Arbovirus Circulation among Patients with Acute Encephalitis: West Nile Virus Infection among Humans in Bangladesh, 2022.

West Nile virus (WNV) is an emerging infectious disease causing neuroinvasive diseases, including meningitis and encephalitis. Although infection has been documented in birds in Bangladesh, WNV has not been detected in humans. Since 2007, the Institute of Epidemiology, Disease Control and Research in Bangladesh has conducted hospital-based acute encephalitis syndrome (AES) surveillance to monitor Japanese encephalitis (JE), which is typically detected in 2% to 3%. Our study aimed to determine the presence of WNV, dengue virus (DENV), and chikungunya virus (CHIKV) among persons enrolled in AES surveillance who tested negative for JE. We identified 300 randomly selected JE-negative sera specimens collected from January through May 2022 and tested for WNV, DENV, and CHIKV for evidence of acute infection using ELISAs. We prepared a semistructured questionnaire and interviewed consenting individuals by telephone. Among 300 AES specimens, 7 (2.3%) tested IgM positive for WNV, indicative of acute/recent infection. Of these, five (71%) were from males, and four (57%) were from children younger than 15 years old. Six (86%) were from rural areas. All WNV-positive cases reported fever, neck stiffness, and other symptoms consistent with encephalitis. Two (29%) of seven died during hospitalization. Additionally, 6 (2%) of 300 specimens tested positive for DENV, whereas none tested positive for CHIKV. Our study documented the first probable cases of WNV infection among humans in Bangladesh; DENV was also detected among cases. Expanding AES surveillance to include detection of WNV and other arboviruses is essential for monitoring emerging threats and guiding public health responses in Bangladesh.