Disease Dilemmas
Diseases can be Classified and their Patterns Mapped. The Spread of Diseases is Complex and influenced
by a number of factors
• Infectious diseases- diseases spread by pathogens, such as viruses, parasites and fungi
• Contagious diseases- class of infectious diseases easily spread by direct or indirect contact between
people
• Communicable diseases- infectious diseases which spread from host to host but do not require
quarantine
• Endemic- diseases that exist permanently in a geographical area or population group, e.g. Chagas
disease in Central and South America
• Epidemic- an outbreak of a disease that attacks many people at the same time and spreads through a
population in a restrictive geographical area
• Pandemic- an epidemic that has spread worldwide
GLOBAL DISTRIBUTION OF MAJOR DISEASES
1) Malaria
◦ Concentrated in Africa, S America and South Asia
◦ 3.2 billion people at risk in 97 countries
◦ Malarial parasite transmitted to humans by Anopheles mosquito
◦ Malaria absent in cooler and drier conditions
2) HIV/AIDS
◦ In 2015, 35m people infected globally
◦ Highly uneven distribution
◦ Main concentration in Sub-Saharan Africa- in Lesotho more than 1/4 of population
3) Tuberculosis
◦ In 2013, nearly 9 million cases, 1.5 million death
◦ Associated with poverty and overcrowded living conditions
◦ Present in all regions, but 95% of deaths occur in lower income countries
◦ Africa highest (94/100,000 mortality rate in Nigeria), also high in Asia
4) Diabetes
◦ Afflicts nearly 250m people globally, responsible for 4m deaths annually
◦ Most strongly concentrated in North America and SE Asia
5) Cardiovascular Disease
◦ Includes coronary heart disease, strokes, hypertension and angina
◦ Major cause of mortality in ageing populations
◦ Highest mortality rates in Russia, SS Africa and Arabia
◦ Responsible for 17m deaths a year, 80% in EDCs and LIDCs
, DISEASE DIFFUSION
Types of Diffusion
1) Expansion diffusion- has a source and spreads outwards into new areas
2) Relocation diffusion- when a disease leaves one area and moves into other areas
3) Contagious diffusion- through direct contact with a carrier, strongly influence by distance
4) Hierarchical diffusion- disease spreads through an ordered sequence of places, usually from centres with
highest connectivity to more isolated areas
Barriers to Diffusion
1) Physical
◦ Distance- in general probability of a contagious disease spreading to an area is inversely proportional
to the distance from the source
◦ Mountain ranges, seas, oceans, deserts
◦ Climate also major factor in epidemiology and distribution of diseases such as malaria and sleeping
sickness
2) Socio-Economic
◦ Political borders check the international movement of carriers
◦ Spread of disease can be controlled by imposing curfews, e.g. Sierra Leone in 2015 with Ebola
◦ Quarantine
◦ Wearing face masks in public, cancelling public events
◦ Mass vaccination programmes
◦ Health education
Hagerstrand's Diffusion Model
• Probabilistic rather than fixed or deterministic models
• Neighbourhood Effect- people living in close proximity to carriers have a greater probability of contracting
disease- distance decay
• After slow beginning- number infected accelerates rapidly until it levels out, as most of susceptible
population been infected
• Interruption of physical barriers
Diseases can be Classified and their Patterns Mapped. The Spread of Diseases is Complex and influenced
by a number of factors
• Infectious diseases- diseases spread by pathogens, such as viruses, parasites and fungi
• Contagious diseases- class of infectious diseases easily spread by direct or indirect contact between
people
• Communicable diseases- infectious diseases which spread from host to host but do not require
quarantine
• Endemic- diseases that exist permanently in a geographical area or population group, e.g. Chagas
disease in Central and South America
• Epidemic- an outbreak of a disease that attacks many people at the same time and spreads through a
population in a restrictive geographical area
• Pandemic- an epidemic that has spread worldwide
GLOBAL DISTRIBUTION OF MAJOR DISEASES
1) Malaria
◦ Concentrated in Africa, S America and South Asia
◦ 3.2 billion people at risk in 97 countries
◦ Malarial parasite transmitted to humans by Anopheles mosquito
◦ Malaria absent in cooler and drier conditions
2) HIV/AIDS
◦ In 2015, 35m people infected globally
◦ Highly uneven distribution
◦ Main concentration in Sub-Saharan Africa- in Lesotho more than 1/4 of population
3) Tuberculosis
◦ In 2013, nearly 9 million cases, 1.5 million death
◦ Associated with poverty and overcrowded living conditions
◦ Present in all regions, but 95% of deaths occur in lower income countries
◦ Africa highest (94/100,000 mortality rate in Nigeria), also high in Asia
4) Diabetes
◦ Afflicts nearly 250m people globally, responsible for 4m deaths annually
◦ Most strongly concentrated in North America and SE Asia
5) Cardiovascular Disease
◦ Includes coronary heart disease, strokes, hypertension and angina
◦ Major cause of mortality in ageing populations
◦ Highest mortality rates in Russia, SS Africa and Arabia
◦ Responsible for 17m deaths a year, 80% in EDCs and LIDCs
, DISEASE DIFFUSION
Types of Diffusion
1) Expansion diffusion- has a source and spreads outwards into new areas
2) Relocation diffusion- when a disease leaves one area and moves into other areas
3) Contagious diffusion- through direct contact with a carrier, strongly influence by distance
4) Hierarchical diffusion- disease spreads through an ordered sequence of places, usually from centres with
highest connectivity to more isolated areas
Barriers to Diffusion
1) Physical
◦ Distance- in general probability of a contagious disease spreading to an area is inversely proportional
to the distance from the source
◦ Mountain ranges, seas, oceans, deserts
◦ Climate also major factor in epidemiology and distribution of diseases such as malaria and sleeping
sickness
2) Socio-Economic
◦ Political borders check the international movement of carriers
◦ Spread of disease can be controlled by imposing curfews, e.g. Sierra Leone in 2015 with Ebola
◦ Quarantine
◦ Wearing face masks in public, cancelling public events
◦ Mass vaccination programmes
◦ Health education
Hagerstrand's Diffusion Model
• Probabilistic rather than fixed or deterministic models
• Neighbourhood Effect- people living in close proximity to carriers have a greater probability of contracting
disease- distance decay
• After slow beginning- number infected accelerates rapidly until it levels out, as most of susceptible
population been infected
• Interruption of physical barriers
