Disease Dilemmas

Disease Classifications

Infectious - spread by pathogens such as bacteria, viruses and parasites, e.g. malaria. Most can be transmitted from one person to another.

Non-Infectious - are diseases that are not caused by micro-organisms, e.g. cancer, diabetes.

Communicable - infectious diseases which spread from one person to another but do not require quarentine, e.g. HIV, Chickenpox.

Non-Communicable - these are not spread from person to person but have causes related to lifestyle, e.g. heart disease, some cancers; to nutritional deficiencies, e.g. rickets; or to genetic inheritance, e.g. heart disease.

Contagious - a class of infectious disease easily spread by direct or indirect contact between people, e.g. typhoid, Ebola.

Non-Contagious - these cannot be spread between people, e.g. Asthma.

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Disease Classifications 2

Epidemic - a disease outbreak that attacks many people at the same time and spreads through a population in a restricted geographical area.

Endemic - exists permanently in a geographical area or population, e.g. sleeping sickness in rural areas of sub-Saharan Africa.

Pandemic - an epidemic that spreads globally, e.g. Asian flu (1957-1958)

Zoonotic - infectious diseases transmitted from animals to humans, e.g. rabies, plague.

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Disease Diffusion and Spread

  • Expansion Diffusion - the disease has a source and spreads outwards into new areas. The source area remains infected.
  • Relocation Diffusion - the disease leaves the area of origin and moves to new areas.
  • Contagious Diffusion - the spread through direct contact with a carrier.
  • Hierachical Diffusion - disease spreads through a structured sequence of locations, usually from large, well-contained centres to smaller, more isolated areas.

Hagerstrand's Diffusion Model:

this model has been applied to the contagious diffusion of disease. The most important concepts are:

  • a neighbourhood effect: the probability of contact between those infected and those not infected and the influence of distance decay.
  • the number of people infected: represented by an S-shaped curve over time.
  • the interruption of the progress of disease by physical barriers.
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Phases of Diffusion in Hagerstrand's Model

  • Primary Stage: there is a strong contrast in disease incidence between the area of outbreak and remote areas.
  • Diffusion Stage: new centres of disease outbreak occur at distance from the source and this reduces the spatial contrasts of the primary stage.
  • Condensing Stage: the number of new cases is more equal in all locations, irrespective of distance from the source.
  • Saturation Stage: diffusion decelerates as the incidence of the disease reaches its peak.

Physical Barriers - e.g. distance, mountains, sea, deserts, climatic change or general climatic conditions such as tropical or continental.

Socio-Economic Barriers - e.g. political border checks, imposition of curfews or quarentining. Most of these are put in place by international organisations and/ or governments.

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Physical Factors and Disease

  • Climate (temperature and precipitation) - climate affects where disease vectors live. The most frequently referred- to example is that mosquitoes and tsete flies (which transmit sleeping sickness): both favour warm, humid, tropical conditions.
  • Relief - altitude leads to falling temperatures and increasing rainfall. In parts of Africa, at higher altitudes it is too cold for mosquitoes. Flat floodplains can lead to diseases during periods of flood in LIDCs, e.g. hepatitis A and E and dysentery.
  • Water Sources - stagnant water affects the prevalence of water-borne diseases; parasitic worms in infected water spread diseases.
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Physical Factors and Vectors

Example of vectors include mosquitoes, tsetse flies, fleas, parasitic worms and some snails. Vecot-borne diseases include dengue fever and African sleeping sickness. Malaria is the most widespread vector-borne disease and is affected by the following physical factors:

  • Rainfall (puddles at the end of rainy season)
  • Temperature (particularly active in places where average temperatures are between 18-40 degrees celsius).
  • Humidity (where average monthly relative humidity is over 60%)
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Seasonal Variations and Disease Outbreaks

  • Epidemics of influenza and respiratory illness peak in the winter months in the Northern hemisphere.
  • Vector-borne diseases transmitted by mosquitoes, flies and ticks peak during the rainy season in the tropics and sub-tropics.
  • Fly populations are highest in South Asia in the pre-monsoon (March-April) and end of monsoon (September-October) seasons.
  • The tsetse fly, which transmits sleeping sickness in west and central Africa, can live longer in the wet season.
  • Freshwater snails, which transmit bilharzia to humans, follow a seasonal lifestyle pattern linked to precipitation and temperatures of 10-30 degrees celsius.
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Climate Change and Emerging Diseases

Warmer and wetter conditions mean that vector-borne diseases such as malaria and dengue fever will spread in terms of their geographical area. Climate change is also responsible for the spread of Lyme disease and trypanosomiasis (sleeping sickness) as both diseases spread northwards. As temperatures rise, the World Health Organisation (WHO) predicts that sleeping sickness will spread to southern Africa and affect 77 million people by 2090. A further consideration is that such diseases may disappear from some areas that become too hot, e.g. East Africa.

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Conditions and Zoonotic Diseases

Zoonotic diseases spread from animals to humans by viruses, bacteria, parasites and fungi. They include malaria, dengue fever and sleeping sickness. Dogs, bats, foxes and raccoons can all transmit rabies; poultry can transmit Asian flu. Probability of the spread of zoonotic diseases increases where:

  • there is free movement of infected animals.
  • urbanisation creates habitats for animals, e.g. foxes, and brings them into closer contact with human populations.
  • there is not an effective vaccination programme for pets and livestock.
  • hygiene and sanitation is poor.
  • there is prolonged close contact between humans and animals, e.g. poultry farms.
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Epidemiological Transition

As countries develop, the health and wellbeing of the nation should also improve as more money is available to spend on agriculture, health services and basic infrastructure.

Economic Developments:

  • Investment in agriculture to raise yields and farming efficiency in order to provide adequate good-quality food.
  • Improved infrastructure so that food can be stored and distributed efficiently and basic services such as energy, sewage and clean water can reach the whole population.
  • Investment in the health service.

Social Developments:

  • Better education on sanitation, healthy diet and the spread of disease.
  • Advances in medical care and availability of basic medicines and vaccinations.
  • Better education and more opportunities to become fully trained health care professionals.
  • Reduced infant mortality rates.
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Epidemiological Transition Model

A  model suggests that over time as a country develops there will be a transition from infectious diseases to chronic and degenerative diseases as the main cause of death. The model, based on a line graph was put forward by Abdul Omran in 1971. It can be seen as a sub-section of the Demographic Transition Model in the stages where medical advances impact on birth and death rates.

Phases:

1. Age of Infection and Famine (LE= 20-40 years) - poor sanitation and hygiene, unreliable food supply. Infections and nutritional deficiencies cause mortality and mortality.

2. Age of Reducing Pandemics (LE= 30-50 years) - improved sanitation, better diet. Reduced number of infections, increases in occurence of strokes and heart disease.

3. Age of Degenerative and Man-Made Diseases (LE= 50-60 years) - increased ageing; lifestyles associated with poor diet , less activity and addictions. M&M- high blood pressure, obesity, diabetes, smoking-related cancers, strokes, heart disease and pulmonary vascular disease.

4. Age of Delayed Degenerative Diseases (LE= c.70+ years) - reduced risk behaviours in the population, health promotion and new treatments. M&M - heart disease, strokes and cancers are the main cause of mortality but treatment extends life. Dementia and ageing diseases start to appear more.

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Contexts to the Model

  • Classified/Western Model - e.g. western Europe where a slow decline in death rate is followed by low fertility
  • Accelerated Model - e.g. parts of Latin America where falls in mortality are much more rapid.
  • Contemporary/Delayed Model - e.g. sub-Saharan Africa where decreases in mortality are not accompanied by a decline in fertility. 
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Reasons for Prevalence of Diseases

  • Communicable diseases have largely been eliminated in ACs through diagnosis, treatment, high standards of living, clean water and good nutrition.
  • Prolonged life in ACs means that degenerative illnesses have increased.
  • In ACs, overnutrition and excess consumption of sugar, fats and salts has increased the incidence of non-communicable diseases such as cardiovascular disease and type-2 diabetes.
  • Overnutritionn is becoming an increasing problem in EDCs as affluence increases and dietary choices change. Other non-communicable diseases such as cancer are now increasing in EDCs and LIDCs.
  • Geography is also a factor in the prevalence of communicable diseases in LIDCs. Tropical and sub-tropical locations give rise to diseases such as dengue fever, malaria, sleeping sickness, yellow fever and Ebola.
  • Communicable disease accounts for the majority of deaths in the poorest countries because of poverty, lack of resources, inadequate nutrition, water pollution and poor hygiene.
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The Role of International Organisations

A range of international organisations have roles in the prediction and mitigation of disease. These include WHO, UNICEF and NGOs auch as Medecins Sans Frontieres.Increasing global mobility has the effect of leading to wider disease diffusion because of greater international flows of people, but improvements in transport and the effect of a 'shrinking world' can also enable international organisations to respond rapidly to disease outbreaks.

The World Health Organisation (WHO):

The directing coordinating body for global health, established in 1948, the WHO operates within the UN in Geneva, and has 194 member states. Wide-ranging activities include:

  • Data collection, research and monitoring.
  • Providing leadership in health matters.
  • Technical Support.

The WHO publishes World Health Statistics annually, which gives a country-by-country insight into health risks, mortality rates, spread of disease and government spending. The Who funds projects and takes a major role in responding to disease outbreaks, e.g. the Zeka virus. They also deliver emergency aid.

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Physical Barriers and Mitigation

Barriers of disease diffusion can be classified as natural, physical or human. The most important barrier is disease decay- the further away, the lower the incidence. Other physical barriers include remoteness (mountain regions, rural peripheries). They can limit the spread of disease by vectors also.

Positive Effects - physical barriers isolate communities and reduce the spread of disease. Physical barriers restrict population movements and therefore limit the spread of disease.

Negative Effects - isolation may delay the arrival of medical care, lack of contact with other people may reduce immunity, large water bodies in certain physical contexts (e.g. flood plains) may be more susceptible to flooding, leading to issues with the spread of disease from standing water.

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Mitigation Strategies for Global Pandemics

In 2007, WHO in conjunction with FAO (the Food and Agriculture Organisation) and the World Bank reviewed the status of H5N1 avian influenza (bird flu) and assessed the related risks to human health following the emergence of a pandemic virus. The strategic plan was:

  • Reduce human exposure to H5N1 virus - reduce opportunities for infection and reduce opportunities for pandemic virus to emerge.
  • Strengthen the early warning system - ensure that affected countries, WHO and the international community have all the data and specimens needed for an accurate risk assessment.
  • Build capacity to cope with pandemic - ensure that all countries have formulated and tested pandemic response plans and that WHO is fully able to perform its leadership role.
  • Coordinate global scientific research and development - ensure that pandemic vaccines and antiviral drugs are rapidly and widely available shorty after the start of a pandemic and that scientific understanding of the virus evolves quickly.
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Mitigation Strategies for Global Pandemics 2

At the individual country (government) level, strategies may include providing guidance for members of public and businesses on symptoms and on how to avoid catching and spreading the illness and what action to take on becoming unwell. Other strategies include: overseeing a coordinated response with health professionals, media, businesses, communities and voluntaary organisations; and a prediction of possible socio-economic impacts.

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Medicines from Nature

Many modern medicines originate from wild plants and other natural sources such as microbes and animals (e.g. snake venom in drugs to treat heart conditions). This is not new- long before scientific medicine, plants were used for medicine, as reflected in common names, e.g. woundwart and liver wort. Medicinal drugs derived from natural compounds include:

  • Caffeine - (source= tea, coffee, cocoa e.t.c.) growing conditions are tropical and sub-tropical conditions; temperatures 20-27 degrees celsius, rainfall 1000-2000mm/yr. Medical usage= stimulant for central nervous system, heart, muscles, Migraine, epidural, anaesthesia etc.
  • Quinine - (source= dried bark of cinchonas) growing conditions are average temperatures above 20 degrees celsius, humid conditions, rainfall average 200mm over at least 8 months. Medical usage= malaria.
  • Morphine - (source= opium poppy- dried latex seed pods) growing conditions are warm, humid, temperatures 30-38 degrees celsius. Medical usage= pain reliever.
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Conservation Issues and Medicinal Plants

Supply and demand: medicinal plants come mainly from wild sources. 80% of people in the developing world rely on traditional medicines- so demand is high. The most sought after species are under pressure.

Protection of habitats and natural ecosystems: habitat destruction, in particular deforestation in the tropics, is a greater concern than over-collection of plants. Tropical rainforests contain 70% of terrestrial plant species and only 1% has been screened for medicinal use, so the potential is huge. There are further concerns over biopiracy- when medicinal drugs from wild environments are exploited by pharmaceutical companies with little or no benefit to indigenous people. One possible response is for pharmaceutical companies to work with local people and in return for habitat and ecosystem conservation, company profits will be used to fund local community projects.

Survival of wild medicinal plants: increasingly, sourcing supplies is becoming unsustainable. Over-harvesting is wide spread. In the worst cases, it will result in extinction. Slow-growing plants and those with a specialised niche are particularly vulnerable. 4000 medicinal plants are threatened. 

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Disease Eradication at Global Scale

Guinea worm (Dracunculiasis) is the first parasitic disease set for eradication. This is because diagnosis is easy (it relies on visual recognition of emerging worm), the intermediate host is restricted to stagnant water bodies, interventions are simple and cost-effective, the disease has limited geographical distribution, and several countries in Africa, Asia and Middle East have successfully eliminated the disease.

The process of eradication takes time: in 1981 WHO's decision-making body, the World Health Assembly (WHA), adopted a resolution supporting the opportunity to elimate guinea worm. In 2011, the WHA called on all member states to enforce nationwide surveillance to ensure the eradication of guinea worm. This strategy involves:

  • Mapping all endemic villages.
  • Implementing effective case containment measures in all endemic villages.
  • Implementing specific interventions such as ensuring access to safe water and health education.
  • Reporting on a regular basis.
  • Managing a certification process for global eradication country by country.
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National and Local Scale

Pakistan is one of the only three countries in the world categorsed as endemic by the Global Polio Eradication Initiative (GPEI), along with Afghanistan and Nigeria. Details of Pakistan's 2015 National Emergency Action Plan (NEAP) include the following:

  • Emergency Operations Centres to be established at local level.
  • Frontline health workers (mainly women) to be boosted by improved training and tools (including mobile phone apps), better communication systems and regular on-time payment.
  • Vaccinations to be made the norm for a community through the Emergency Operation Centres.
  • Vaccine management including better refrigeration of vaccines.
  • Improved health, sanitation and nutrition for the most vulnerable.
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Grassroot Strategies

Grassroot strategies (bottom-up) are usually small, community-based projects that focus on the needs of the people and are often favoured by NGOs such as Oxfam, Education, assistance and engagement of local people are key features of such strategies.

Women play a significant role in combating disease risk. Reasons why include:

  • They are often the primary carers for children and therefore are key to understanding and using vaccination and health awareness programmes.
  • Increasingly, female frontline health workers have a greater impact on education and vaccination programmes than male workers because they can engage and relate to women more efficiently and they understand that a particular role undertaken by women can spread disease (e.g. women sourcing clean drinking water).
  • Women may have a specific role to play where a disease is passed on through pregnancy, e.g. Zika virus.
  • In many societies women have the primary responsibility for maintaining hygiene in the home and for food preparation; poor experience in both allows disease to spread.
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