The mystery fever hit Uttar Pradesh 20 years ago. It was linked to viruses like Nipah, Chandipura, West Nile and JE. The JE virus was the most accepted causal agent even though the authorities failed to find the virus in the samples collected. In Saharanpur, out of 99 cases of acute viral encephalitis reported in hospitals in 2006, only two were found positive. Previously, Vipin Vashishtha had identified the disease as Reye's syndrome. The fever has now spread to the neighbouring states of Uttrakhand and Haryana, affecting children from poor rural families.