Cholera as an example of a bacterial disease

5 – Water Resources and Management: Pathogenic Diseases (Case Study – Cholera)

5.1 Linking Water Resources to Human Health (AO1)

• Why water quality matters: Safe water is a core indicator of water‑resource performance. Contamination can trigger disease outbreaks, which in turn raise the demand for, and shape the management of, water supplies.

Global Water‑Resource Overview (Syllabus 5.1)

Resource type	Typical distribution	Key relevance to health
Surface water
Rivers & streams	High in humid & temperate zones; scarce in arid basins	Major source of drinking water; prone to contamination during floods
Lakes & reservoirs	Concentrated in glaciated and tectonic depressions	Storage for domestic supply; stagnation can foster pathogen growth
Groundwater
Aquifers (unconfined & confined)	Widespread; depth varies with geology and climate	Often “safe” from surface contamination, but vulnerable to over‑extraction & salinisation
Snow & glacier melt
Seasonal meltwater	High‑altitude basins (Himalaya, Andes, Rockies)	Critical for dry‑season supply; climate change reduces reliability
Rain‑water
Direct capture & rooftop harvesting	Anywhere with sufficient precipitation	Useful in water‑insecure regions; quality depends on storage hygiene

Factors Influencing Water Resources (Syllabus 5.2)

• Physical drivers
  • Climate – precipitation patterns, temperature, seasonality.
  • Geology & soils – permeability, aquifer recharge rates.
  • Topography – slope, river network density, flood‑plain extent.
• Human drivers
  • Population growth & migration – higher per‑capita demand.
  • Agriculture – irrigation withdrawals, pesticide runoff.
  • Industry & energy – cooling‑water use, dam construction.
  • Urbanisation – impervious surfaces increase runoff and reduce infiltration.
• Each driver can increase the likelihood of water‑borne disease. Example: intense monsoon rainfall (physical) + inadequate sanitation (human) → cholera‑risk spikes.

Water Security & Water‑Stress (Syllabus 5.3)

Water security is the ability of a population to access sufficient, safe water for health, livelihoods and ecosystem needs, now and in the future. Water‑stress occurs when demand exceeds reliable supply, often leading to compromised sanitation and higher disease risk.

Illustration: A high‑income, water‑secure country (e.g., Germany) experiences rare cholera cases because robust treatment and monitoring break the pathogen cycle. In contrast, a low‑income, water‑insecure country (e.g., Haiti) faces frequent outbreaks when infrastructure collapses after a disaster.

Management of Water Supply and Demand (Syllabus 5.3)

• Supply‑side strategies
  • Infrastructure – dams, reservoirs, rain‑water harvesting, managed aquifer recharge.
  • Source protection – upstream sanitation zones, riparian buffers, watershed reforestation.
• Demand‑side strategies
  • Pricing & metering – encourage efficient use.
  • Water‑conservation campaigns – low‑flow fixtures, leak‑repair programmes.
  • Behavioural change – safe storage, hand‑washing.
• Both sides influence cholera risk: increased supply without safe treatment can spread pathogens; demand‑reduction can lessen pressure on sanitation systems.

Systems Thinking (Geographical Framework)

• Input – contaminated water (physical, chemical, biological).
• Process – pathogen survival, replication, human exposure.
• Output – health impacts, economic loss, behavioural and policy responses.

5.2 Cholera – A Water‑borne Bacterial Disease (AO1)

Etiology and Transmission

• Pathogen: Vibrio cholerae, Gram‑negative, comma‑shaped bacterium.
• Primary reservoir: Brackish water, estuaries and coastal lagoons.
• Transmission route: Ingestion of water or food contaminated with faeces containing the bacterium.
• Incubation period: 2–5 days (range 1–10 days).

Symptoms, Mortality and Vulnerable Groups (AO3)

• Profuse “rice‑water” diarrhoea, vomiting, rapid dehydration.
• Case‑fatality rates:
  • Without treatment: 50–60 %.
  • With oral rehydration therapy (ORT): <1 %.
• High‑risk groups: Children, the elderly, pregnant women, and residents of informal settlements where safe water and health services are limited.

Scale of Analysis

Scale	Key Focus	Geographical Example
Local (urban slum)	Household water source, latrine coverage, community ORT points	Rural districts of Bangladesh (2022 outbreak)
National	National water‑supply infrastructure, public‑health policy, vaccination programme	Haiti (post‑2010 earthquake)
Global	Climate‑driven sea‑level rise, trans‑boundary river management, international aid response	Yemen (conflict‑driven water scarcity, 2017‑2021)

Change Over Time – Historical vs. Contemporary Outbreaks

• 19th‑century pandemics (1817‑1923): Six major waves spread along trade routes and river navigation, highlighting the role of early industrial‑urban water systems.
• 21st‑century outbreaks: Climate variability (monsoon flooding), displacement (earthquakes, conflict) and breakdown of sanitation produce rapid, localized spikes.
• Trend: Global incidence has declined, but the *risk* is rising in climate‑vulnerable low‑income regions.

Cross‑Topic Links (Population & Migration, Urban Areas, Climate Change)

• Population & migration: Rapid urbanisation and rural‑to‑urban migration increase population density in peri‑urban water networks, amplifying exposure.
• Urban areas & informal settlements: Limited piped water, overcrowding and inadequate waste disposal create hotspots for cholera transmission.
• Climate change: Projected sea‑level rise and altered precipitation patterns expand brackish‑water habitats and increase flood frequency, elevating cholera risk in low‑lying basins.

5.3 Quantitative Analysis of Outbreaks (AO2)

Detailed Specific Examples (Syllabus 5.3)

Year	Location (Income Group)	Water‑resource challenge	Management actions taken	Evaluation of success
2010	Haiti (Low‑income)	Earthquake destroyed water‑distribution network; sewage overflow contaminated surface water.	Emergency chlorination of wells, distribution of ORT kits, temporary latrines, WHO‑led vaccination campaign.	Incidence fell by ~30 % within 6 months, but logistics delays and ongoing displacement limited long‑term impact.
2022	Bangladesh (Lower‑middle‑income)	Monsoon flooding merged river water with household waste; high population density on riverine plains.	Pre‑emptive point‑of‑use chlorination, community health‑worker training, oral cholera vaccine (OCV) in high‑risk unions.	Case numbers reduced by ~45 % compared with 2019 baseline; sustained community engagement kept mortality <1 %.

Hydrograph Interpretation (Sample)

In a flood‑prone basin, peak river discharge often coincides with the highest cholera risk:

|   Q (m³ s⁻¹)                     *
|                                 *
|                                 *
|            *                *
|           * *              *
|          *   *            *
|_________*_____ *_________*____ Time (days)
          0   10  20  30  40  50

• Peak flow (day 20‑30) → mixing of sewage with surface water → heightened exposure.
• Management implication: pre‑emptive chlorination and ORT distribution before the flood peak.

Economic Impact Formula (AO3)

For a population N, the estimated economic loss L from a cholera outbreak can be expressed as:

\[ L = N \times \bigl(C_{\text{treatment}} + C_{\text{productivity\ loss}}\bigr) \]

• C_treatment – average cost of medical care per case (hospitalisation, ORT, antibiotics).
• C_{productivity loss} – value of lost work‑days (average daily wage × days absent).
• Illustrative calculation (Bangladesh 2022):
  N = 45 000 cases, C_treatment ≈ US $30, C_{productivity loss} ≈ US $20 → L ≈ US $2.25 million.

5.4 Management and Mitigation Strategies (AO3)

Supply‑Side Interventions

• Chlorination and point‑of‑use filtration (ceramic filters, UV pens).
• Protection of source waters – upstream sanitation zones, riparian buffers, managed aquifer recharge.
• Infrastructure upgrades – dams, reservoirs, rain‑water harvesting to ensure reliable, treatable supply.

Demand‑Side Interventions

• Water‑pricing and metering to encourage conservation.
• Community campaigns on safe storage, hand‑washing and water‑saving practices.
• Behaviour‑change education on ORT preparation and food safety.

Health‑Education & Community Engagement

• Behaviour‑change campaigns on hand‑washing, safe food handling, and ORT preparation.
• Training of local health volunteers to identify and treat cases early.

Vaccination

• Oral cholera vaccine (OCV) – two‑dose schedule; deployed in high‑risk zones (e.g., refugee camps, flood‑prone districts).
• Integration with routine immunisation programmes where feasible.

Policy, Governance & International Support

• National Water Safety Plans that embed disease surveillance with water‑resource monitoring.
• Legislation for safe‑drinking‑water standards (WHO/UNICEF Joint Monitoring Programme).
• International mechanisms (WHO, UNICEF, Red Cross) for emergency water provision, capacity building and technical assistance.

5.5 Population & Migration Linkages (Topic 4 – AO1)

• Urban‑slum dynamics: High density, informal housing, limited piped water → rapid disease transmission.
• Displacement: Earthquakes, conflict and climate‑related migration concentrate people in temporary camps where water and sanitation are often inadequate (e.g., Haiti 2010, Yemen 2017).
• Migration as a vector: Mobile populations can carry the pathogen to new catchments, creating secondary hotspots.

5.6 Geographical Skills – Mapping & GIS (AO2)

• Hot‑spot mapping: Plot cholera incidence per 10 000 population against water‑quality indicators (E. coli counts, turbidity) to reveal spatial correlation.
• Layered GIS analysis:
  • Base layer – river basins and flood‑plain extents.
  • Overlay – settlement density, latrine coverage, health‑facility locations.
  • Result – identification of priority intervention zones.
• Temporal GIS: Animate outbreak data over successive months to visualise spread linked to flood peaks.

5.7 Key Take‑aways for Geographers (AO1)

• Water‑resource management is inseparable from public‑health outcomes; disease risk is a critical performance indicator.
• Scale matters: local sanitation upgrades, national water‑policy reforms, and global climate‑change mitigation all influence cholera dynamics.
• Understanding change over time (historical pandemics vs. modern climate‑driven outbreaks) helps predict future risk patterns.
• Systems thinking links physical processes (flooding, river flow) with human processes (migration, urbanisation) and biological agents (pathogens).
• Spatial variation and inequality determine who is most affected; equitable interventions are essential for sustainable development.

Suggested Diagram – Cholera Transmission System