Story highlights 18 dead and 5 being treated, Nigeria says

Locally brewed alcohol is suspected

Some patients have died within hours

(CNN) A mysterious affliction has killed as many as 18 people in southwestern Nigeria, leaving health officials scrambling to determine its cause.

The cases have all occurred in Nigeria's Ondo state since April 13, health officials said Sunday.

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Dr. Dayo Adeyanju, Ondo's state commissioner for health, said 18 people have died and five people are being treated. Those affected are between the ages of 25 and 60. The disease does not appear to be contagious, he said.

Symptoms include headaches, blurred vision, loss of sight and unconsciousness, Adeyanju said.

Some suspect it may be the result of locally brewed alcohol.

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