Mapping the last mile: micro-stratification for sustained visceral leishmaniasis elimination in Bangladesh
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Background
Bangladesh became the first country to achieve World Health Organization (WHO) validation for eliminating visceral leishmaniasis (VL, Kala-azar) as a public-health problem in 2023. Sustaining this milestone demands a post-validation surveillance strategy that concentrates its efforts on residual transmission foci and deploys resources efficiently. We therefore conducted the country’s first Mouza-level micro-stratification to refine risk maps and guide targeted interventions.
Methods
The study used routinely reported VL line-list data (2017-2022) from the national DHIS2 platform for every Upazila that recorded ≥1 VL case. Each Mouza—the smallest administrative unit—was categorised as high (≥3 new VL cases), moderate (2 cases), low (1 case) or non-endemic (0 cases) over the six-year period. Hot-spot maps were created in Python. Associations between endemicity (endemic vs non-endemic) and mean annual climate variables were tested with chi-squared statistics, yielding odds ratios (OR) with 95% confidence intervals (CI). Historical sand-fly density data from 51 purposively sampled Mouzas were compared across endemicity strata using one-way ANOVA. Among 15,982 Mouzas in 119 case-reporting Upazilas, only 428 (2.7%) reported ≥1 new VL case between 2017 and 2022. High-endemic Mouzas (n = 29; 0.18 %) accounted for 36% of total incident cases and clustered primarily in Mymensingh, Dhaka and Rajshahi divisions. However, year-on-year mapping showed contraction of endemic Mouzas with no sustained new foci.
Conclusions
VL transmission in Bangladesh is now intensely focal, confined to <3% of Mouzas within historically endemic Upazilas. Restricting surveillance, IRS and active case detection through micro-stratification of endemic areas could largely cut vector-control costs while safeguarding elimination. Periodic updating Mouza-level risk maps and integrating high-resolution climate and entomological data will be essential to prevent resurgence and can serve as a model for other countries nearing VL elimination.
Author Summary
We studied visceral leishmaniasis (also called kala-azar), a parasitic disease spread by sand flies that can be deadly if not treated. Since Bangladesh met global targets for public health elimination of this disease in 2023, the key challenge now is to keep it from coming back. We asked a simple question: where, exactly, do cases still occur? Using routine records from the national health information system (2017–2022), we created detailed maps at the level of mouza (small villages or village clusters). We found that recent illness was highly concentrated. Only about 3% of villages reported any new case over six years, and fewer than thirty villages held more than one-third of all cases. This pattern tells us the disease now survives in small pockets rather than everywhere. By pointing health teams to these pockets, our maps can help focus actions such as going door-to-door to find patients early, supporting their care, and controlling sand flies in the right places. We share a practical approach that can guide local planning in Bangladesh and can be adapted in other countries working to sustain control.
