Classification of diseases and their diffusion

• Infectious


  Spread by pathogens such as bacteria, viruses, parasites and fungi. They can be transmitted directly or indirectly from one person to another
• Non-communicable


  A disease due to age, genetics, lifestyle. It cannot be spread between people - it is non-infectious or non-contagious
• Communicable


  Spread from host to host. Pathogens passed from to person to person or animal to person can cause it
• Contagious


  A type of infectious disease easily spread by direct physical contact or indirect contact between people
• Non-contagious


  A class of infectious disease which are spread by disease vectors such as mosquitoes, worms and their larvae, but not by people
• Epidemic


  An outbreak of disease that attacks many people at the same time and spreads through a population (small area/region)
• Endemic


  Exist permanently in a geographical area or population group
• Pandemic


  An epidemic that has spread worldwide
• Disease diffusion


  How they spread - communication
• Expansion diffusion


  Disease spreads outwards from a source area to new areas, source area remains affected
• Contagious diffusion


  Spreads through direct contact with carrier, strongly influenced by distance
• Relocation diffusion


  A disease leaves one area and moves to a new area
• Hierarchical diffusion


  Spreads through an ordered sequence of places, from largest centres with good connectivity to smaller isolated centres, can be channelled by road, rail and air
• Expansion diffusion example


  Tuberculosis
• Relocation diffusion example


  Haiti cholera brought by aid workers from Nepal
• Contagious diffusion example


  Ebola
• Hierarchical diffusion


  Swine flu and Covid 19 spread along international flight routes
• What model is used to track how disease spreads?


  Hagerstrand’s diffusion model