Dengue virus is an under-recognised causative agent of acute encephalitis syndrome (AES): Results from a four year AES surveillance study of Japanese encephalitis in selected states of India.

• Dengue virus is one of the three most common agents identified in AES. • Existing surveillance for acute encephalitis syndrome (AES) does not include routine testing for dengue. • Dengue accounts for 5% of AES cases in India especially in the absence of laboratory evidence for other pathogens tested. • Testing for dengue in AES cases must be included in routine surveillance. Acute encephalitis syndrome (AES) surveillance in India has indicated that Japanese encephalitis virus (JEV) accounts for 5-35% of AES cases annually; the etiology remains unknown in the remaining cases. We implemented comprehensive AES surveillance to identify other etiological agents of AES, with emphasis on dengue virus. Serum and cerebrospinal fluid (CSF) specimens were collected from patients enrolled prospectively in AES surveillance from 2014-2017 at selected sites of three high burden states of India. All samples were initially tested for JEV IgM. Specimens negative for JEV by serology were tested for IgM to scrub typhus, dengue virus (DEN), and West Nile virus; all JEV IgM-negative CSF samples were tested by PCR for S. pneumoniae, N. meningitidis, H. influenzae , herpes simplex virus type 1, enteroviruses and DEN. Of 10,107 AES patients, an etiology could be established in 49.2% of patients including JEV (16%), scrub typhus (16%) and DEN (5.2%) as the top three agents. Amongst the DEN positive cases (359/6892), seven (2%) were positive only for dengue virus RNA: one in serum and six in CSF. Amongst the pathogens identified, dengue accounted for 5% of all AES cases and was one of the three common etiological agents. These results underscore the importance of including dengue virus in routine testing of AES cases. [ABSTRACT FROM AUTHOR]