Why is sickle cell anemia still prevalent in parts of the world today?

See below: Carrying sickle cell trait is not typically dangerous, so it is likely that persons with sickle trait will have children. These children are more likely to be born with sickle cell anemia. In some cities in africa, where sickle cell disease is common, there is an increased knowledge of all those who have sickle trait. This is done to attempt to decrease the amount of sickle cell disease.