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A CLOSER LOOK AT DISEASE

TYPES of DISEASE


Diseases can be classified into various categories.
Infectious diseases are caused by pathogenic organisms, as described previously. Two examples in this category are pulmonary tuberculosis, and measles.
Disease Pulmonary tuberculosis (TB)Edexcel MeaslesEdexcel
Type of causative agent bacterium (Mycobacterium tuberculosis or M. bovis) virus
Symptoms of this disease no symptoms in early stages; later: fever, loss of weight ("consumption"), damage to lungs - chest pain, sometimes a persistent cough fever, catarrh, puffy eyelids, rash inside mouth fever, skin rash - red blotches over face and body;in malnourished children (+vitamin A deficient):blindness, brain damage, death
Method of transmission of disease, i.e. how it is spread inhalation (airborne droplets from cough or sneeze), or drinking infected milk airborne droplets
Means of control i.e. prevention of disease antibiotic streptomycin may cure infections ( 6-12 month course); elimination of poverty &overcrowding; pasteurisation of milk, (badger gassing was out of favour, but a widespread trial has now shown that badger culling is successful in that it reduces the reservoir of infection, but has the opposite effect of causing infected badgers to move to new areas and spread the infection ), mass radiography (chest x-rays), BCG injections to immunise young people MMR vaccine in UK - needs booster treatment elimination of poverty & overcrowding and insanitary conditions
Reasons for control measures spreads easily in crowded conditions if untreated, may last for years High population cover is necessary to control - booster followup difficult with migrants/refugees

In 1995 TB killed more people worldwide than any other disease. Other 1995 estimates include:
worldwide incidence of TB - 9 million cases (5000 in UK) - mortality 3 million.
TB is often the first infection to strike HIV+ people.
The emergence of strains with multiple resistance to antibiotics is likely to present an increasing problem.
Measles 1993 estimates: 45 million cases, 1.16 million deaths (9th leading cause of death worldwide)


There are also many types of non-infectious diseases.
Explain what is meant by each category of non infectious disease, and give one or more examples.


Category of
disease
Your explanation or definition Examples
Degenerative
gradual decline in body functions coronary heart disease, multiple sclerosis, Huntington's
Physiological
abnormal functioning of body heart problems, sickle cell anaemia
Dietary
deficiency (absence) of substances in diet scurvy (not enough vitamin C) -anaemia (not enough iron)
Environmental due to chemical/physical influences in environment asbestosis, asthma, lung cancer
Inherited
genetic "fault"- passed on from one generation to next - perhaps by "carriers" haemophilia, cystic
fibrosis,Huntington's


Is there a problem with this way of categorising diseases?
Some diseases fit in more than one category

Spread of pathogens

Edexcel Diseases caused by various pathogens are spread by different methods.
Taking these examples, match up the disease to the transmission method, and describe the type of organism involved. Add a further example for each category.

Examples:
athlete's foot cholera dysentery hepatitis B influenza malaria Salmonella

Method of disease
transmission
Example of disease Type and further details of
causative organism
Another
example
in air (droplets) influenza virus
in food Salmonella bacterium
in water cholera bacterium
by contact athlete's foot fungus - spread by damp
by body fluids hepatitis B virus - blood products
by animal vector
(and name of vector)
malaria protozoan/protoctistan
(Anopheles mosquito)
by animal vector
(and name of vector)
dysentery bacterium
(housefly)

Sterilisation methods

Sterilization is the destruction of (potentially pathogenic?) micro-organisms.
There are 3 main methods of sterilisation: using heat, chemical methods and irradiation.
List some things that heat is used to sterilise.
food
microbiological media, medical and dental equipment


What are the drawbacks?
overcooked taste (in food)
waste of energy


List some examples of chemicals that are used as sterilising agents, and in what contexts?
chlorine in swimming pools
sodium metabisulphite in brewing

What are the drawbacks?
chemical may persist

List some types of irradiation, and situations in which they are used.
gamma - prawns
medical instruments

What are the drawbacks?
will not destroy toxins left in food

Pasteurisation

Edexcel Pasteurisation (named after Louis Pasteur) is a method of reducing the number of bacteria (using heat), usually in a liquid food substance, e.g.milk, beer.
Edexcel Milk (and similar foods) naturally contains a large number of bacteria. Some of these may be pathogenic organisms, and others, whilst not actually harmful in themselves, may simply reduce the keeping quality.
The combination of temperatures and treatment times used in pasteurisation are designed to kill most vegetatively growing bacterial cells, without going high enough to cause a "cooked"taste. Several methods of treatment are recognised, and some require quite extensive technological plant and process control equipment.
What is meant by "vegetatively growing bacterial cells"?
ones which are actively growing, dividing, absorbing nutrients etc

Why does pasteurisation not kill all bacterial cells?
(inactive) ones with spores will survive - able to grow again later

In the simplest method (the "holder"process), batches of milk (200-1500 litres) are held for at least 30 minutes at a temperature of 63-66 C. This is usually performed in a vat heated with a steam or hot water jacket. Various regulations cover the process:
- agitation is required (using a stirrer paddle)
- temperature must be recorded over the time of the processing, and a separate thermometer must show the current temperature
- after treatment, milk is discharged from the lowest point of the vessel and cooled quickly to 4-5 C.

What is the function of the stirrer?
to even out the temperature - ensuring no pockets of cooler temperature
Why are 2 thermometers used?
to cross check with one another - but one gives record (on chart) of temperature as well as time above lower limit - and the other gives instantaneous reading
Why must treated milk flow out from the lowest point?
so no milk stays behind after processing = to become contaminated

The HTST (high temperature, short time) process is a much more popular process, although it requires more dependable equipment in order to process greater volumes of milk more quickly. Stainless steel plant is used because it can be easily cleaned and sterilised, and pumps and heat exchangers are produced by specialist companies. Legally, milk must be heated to 72C for a minimum of 15 seconds, and the speed of pumping is adjusted to achieve this. Strict controls are in force to ensure that the automatic settings are not overridden. It must then be cooled quickly to below 10C - and usually 4 -5C.
Sterilised milk is not popular in all parts of the UK, but this is obtained by pre-heating milk in bottles then into a machine which put them under a pressure of 2.5 bars (125 C) for 10 minutes, after which they spend 20 minutes in cold water. The resulting product has a "cooked " flavour and a creamy texture, and possibly a brownish coloration due to caramelisation of lactose (milk sugar). However the shelf life of this product is not assured.
UHT (ultra heat treatment) uses even higher temperatures (at least 132 C) with much shorter holding times (at least 1 second), but there is more latitude on the "safe " side, so this may also result in alteration in the flavour. It is especially dependent on a quick and steady supply of waxed cartons produced in the milk treatment machine from a tube on a continuous roll. Sterilisation of the internal parts of the plant is very tricky, and chemicals such as hydrogen peroxide are used.
UHT treated products can keep for several months, and do not require refrigeration.
Why do these need to be consumed quickly once opened, however?
bacteria etc will grow (more easily?) so they will be like other products
This treatment is also used for various reconstituted fruit juices and mixtures - only some of which are described as "longlife" products.

Antiseptics and disinfectants

Edexcel Both of these categories are chemicals which kill bacteria and other micro-organisms, but there is a subtle distinction as to the power of their action and the circumstances in which they may be used.
Antiseptics are used to cleanse areas of the body which may be contaminated - such as a cut or graze or an area of the body which is to be operated on, and there are several alternatives, differing in strength and gentleness.
Give an example of an antiseptic and a situation in which you might use it.

Disinfectants are much stronger (often caustic) and designed to kill all micro-organisms, e.g. in drains and more heavily contaminated areas where the priority is killing power.
Give an example of a disinfectant and a situation in which you might use it.







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