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What are the global patterns of disease and can factors be identified that determine these? Key Idea 1a:Diseases can be classified and their patterns mapped. The spread of disease is complex and influenced by a number of factors. Learning Objectives: To analyse how disease spreads (diffusion). To analyse the physical and socio-economic barriers to diffusion.

Diffuse is defined as ‘to disperse or be dispersed from a centre; to spread widely, disseminate’. Infectious diseases don’t stay put - they tend to move and spread. Diseases are more mobile than previously, because we are more mobile than before [WHY?] + we carry diseases with us [example?] In a globalised world, increasingly connected by an integrated transport system there is strong evidence to suggest that disease can spread quickly via roads at the national scale + airports at regional/global scale.

Why pandemics spread: watch + interactive Diseases are more mobile than previously, because we are more mobile than before … in a globalised world, increasingly connected by an integrated transport system there is strong evidence to suggest that disease can spread quickly via roads at the national scale + airports at regional/global scale. Why pandemics spread: watch + interactive In a globalised world, increasingly connected by an integrated transport system there is strong evidence to suggest that disease can spread quickly via roads at the national scale + airports at regional/global scale.

WHY ARE DISEASES SPREAD? Crowded living + working conditions Inadequate sanitation Unclean water supplies Inadequate nutrition - too little or too much! Low income - no medical help, no resources [e.g. soap/household cleaners, mosquito net/repellent, antiseptic cream etc. Long working hours Physically exhausting work Lack of or inaccessible health care Exposure to health risks at work as legislation is not enforced Inadequate education, e.g. HIV/AIDS sufferers not understanding the concept of safe sex

Frictional Effect of Distance (Distance Decay) It is well documented that incidence [no. of NEW cases] of a disease is likely to be affected by distance Places closer to the source (of disease) are more likely to see a higher incidence Areas further away from the source are less likely to be affected and/or will be affected at a later date Incidence of disease X Distance from source of disease

Graph: shows incidence of AIDS rates falling the further away from the source in San Francisco, USA It is superimposed over the typical pattern of contagious spread of disease

Disease Diffusion Diffusion means a disease is transmitted/spread outwards from its origin across space to a new location. The spread of disease could be contagious from one directly infected person to another non-infected person.

4 Types of Spatial Diffusion Expansion Contagious Hierarchical Relocation Note: a disease can spread with a combination of above types A Level textbook

1. Expansion Diffusion Infection spreads out from source in all directions from point of origin. Expanding disease diffuses outwards into new areas. The disease often intensifies in the originating area. An outbreak of TB is an example of expansion diffusion. t1, t2, t3> denote time 1, 2 & 3 respectively

Example of Expansion Diffusion 1918 Spanish Flu killed an estimated 40 million people worldwide within just a few months. Also the recent H1N1 swine flu virus from Mexico.

2. Contagious Diffusion Infection is spread through direct contact with the carrier. Individual hosts carrying the disease pass it on to new contacts. Strongly influenced by distance - nearby individuals/regions have much higher probability of contact than remote ones. Contagious spread tends to occur in a centrifugal manner from the source region outward.

Early medical geography map by Jon Snow identifying the cluster + source of a cholera outbreak at Broad Street, London in 1852

Example of Contagious Diffusion The Common Cold: Max gets a cold. In the next few days those who sit near him in class get the same cold from him sneezing near them or touching desks, etc. Those people can then get the same cold and pass it to people sitting near them. And then spread it in their form groups or take it home or give it to people in Heathfield or on planes/trains/tube etc. The Ebola epidemic in West Africa in 2014-15 is a classic example of contagious diffusion.

3. Hierarchical Diffusion The infection spreads down through a particular system. Spreads through an ordered sequence of classes or places, usually form the largest centres with the highest connectivity to smaller, more isolated centres. E.g. from cities to large urban areas to small urban areas. Diffusion is also channelled along road, rail and air transport networks which facilitate contact between carriers and a susceptible population.

Examples of Hierarchical Diffusion HIV/AIDS in USA appeared first in San Francisco + then major cities such as LA/ New York - it then spread to smaller cities and then towns In 2009, H1N1 [Swine Flu] Virus - this disease first started in Mexico City, but first saw prevalence in other large cities (LA, NYC, Chicago) before seeing a presence in smaller cities or rural towns. It became a pandemic via international flight routes and airports. In the USA, it resulted in 61 million cases and 12,500 deaths.

4. Relocation Diffusion Infection spreads into a new area, leaving behind its origin or source of the disease It dies out in its previous location t1, t2, t3> denote time 1, 2 & 3 respectively

Example of Relocation Diffusion Migration of disease carrier e.g. migrant infected with HIV moving into a new location [BUT not contracted by all in path – WHY?] Disease spreads via transportation networks. Spread of HIV in southern Africa along lorry routes Cholera in Haiti 2010 killed 7000 was brought in by emergency aid workers flown in from Nepal.

There are some cases of malaria in the US every year for example, and most of those are close to airports. Mosquitoes survive in the plane just long enough to bite someone when they leave.

Possible Exam Questions Explain how the geographic concept of diffusion by _____*______ applies to the spread of diseases with reference to one disease. *Insert any diffusion type in the blank space

This is Torsten Hagerstrand. He developed a model to show how farm subsidies spread in southern Sweden. This model was later applied to the contagious diffusion of diseases.

Several concepts in the diffusion model: Neighbourhood effect probability of contact between a carrier + non-carrier is determined by the number of people living in each 5x5km grid square + their distance apart. People living close to carriers have a ? probability of contracting the disease than those further away. Number of people infected by an epidemic gives an S-shaped or logistic curve over time.After a slow start, number of infected increases quickly until finally levelling out as most of the susceptible population have been infected. Progress + diffusion of a disease may be interrupted by physical barriers.

Logistic or S-curve

Barriers to stop the spread of disease? IN PAIRS: Think of + jot down some ways that the spread of diseases can be stopped. For each way explain how it can and can’t contain the disease (if applicable). Can these ‘barriers’ be categorised?

BARRIERS TO DISEASE DIFFUSION PHYSICAL BARRIERS TO DISEASE DIFFUSION SOCIO-ECONOMIC PRINT – for note-taking

Barriers to Diffusion The most important physical barrier is distance decay or friction of distance [further from source = lower incidence of disease] Some physical features act as a barrier towards diffusion [they limit in/outward migration of carriers]: Mountains Desert Bodies of water e.g. lake, sea, ocean Rural periphery Remoteness Extreme climate: v dry/hot/wet/humid/cold – e.g. distribution of malaria. Political, social + economic boundaries may also limit the spread of disease. Travel restrictions/migration control and screening of travelers can form ‘human’ barriers [health monitoring + borders can be closed] Public health education/advice: heightened awareness of hygiene e.g. hand washing/safe sex advice/face masks/free needles for drug addicts Quarantine [Western aid workers returning from Ebola work in W Africa] or curfews [Sierra Leone 2015 + Ebola] or cancelling public events . Mass vaccination programmes e.g. flu jabs. THINK: What reduced the barriers to cholera in Haiti 2010?

Factors that have hindered reduction in incidence of disease Social stigma e.g. HIV/AIDs ‘gay disease’ e.g. USA 1970/80s, Russia now. Culture/religion e.g. AIDs and denial in Sub-Saharan Africa. Multiple use of water source e.g. washing, cooking, sewerage, garbage  diarrhea. Over-use of pesticides  resistance and build up in food chain. e.g. DDT. Medication side-effects e.g. malaria drugs and liver failure. Cost e.g. TB vaccination. Poverty/inequality e.g. lack of access to health care, overcrowding, lack of clean water + sanitation. Poor education. Low status of women [why might this is a factor?]. Food source e.g. stagnant water in rice paddy fields. Globalisation: Increased air travel Risk of disease due to change in culture Livestock transportation via road/rail/boat

Your demonstrate task… 10 minutes What if....? How could Hagerstrand’s model explain this... A disease moves from one continent to another People on one side of a lake having an outbreak, but others not A large capital city having an epidemic first, but it only reaching a mountainous village 2 months later. CHALLENGE: Can you criticise or evaluate the Hagerstrand Model’s usefulness? Create a table of positives (examples of it being used or working) and negatives (things it misses). Does it help us understand how diseases may spread?

EXTRA SHEETS

Access the Centers for Disease Control and Prevention website: www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/previous-case-counts.html Download the data for the cumulative number of Ebola cases in Liberia between March 2014 and June 2015 onto an Excel or Numbers spreadsheet Plot the cumulative number of cases against time as a line or bar chart [see p.515-7 in textbook] Describe + explain the main features of the time trend you have plotted