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Transcript of Infectious Disease
Why do we get sick?
How do we get better?
Year 11 Biology
What we will cover:
A - definitions
B - types of disease-causing organisms (
C - how disease is passed on
D - how pathogens get into our body
E - how the body initially reacts to infection
F - how we get rid of infections
G - local, national and global issues
Whilst no information was directly used from this site, I need to acknowledge an article called "Immunology Overview" by Armond S. Goldman and Bellur S. Prabhakar and published by the National Center for Biotechnology Information (found here: http://www.ncbi.nlm.nih.gov/books/NBK7795/) in 1996. Things have progressed since then but I constantly referred to this article to get an overview and yet also an understanding of the minutia of the process of immunity. Thank you.
Another important source was the US Centre of Disease Control and in particular, this page "Principles of Epidemiology" (http://www.cdc.gov/ophss/csels/dsepd/ss1978/lesson1/section11.html), which succinctly summarised the key ideas associated with epidemics and pandemics.
I would also like to acknowledge the use of many cartoons by the brilliant "Pedromics". Check out his Facebook page for more details. The cartoons are used with permission.
I also used a few diagrams from Wikimedia and acknowledged the authors where appropriate. Any other pictures or diagrams were used from copyright free resources and I have acknowledged the authors when I can.
Most of the diagrams are my own. Whilst they pale in comparison with, say the cartoons of Pedromics, nevertheless they are original. They can be re-used. Just contact me at: email@example.com. I'm pretty friendly so feel free - especially if you see some errors.
Finally, if you see or read something that you think is yours and shouldn't have been used, again contact me at firstname.lastname@example.org and I will remove it.
: when something is wrong with the
working of the body, or parts of the body, that disrupt the
of the body. Note: this applies to any living organism, not just humans.
A1.1. 'Normal' is a vague term but it can be summarised in humans as: when the temperature is about 37C; pH of the blood is in the range of 7.35 to 7.45; normal levels of CO2 in the blood is between 32 and 55 mm Hg etc. There are various factors that can be measured and checked with what is 'normally' expected in humans.
A1.2. A 'vital function' is some process that the body is directly dependent on. e.g. breathing, circulation of the blood, filtration of the blood in kidneys
: when something is wrong with the
working of the body, or parts of the body, that disrupt the
of the body that is caused by infectious organisms (
) which can include: bacteria, viruses, fungi and parasites.
A2.1. Pathogen: any disease causing organism
B. Types of Pathogens
Viral DNA or RNA
B2. An electron micrograph of the Herpes virus
Source: By George W. Beran - http://www.aphis.usda.gov/publications/animal_health/content/printable_version/pseudo_rabies_report.pdf, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11215668
B2.1. Types of viruses that cause infectious disease in humans include: the cold virus, 'flu, hepatitis B, Ebola, Zika.
B2. An 'antigen' is a molecule that sits on the outer surface of an organism and usually has a structure unique to that organism. It 'identifies' that organism.
Outer cell wall and membrane
Flagellum (or tail)
Electron micrograph of bacteria.
Source: Janice Haney Carr, USCDCP, http://www.public-domain-image.com/free-images/science/microscopy-images/scanning-electron-micrograph-sem-of-a-number-of-pseudomonas-aeruginosa-bacteria/attachment/scanning-electron-micrograph-sem-of-a-number-of-pseudomonas-aeruginosa-bacteria
B1.1. Bacteria can cause infectious diseases in humans including:
Food poisoning, tetanus, pneumonia, chlamydia.
B3. Fungus (e.g Yeast)
Reserve food stores
Electron micrograph of fungus threads.
Source: Janice Haney Carr, Robert Simmons, USCDCP, http://www.public-domain-image.com/free-images/science/microscopy-images/dematiaceous-filamentous-fungus-curvularia-geniculata-2
B3.1. Types of fungal infections that cause infectious disease in humans include: Candidiasis, athlete's foot, ringworm (!).
When you know that you have been studying fungi for too long...
(e.g Plasmodium - causes malaria)
Source: By Jfbranch14 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19558260
B4.1. Other parasites that cause disease in humans include: tapeworms, liver flukes and bot flies
C. How are pathogens passed on (transmitted) to others?
C1. Transmitted through indirect contact e.g. contaminated food/water
C2. Transmitted through direct contact e.g. sneezing
C3. Transmitted through contact with body fluids e.g. wounds in the skin
C4. Transmitted through vectors such as insects e.g.
transmission by mosquitoes
Bacteria on chicken skin
Source: NutritionFacts.org, https://i.ytimg.com/vi/RHfa4R3JChM/maxresdefault.jpg
C1.2. If this chicken is not cooked or stored correctly, these bacteria could cause food poisoning.
Source: By James Gathany - CDC Public Health Image library ID 11162, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6701700
C2..2 Sneezing can spread diseases like colds and 'flu but only if the droplets make direct contact with the respiratory system e.g. the mouth
C2.3. Clearly not real! Open wounds leave the body vulnerable to infection
Source: Daniel Hollister, https://www.flickr.com/photos/dhollister/2596483147 under Creative Commons.
Source: By Jim Gathany - This media comes from the Centers for Disease Control and Prevention's Public Health Image Library (PHIL), with identification number #5814, Public Domain, https://commons.wikimedia.org/w/index.php?curid=799284
D. How do pathogens get into the body in humans?
D1. In through the mouth and into the digestive tract.
D1.1 Barriers: saliva, mucous and stomach acid
D2. In through the mouth/nose and into the respiratory tract
D2.1. Barriers: nose hair, cilia and mucous
D3. In through cuts in the skin
D3.1. Barriers: skin, sweat, oils and other micro-organisms.
D4 In by penetrating the skin
D4.1. Barriers: skin and human behaviour (e.g. swatting)
Source: By BruceBlaus - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44923646
Source: By Artwork by Holly Fischer [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
Source: By National Heart Lung and Blood Institute - National Heart Lung and Blood Institute, Public Domain, https://commons.wikimedia.org/w/index.php?curid=29583059
Source: No author, https://en.wikipedia.org/wiki/Paper_cut
A bed bug
Source: By Content Providers(s): CDC/ Harvard University, Dr. Gary Alpert; Dr. Harold Harlan; Richard Pollack. Photo Credit: Piotr Naskrecki - http://phil.cdc.gov/phil, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2119254
First line of defense
tears in the eyes contain enzymes to kill pathogens
wax in the ears traps pathogens
acidic pH in the vagina kills pathogens
E. How does the body initially react to infections?
E2. Example 2 - viral infection of the lungs
E1. Example 1 - bacterial infection through a cut in the skin
Skin Cell Layers
response to infection
The innate immunity:
is a quick response to infection
found in all animals and in plants
helps activate the adaptive immune system (see below)
Here are three things that may happen during this response:
Red blood cells
E1.2.1. Formation of blood clots over the wound
(White blood cell)
(chemicals released by the macrophage to summon other cells to the site of infection)
E1.2.2. Phagocytic cells (usually dendrites) engulf invading pathogens
1.2.3. Complement system activated
tag the pathogen
can form holes in the pathogen cell wall and membrane
and signal to other cells to help remove the pathogen
E1.1.Break in the skin allows pathogens to enter the open wound...
E.1.2.4 Other innate responses:
- redness of the skin; dilation of blood vessels; pain; swelling
- release chemicals to signal other cells to come to the infected region
cells - release chemicals which kill pathogens. They are the most abundant white blood cells in the body.
second line of defense
against infection. It is also a
; that is, it occurs during infection by
F1. But what if the innate system is not enough...enter the
immune system consists of cells that are specifically design to deal with a particular infection
F1.2 B lymphocytes reside in the lymph nodes. They are 'exposed' to foreign antigens in multiple pathways
F1.2.1 Dendritic cell presents the antigen on their surface or via T - lymphocytes
F1.2.4. Antigen sent to cell membrane
F1.2.2 Dendritic cell engulfing pathogen
F1.2.3. Pathogen broken down and antigen is isolated
F1.2.5. Antigen presented directly to the B-lymphocyte
F 1.3 B-lymphocyte waits until a T-helper cell binds to the MHC molecule and then matures.
Chemical signals to the B-lymphocyte
B - lymphocyte
B - lymphocyte in lymph node
T - helper cell
F1.4 B-lymphocytes are now called plasma cells.
They reproduce and produce specific antibodies (also called 'immunoglobulins')
E1.4.1. When a plasma cell is active, it can produce up to 1,000 antibodies per second!
Source: Yuichiro Shimizu and Linda M. Hendershot, 2009, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819804/. Viewed 19/5/16.
F1.5. Antibodies cause the pathogens to clump together and may even punch holes in the cell wall/membrane
F1.6 After the infection has been defeated, excess plasma cells are removed by
but some remain as
F1.6.1. Self-induced cell death.
F1.6.2. Memory cells remain in the blood and quickly become active again if the
specific pathogen re-infects the body.
Apoptosis in Mouse Liver cells
Source: By Laboratory of Experimental Pathology, Division of Intramural Research, NIEHS (NIH) - http://dir.niehs.nih.gov/dirlep/liverpath/necrotic/apoptosis5.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1898251. Accessed 19/5/16
Movie of cancer cells undergoing apoptosis
Source: Birgit Janicke, Phase Holographic Imaging AB (PHIAB) under Public Domain. http://www.cellimagelibrary.org/images/43705. Accessed 19/5/16)
Formation of B-memory cell
...the body deals initially with infection through the
innate immunity system
E2.1. Viruses invade the cells lining the respiratory tract
Cells of the respiratory tract
E2.3 Cell of Respiratory Tract and single virus (note: removal of cilia for clarity)
E2.4 Virus drawn into cell by receptor
E2.5 Virus is 'unpacked and its DNA/RNA is sent to cell nucleus
E2.6 Virus DNA/RNA is inserted into cell DNA. Cell DNA is used to make many viral parts to create new viruses.
E2.6.1. Note: cell sends some antigens to cell surface as a result of being infected.
E2.7. Newly created viruses burst out of the cell and infect other cells of the body e.g nose, sinuses, cells deep into the respiratory system
F2 Is there any defense against this attack?
Natural Killer T-Cells
to the rescue!
F. How the body gets rid of infections (part 2)
F. How the body gets rid of infections (part 1)
E2.2. The innate immune system can work here but it gets harder because viruses get into cells and so are less exposed to the threats of this immune system.
Let's look at the way that viruses cause problems...
F2.1 NK T-Cells
deal with cells that are infected by viruses and cancerous cells. They detect the presence of foreign antigens or cells with cancer-causing DNA.
F2.2 Whilst the virus is reproducing, NK T-cells detect the antigens on the surface of the cell under attack.
Receptor on cell surface that fits the viral antigen
Body cell attacked by virus
F2.3. NK T-cells release chemicals which cause the body cell to undergo cell death through
F2.4. The body cell is dying and thus the viruses won't be released to infect other cells.
Chemicals released by NK T-cells
Source: Pedromics. Used with permission.
Source: Pedromics. Used with permission
adaptive immune system
is slower to respond to infection
found only in vertebrates
results in long-term solutions to infection
F2.1.1. Natural Killer T-cells are also part of the second level of defense against infection but are very important in the
Acquired Immune System
A video summary of this process:
G. What happens if we infect other people?
G1. Obviously we might infect our family and workmates if we decide not to isolate ourselves when we get an infection. This may have social and even global consequences. Firstly, some concepts need explaining.
G1.1 Baseline or '
' level of the disease
The endemic level of a disease is the 'normal' level that occurs throughout the year.
G1.2 Levels of the disease when it reaches '
An epidemic has occurred when there is a sudden increase in the disease above 'normal' levels.
Used with permission, granted on the 31st of May, 2016.
is the same as an epidemic, but refers to a limited geographical area.
G1.3.1 Here is an example of an outbreak of yellow fever in western Angola, Africa in 2015-16
Source: Yellow Fever Situational Report, World Health Organisation; http://www.who.int/emergencies/yellow-fever/en/; accessed 31st of May, 2016.
is an epidemic, but one that is spread over a number of countries and involves large numbers of people.
G1.4.1 Here is an example of a recent pandemic. The map shows the distribution of countries affected by the H5N1 influenza epidemic.
Source: By HotWikiBR - Own work (derivated)., Public Domain, https://commons.wikimedia.org/w/index.php?curid=6747576
F3. How do vaccinations work?
F3.1 Vaccinations contain antigens from pathogens or weakened (non-infectious) pathogens.
F3.2 Vaccinations are then injected into the muscle of the human (or animal).
Muscle in skin
F3.3 As with a 'normal' infection, the body identifies these antigens as foreign (or 'non-self') and B-lymphocytes whose surface receptors match the antigen are activated.
Chemicals which help activate the B-lymphocyte
F3.4 The now mature Plasma cells produce antibodies to match the antigen.
F3.5 Some of these plasma cells will later become memory cells.
F3.5 If the human or animal is infected with the actual disease (e.g. measles), the memory cells become active and produce antibodies to quickly remove the infection.
Try this game: Solve the Outbreak
Here's an animated summary
Another more dramatic summary of viruses and viral infection.
and this 'Vax' game. Here you can choose who to vaccinate and quarantine to save as many people as possible.
NKT cells targeting cancer cells using the same method
Summary of the process of infection
1. Gain access to the host
2. Attach to the cells of the host
3. Survive the hosts defenses
4. Reproduce and spread inside the host
Are proteins found on the surfaces of cells that help the immune system recognize foreign substances
Viruses exiting cell after reproduction
Phagocytosis in action
Phagocytes moving to an injury site.
Inside a lymph vessel
Source: By KC Panchal (Own work) [Public domain], via Wikimedia Commons, https://commons.wikimedia.org/wiki/File%3ASchematic_of_lymph_node_showing_lymph_sinuses.svg