Signs and Symptoms
Yellow fever begins after an incubation period of three to six days. Most cases only cause a mild infection with fever, headache, chills, back pain, loss of appetite, nausea, and vomiting. In these cases the infection lasts only three to four days.
In fifteen percent of cases, however, sufferers enter a second, toxic phase of the disease with recurring fever, this time accompanied by jaundice due to liver damage, as well as abdominal pain. Bleeding in the mouth, the eyes, and the gastrointestinal tract will cause vomitus containing blood (giving the name black vomit). The toxic phase is fatal in approximately 20% of cases, making the overall fatality rate for the disease 3% (15-20%). In severe epidemics, the mortality may exceed 50%.
Surviving the infection provides lifelong immunity, and normally there is no permanent organ damage.
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