WHO/AFRICAN SERIES / WHO-Spx-Dx-Africa03-MedRes
After a person has been infected, there is a period during which he has no symptoms. This, the incubation period, is usually 12 days in length but may be as short as 7 days or as long as 17 days. The illness begins with fever. The patient feels sick and has symptoms such as headache and backache. A rash appears after 2 to 4 days.