Download Biology – The Search for Better Health

Biology – The Search for Better Health
Section 2: Over 3000 years ago the Chinese and Hebrews were advocating
cleanliness in food, water and personal hygiene.

Distinguish between infectious and non-infectious diseases
An infectious disease is a disease that is caused by an organism or infective agent.
These causative agents are known as pathogens. Some examples of infections
diseases are measles, chickenpox, AIDS, hepatitis and influenza.
A non-infectious disease is a disease that is not caused by a pathogen and, with the
exception of inherited diseases, cannot be passed on from one person to another.
Non-infectious diseases have a number of causes including inherited, nutritional or
environmental.
Some examples of non-infectious diseases are Down syndrome, cystic fibrosis,
haemophilia, multiple sclerosis and scurvy.

Identify the conditions under which an organism is described as a pathogen.
A pathogen can be defined as any organism that lives in or on another living
organism (called host), and causes a disease. To cause disease the pathogen needs
the right conditions to multiply and be transmitted.
There are different types of pathogens such as prions, viruses, bacteria, protozoans,
fungi and micro-parasites. There are a number of ways in which the pathogens that
cause infectious diseases can be transmitted:
- The transmission can be direct, where the pathogens directly pass from one
person to another.
- The transmission can be indirect, where the pathogen is transferred from
the environment (eg air, food and water) to the person.
- The pathogen could also be transmitted from person to person by being
carried by another organism (a vector). For example, the mosquito is a vector
that can transmit the malaria parasite.
There are two types of pathogens – micro organisms or microbes and macroscopic
parasites. The latter are visible to the naked eye.
Pathogens are also referred to as disease causing parasites. Parasites are organisms
that live on or in the body of another organism.
A pathogen is a disease causing organism.
If a pathogen is to cause disease it must satisfy a number of criterions:
1) It must have enough virulence (the number of the particular pathogen
needed to cause the disease is low). Eg. Tuberculosis is very virulent
which means that only a small number of pathogens are required to
cause the disease whereas tinea (athlete’s foot) is much less virulent.
2) The pathogen may need to survive outside the host, hence it must be
adaptable to such conditions
3) An incubation period is usually prevalent (the time between infection and
the onset of symptoms). The organism must be able to survive in this
period – i.e. food and nutrient resources may be self-sufficient.
4) A reservoir for the pathogen (eg. Contaminated water supply) is needed.
5) A potential host with a poor ability to fight off infection is ideal
6) The need for contact between an infected host and an unaffected host
(this also includes the presence of vectors).
Pathogens cause disease symptoms in a number of ways:
1) Large pathogen numbers impair the proper functioning of tissue. Eg.
AIDS virus destroys the immune system of the host.
2) Cells and tissue are destroyed – E.g. Leprosy (Hansen’s disease) –
bacterium causes the destruction of nerve cells.
3) The pathogen produces a toxin – Eg. Tetanus Bacterium – Toxin blocks
nerve impulses.
4) An excessive immune response by the host may cause tissue damage.
Eg. Rheumatoid Arthritis – anaphylactic reaction that blocks the airway.

Explain why cleanliness in food, water and personal hygiene practices assist
in control of disease
Microorganisms are everywhere around us and can easily enter our bodies through
any openings. Not all of these are disease causing, but in order to decrease the
spread and growth of pathogenic microorganisms, and hence control the incidence
and spread of disease, it is important that hygienic practices are followed.
Cleanliness in food, water, and hygiene practices all help to prevent the growth and
transmission of pathogens and therefore help to control disease.
Hygiene
Hygiene can be divided into two types – personal and community hygiene: Personal
hygiene involves keeping our bodies and any openings on them clean to reduce the
risk of pathogens entering our bodies, or transmission of these pathogens to others,
thus causing disease. It also inhibits the build up of microorganisms on our bodies.
Personal hygiene involves the following:
Hands must always be washed with soap and water before preparing and eating
food and after going to the toilet. This prevents the spread of pathogens that cause
diseases such as diarrhoea, and helps control these diseases. The body and hair
should be regularly washed and teeth cleaned to precent the build up of pathogens
(particularly bacteria) to numbers sufficient to cause disease. For example, a build up
of bacteria in the mouth could cause gingivitis thereby resulting in swollen, bleeding
gums and loss of teeth. Coughing or sneezing should always be done into a
handkerchief in order to avoid the spread of air borne droplets of disease causing
microorganisms (pathogens). Sneezing in the hand should also be avoided as the
pathogens will be transferred to the next thing that you touch.
Community Hygiene is important as it helps to prevent the build-up of pathogenic
organisms in the community and reduces the spread of disease. When the
infrastructure that supports and maintains community hygiene breaks down there is
a rapid spread of disease, as seen in the aftermath of the Asian tsunami in 2005.
Community hygiene involves the following:
Sewage and garbage disposal, which is important as it reduces the risk of pathogen
numbers increasing and spreading throughout the community, thus controlling
disease. Sterilisation and disinfection of equipment reduces the risk of the spread of
pathogens from one person to another. City planning which reduces overcrowding
and therefore reduces the risk of transmission of diseases throughout population –
this is important in controlling disease.
Cleanliness in food
Many pathogens can be transferred from person to person, or environment to
person, food. For example, salmonellosis is a disease caused by bacteria called
Salmonella and is transmitted in undercooked food, especially foods of animal origin.
Hepatitis A is another disease that can be transmitted by eating foods that have
been handled by somebody who has the disease. It can also be transmitted when
uncooked shellfish that has grown in waters polluted with sewage is eaten.
The incidence of food borne disease has increased due to the trend to eat out on a
more regular basis or consume more takeaway foods. Bacteria will multiply quickly
in food if the conditions are right – availability of nutrients, correct temperature and
availability of moisture. In order to
control the transmission of disease
from food sources, guidelines that
must be followed by food handlers
have been introduced for storing,
preparing and serving food.
These guidelines follow typical
conventions of society such as
washing hands before dealing with
food, using different chopping
boards for different foods to prevent cross contamination, thawing frozen foods in
microwave (not on bench). Washing vegetables before eating, correct refrigeration
(air flow and temperature at five oC. The more closely these procedures are
followed, the less chace that microbes in the food will multiply and hence the
spread of food-borne disease will be minimised.
Cleanliness in Water
It is important that water quality is maintained in order to minimise the risk of
pathogens multiplying and to reduce the risk of the transmission of pathogens in
contaminated water. Domestic water supply must comply with strict guidelines in
order to reduce the incidence of disease. In Australia, governments establish these
standards and the water is tested daily to ensure these standards are met. Water
that has been contaminated with the faeces of animals could contain unsafe levels of
pathogens such as the protozoan Giardia which will cause symptoms such as
diarrhoea, nausea, vomiting and abdominal cramps.
The treatment of water to destroy pathogens and prevent their further
multiplication will reduce transmission of disease and is very important in the
successful control of disease.

Describe the ways in which drinking water can be treated and explain how
these methods reduce the risk of infection from pathogens.
A combination of coagulation, flocculation, sedimentation, filtration (to remove
particular matter); and disinfection (to kill or inactivate microbiological organisms) is
the most widely applied water treatment technology around the world.
Sedimentation, coagulation and flocculation:
Some particles will settle out from still water in the process called sedimentation.
When particles are slow to settle or will not settle, a coagulant is added to the
water, causing the particles to stick together and form larger particles called floc.
This process is called flocculation. The floc will either sink and be removed as sludge,
or float and be skimmed off the top.
This reduces the risk if infection from pathogens because is it very effective at
removing fine suspended particles that attract and hold bacteria and viruses from
water supplies. They can remove up to 99.9% of the bacteria and 99% of viruses
from the water, hence reducing the risk of infection.
Filtration:
Whatever particles are left in the water are removed by the process of filtration. This
occurs in many cases by the water being passed through a bed of fine sand particles.
Membrane filtration in the form of micro-filtration (passing water at pressure
through the membranes with a small pore size) is the most widely used method of
filtration in Australia. This is able to remove micro-organisms that are larger than 0.1
nm which counts for more that 99.99% of all known bacteria and microorganisms.
Hence, filtration can remove some of the “larger” micro-organisms from the water,
which will again reduce the risk of infection from pathogens in the water.
Disinfection:
After all the particulate matter has been removed from the water, it is disinfected,
usually by adding chlorine in some form. Other methods of disinfection include
treating water with ozone or irradiation with ultraviolet UV radiation. If chlorination
is used for disinfection, enough should be added to ensure that the water remains
free of microorganisms on its journey to the consumers.
The addition of chlorine works in the following manner: When chlorine is poured
into water it breaks into several compounds including hypochlorous acid and
hypochlorite ion. Both these substances attach the micro-organisms and bacteria in
the water by going after the lipids in their cell walls and destroying the enzymes.
After they destroy the structure inside the cells the chemical compounds leave the
bacteria cells oxidised which kills the cell, hence leaving it harmless.