(CNN) Almost 50 children have died in northern India over the past three weeks from a brain disease that has been linked to toxins in lychees.

Health authorities in the state of Bihar said Thursday that 47 children have died of acute encephalitis syndrome, which involves inflammation of the brain. Two hospitals in the city of Muzaffarpur had registered a total of 179 cases since January, they said, but the deaths occurred only in the past few weeks.

In 2013, at least 351 people died of encephalitis in the northern state of Uttar Pradesh.

"This year, the number [of cases] has gone up a bit. The heat wave has been too intense, and it has gone on for too long," said Sanjay Kumar, a senior state health official.

The state health department has blamed hypoglycemia -- low blood sugar -- for the children's deaths but said that lychee fruit, which is widely grown in the region, also plays a role.

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