Ebola fears are casting a cloud over the opening of the second Youth Olympics in the eastern Chinese city of Nanjing.

The games, featuring more than 3,000 athletes aged 15 to 18, were set to officially open Saturday evening with Chinese President Xi Jinping and U.N. Secretary-General Ban Ki-moon in attendance.

Preparations for the ceremony have been overshadowed this week by concerns about the participation of competitors from the Ebola-affected region of Africa, three of whom have been barred from competition because of the risk of infection.

Organizers are conducting regular health checks on all athletes and officials from the four West African nations affected — Guinea, Sierra Leone, Liberia and Nigeria — to prevent the spread of the virus that has killed more than 1,000 people.

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