The outbreak has been traced, tentatively, to three children who ate a bat, the W.H.O. said, and known threats like Ebola and Marburg have been ruled out.

KINSHASA — An unknown illness has killed over 50 people in northwestern Congo, according to doctors on the ground and the World Health Organization on Monday.

World Health Organization officials said the outbreak appeared to originate from a village where three children died after reportedly eating a bat carcass.