Studied by 3 peoplewhat is an infectious disease?
a disease spread by pathogens
bacteria, viruses, parasites
most, not all, transmitted from one person to another
Ebola
what is a non-infectious disease?
non-communicable
nutritional deficiencies, lifestyle, genetic inheritance
main cause of death in ACs
diabetes, cancer
what are communicable diseases?
an infectious disease that spreads from person-person
spread through direct + indirect contact
Covid-19
what are non-communicable diseases?
a non-infectious disease that cannot spread through infection or by other people
lifestyle choices, nutritional deficiencies, genetic inheritance
Coronary Heart Disease
what is a contagious disease?
a class of infectious disease
easily spread by direct or indirect contact between people
Ebola
what is a non-contagious disease?
spread by disease vectors
worms, mosquitoes
malaria
what is a host?
an animal that sustains a reservoir for pathogens
bacteria, viruses
bats + rabies, rats + plague
what is a vector?
a carrier of disease
mosquitoes are vectors of malaria
what are zoonotic diseases?
infectious diseases transmitted from animals to humans
60% infectious diseases spread from animals
rats + fleas + plague
what are endemic diseases?
permanently exist in a defined geographical area or population group
sleeping sickness contained in rural areas of sub-Saharan Africa
what is an epidemic?
outbreak of a disease that attacks many people at same time
spreads through a population in a restricted geographical area
Ebola, West Africa 2014, 10500 deaths
what is a pandemic?
epidemic which has spread worldwide
2020 Covid-19 pandemic, 180,000 deaths England
what is a degenerative disease?
diseases that reflect an aging population
due to medical improvements, unhealthy lifestyle choices, pollution
stroke, dementia, cancer
in 2019, responsible for 70% deaths worldwide
Global distributions of Malaria
infectious, non-contagious tropical disease
concentrated in Africa + South Asia
in 2018, 220 million infected with malaria
malarial parasite transmitted to humans by Anopheles mosquitoes
thrive in warm, humid environments
Australia eliminated malaria - public health measures
Global distribution of HIV/AIDS
infectious, contagious disease
HIV spread by human bodily fluids - blood + semen
in 2020, 38mil infected worldwide
uneven distribution, Nigeria + South Africa most cases
Global distribution of tuberculosis (TB)
infectious + highly contagious
associated with poverty + overcrowded living conditions
in 2018, 10mil cases worldwide
95% TB deaths in LIDCs - Africa
Global distribution of diabetes
non-communicable
caused by deficiency of insulin, secreted by pancreas
globally, 4.2mil deaths annually
widespread, concentrated North America + Asia
Type 1 - genetic
Type 2 - poor lifestyle choices
Global distribution of cardiovascular disease (CVD)
CVD is range of illnesses - stroke, coronary heart disease
highest mortality rates in Russia + sub-Saharan Africa
globally, 17mil deaths annually
80% CVD deaths in EDCs + LIDCs
linked to poor lifestyle choices - degenerative diseases
what is diffusion (in relation to disease)?
the process where diseases spread outward from their origin and across geographical space
what are the 4 types of disease diffusion?
expansion
relocation
contagious
hierarchal
what is expansion diffusion?
disease has a source + spreads out into new areas
carries in the source area remain infected
in 1918, Spanish flu, killed 40mil worldwide
what is relocation diffusion?
disease leaves the area of origin + moves into new area
cholera Haiti 2010, killed 7000, originated in Nepal brought to Haiti by international aid workers for earthquake
what is contagious diffusion?
disease spread through direct contact with a carrier
strongly influenced by distance
2014 Ebola epidemic West Africa
what is hierarchical diffusion?
disease spreads through an ordered sequence of places
usually from largest centres with highest connectivity to smaller more isolated rural centres
diffusion channelled along road, rail + air transport. carriers contact with susceptible population
in 2019/2020, Covid-19 virus became pandemic due to flights + rail journeys, killed over 700,000 globally
what are 5 physical barriers to diffusion?
distance - probability of contagious disease spreading to area inversely proportional to source distance
mountain ranges
seas + oceans
deserts
climate
what are 6 socio-economic barriers to diffusion + example?
political boarders - check international movement of carriers of infectious disease
imposing curfew + limiting contact between people
quarantining
wearing face masks in public places
cancelling public events
vaccination programmes, if available
all shown in England during Covid-19
what is neighbourhood effect of the Hagerstrand diffusion model?
neighbourhood effect - probability of contact between a carrier + non-carrier is determined by number of people living in each 5×5km grid square + their distance apart. More likely to be infected with closer proximity
what is the logistic curve of the Hagerstrand diffusion model?
number of people infected by epidemic approximates an S-shaped or logistic curve over time - slow beginning, number infected rapidly increases, then even out as most have become infected
what is the progress of diffusion of the Hagerstrand diffusion model?
the progress + diffusion of a disease may be interrupted by physical barriers
what are global patterns of temperature + how it affects patterns of disease?
drives of vector-born diseases
malaria, yellow fever and sleeping sickness depend on warm, humid conditions - are endemic to topics
climate influenced diseases show seasonal patterns
determines vector development
what are global patterns of precipitation + how it affects patterns of disease?
seasonal in topics
create aquatic habitats - ponds + stagnant pools
allow insects + disease vectors to flourish + complete life cycles
what are global patterns of relief + how it affects patterns of disease?
altitude causes sudden changes in climate + disease habitat
in Ethiopia, malaria concentrated in humid lowlands + largely absent in cooler highlands
what are global patterns of water sources + how it affects patterns of disease?
water-borne diseases
millions rely on water from wells + surface supplies contaminated by sewage - bacteria (cholera) thrive
unprotected + stagnant drinking water supplies are habitats for disease vectors - copepod vectors, Guinea worm, West Africa
what are physical factors that influence disease vectors - Dengue fever
infects 400mil globally
climate controls epidemiology - life cycle of mosquitoes that transmit to humans
mosquitoes thrive in warm + humid
temps more than 32 + humidity levels about 95% cause dengue epidemic in South Pacific - summer/exceptional rainfall
what are seasonal variations in disease outbreaks?
winter in northern hemisphere, influenza - lower temps + atmospheric humidity
topics + sub-tropics, vector-borne diseases peak at rainy reason
diarrhoeal disease in South Asia peaks pre-monsoon + end of monsoon rainfall (March-September)
drought can cause less vector-borne diseases
how does climate change provide conditions for emerging infectious diseases?
increases rainfall, temp, humidity - stimulated vector-borne diseases + increased their geographical range
West Nile Virus (WNV) - transmitted by mosquitoes, birds main host, spread globally. In 2012, 5500 cases reported in USA, high temps Texas worst affected
Tick seasons longer due to warmer conditions - more Lyme disease, spreading northwards in USA
Tsetse fly increase - cause sleeping sickness, sub-Saharan countries currently but predicted to spread to South Africa. WHO predict will affect 77mil by 2090
even with climate change ACs still less at risk due to public health services - anti-malarial drugs
how do zoonotic diseases spread to humans?
viruses
bacteria
fungi
parasites
domestic animals - dogs spread rabies
poultry - wild bird flu
when does the probability of zoonotic diseases being transmitted to human increase?
movement of infected wild animals unrestricted by physical barrier or infected domestic animals by political barriers
ineffective control of movement of diseased domestic animals
urbanisation creates habitats for racoons + foxes
vaccination of pets + livestock is sparse
limited control in urban areas of feral cats, pigeons …
poor hygiene + sanitation, drinking water contaminated by animal faeces + blood, man-made habitats (lakes) encourage vectors to breed
prolonged contact between humans + animals - poultry farms
what is epidemiological transition?
Relationship between development and changes in age, mortality, fertility and cause of death
What is the first phase of the epidemiological transition?
Age of pestilence and famine
Pre industrial societies morbidity is high
Life expectancy is low
Poor sanitation, lots of contamination
Slow population growth
What is the second phase of the epidemiological transition?
The age of receding pandemics
Industrial societies that have medical advancement, hygiene
Life expectancy rises
Many LIDC and EDC are in this stage today
What is the third phase of the epidemiological transition?
Post industrial society mortality slackens
Further medical improvement, hygiene and standard of living
Mortality to infectious disease is rare
Degenerative disease is the main cause
Cancer more common
Many EDC are in this stage
However ACs fall in a further 4th stage
Why does non-communicable disease increase in Advanced Countries?
Cancer and CVD dominate
Overnutrition and poor life style choices such as lack of physical activity and diet all lead to these things
Communicable diseases death mostly eliminated due to better standard of living and medical advancement
Why does communicable disease increase in Lower Income Developing Countries?
They rely on natural water for drinking so its often contaminated causing cholera and diarrhoea
Inadequate healthcare services
Malnutrition
Lack Vitamin D leads to rickets, Lack Vitamin C leads to scurvy
Slum housing and overcrowding has poor sanitation
Who are the WHO?
World Health Organisation
1948 they headquartered in Geneva
They direct and coordinate on health with the UN
Work closely with NGOs such as UNICEF, Red Cross
What is WHOs brief?
Gather health data
Identify priority areas
Research different health problems
Support UN member states in making decisions
Provide support during health crisis
Why is the quality of WHOs data sometimes unreliable?
Because 2/3 of deaths are not registered
What happened during the 2009-2010 influenza pandemic?
April 2009 swine flu identified in Mexico
Spread to North America
WHO declared international public health emergency
By June pandemic in 74 countries
In June cases doubled every 15 days
In autumn numbers began to decrease
May 2010 there was steep decline
They quoted 18,000 deaths but likely to be way over 300,000
What are physical barriers to mitigation strategies?
remote communities can be at an advantage in terms of infection but also very hard to access for medical assistance
e.g. Amazon rainforest has many indigenous tribes who previously lived peacefully but then exploiters cam in and were carriers of disease that the indigenous had not been vaccinated against
What is HIV/AIDS?
First identified in USA 1981
Weakens human immune system
Leads to AIDS if untreated
70% of people with it in Sub-Saharan Africa
Funding by governments and WHO HIV infections were 35% lower in 2013 than 2001
Poorest places in Africa worst affected
How do we mitigate against HIV/AIDS?
Education and public understanding of the fact it is spread through semen and blood
Promote safe sex and needle usage
Free condoms, dirty needle bins
Protect human rights of the groups worst affected such as gay men, women and girls, refugees
More tolerant attitudes of people so help is less shameful
How are people diagnosed with HIV?
screening for HIV antibodies in blood/saliva
Widely used in ACs
How is HIV managed?
Antiretroviral drugs suppress HIV and halt its progression into AIDS
Low cost drugs are available
But not low enough for poorest countries
How does nature provide medicine?
Many medicines originate from natural plants
Hippocrates recorded more than 300 plants and herbs
First naturally deprived medicine was morphine in 19th centaury
Give 2 examples of drugs made from natural sources?
Caffeine
From tea, coffee and cocoa plants
Grows in tropical conditions
Stimulates the central nervous system
Nicotine
Comes from tobacco plant
Grows in 20-30 degree
Helps with Alzheimer’s and depression
How are wild medical plants surviving?
At the moment its unsustainable
Over harvesting is wide spread
Reduces plant populations and genetic diversity
Results in extinction
Slow and niche growing conditions are most vulnerable
Why do habitats need to be protected?
Deforestation is 325km² a day
At least one potential drug is lost every 2 years
Pharmaceutical companies majorly profit and often steal of indigenous tribes
As a result part of the HIV drug prostialin’s revenue goes back to the Samoa tribe as compensation to protect the rainforest
When was smallpox eradicated?
1980
What diseases is WHO currently trying to eradicate?
Polio which got a vaccine in 1952
Previously paralysed 600,000 a year
Global polio eradication initiative in 1988
By 2011 it was only an endemic in 3 countries Afghanistan, Pakistan and Nigeria
What top down strategy is being used to eliminate malaria?
In Mauritius malaria was an epidemic in 1867 and killed 1/8 of the population
Major government campaign in 1948
Spray buildings and breeding sites of mosquitos with DDT
1973 WHO announced elimination of malaria in Mauritius
2 years later cyclone causes another outbreak and further spraying an drugs implemented
Only been 1 case since 1997
How is guinea worm being eradicated?
Ghana West Africa
Partner with the Red Cross Women’s Clubs
Teach women volunteers about prevention
They then visit the villages and educate
Previously tried this with men but women are the ones collecting water so they need to be told about it
What are the responsibilities of the women volunteers?
Monitor identify and report new cases
Ensure infected don’t contaminate the water
Distribute replace and check the filters that remove water fleas
Identify where there are water sources
What is the life cycle of a guinea worm?
Drink water containing water fleas infected with guinea worm larvae
Fleas are digested and release larvae into abdomen where they mate
Female worms growing up to 1m move through body
A year later a worm emerges from a blister its created causing immense pain making a person rush to water
They then infest water and worm releases larvae
Water fleas then consume the larvae
Note
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