Liberia has placed 153 people under surveillance for Ebola after three new cases emerged in the West African nation this past week, months after it had twice before been declared free of the disease.
World Health Organizations (WHO) investigators were working to unlock the mystery of how a new cluster of cases emerged in Monrovia because there was no evidence yet of the usual factors, such as contact with a person suffering from Ebola, handling remains of an Ebola victim or traveling to a region where the virus is prevalent, said Margaret Harris, a spokeswoman for WHO.