Disease dilemmas. Flashcards
1
Q
List the ways in which diseases are classified
A
- Infectious
- Non-infectious
- Communicable
- Non-communicable
- Contagious
- Non-contagious
- Endemic
- Epidemic
- Pandemic
2
Q
Define ‘infectious’
A
- Diseases caused by organisms - such as bacteria, fungi, protoctista and viruses, passed directly or indirectly from person to person
3
Q
Define ‘non-infectious’
A
- Diseases NOT caused by pathogens: these include - lifestyle factors, environmental toxins or gene mutation.
4
Q
What is an example of an infectious disease that is non-contagious?
A
Malaria
5
Q
Define ‘communicable disease’
A
- Diseases carried by micro-organisms that are transmitted through people, animals, surfaces, food or air.
6
Q
Define ‘contagious disease’
A
- Diseases that are passed directly from person to person through close proximity or physical contact.
7
Q
What is a zoonotic disease?
A
Infectious diseases such as plague and rabies - transmitted from animals to humans.
8
Q
What % of diseases originate from animals (zoonotically)
A
- 60%
9
Q
Define endemic
A
- A disease that exists permanently within a geographical area or human group
10
Q
Define epidemic
A
- A disease outbreak that spreads quickly through a usually restricted geographical area.
11
Q
Define pandemic
A
- An epidemic that spreads worldwide
12
Q
What are 3 OVERVIEW factors to consider in the spread of disease?
A
- Social
- Economic
- Environmental
13
Q
What are some environmental factors in the spread of disease?
A
- Prevalence of vectors
- Climate conditions
- Natural disasters
- Physical barriers (prevent)
- Proximity to animals
14
Q
What are some social factors in the spread of disease?
A
- Cultural practice
- Migration
- Increased global mobility
- War
- Population density
15
Q
What are some economic factors in the spread of disease?
A
- Sectoral change
- Access to healthcare
- Provision of vaccinations
- Housing quality
- Globalisation
- Developed infrastructure (sewage)
16
Q
What classification of disease is malaria?
A
- Infectious but NON-contagious
17
Q
What 5 diseases do we need to know the global distribution for?
A
- AIDS/HIV
- Tuberculosis
- Malaria
- Cardiovascular disease
- Diabetes
18
Q
Where is malaria concentrated?
A
- Concentrated in: Africa, Latin America, South Asia and South-East Asia.
19
Q
How many people are at risk of malaria and in how many countries?
A
- Overall, 3.2 billion are at risk
- 97 countries
20
Q
How is malaria transmitted?
A
- The malarial parasite (plasmodium) is transmitted via anopheles mosquitos within warm and humid climate.
21
Q
What classification of disease is HIV/AIDS
A
- Infectious AND contagious
22
Q
How is HIV/AIDS transmitted?
A
- The HIV virus is spread by human body fluids such as blood and semen.
23
Q
How many people have a HIV status worldwide, and how many new infections were there in 2024?
A
- 40 million worldwide in 2024
- 1.3 million new cases.
24
Q
What is the distribution of HIV/AIDS?
A
- The main distribution is in sub-Saharan Africa, South Africa and Nigeria.
- Despite this, AIDS/HIV is distributed worldwide, but in lower quantities.
25
How many people contracted TB in 2024, and what was the death toll from the previous year?
- 8 million worldwide
- 1.25 million died in 2023
26
What classification of disease is TB?
- Infectious and highly contagious.
27
What is the global distribution of TB (tuberculosis), and where is the highest mortality?
- TB is present in all global regions, however 95% of deaths occur in LIDCs and EDCs.
- Africa has the highest number of TB deaths, commonly co-morbid with AIDS.
28
What classification of disease is diabetes?
- Non-communicable
29
How many people, in 2024, have diabetes worldwide and how many deaths occur yearly?
- 800 million have diabetes
- 6.7 million die as a result annually.
30
Where is diabetes distributed?
- Diabetes is widespread across both the developed and less developed world.
- Highest concentration is in North America and South Asia.
31
- Where is cardiovascular disease distributed (including what countries have the highest CVD mortality)?
- It is more commonly morbid in aging populations, associated with AC status.
- The countries with the highest CVD mortality are when standardized by age are: Russia, sub-Saharan Africa, and the Arabian peninsula
- 3/4s of CVD deaths are in middle to low income countries (inversely related to income)
32
What is meant by diffusion of disease?
- The way in which disease spreads outwards from its origin across space.
33
What model is used to explain diffusion?
- The Hägerstrand's diffusion model
34
What are the 4 main types of diffusion under Hägerstrand's model?
- Expansion diffusion
- Relocation diffusion
- Contagious diffusion
- Hierarchal diffusion
35
Describe expansion diffusion
- In **expansion diffusion** a disease has a source and spreads outwards into new areas, during this carriers in the source area remain infected.
36
Give an example of a disease outbreak that undergoes expansion diffusion
- A tuberculosis outbreak
37
Describe relocation diffusion
- In **relocation diffusion** a disease leaves the area of origin and moves to new distinct areas.
38
Give an example of disease outbreak that *underwent* relocation diffusion
- The cholera epidemic in Haiti 2010.
- The disease originated in Nepal and was brought by international aid workers.
39
Describe contagious diffusion
- In **contagious diffusion** is where disease spreads through **direct contact** with a carrier, strongly influenced by proximity.
40
Give an example of a disease outbreak that *underwent* contagious diffusion
- The Ebola epidemic in West Africa in 2014-15.
41
Describe hierarchical diffusion
- In **hierarchical diffusion** a disease spreads through an ordered sequence of places, usually from the largest centers with high connectivity to smaller, more isolated centers.
- Hierarchical diffusion is channeled along road, rail and air transport networks that facilitate contact between carriers and a susceptible population.
42
Give an example of disease outbreak that *underwent* hierarchical diffusion
- The COVID-19 pandemic
- This was due to mobility by rail journeys and international air flights.
43
What is included in Hägerstrand's model?
- Expansion diffusion
- Relocation diffusion
- Hierarchical diffusion
- Contagious diffusion
- 'Neighborhood effect'
- Barriers to diffusion
- S-shaped logistic curve
44
What is the neighborhood effect in Hägerstrand's model?
The idea that the probability of contact between a carrier and non-carrier is determined by the number of people residing in a 5x5km grid square, and their distance apart.
45
What does the S-shaped logistic curve represent in Hägerstrand's diffusion model, and explain it
- It represents how the number of people infected by an epidemic approximates an S-shaped or logistic curve over time.
- In this, after a slow beginning, the number infected accelerates rapidly until eventually plateauing, as most of the susceptible population have been infected.
46
What are the two types of barriers to disease in Hägerstrand's diffusion model?
- Socio-economic barriers
- Physical barriers
47
List the 4 *phases* of diffusion in Hägerstrand's diffusion model
- Primary stage
- Diffusion stage
- Condensing stage
- Saturation stage
48
What happens in each *phase* of diffusion in Hägerstrand's model?
- **Primary stage**: there is a strong contrast in disease incidence between the area of outbreak and remote areas.
- **Diffusion stage:** new centers of disease outbreak occur at distance from the source, reducing spatial contrasts seen in 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 disease reaches its peak.
49
Describe some socio-economic barriers to disease
- Political border checks
- Imposing curfews or quarantining
- Mandating facemasks in public places such as hospitals
- health education
50
Describe some physical barriers to disease
- Distance between areas
- Mountain / topographical barriers
- Climate conditions
51
What 4 physical factors influence the prevalence of disease?
- Temperature (climate)
- Precipitation (climate)
- Relief
- Water sources
52
How does global patterns of temperature influence patterns of disease?
- Temperature, being part of climate, influences disease.
- Warm temperatures, such as in the Sub-tropics and Tropics, are favored especially by diseases caused by vectors such as malaria and sleeping sickness due to having a warm, humid tropical condition for breeding to occur.
- Colder temperatures, such as in North America and Europe, tends to be favored by respiratory diseases such as influenza, thriving off of the environments influence on the immune system.
53
How does global patterns of precipitation influence patterns of disease?
- Precipitation, being part of climate, works alongside temperature to provide a humid environment - such as in the Tropics that facilitate the reproduction of vectors carrying disease.
- Precipitation also provides aquatic habitats such as ponds and stagnant pools, allowing insects and other vectors to flourish and complete their life cycles.
54
How does global patterns of relief influence patterns of disease?
- A rise in altitude corresponds with lowering temperatures and increasing rainfall.
- In parts of Africa, such as the highlands in Ethiopia being virtually free of malaria whilst the *Western Lowlands* have high prevalence of malaria, this is because higher altitudes are too cold for the mosquito vector to thrive.
- If the topography/relief is flat, floodplains form during periods of flood leading to water-borne diseases such as hepatitis A and dysentery.
55
How does global patterns of water sources influence patterns of disease?
- There is higher stagnant water sources within warmer areas, affecting the prevalence of water-borne diseases and parasites.
56
How do the **4** physical factors in the specification affect the prevalence of vectors (mosquitoes)
- **Precipitation**: Malaria requires mosquitoes to complete their lifecycle and reproduce effectively, this requires precipitation to create stagnant water sources, in turn, average monthly relative humidity needs to be over *60%*.
- **Temperature**: Malaria favors, and is active in places with temperatures averaging between 18-40 degrees annually.
- **Relief**: Mosquitoes favor areas of lower relief due to hosting warmer temperatures in relation to altitude and being vulnerable to flood events.
- **Water-sources**: Mosquitoes require stagnant water for their lifecycle, which includes laying eggs in areas with extensive water sources.
57
In what ways does seasonal variations influence disease outbreaks?
- Winter months lead to peaking epidemics of influenza and respiratory illnesses in the Northern Hemisphere.
- Monsoon seasons in the tropics and sub-tropics lead to an increase in vector-borne diseases such as mosquitoes carrying malaria.
In addition, monsoon seasons allow vectors, such as the tsetse fly (sleeping sickness) in West and Central Africa to extend their lifespan.
- Bilharzia, a disease spread from flatworms and freshwater snails increases with seasonal precipitation and temperature increase above 20 degrees due to their seasonal lifecycle being linked to these events.
58
In simple, in what ways has climate change influenced infectious diseases?
- Climate change, characterized by increase in temperature, rainfall and humidity has *stimulated transmission* of infectious disease and *extended their geographical range**!!
59
How is West Nile Virus affected by climate change?
- West Nile Virus is transmitted via mosquitos, with it's spread being facilitated by climate change bringing warmer and wetter conditions for the vector.
- As a result of climate change, WNV is developing an *extended geographical range*, it is prevalent throughout Africa, In the Americas it is found from Canada to Venezuela and can be traced in parts of Europe, West Asia and Australia.
- The USA has seen how high temperatures favor transmission - hence, Texas being the state most severely effected.
- WNV, as a result of climate change has developed NEW HOSTS in birds.
60
How is Lyme's disease affected by climate change?
- Climate change is responsible for Lyme's disease spreading Northwards as temperatures rise.
- As a result, ticks (the vectors of Lyme's disease) are predicted to colonize Canada.
61
How is sleeping sickness affected by climate change?
- Sleeping sickness is transmitted by tsetse fly, a vector.
- Outbreaks of the disease occur in temperatures in the range of 20.7-26.1 degrees.
- Future climate change will effect the vectors growth rate and geographical distribution of the disease. FOR EXAMPLE: as temperatures rise, sleeping sickness is likely to spread into Southern Africa and affect up to 77 million more - WHO.
- Despite this, a positive is that climate change may mean the disease can disappear completely from East Africa as climate may be too hot for Tsetse larvae to survive.
62
What is an anomaly to the idea that climate change will spread malaria over a wider geographical area?
- Malaria was previously found to be endemic in Europe and other temperate regions, even when climate was colder than in the modern day.
- In addition, even if future climate becomes more suitable for malaria in Southern Europe, parts of Asia and the USA - a large endemic is unlikely here due to availability of anti-malarial drugs and high standards of public health services, associated with ACs.
63
Define what is meant by a zoonotic disease
Diseases spread from animals to humans by viruses, bacteria, fungi and parasites - these include diseases such as malaria, dengue fever, sleeping sickness and rabies.
64
Zoonotic infections can only be transmitted by wild animals, true or false?
False!
- For example, poultry (a domestic animal) present a greater risk of transmitting Asian flu than wild birds.
65
What conditions increase the transmission of zoonotic illnesses to humans?
- There is free movement of infected animals
- Ineffective country controls on the movement of diseased domestic animals
- Urbanization creates new habitats for animals such as foxes, bringing them in closer proximity to humans.
- Sparse vaccination of pets and domestic livestock.
- Lack of animal control for rabid/feral animals
- Hygiene and sanitation are poor, as drinking water sources are contaminated by animal faeces
- There is prolonged contact between humans and animals, for example the wet meat markets in China and farms (poultry with avian flu and cattle with anthrax).
66
What is the link between diseases and levels of economic development (specification point)
As countries develop, the frequency of communicable diseases decreases, whilst the prevalence of non communicable diseases rises. (diseases of affluence)
67
Who created the epidemiological transition?
Omran
68
What does the epidemiological transition describe?
- The model of the epidemiological transition describes the relationship between development and changing patterns of population age distribution, mortality, fertility, life expectancy and causes of death.
- Changes are driven by improvement in health care, standards of living and the quality of the environment
69
According to Omran under the epidemiological transition, what are the 3 epidemiological stages?
- 1) The age of pestilence
- 2) The age of receding pandemics
- 3) Post industrial societies mortality rate slackens
70
What is the proposed 4th stage to the epidemiological transition?
- 4) The age of delayed degenerative diseases
71
What are some criticisms of the epidemiological transition?
- The model is too optimistic
- There is counter-evidence, such as the rate of improvement of life expectancy slowing in developed countries, and even falling in countries such as the UK
- Globalization may increase spread of pandemics, so infectious diseases still remain an issue.
- Development can be attributed to industrial output and destruction of ecosystems - so zoonotic diseases are more easily facilitated
- COVID-19 as an event has reminded us that both governments and populations of the 'developed world' are not immune to communicable disease.
72
Explain what occurs in the 3 stages of the epidemiological transition
- **The age of pestilence and famine**
Pre-industrial societies see high mortality and low life expectancy. Poor sanitation, contaminated drinking water and low standards of living make people susceptible to infectious diseases. Population growth is slow and intermittent.
- **The age of receding pandemics**
Industrial societies see advances in medical technology, diet and hygiene, and also improvements in living standards. Epidemics causing large scale mortality become rare, life expectancy rises above 50 and population growth is sustained. There is a shift from main death being caused by infectious diseases to chronic and degenerative diseases.
- **Post-industrial rate of mortality slackening**
Further improvements in medical technology, hygiene and living standards means that mortality related to infectious disease is rare. Degenerative disease becomes the main cause of mortality.
73
For what reasons do ACs have a higher prevalence of non-communicable diseases?
- Lengthened life expectancies inevitably increases the proportion of deaths and illnesses connected to degenerative diseases and aging.
- Overnutrition and excessive consumption of sugar, carbohydrates, fats and salt are increasing NC diseases such as CVD, type-2 diabetes, hypertension etc..
- Sectoral change, and higher incomes, increases office jobs which requires minimal physical activity. This allows accessibility to food such as meat, leading to overconsumption of this.
- Standards of living rising has a correlation with prevalence of non-communicable diseases - cancers are higher in ACs compared to LIDCs and EDCs. Cancer rates are over double in ACs compared to LIDCs.
74
For what reasons do LIDCs have a higher prevalence of communicable diseases?
- Communicable diseases can be categorized into 3: animal-borne, water-borne and food-borne.
- Waterborne diseases remain endemic in LIDCs, and are eliminated in ACs - this is due to lack of infrastructure.
- There is failure to control communicable disease outbreak due to economic state limiting healthcare services and resource provision to tackle this.
- Other factors are malnutrition which is associated with immunosuppression, and lack of resistance to common diseases.
- Many LIDCs witness overcrowding of housing in urban areas, stimulated by work opportunities - this is closely linked to respiratory air-borne disease spread.
- **Environmentally**, LIDCs are common in areas such as the tropics and sub-tropics - climate creates ideal conditions for a wide range of infectious diseases (despite Singapore being an exception with a life expectancy of over 84 years).
