Module 7 - infectious disease

Question 1

What is a disease?

Answer 1

Any process or condition that adversely affects the normal functioning of a living thing or parts of a living thing.

Question 1

General effects of a disease?

Answer 1

• Have signs and symptoms that are objectively measurable factors

Question 2

What is a sign?

Answer 2

Signs can help determine the effect of a pathogen and they can be observed by other people. for example a rash

Question 3

What is a symptom?

Answer 3

Helps determine the effects of a pathogen. Cannot be directly observed by other people. For example, headache or nausea.

Question 4

Classification of a pathogen?

Answer 4

Microscopic and macroscopic
Microscopic are either cellular or non cellular organisms.
Macroscopic are organisms that live inside and outside the body.

Question 5

Examples of microscopic organisms?

Answer 5

-Protozoa
-Fungi
-Prokaryote
-Virus
-Prion

Question 6

What are Protozoa?

Answer 6

Resemble a prokaryote due to features.
Transmit most commonly through vectors (Mozzies).
Some are pathogenic others are not.

Question 7

What is fungi?

Answer 7

Eukaryotic organisms that have a cell wall composed of Chitin.
Fungi are heterotrophic (must seek its own food) but are mostly saprophytic,
which means they feed on dead plant and animal material.
Fungal infections are transmitted through direct contact with a contaminated
person, animal or object.

Question 8

What is bacteria?

Answer 8

Bacteria are single-celled prokaryotic organisms with a cell wall but no membrane
bound nucleus or organelles.
Transmission of bacterial diseases may occur directly through close contact with an
infected organism or object.

Question 9

What is a virus?

Answer 9

-Strands of DNA and RNA in a protein coat, some can also be found in an envelope composed of mostly glycoproteins.
- They are not living meaning they cannot reproduce, instead they invade the cells mechanisms and produce proteins the replicate the DNA.
-Viruses are transmitted via direct contact with infected
individual and objects.

Question 10

What is a prion?

Answer 10

Prions are abnormal proteins that are capable of causing
degenerative disease of the nervous system.

Prions are the smallest of all pathogens and contain no
genetic material.

Prions cause abnormal folding of normal proteins and can
be transmitted through;
1.Ingestion of prions

2.Contaminated organs/hormones from donors

3.Inheritance of mutated gene that codes for prions

4.Spontaneous formation of prions.

Question 11

What are the two macroscopic pathogens?

Answer 11

-Endoparasites (Tape worm)
- Ectoparasites (Fleas)

Question 12

What are endoparasites?

Answer 12

Endoparasites live inside a hosts
body and adversely affect the
host in some way.

They often lay eggs in a manner
where the host can remove them
from the body, such as in faecal
matter.

Question 13

What are ectoparasites?

Answer 13

Ectoparasites live on the outside of the host
and most commonly feed on blood, some of
which inject toxins whilst feeding.

Some ectoparasites can act as vectors for
pathogen, such as fleas for the Yersinia
pestis (bubonic plague).

The ectoparasites lays eggs on the host
skin/fur/hair and hatch there or fall off when
the host moves.

Question 14

What things are features are used to identify pathogens in food and water?

Answer 14

Colour

Margin

Form (basic shape)

Elevation (shape of cross section)

Surface features (smooth, dull, wrinkled)

Question 15

What is the chain of infection and what does it do?

Answer 15

In order for pathogen to spread to other hosts, they must achieve what is known as
a chain of infection. A chain of infection has 3 elements;

A host that is susceptible to the disease

A pathogen that is capable of causing disease

A mode of transmission

Question 16

What are the three types of transmission of infectious disease?

Answer 16

Direct contact

Indirect contact

Vector transmission

Question 17

What is direct contact?

Answer 17

Direct contact occurs when a potential host makes physical contact with an
infected individual.

Contact between the same generation (e.g. between siblings) is known as
horizontal transmission. Contact between the different generations (e.g. mother
and child) is known as vertical transmission.

Physical contact include, but is not limited to;

Touching

Sexual contact

Contact with bodily fluids/wounds

Prenatal (before birth)or perinatal (during birth) transmission

Question 18

What is indirect contact?

Answer 18

Transmission occurs between an infected individual and a potential host without
any direct contact.

This transmission occurs due to contact with a reservoir that the host has created
outside of itself e.g. contaminated material or object. Any substance or object that
carries infection is known as a fomite.

Indirect transmission includes;

Airborne transmission – coughing/sneezing

Contamination of food/water/object

Incorrectly sterilised equipment

Question 19

What is vector transmission?

Answer 19

Vector transmission is similar to indirect contact, however, it occurs due to the
transmission of a pathogen through;

A bite from an arthropod vector.

Ingesting a vector.

Question 20

What did Koch’s and Pasteurs theory uncover?

Answer 20

established the
‘germ theory of disease’. This theory states that all micro-organisms come from
pre-existing micro-organisms.

Question 21

What were Koch’s postulates?

Answer 21

Koch studied rod shaped bacteria, anthrax bacillus, found in sheep that died from
anthrax. He cultured this bacteria and injected it into uninfected sheep who later died
from anthrax.

He determined that each disease is caused by different micro-organisms and formed 4
principles that later became known as Koch’s postulates. These are;

The same micro-organism must be present in every diseased host.

The micro-organism must be isolated and cultured in the laboratory and accurately
described and recorded.

When a sample of pure culture is inoculated into a healthy host, they must exhibit the
same symptoms as the original host.

The micro-organism must be able to be isolated and cultured from the second host and
be identified as the same as the original host.

Question 22

What did Louis Pasteur do?

Answer 22

Pasteur started work on alcohol and vinegar, discovering that the reason for
spoilage was due to micro-organisms.

To prevent this, he determined that heating the mixture would destroy the
microbes. This process was later named pasteurisation and is still used in modern
food preparation to remove microbes.

Pasteur continued this research with his now famous experiments. The
experiments involved two flasks, one was a ‘swan necked’ flask and the other a
regular open flask. When left undisturbed, microbes would easily fall from the air,
carried on dust and other particles, into the open flask. While the swan necked
flask prevented this from occurring.