Infectious Disease

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Infectious Disease
Sarah Jones

What is a healthy organism?
Health is the wellbeing of the organism. All our
body functions, which are under the control of
our genes, work together to maintain health.
karmajello.com

Disease is any condition that adversely affects
the function of any part of a living thing.
commons.wikimedia.org

An infectious disease is one that is caused by
an organism and that can be transferred from
one person to another. The transfer may be
directly from person to person, or it may be
carried out by a vector, such as a blood-
sucking insect.
keysmosquito.org

Examples of infectious diseases are colds,
influenza, chicken pox, herpes and measles.
http://www.huffingtonpost.com/2014/01/13
Hepatitis C Virus

https://en.wikipedia.org/wiki/Plague_doctor

Impact of Infectious Diseases on Development
of Human Societies - an interesting link
from Miami University on microorganisms and
human disease.
www.independent.co.uk

• Link to CDC (Centers for Disease Control and
Prevention)
• Link to WHO (World Health Organization)

Non-infectious diseases are diseases that are
not due to disease-causing organisms. They
include genetic diseases, such as Down
syndrome, haemophilia, and those that are
related to lifestyle or environment, such as
cardiovascular disease and skin cancer.

Organisms are called pathogens when they
cause disease. To cause disease, organisms
need the right conditions to multiply and be
transmitted.
Ebola
Pathogens

An infectious disease is caused by a pathogen and
can be passed from one organism to another e.g.
Bacteria, Protozoans, Fungi, Viruses, and Prions
http://www.cfr.org/interactives/GH_Vaccine_Map/index.html#map

Research and give an example of each
of the following pathogens.
• Bacteria
• Protozoan
• Fungi
• Virus
• Prion
colinpurrington.com

How are diseases spread?
• Airborne
• Contact
• Faeces
• By other organisms
• The Asian tiger mosquito is responsible for the
transmission of dengue and yellow fever plus
20 other viral diseases.

Pathogens and Epidemics
During the Middle Ages waves of infectious
diseases such as cholera and plague swept
through Europe.
Plague victims being blessed by a priest

• Link to Hartford University Article on the
History of Plagues
• Until the mid-19th century most people
believed that living things came into existence
by spontaneous generation.
iws.collin.edu

Macroparasites
Macroparasites are large parasites that can be
seen with the naked eye. They may be internal
or external parasites. Examples of internal
include, tapeworms, roundworms and
flukes. External parasites include lice, ticks and
fleas.
sph.unc.edu

Kinnear and Martin, Nature of Biology, 2006

Immune Response – The Body's
Response to Micro-Organisms
Flu Pneumonia German Measles

Identifying Microbes That
Cause Disease
During the second half of the nineteenth
century, the work of Pasteur and Koch and
other scientists stimulated the search for
microbes as causes of disease.

Louis Pasteur
• Solved the mysteries of rabies, anthrax,
chicken cholera, and contributed to the
development of the first vaccines.
• Debunked the widely accepted myth of
spontaneous generation.
• Described the scientific basis for fermentation,
wine-making, and the brewing of beer.

Robert Koch
Robert Koch was a German
physician and bacteriologist. He
was awarded the 1905 Nobel Prize
in physiology or medicine for
developing a test used in
diagnosing tuberculosis. He
isolated the bacilli causing anthrax,
tuberculosis, and Asiatic cholera.
Koch developed a vaccine for
treating anthrax and rinderpest.
(Source: How Stuff Works, 2009)

Koch described the criteria which must be met if we are
to be sure that a particular microorganism causes a
particular disease.
Koch's Postulates
1. The specific microorganisms must be present in
every host with the disease.
2. The specific microorganisms must be isolated from
the host and grown in a pure culture.
3. A potential host, when inoculated with the
microorganism, must develop the same symptoms
as the original host.
4. The specific microorganism must be able to be
isolated from the second host and identified as the
same species as originally cultured.

The Role of Antibiotics
Antibiotics destroy or inhibit the growth of
bacteria. They are chemicals that act selectively
on pathogens without destroying the host. They
are not effective against viruses. Alexander
Fleming discovered the first antibiotic, penicillin,
in 1928.
www.biography.com

Bodies Defence
1. Physical (skin and mucous)
2. Nonspecific defensive cells (phagocytes,
white blood cells, inflammation and fever)
3. Immune Response (lymphatic system-
recognition of foreign cells)
medfitrehab.com

Our bodies contain very large numbers of
bacteria (approximately 15% of your body
weight) and many of those in the intestine are
essential for our wellbeing (microflora).
www.huffingtonpost.com

Defence Barriers
• Skin
• Mucous membranes
• Cilia
• Chemical barriers
• Specific response - Immune response
www.rmhc.org.uk

• Inflammation response
• Phagocytosis
• Sealing off the pathogen
Electron Micrograph of a Macrophage Phagocytosis of E. coli
Defence Adaptations – Non-Specific
Responses

Types of Immunity
Non-specific immunity involves many physical
and chemical barriers to infection and is not
affected by prior contact with a particular micro-
organism. It has no ‘memory’ of a prior
infection.
www.nsf.gov/news/mmg/media/images/immunity1_h.jpg

Specific immunity involves the production of
antibodies which act against a particular
infection. Specific immunity has a ‘memory’ so
that when another infection from the same
organism occurs, an increased response is
obtained.
http://web.science.uu.nl/hpps/?p=370

The Immune Response
The key to a healthy immune system is its
remarkable ability to distinguish between the
body’s own cells (self) and foreign cells
(nonself).
http://www.sketchyscience.com

The body’s immune defences normally coexist
peacefully with cells that carry distinctive "self"
marker molecules. But when immune defenders
encounter cells or organisms carrying markers
that say "foreign," they quickly launch an attack.

Anything that can trigger this immune response
is called an antigen. An antigen can be a microbe
such as a virus, or even a part of a microbe.
http://www.huffingtonpost.com/2014/01/13

Tissues or cells from another person (except an
identical twin) also carry non-self markers and
act as antigens. This explains why tissue
transplants may be rejected.
spectrum.ieee.org

Phagocytes and Killer Cells
Phagocytes are white blood cells that engulf and
destroy micro-organisms and other foreign
materials that enter the body. Phagocytes are
produced by cells in the bone marrow and
include neutrophils, the most common of the
white blood cells, and monocytes, the largest of
the white blood cells.
en.wikipedia.org

https://en.wikipedia.org/wiki/White_blood_cell

• When we are exposed to an antigen for the first
time, our body responds by producing
lymphocytes.
• Lymphocytes are a type of white blood cell; the
two main types are T cells and B cells (also
called T lymphocytes and B lymphocytes).
http://www.sketchyscience.com

All lymphocytes are produced in the bone
marrow. Some mature in the bone marrow into
B lymphocytes or B cells. Other lymphocytes
leave the bone marrow before they are fully
developed and travel to the thymus gland where
they differentiate into mature T lymphocytes or
T cells. (T cell stands for ‘thymus- dependent’
cell.)
http://www.daviddarling.info

immense-immunology-insight.blogspot.com

B cells have immunoglobulins on their surfaces.
Immunoglobulins are proteins that identify
antigens. Immunoglobulins are also called
antibodies. The immunoglobulins of each B cell
have a specific structure and recognise only one
kind of antigen.
course1.winona.edu

• When T cells mature in the thymus, many
different kinds of T cells are produced which
recognise many different antigens. T cells do
not make antibodies. There are different types
of T cells and each type reacts with other cells
in the immune response.
• Immunity involving T cells and phagocytes is
called cellular immunity.
www.vetmed.wisc.edu

Phagocytes that have ingested foreign material
carry some of the foreign antigen on their
surfaces. Helper T cells (Th), recognises these
antigens and stimulates B cells. B cells will not
reproduce and form plasma cells without this
assistance from Th cells.

Cytotoxic T Cells
• Kill body cells that have been infected with a
virus. Tc cells kill the infected cell by secreting
proteins that punch holes in the membrane of
the cell and the contents ooze out.
• Tc cells cannot kill isolated virus particles.
They can kill the virus only when it is inside a
cell.
• Some Tc cells also destroy cancer cells.

The Lymphatic System

How T and B Cells Travel
• B and T cells develop from primary lymphoid
tissues: bone marrow and thymus.
• The immune system also contains a number of
other lymphoid tissues and organs: the
spleen, tonsils and lymph nodes, which are
connected by a network of lymphatic vessels.
www.nature.com

• Lymphatic vessels contain lymph, which drains
from nearby tissues. Memory T and B cells, in
particular, circulate in the lymph, ready to
react with their antigens.
• Antigens that enter the body are carried in
lymph to a lymphatic organ where there is a
high concentration of white cells.
• Large numbers of lymphocytes (mainly B cells)
reproduce by mitosis. As a result, your lymph
nodes can become swollen and sore.

What are the ethical concerns in the
research and implication of vaccines?
http://www.cfr.org/interactives/GH_Vaccine_Map/index.html#map

Research and explain how Herd
Immunity works.
https://en.wikipedia.org

Infectious Disease

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