Diseases

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Classifications

Types of Diseases:

  • Infectious - Diseases spread by bacteria, viruses, fungi, parasites etc. Influenza
  • Non - Infectious - Non-communicable, the result of age, lifestyle, genetics like heart disease
  • Communicable - Diseases that can spread host to host like Ebola 
  • Non - Communicable - Diseases that cannot be passed from host to host like diabetes
  • Contagious - diseases spread by indirect contact between people, flu
  • Non - Contagious - diseases that cannot be passed from contact with other people

Type of Wide Spread Incidences:

  • Endemic - a series of incidences that occur within a specific geographical area or population
  • Epidemic - an outbreak that attacks most people in a population or geographical area in a small amount of time
  • Pandemic - where a series of Epidemics occur in various different populations, this can be neighbouring states etc. but usually needs to be on a different continent to declared as a pandemic, like the black death
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Degenerative Diseases

  • 60% of deaths caused by disease are degenrative
  • This is a result of an aeging global population and increasingly unhealthy lifestyle
  • Examples:
  • Cardiovascualr Diseases (Angina, Coronary Heart Disease, Strokes and Aortic Diseases etc.)
  • Some Cancers
  • Chronic Respitory Issues
  • In 2013 16 million under 70's dieds from this kind of diseases
  • 82% of them lived in LIDC's and EDC's
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Global Distribution of Diseases - Malaria

Malaria

  • Infectious, non-contagious
  • Tropical
  • Incidences mainly concentrated around the equator: Africa, Southeast Asia, Latin and South America, parts of South Asia
  • 3.2 Billion at risk in 97 countries 
  • Transmitted through a parasite carried by the Anopheles mosquito
  • This type of mosquito thrives in warm and humid environments like those experienced in the tropics along the equator
  • Even in these areas, malaria is absent almost completely from drier cooler areas like in mountains dessert and urban regions
  • In the Gulf of Mexico and Australia despite a risk existing thanks to public health measures malaria has been effectively eradicated 
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Global Distribution of Diseases - HIV/AIDS & TB

HIV/AIDS 

  • Infectious and Contagious disease
  • Spread through fluids like blood and semen
  • 2015 - 3.5 million confirmed infected with the disease 
  • Distribution of incidences very uneven, highest concentrations tend to be places in: Sub Sharan Africa such as  Nigeria, South Africa, Swaziland, Lesotho

Tuberculosis (TB)

  • Infectious and highly infectious
  • 9 million global cases
  • 1.5 million deaths a year
  • Associated with poverty, poor and overcrowded living conditions
  • Present in all global regions 
  • 95% of deaths occurs in LIDC/EC
  • Africa has highest amount of mortality rates from TB, for example
  • 94/100,000 in Nigeria
  • 69/100,000 in Mozambique
  • Outside Africa TB rates are highest in parts of South and East Asia, Afghanistan, Myanmar and Cambodia
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Global Distribution of Diseases - Diabetes

Diabetes

  • Non - communicable disease
  • Caused by deficiency of insulin
  • Affects 250 million people worldwide
  •  Responsible for 4 million deaths annually
  • Spread throughout developed and less developed world
  • Mainly concentrated in North America as week as East and South Asia
  • Type 1 is genetic
  • Type 2 occurs usually down to poor diet, obesity Abd physical inactivity 

 

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Global Distribution of Diseases - CVD

Cardiovascular Disease (CVD)

  • Covers range of diseases 
  • Stroke
  • Hypertension
  • Coronary Heart Disease
  • Angina
  • Incidences increase with age
  • Using age, the places with the highest level of CVD mortality are Russia, Sub-Saharan Africa and the Arabian Peninsula 
  • CVD causes 17 million deaths a year
  • 80% occur in LIDC's and EDC's
  • Premature death from CVD is linked to lifestyle like tobacco consumption, poor diet and lack of physical activity 
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Disease Diffusion

  • The phrase used to refer to the spread of a disease from its origin point.
  • There are 4 different models:
  • Expansion diffusion: a disease spreads outwards from a source into new areas while the carriers in the source area remain infected, like TB.
  • Relocation diffusion: is when a disease completely leaves one location and moves into another location like Cholera moving from Nepal to Haiti
  • Hierarchal diffusion: is where a disease spreads through an ordered sequence of places usually from the largest centers with the biggest levels of connectivity to smaller areas with less connectivity.
  • Contagious diffusion: the spread of disease through direct contact with a carrier, strongly influenced by distance. Ebola
  • Barriers
  • Most barriers are either socio-economic or physical.
  • The most important barrier is distance, generally, the probability of a disease spreading to a an area is inversely proportional to the distance from its source 
  • Things like mountain ranges, seas, oceans, desert and climate 
  • Climate is important in terms of epidemiology and distribution of diseases like as malaria
  • Political borders can also check the movement of disease, this is determined through things like curfews, quarantining people including aid workers, face marks for the public, mass vaccination such as in flu and public health education 
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Hagerstrand's Diffusion Model

  • A model originally for farm subsidies and then applied to diseases is a probabilistic model rather than a fixed one and returns slightly different results every time it is applied.
  • There are several concepts important to the model:
  • The neighborhood effect: the probability of contact between a carrier and non-carrier is determined by the amount of people living in each 5 by 5 grid square and their distance apart. People living in close proximity to carriers have a greater probability of contracting a disease than those located further away, this is known as distance decay function and is assumed to be geometric.
  • The number of people infected by an epidemic follows an s-shaped or logistic curve, after a slow start many people will get infected very quickly until leveling out as most susceptible population have been infected.
  • The progress and diffusion of a disease may be interrupted by physical barriers.
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The Effect of Global Patterns of Climate and Relie

  • Temperature and Precipitation are major influencers of vector-borne disease and epidemics such as malaria, dengue fever, yellow fever, and sleeping sickness whose epidemiology depends on warm, humid conditions and are endemic to the tropics and sub-tropics along the equator.
  • Disease affected by climate usually show seasonal differences, partly because temperature determines vector development and behavior as well as viral replication. Precipitation in humid areas also tends to create aquatic habitats like ponds and stagnant pools which allow insects and diseases to flourish such as the parasite Guinea Worm in West Africa.
  • Things like mountains can cause abrupt changes in climate and disease habitats.
  • In Ethiopia malaria is concentrated around the humid lowlands but is often absent from in the cooler highlands.
  • Waterborne diseases are very common in these areas and this made worse by the reliance on in the developing world on water coming from wells and contaminated surface water.
  • Bacteria that causes cholera and other infections thrive in these conditions
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Physical Factors and Disease Vectors (Dengue Feve

  • Dengue Fever (Schistosomiasis) is widespread in the tropics
  • Infects 400 million and causes 25,000 deaths every year
  • Climate is main factor in its epidemiology and the life cycle of its disease vector, Aedes mosquito
  • The mosquitos thrive in humid conditions which also helps the outbreaks of dengue
  • In the South Pacific, prolonged temperatures of 32C+ and humidity levels of 95%+ trigger epidemics
  • The outbreaks occur in the summer months, but short term weather change and excessive rainfall also trigger epidemics.
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Seasonal Variations in Disease Outbreaks

  • Health risks associated with diseases often a strong seasonal bias. In the temperate regions of the northern hemisphere, epidemics of influenza, peak in winter months.
  • The actual reason for the seasonal differences is not known, it's known that transmission of flu is most efficient at temperatures such as 5C and when humidity is low, these conditions occur mostly in winter.
  • In the tropics and sub-tropics, vector-borne diseases, transmitted by, mosquitoes, flies, ticks, fleas, and worms peak in rainy seasons.
  • Diarrhoeal disease in South Asia rises just before and after monsoon periods when fly populations are highest.
  • Sandflies, which transmit protozoan-causing leishmaniasis, are also abundant in the rainy season.
  • Bilharzia or schistosomiasis used by a trematode flatworm hosted by freshwater snails kills around 200,000 every year, Infection rates follow the life cycle of the snail, which is influenced by seasonal precipitation and temperatures of 10-30C
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Climate Change’s Effect on Emerging Infectious Dis

  • Increases in temperatures, rainfall and humidity have increased incidences and geo-graphic range of vector-borne diseases. Humid conditions like those in the tropical region have increased the growth and spread of mosquitos carrying disease like West Nile Virus, malaria, and dengue fever.
  • WNV appeared in Uganda in 1937 transmitted by the Culex mosquito. Birds are the main hosts of the virus. WNV has spread globally through Africa; from Venezuela to Canada in the Americas; parts of Europe, West Asia, and Australis. 5500 cases of WNV were reported in the USA ion 2013. Texas is one of the most affected by higher temperatures.
  • Climate change increases incidences of Lyme disease and trypanosomiasis. Ticks thrive in warmer conditions. In the USA, it is expanding northwards and could colonize Canada.
  • In Africa, trypanosomiasis, or sleeping sickness, is endemic in 36 sub-Sharan counties and affects 70 million.
  • It is transmitted by the tsetse fly. Outbreaks occur when temperatures are in the range 20.7-26.1C. In future climate change will affect growth rate and geographical distribution of the disease. As temperatures rise it is likely to spread into southern Africa and will affect 77 million more people by 2090 according to the WHO,
  • However, the disease may be wiped out in East Africa where the climate may become too hot for the larvae.
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