Many thanks to Ronan Kelly for sending the link to this page at FluTrackers: India Encephalitis 2014 - 19 fatalities. It has an excerpt from a Current Science article (with link) offering a new hypothesis about the seasonal scourge of encephalitis in Bihar state (and by implication the same problem in Uttar Pradesh). Excerpt:
These studies documented that cases coincided spatially and temporally with lychee cultivation. The investigators noted colonies of fruit-eating bats and the tendency of children eating fruits fallen to the ground and suggested the possibility of a bat virus (through saliva contamination on fruits) as a cause of the disease (2).
Other studies concluded that the disease was not due to infection, but was due to heat stroke (4,5). ...
Our hypothesis is that the Muzaffarpur AES is caused by MCPG [methylenecyclopropyl-glycine] in lychee. However, we do not know if it is present only in the seed or also in the edible fruit flesh (in ackee and lychee, the aril is transformed as the edible part) and if unripe lychee has more MCPG than ripe fruits.