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.

“My gut feeling,” said Dr. Peter Piot, the director of the London School of Hygiene and Tropical Medicine, who helped discover the Ebola virus in 1976, is that the evidence points to “infection before the current epidemic.”

Medical detectives in West Africa are now seeking to establish whether the virus had previously infected people there. The research is part of a broader push to better understand where Ebola might strike next, and to strengthen surveillance and health systems in hopes of preventing future outbreaks.