Three cases of yellow fever in humans have been reported from Bo, Southern District, Sierra Leone. 

Source:   ProMED 

Comment 
Yellow fever is a serious hepatitius and is caused by a virus which is found in tropical Africa, especially West Africa. The virus is found in monkeys and is transmitted to humans by mosquitos. The reported cases emphasize the importance of immunization against yellow fever, not only of visitors to Sierra Leone, but to tropical Africa in general.