Toxigenic and non-toxigenic Vibrio cholerae serogroups co-circulate across multiple drinking water source types during cholera outbreaks in Zamfara State, northwestern Nigeria

Background

Cholera remains a recurrent public health emergency in Zamfara State, northwestern Nigeria, where communities depend predominantly on untreated and poorly protected water sources. Environmental water bodies serve as reservoirs for Vibrio cholerae , sustaining transmission cycles between outbreaks. Despite the severity of recurrent outbreaks in the region, data on the molecular characteristics and serogroup distribution of V. cholerae across different drinking water source types in Zamfara State remain critically limited.

Methodology/Principal Findings

A cross-sectional environmental surveillance study was conducted between 13 October and 26 November 2025 across five cholera-affected Local Government Areas (LGAs) of Zamfara State: Gusau, Bungudu, Talata Mafara, Zurmi, and Shinkafi. A total of 142 water samples were collected from five source types — rivers, boreholes, wells, tap water, and sachet water. Presumptive isolation was performed on Thiosulfate-Citrate-Bile Salts-Sucrose (TCBS) agar following alkaline peptone water enrichment. Fifty-five presumptive isolates underwent PCR-based molecular confirmation and serotyping using three gene targets: ompW (species confirmation, 588 bp), ctxA (O1 toxigenicity marker, 302 bp), and tcpA (O139 colonisation factor, 120 bp). Presumptive V. cholerae was recovered from 55 of 142 samples (38.7%; 95% CI: 30.5–47.3%), with well water recording the highest positivity rate (69.7%; 95% CI: 51.3–83.7%). A statistically significant association was observed between water source type and presumptive V. cholerae occurrence (χ² = 23.11, df = 4, p < 0.001). Molecular analysis confirmed 29 isolates (52.7%; 95% CI: 39.2–66.0%) as V. cholerae , comprising 22 O1 serotypes (75.9%), one O139 serotype (3.4%), and six non-O1/non-O139 serotypes (20.7%). Toxigenic O1 strains were detected across all five LGAs and in all five water source types, including commercially packaged sachet water. The O139 serotype was identified in a single well-water isolate from Zurmi LGA, representing the first environmental detection of this serotype in Zamfara State.

Conclusions/Significance

The co-circulation of toxigenic O1, O139, and non-toxigenic non-O1/non-O139 V. cholerae serogroups across five distinct drinking water source types confirms that community water environments serve as genetically diverse reservoirs sustaining cholera transmission in Zamfara State. These findings underscore the urgent need for integrated water quality surveillance, sanitation infrastructure investment, and sustained molecular monitoring of environmental V. cholerae populations.

Author Summary

Cholera is a severe diarrhoeal disease that kills tens of thousands of people every year, mostly in countries where clean drinking water is difficult to access. It is caused by a bacterium called Vibrio cholerae , which can survive and spread through rivers, wells, boreholes, and even commercially packaged drinking water. In Zamfara State, northern Nigeria, cholera outbreaks have returned repeatedly in recent years, yet very little scientific information exists about which types of V. cholerae are present in the water people drink every day.

In this study, we collected 142 water samples from five different types of drinking water source — rivers, boreholes, wells, tap water, and sachet water — across five cholera-affected Local Government Areas (LGAs) of Zamfara State. Using a highly sensitive DNA test called PCR, we identified the specific strains of V. cholerae present and determined whether they were capable of causing disease.

We found disease-causing V. cholerae in all five types of water source, including sachet water that people commonly assume is safe. We also made the first-ever detection of a particularly dangerous strain type, called O139, in Zamfara State. Our findings show that no single water source in these communities can be regarded as reliably free of contamination, and that regular water quality monitoring, sanitation improvements, and targeted public health interventions are urgently needed to protect communities from cholera across Zamfara State and similar settings in sub-Saharan Africa.