Microbial Spectrum of Acute Encephalitis Syndrome With Special Reference to Non-Japanese Encephalitis Cases

Northeast India is endemic for Japanese encephalitis (JE), which causes acute encephalitis syndrome (AES). Though there is no specific therapy for JE, many etiological agents of AES are treatable. Hence, this study aims to evaluate the AES cases for their etiologies, laboratory parameters, and associated clinical manifestations.

A hospital-based prospective observational study was carried out, enrolling all consecutive cases of AES satisfying the World Health Organization (WHO) definition. Blood was tested for the malaria parasite. Cerebrospinal fluid (CSF) samples were processed by Gram staining, India ink staining for Cryptococcus, Ziehl-Neelsen staining for acid-fast bacilli (AFB), and culture for other bacteria and fungi. Serum and CSF samples lacking the Japanese encephalitis virus (JEV) IgM were processed for the detection of other etiologies. The CSF polymerase chain reaction (PCR) method was used to detect Enterovirus, Haemophilus influenzae, Neisseria meningitidis, and herpes simplex virus, and serum IgM enzyme-linked immunoassay (ELISA) detected scrub typhus, Leptospira, dengue, chikungunya, and West Nile antibodies.

Out of 395 AES cases tested, 77 were found to be positive for non-JE etiologies. Of these, dengue virus (n=32/371; 8.6%) was the most common, followed by scrub typhus (n=16/348; 4.6%) and Leptospira (n=10/362; 2.8%). Positive cases showed CSF pleocytosis (>5 WBC/cumm) and significantly higher protein level (n=6/11; 55%) and sugar level (n=8/11; 73%) in Streptococcus pneumoniae. All cases presented with fever (n=11/11; 100%), followed by altered mental status (n=18/19; 94.7%) and seizure (n=22/32; 68.7%).

The number of non-JE causes of AES in Assam is higher. Scrub typhus, dengue virus, and Leptospira are other major infectious etiologies of AES that are treatable. Timely diagnosis of such cases will help reduce AES-related complications and mortality.