key to preventing yellow fever falls to keeping them away (see Mosquito for a more general discussion of how humans in the Fifth World prevent mosquito-borne diseases by controlling mosquito populations).