Transcript Document 7112347

PATHOGENS
WHAT IS A PATHOGEN?
 Microorganisms that cause disease
WHAT IS A DISEASE?
 A disease is not a single thing
 It is a description of certain symptoms
 Either physical, mental or both
 Disease suggests a malfunction of body or mind
 Has mental, physical and social aspects
MICROORGANISMS AS PATHOGENS
 For a microorganism to be considered a pathogen, it
must;
 Gain entry to the host
 Colonise the tissues of the host
 Resist the defences of the host
 Cause damage to the host tissues
 Pathogens include the following;
 Bacteria – eg pathogen responsible for food poisoning
 Viruses – eg pathogen responsible for HIV
 Fungi – eg pathogen responsible for athletes foot
 Infection – when a pathogen gains entry into the host and
colonises its tissue
 Disease – occurs when an infection leads to recognisable
symptoms in the host
 Transmission – the transfer of a pathogen from one
individual to another
HOW MICROORGANISMS GAIN
ENTRY INTO THE HOST
 Penetration of one of the organism’s interfaces with the environment
 Such an interface is the skin
 This forms a thick, continuous layer, which is an effective barrier to
infection
 Invasion usually occurs when the skin is broken by cuts/abrasions/bites
 Some interfaces of the body have evolved to allow exchange of material
between the internal and external environments
 Therefore, the body linings at such surfaces have the
following characteristics;
 thin
 moist (and therefore sticky)
 large surface area
 well supplied with blood vessels
 Just as these characteristics allow for easy entry of
molecules, they also make for easy entry of pathogenic
microorganisms
 Interfaces of the body are common points of entry and include the
following;
 The gas exchange system – pathogens that cause influenza,
tuberculosis and bronchitis infect through the gas exchange surfaces.
 The digestive system – food and water may carry pathogens into the
stomach and intestines via the mouth. Cholera, typhoid and dysentery
pathogens enter the body by this means.
To help prevent the entry of pathogens the body has a number of
natural defences. These include;
 A mucous layer – this covers exchange surfaces and forms a
thick sticky barrier that is difficult to penetrate
 The production of enzymes – breaks down the pathogens
 The production of stomach acid – kills microorganism
HOW DO PATHOGENS CAUSE DISEASE?
Pathogens affect the body in two main ways;
 By damaging host tissues
 Sometimes, the number of pathogen causes damage, eg by
preventing tissues functioning properly
 Viruses prevent the synthesis of DNA, RNA and proteins by
the host cell
 By producing toxin
 Most bacterial pathogens produce toxins
 Eg, the cholera bacterium produces a toxin which leads
to excessive water loss from the lining of the intestines
 Some diseases, such as malaria, have a single cause
 Others like heart disease, have a number of causes
 Pathogens, lifestyle and genetic factors can all cause
disease
 How quickly a pathogen causes damage (and hence the onset
of symptoms) is related to how rapidly the pathogen divides.
 Pathogens like those causing gastroenteritis divide about
every 30 minutes – so symptoms of diarrhoea and vomiting
become apparent within 24 hours of infection.
 The gastroenteritis pathogen also causes damage only if
present in very large numbers.
 Pathogens such as the typhoid bacterium, cause harm even
in relatively small numbers
DATA AND DISEASE
EPIDEMIOLOGY
 Study of the incidence (number of cases) and pattern of a
disease
 Used to find the means of preventing and controlling
disease
What pattern/relationship does this graph show you?
ANALYSING AND INTERPRETING DATA
ON DISEASE
 All the lines are more or less at zero at the age of 30
 All the lines follow approximately the same pattern – what
does this show?
 What about the differences between the four coloured
lines?
 What is the overall interpretation?
CORRELATONS AND CAUSAL
RELATIONSHIPS
 A correlation occurs when a change in one of the two
variables is reflected by a change in the other.
 Graph shows that there is a correlation between drinking
alcohol and breast cancer.
 Cannot conclude that drinking alcohol is the cause of breast
cancer
LOOKING CRITICALLY AT DATA
 Has the right factor been measured and have the correct
questions been asked?
 How were the data gathered? Was the method reliable?
 Do those collecting the data have a genuine interest in the
outcome of the research?
 Has the study been repeated and the same results found?
 Are there still unanswered questions?
LIFESTYLE AND
HEALTH
 Number of disorders that result from lifestyle
choices
 In some cases, harmful consequences are known at
outset
 In some cases, damage may only become apparent
later
WHAT IS RISK?
A measure of the probability that damage to health will
occur as a result of a given hazard
Concept of risk has two elements;
 The probability that a hazardous event will occur
 The consequences of that hazardous event
This affects how we view risks
We become concerned when probability is high and
consequences severe
MEASUREMENT OF RISK
 Can be measured as a value that ranges from 0% (no harm
will occur) to 100% (harm will definitely occur)
HEALTH RISKS NEED A TIMESCALE
 To tell someone their risk of dying is 100% is meaningless
 To tell someone that their risk of dying in the next month is
100% has a different meaning altogether
RISK IS OFTEN RELATIVE
 Risk is measured by comparing the likelihood of harm
occurring in those exposed to a hazard with those who are
not exposed to it.
 Even when a risk is quantified, there are loads of factors
to consider that it is difficult to understand the risk.
For example
 smokers may be 15 times more likely to develop lung cancer
than non smokers
 Over what time period does this occur?
 How does the number of cigarettes smoked a day affect
the figure?
 do stress levels, alcohol intake, occupation, gender, pollution
or other factors have an influence?
 Does it change depending on where the smokers live?
RISK FACTORS AND CANCER
 Cancer is not a single disease and does not have a
single cause
 Some causal factors are beyond individuals control,
e.g. age and genetic factors
 Others are lifestyle factors
LIFESTYLE FACTORS AND CANCER
 Our lifestyle can expose us to environmental
factors and carcinogenic factors that put us at risk
of contracting cancer.
 Thought that half the people who are diagnosed
with cancer in the UK could have avoided getting the
disease by altering their lifestyle.
 Smoking – smokers and passive smokers at risk of getting
cancer.
 Diet – evidence suggests that a low-fat, high-fibre diet,
rich in fruit and vegetables, reduces the risk
 obesity – being overweight increases the risk of cancer.
 Physical activity – people who take regular exercise are at
lower risk from some cancers.
 Sunlight – the greater the exposure to sunlight or light
from sunbeds, the greater the risk of skin cancer
LIFESTYLE CHOICES AND CORONARY
HEART DISEASE (CHD)
 CHD is the largest cause of death in the UK.
 There are a number of factors that increase the risk of an
individual suffering from CHD.
 When combined together, four or five such factors produce a
greater risk.
 Factors such as genes, sex and age are beyond our control, but
there are others we can do something about.
LIFESTYLE CHOICES AND CHD
 Smoking –smokers are between two and six times more
likely to suffer from CHD. Giving up smoking is the single most
effective way to increase life expectancy.
High blood pressure – prolonged stress, certain diets and
lack of exercise all increase blood pressure, therefore the
risk of CHD.
 Blood cholesterol levels – can be kept lower by including
fewer saturated fatty acids in the diet.
 Obesity – a BMI of more than 25 brings an increased risk of
CHD.
Diet – high levels of salt in the diet increase blood pressure,
whilst high levels of saturated fatty acids increase blood
cholesterol concentration. Both increase the risk of CHD.
Foods such as fibre reduce the risk of CHD by lowering blood
cholesterol levels.
 Physical activity – aerobic exercise can lower blood pressure
and blood cholesterol as well as helping to avoid obesity – all of
which reduce the risk of CHD.
REDUCING THE RISK OF CHD AND
CANCER
Avoid doing all the things that increase the risk!
 Giving up or not taking up smoking.
 Avoid becoming overweight.
 Reducing salt intake in the diet.
 Reducing intake of cholesterol and saturated fats in the
diet.
 Taking regular aerobic exercise.
 Keeping alcohol consumption within safe limits.
 Increasing the intake of fibre and antioxidants in the diet.