"Blood samples will not help to diagnose the virus, unless we have samples of brain tissues," he said.
A senior government doctor at the Patna Medical College and Hospital said on condition of anonymity, "Three days ago, the state government had hinted that it may declare the disease an epidemic, but a day after it downplayed the need for it," he said.
He said the state government should declare the disease an epidemic without further delay.
Bihar Health Minister Ashwani Kumar Choubey had said on Monday that the disease would be declared an epidemic, but later said that there was no need for such a move.
A team from the central government has already visited Muzaffarpur, the worst affected district, to collect blood samples on Wednesday.
The government has cancelled the leaves of doctors in ten districts of the state.
Principal Health Secretary Vayasji said the health department has constituted teams of doctors in the six worst affected districts to identify patients for treatment.
"All medical college and hospitals have been directed to provide free medicines to patients showing symptoms of AES," he said.
"Free medication will be provided to patients in rural areas," Vayasji said.
Last year, encephalitis, a mosquito-borne disease, had claimed nearly 150 lives in Muzaffarpur and Gaya districts.