Cholera

What it is

Cholera is an acute bacterial intestinal infection caused by toxigenic Vibrio cholerae, serotypes O1 and O139. The bacterium lives in freshwater and brackish water environments, and infection occurs almost exclusively through ingestion of contaminated drinking water or undercooked seafood. The signature presentation is profuse, painless diarrhea of a pale, watery character that can cause fatal dehydration within hours. Without treatment, the case-fatality ratio reaches 50%. With prompt oral or intravenous rehydration, it falls below 1%. Antibiotics (doxycycline, azithromycin) reduce fluid requirements and illness duration but are secondary to fluid replacement. The disease is a sentinel of failed water and sanitation systems: it does not circulate in places where sewage is reliably separated from drinking water.

History

Seven cholera pandemics have been recorded since 1817, all originating in South Asia. The current seventh pandemic began in 1961 in Indonesia, carried by the El Tor biotype of V. cholerae O1, and has never been declared over. Earlier pandemics helped build modern epidemiology: John Snow's 1854 mapping of a London outbreak to a single contaminated Broad Street pump established the foundational method of disease field investigation. The 2010 Haiti outbreak, introduced by UN peacekeepers following the January earthquake, killed more than 10,000 people and infected 800,000, demonstrating how a pathogen entering an immunologically naive population can explode when sanitation collapses. The O139 serogroup, first detected in Bangladesh and India in 1992, was initially feared as the seed of an eighth pandemic but has since remained regionally confined.

Current state

WHO declared the ongoing multi-country outbreak a grade-3 emergency in 2023, its highest internal classification. In 2024, 60 countries reported cholera cases, up from 45 in 2023. Full-year 2025 data logged 614,828 cases and 7,598 deaths globally across five WHO regions. The Eastern Mediterranean, led by Yemen and Sudan, reported the highest case count at 359,052. Africa followed with 242,344 cases across 22 countries. In January 2026, WHO recorded 16,912 new cases across 19 countries and 182 deaths, a 20% rise in mortality from December despite a 6% drop in case counts. Oral cholera vaccine (OCV) stockpiles stood at 2.6 million doses in August 2025, well below the 5-million-dose emergency threshold, meaning demand routinely outstrips supply. In southern and central Africa, flooding drove a sevenfold year-on-year rise in cases in the first six weeks of 2026. In June 2026, the Central African Republic declared its fifth recorded cholera epidemic, with 197 cases and 24 deaths near Bangui.

Relationships

WHO leads global surveillance and outbreak response, coordinating the International Coordinating Group (ICG) that manages the OCV emergency stockpile alongside Gavi, the Vaccine Alliance, UNICEF, and MSF. The disease intersects directly with the water and infrastructure cluster: every outbreak maps onto some failure of piped water or sanitation. Conflict accelerates spread by destroying that infrastructure and forcing displacement into areas with no sanitation coverage. Climate shocks, particularly seasonal flooding and drought, are now the dominant trigger for new outbreak waves, a pattern WHO has explicitly named. Cholera is also an accountability issue: the UN eventually acknowledged institutional responsibility for the Haiti outbreak and set up a trust fund, though compensation disbursements remained deeply inadequate by the time the fund was wound down.

What to watch

• OCV stockpile replenishment, the 5-million-dose emergency reserve has not been consistently maintained since 2022, and each rainy season across Africa tests the gap
• Africa's 2026 outbreak trajectory, especially whether the central African cluster expands from the Central African Republic into the Democratic Republic of Congo, which carries a chronically endemic burden
• WHO's quarterly multi-country epidemiological updates, the primary public data release for the global pandemic
• Sudan and Yemen, both of which led Eastern Mediterranean case counts through 2025 and remain at acute risk from ongoing conflict-related infrastructure collapse
• Any emergence of novel V. cholerae serogroups outside O1 and O139, which would reset vaccine coverage assumptions