IB Geography F.2.4 Vector-borne and Water-borne Diseases Notes

Disease Patterns Reflect Transmission Routes and Uneven Vulnerability

1. Incidence: is shaped by the pathogen, its transmission route, the physical environment and the population’s exposure and access to prevention or treatment.
2. Diffusion: follows mosquito habitats, water systems, roads, migration routes and settlement patterns rather than spreading evenly across space.
3. Impacts: vary with age, pregnancy, immunity, income, health services and the timing of infection in the agricultural or school calendar.
4. The required contrast: is between one detailed vector-borne example and one detailed water-borne example.

Vector-Borne Disease Requires a Living Carrier

Mosquitoes Connect Infected and Susceptible Hosts

1. A vector: carries a pathogen between hosts without being the disease itself.
2. The reservoir: is an infected host from which a mosquito takes up the pathogen during a blood meal.
3. The incubation period: allows the pathogen to develop inside the mosquito before the next infectious bite.
4. The cycle: continues when the newly infected person becomes a source for another mosquito.

Nigeria: Malaria Is Endemic but Uneven

1. Disease and agent: malaria is caused by Plasmodium parasites and transmitted mainly by female Anopheles mosquitoes.
2. National burden: Nigeria accounted for about 27% of global malaria cases and 31% of global malaria deaths in the WHO figures used for this case study.
3. Climate: warm temperatures support parasite development, while seasonal rainfall creates breeding sites and produces peaks after the rains.
4. Standing water: forms in pools, drains, containers and irrigated areas, especially where drainage is weak.
5. Population exposure: is high because a large, dense population lives across areas suitable for transmission.
6. Spatial pattern: is endemic transmission throughout much of the country rather than a single short outbreak.

Demographic and Socio-economic Impacts

1. Children under five: carry a large share of deaths because they have not yet developed partial immunity.
2. Pregnancy: raises the risk of maternal anaemia, low birth weight and stillbirth.
3. Education and work: lose days through repeated illness, while farm labour can fall during the planting season.
4. Household budgets: lose income and gain treatment costs at the same time.

Responses and Limits

1. Insecticide-treated nets: reduce contact between mosquitoes and sleeping people.
2. Indoor residual spraying: kills mosquitoes that rest on treated walls.
3. Artemisinin-based combination therapy: clears infection and reduces severe illness when diagnosis and treatment are prompt.
4. Preventive treatment in pregnancy: is delivered through antenatal care, but clinic attendance does not guarantee that every woman receives the full course.
5. Resistance: reduces effectiveness when mosquitoes survive insecticides or parasites survive medicines.

Water-Borne Disease Uses Contaminated Water or Food

The Faecal-Oral Route Links Sanitation to Drinking Water

1. Waste: releases a pathogen from an infected person into the environment.
2. Contamination: occurs when sewage enters a shared water source through leaks, poor sanitation or flooding.
3. Exposure: occurs when another person drinks the water or eats food washed or cooked with it.
4. Renewed transmission: occurs when the newly infected person sheds the pathogen and the loop repeats.

Haiti: Cholera Spread Through Water and Transport Networks

1. Disease and agent: cholera is caused by Vibrio cholerae and spreads by the faecal-oral route through contaminated water or food.
2. Place and date: the outbreak began in Haiti in October 2010 after cholera was introduced into a population with no recent immunity.
3. Pre-existing vulnerability: the January 2010 earthquake had damaged water and sanitation systems and displaced more than one million people.
4. Initial spread: followed the Artibonite River from the first cases and then moved through river and road networks.
5. Scale: about 820,000 cases and 9,792 deaths were reported between October 2010 and February 2019.
6. Recurrence: confirmed cases returned in 2022 after more than three years without a reported case, exposing the unresolved sanitation gap.

Demographic and Socio-economic Impacts

1. Acute dehydration: can kill within hours without rapid oral or intravenous rehydration.
2. Age and vulnerability: shape mortality because children, older people and malnourished patients have less physiological reserve.
3. Health spending: was diverted to outbreak control while reconstruction needs remained large.
4. Livelihoods: lost labour time, and fear of infection disrupted movement, trade and trust.
5. Institutional trust: was damaged after investigations traced the 2010 introduction to a United Nations peacekeeping base.

Responses and Limits

1. Oral rehydration: prevents many deaths by replacing water and salts quickly.
2. Vaccination: reduces short-term risk but does not replace safe water and sanitation.
3. WASH investment: interrupts the route through protected water, sewage treatment, hygiene and surveillance.
4. Insecurity and displacement: restrict access to treatment and make safe water harder to maintain.

The Two Diseases Require Different Spatial Responses

1. Malaria control: targets the vector, human-vector contact, the parasite in infected people and the environments where mosquitoes breed.
2. Cholera control: targets contaminated water, sanitation failures, rapid rehydration, vaccination and surveillance.
3. Both examples: show that physical suitability becomes a health burden through settlement, infrastructure, poverty and access to care.
4. Both examples: also show that disease management works at several scales, from household behaviour to national surveillance and international support.