A deadly haemorrhagic virus Lassa has killed at least 40 people in Nigeria, Xinhua reported.
A total of 397 cases have been reported in the last six weeks, minister of health Onyebuchi Chukwu said in a statement.
Six of the dead were health workers, two doctors and four nurses, the minister said.
The virus is transmitted primarily though contact with rat excreta.
Chukwu said the outbreak has been reported in 12 states -- Edo, Nasarawa, Plateau, Ebonyi, Taraba, Yobe, Ondo, Rivers, Gombe, Anambra, Delta and Lagos.
The minister said adequate quantities of ribavirin injections and tablets -- the specific antiviral drug for Lassa fever -- have been sent to the affected states.
No travel restriction has been imposed in the affected areas.