Classifying disease

Geographers group diseases in several overlapping ways:

• Communicable (infectious) — caused by a pathogen and able to spread between hosts. Non-communicable diseases (e.g. cancers, heart disease) are not transmitted between people.
• Contagious — a communicable disease spread by direct or close contact.
• Zoonotic — an infectious disease that passes from animals to humans.
• Vector-borne — carried by an organism (a vector) such as a mosquito, which transmits the pathogen.
• Endemic — continually present in a population at a fairly steady level; epidemic — a sharp rise above the expected level in a region; pandemic — an epidemic that spreads across many countries or continents.

Watch the overlap: a disease can be several of these at once - malaria, for example, is communicable, vector-borne and endemic in many tropical regions.

Endemic, epidemic or pandemic?

Disease, environment and development

The geography of disease is shaped by both the physical environment and the level of development:

• Climate and environment — temperature, humidity, standing water and altitude control where vectors and pathogens can survive, giving many diseases a distinct spatial range.
• Development — access to clean water, sanitation, nutrition, housing and healthcare strongly influences which diseases dominate and how deadly they are.
• Inequality — the poorest people, in the poorest places, generally face the heaviest burden of preventable infectious disease.

Evaluate: environment sets where a disease can occur, but development largely determines whether it becomes a serious health problem - so disease burden is as much about society as about nature.

The diffusion of disease

Hagerstrand's diffusion model describes how phenomena spread across space and time. Key types of diffusion are:

• Expansion diffusion — the disease spreads outward while remaining in its source area. It can be:
  • Contagious — spread by direct contact to nearby people (strong distance decay).
  • Hierarchical — spread down (or up) an urban hierarchy, jumping between large cities before reaching smaller settlements.
• Relocation diffusion — the disease moves to new areas and leaves the origin behind, e.g. carried by a migrating or travelling host.

Key terms: the neighbourhood effect means people close to a case are most likely to be infected next; distance decay means the likelihood of spread falls as distance from the source increases.

Cities first

Who is next?

Sort the spread

Tap a card, then tap the category it belongs to.

Your turn — case fatality rate

The epidemiological transition

Omran's epidemiological transition describes how a country's disease burden changes as it develops:

• In less developed settings the main killers are communicable (infectious) diseases, often affecting the young.
• As development brings clean water, sanitation, vaccination and better nutrition, deaths from infection fall.
• In more developed settings the burden shifts to degenerative and lifestyle (non-communicable) diseases - heart disease, cancers, diabetes - affecting an ageing population.

Evaluate: the model captures a real broad trend, but many countries now face a double burden - still fighting infectious disease while non-communicable disease rises - so the transition is neither smooth nor one-way.

Shifting burden

Your turn — incidence rate

Vectors and environmental controls

A vector is an organism that carries a pathogen between hosts. The classic example is the Anopheles mosquito, which transmits the malaria parasite:

• Temperature — both the mosquito and the parasite develop only within a warm temperature range, so malaria is largely confined to tropical and sub-tropical areas.
• Standing water — mosquitoes breed in still or slow-moving water, so wet seasons, marshes and poor drainage raise transmission.
• Altitude — cooler highlands limit the vector, though warming can extend its range upslope.

Why it matters: because transmission depends on climatic controls, environmental management - draining breeding sites, bed nets, indoor spraying - can interrupt the disease without treating every person.

What is a vector?

Global patterns and inequalities

Health outcomes are deeply uneven at every scale:

• Between countries — life expectancy and the disease mix differ sharply between richer and poorer nations.
• Within countries — poorer regions and groups often carry a heavier burden, reflecting income, housing and access to care.
• Access — money, distance, education and political stability all shape who can reach prevention and treatment.

Evaluate: disease patterns are not purely natural - they track wealth and power. Reducing inequality in water, sanitation and healthcare can cut disease burden as effectively as medical breakthroughs.

Your turn — percentage change

Managing disease

Disease can be mitigated and managed at many scales, but each approach faces barriers:

• WHO — the World Health Organization coordinates surveillance, sets guidance and runs global campaigns.
• Vaccination programmes — build herd immunity; effective but need cold chains, funding and public trust.
• Surveillance — early detection and monitoring allow a faster response.
• Health education — changes behaviour (sanitation, bed nets, diet), but depends on literacy and resources.

Barriers to management: poverty, weak health systems, conflict and political instability, remoteness, cultural resistance, and pathogens evolving resistance to drugs and insecticides.

Match the term

Tap a description on the left, then its match on the right.

The big ideas to know

You have worked through the whole Disease Dilemmas debate. Press Finish to see your score.