An unidentified disease that killed at least 18 people in Nigeria's south is "neither contagious nor epidemic," a health official says.
Blood tests found that all victims died of ethanol poisoning, Dayo Adeyanju, the health commissioner of Ondo State where the deaths occurred, said on Sunday on local broadcaster Channels Television.
Initially, officials had feared the outbreak of a deadly, contagious virus.
Patients had complained of a severe headache and later lost their sight before dying.
"Our investigations revealed that the victims, who are commercial motorcyclists, gathered at some local joints to [drink] alcoholic substances mixed with roots and some other local herbs on the evening of the outbreak of the disease," said Adeyanju.
Eighteen people died, while five others had gone blind but survived, said Adeyanju.
The state government of Ondo State had set up an emergency response task team aimed at investigating the cause of the illness.
Spinal fluid, blood and urine samples from victims had been sent to a laboratory for testing.
Nigeria's health department was collaborating with the World Health Organisation and the United States Centres for Disease Control to identify the illness.
