Yellow fever (also called yellow jack, or sometimes black vomit or American Plague) is an acute viral disease. The yellow refers to the jaundice symptoms that affect some patients. The virus is usually carried by mosquitoes. Symptoms in severe cases include fever, chills, bleeding into the skin, rapid heartbeat, headache, back pains, and extreme prostration. Nausea, vomiting, and constipation are common. Jaundice usually appears on the second or third day. After the third day the symptoms recede, only to return with increased severity in the final stage, during which there is a marked tendency to hemorrhage internally. The patient then lapses into delirium and coma, often followed by death. During epidemics the fatality rate was often as high as 85%.
Despite its hideous nature, yellow jack actually benefitted the United States of Atlantis on two separate occasions.
During the Atlantean War of Independence, the terror felt by both sides for yellow jack was such that General Victor Radcliff was able to forestall a British attack on New Hastings by running up flag that signaled the town was suffering a yellow jack epidemic.
In 1852, soldiers of the Atlantean Army were forced to take up residence at Henry Barford's plantation when some of their number developed the yellow jack while transporting firearms to New Marseille. As the soldiers' numbers dwindled, Frederick Radcliff, a slave on the plantation, saw an opportunity to seize the firearms and launch the insurrection which led to the end of slavery in the land.