EBOLA, LYING IN WAIT: “A growing body of scientific clues — some ambiguous, others substantive — suggests that the Ebola virus may have lurked in the West African rain forest for years, perhaps decades, before igniting the deadly epidemic that swept the region in the past year, taking more than 10,000 lives. Until recently, Ebola had been considered a threat mostly to Central African nations. Yet studies tell of possible Ebola antibodies in human blood samples drawn in West Africa long before the current outbreak. And genetic analysis suggests the West African virus broke off from a parent strain in Central Africa at least 10 years ago, possibly as long as 150 years ago.”

Related: Signs Ebola Spreads in Sex Prompt a C.D.C. Warning. “They were acting on evidence suggesting that a Liberian man who recovered from Ebola might have transmitted the virus to his female partner many months later.”