Maria et al. in the American Journal of Tropical Medicine and Hygiene documented the first probable human West Nile virus infections in Bangladesh. Seven of 300 Japanese-encephalitis-negative acute encephalitis sera tested IgM-positive, and two of the seven people died. Islam and Hasan, in the International Journal of Infectious Diseases, mapped seventeen years of chikungunya genomic evolution in Bangladesh and confirmed sustained local circulation of the Indian Ocean Lineage of the ECSA genotype. Both papers were published on 2 July 2026.
Two papers published on 2 July 2026 reported new evidence that West Nile virus and chikungunya virus circulate locally in Bangladesh. The first documents probable human West Nile virus infections in the country for the first time. The second traces seventeen years of chikungunya virus evolution and confirms sustained local circulation. Both findings come from serological and genomic surveillance.
West Nile virus in Bangladesh
The study is by Maria ST, Billah MM, Zaki QA, Sultana S, Averhoff F, Cloherty G, Walsh N and Shirin T. It appeared in the American Journal of Tropical Medicine and Hygiene on 2 July 2026 (PMID 42392066). The team works at the Institute of Epidemiology, Disease Control and Research in Dhaka and the Abbott Pandemic Defense Coalition.
The team tested 300 serum samples from patients with acute encephalitis syndrome who tested negative for Japanese encephalitis. The samples were collected in Bangladesh between January and May 2022. Seven of the 300 samples, or 2.3 percent, tested IgM-positive for West Nile virus. Two of the seven people died. Six further samples, or 2.0 percent, tested positive for dengue virus. The panel showed no chikungunya virus.
The IgM-positive results are the first documented probable human West Nile virus cases in Bangladesh. The paper reports that local transmission has occurred at least since 2022. The surveillance system did not detect it earlier because the testing protocol focused on Japanese encephalitis. The dengue findings show that several viruses cause encephalitis in the same population.
Chikungunya circulation in Bangladesh
Islam S and Hasan M published the chikungunya study in the International Journal of Infectious Diseases on 2 July 2026 (PMID 42392528). The team analysed chikungunya virus genomic data from Bangladesh collected between 2008 and 2025.
All Bangladeshi isolates cluster within the Indian Ocean Lineage of the ECSA genotype. The common ancestor of the lineage dates to around mid-2007. Haplotype diversity is high, while nucleotide diversity is low. That pattern indicates expansion from a limited number of variants, with sharp population growth in 2017. The authors report sustained local circulation with periodic amplification, and they call for continuous genomic surveillance.
The finding means that chikungunya in Bangladesh is not a series of re-introductions from outside the country. The virus has circulated and amplified locally since the late 2000s. The 2017 surge was the point at which the virus reached the population level associated with endemic circulation.
Related findings in other regions
Two papers published in July 2026 describe the same pattern in other regions. Corbel et al. published a Lancet Regional Health Americas paper on the South American chikungunya resurgence. Chuquimia Valdez et al. reported the first chikungunya detection in Bolivia in 2025 in Emerging Infectious Diseases.
Jourdan et al. established a French seroprevalence baseline in Eurosurveillance. The baseline showed that West Nile virus had circulated in southern France and Ile-de-France before any autochthonous human case was identified.
What the findings mean for readers
Both papers report local transmission that routine surveillance had not fully captured. The release of IgM and genomic data helps health authorities target testing and vector control. Dengue, West Nile virus and chikungunya share the same Aedes mosquitoes in many settings.
The measures that reduce exposure to Aedes bites are well established. Empty standing water around the home every week. Cover water stores. Screen windows and doors. Use repellent according to the label. Health authorities use the same measures in vector-control programmes.
Published 2026-07-04 · Mosticare Editorial
This article is general information, not medical advice. Ask a doctor or pharmacist about your own health.