The World Health Organization has sent a six-person team and 40 boxes of personal protective gear to help fight a major outbreak of Lassa fever in Nigeria.

About 615 suspected Lassa cases have been reported in the last six weeks, according to the Nigeria Center for Disease Control; 57 have been fatal. Fourteen health care workers have been infected, and four have died.

Health authorities are also following about 1,400 contacts of confirmed cases.

The outbreak is concentrated in the nation’s southwest, but cases have been found in 17 of the country’s 36 states. For the first time in five decades, the disease has been found in northeastern Borno State, where the Nigerian army is fighting Boko Haram militants.

The new team will join 14 local W.H.O. staffers at the emergency operations center of Nigeria’s C.D.C., the agency said last week. It is also sending reagents for Nigeria’s laboratories to speed up diagnoses.