Changing landscape of acute encephalitis syndrome in India: a systematic review

Seasonal outbreaks of acute encephalitis syndrome (AES) occur with striking regularity in India and lead to substantial mortality. Several viruses, endemic in many parts of India, account for AES. Although Japanese encephalitis virus (JEV) is a key aetiological agent for AES in India, and has attracted countrywide attention, many recent studies suggest that enteroviruses and rhabdoviruses might account for outbreaks of AES. We did a systematic review of published studies to understand the changing landscape of AES in India.

Electronic databases (PubMed, Web of Science and BIOSIS) from the start of the database to 2010. We also hand-searched journals and screened reference lists of original articles, reviews and book chapters to identify additional studies.

We included studies only on humans and from three time-periods: pre-1975, 1975-1999 and 2000-2010.

Independent, duplicate data extraction and quality assessment were conducted. Data extracted included study characteristics, type of study and aetiological agent identified.

Of the 749 unique published articles screened, 57 studies met the inclusion criteria (35 outbreak investigations and 22 surveillance studies).

While most studies from 1975 to 1999 identified JEV as the main cause of AES, many studies published after 2000 identified Chandipura and enteroviruses as the most common agents, in both outbreaks and surveillance studies. Overall, a positive yield with respect to identification of aetiological agents was higher in outbreak investigations as compared to surveillance studies.

The landscape of AES in India has changed in the previous decade, and both outbreak investigations and surveillance studies have increasingly reported non-JEV aetiologies. Because of these findings, there is a need to explore additional strategies to prevent AES beyond vector control and JEV vaccination.