Changing ideas about disease
How infections have effected society and the changing ideas in society brought about by science
Learning outcomes & key terms
- Students can define infection
- Students will understand how ideas about infection and transmission have changed from medieval time to the present as knowledge has developed
- Students will know the scientists who brought about the change of ideas, and their contribution, to our understanding of infectious disease
Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the diseases can be spread, directly or indirectly
A contagious disease is transmitted to other persons, either by physical contact with the person suffering the disease, or by casual contact with their secretions or objects touched by them or the airborne route
A contagious bacterial disease characterised by fever and delirium, typically with the formation of lumps called ‘buboes’ (bubonic plague) and sometimes infection of the lungs (pneumonic plague)
Bubonic plague is a serious, sometimes fatal, infection with the bacterium Yersinia pestis, transmitted by fleas from infected rodents and characterised by high fever, weakness, and the formation of buboes, especially in the groin and armpits
Pneumonic plague is a form of plague characterised by lung disease
Septicaemic plague is an especially dangerous form of plague in which the infecting organisms invade the bloodstream
The ‘germ theory’ of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or “germs” can lead to disease
These small organisms, too small to see without magnification, invade humans, animals, and other living hosts eg plants
Pasteurisation is a process in which water and certain packaged and non-packaged foods are treated with mild heat, usually to less than 100 °C, to eliminate pathogens and extend shelf life of the food
A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells
Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye
Scientific understanding, including models and theories, are contestable and are refined over time through a process of review by the scientific community (ACSHE157)
- considering how ideas about disease transmission have changed from medieval time to the present as knowledge has developed
Infectious diseases in history
An infectious disease is also known as a contagious disease or transmissible disease
Infection is the invasion of a host organism’s bodily tissues by disease-causing organisms, their multiplication, and the reaction of host tissues to these organisms and the toxins they produce
The idea of contagious disease first appeared during the Renaissance
By 1723, there was a large advance in the technology of microscopy allowing the visualisation of micro-organisms
In the past it was suggested that disease was caused by unseen creatures or bad smells. It’s hard to believe given what we know now
Even after microscopes were invented and micro-organisms were discovered, scientists still didn’t believe that they were the cause of the disease – it was like trying to convince the scientists that an ant could kill an elephant
The plague is caused by the bacterium Yersinia pestis, which is spread by fleas on black rats – this disease mostly killed children as their immune system is under-developed
It killed over 50 million people in Europe from 1347-1364
A bacterium mutates because a bacterial colony has natural variation in their genes. A change in environment may be more suited to one variation of genes than another – this variation will thrive and the other variations will decrease in number
The bubonic plague was a painful disease, with black buboes, or swellings, in the groin and armpits. There seemed to be some chance of surviving if the buboes burst
The percentage of people who died, often referred to as the ‘mortality rate’, was 50%
A variant was the pneumonic plague, which attacked the lungs. Victims died quickly, in one or two days. The mortality rate in this case was 90%
Another variant was the septicaemic plague, which infected the blood – again victims died quickly although the mortality rate was close to 100%
Management of the Plague
Doctors thought that the plague was caused by “bad air” and wore masks filled with aromatic herbs to prevent catching the disease
As we now know, people most commonly acquire plague when they are bitten by a flea that is infected with the plague bacteria – people can also become infected from direct contact with infected tissues or fluids while handling an animal that is sick with or that has died from plague Finally, people can become infected from inhaling respiratory droplets after close contact with infected humans and animals
Why are diseases different today than in the past?
There is no quick answer to this question – many scientists agree that most of the new diseases were first spread by animals
Other theories include:
- The climate is getting warmer, making it easier for insects that spread the disease
- People are travelling more and as they do they are taking their germs with them
- Most people now live close together in big cities where they are in contact with more people
- More people are inhabiting areas that were previously wildlife areas – perhaps it our fault for encroaching on these areas?
Advanced explanation of immune system; Your immune System: Natural Born Killer. Crash Course Biology #32
More basic explanation: http://kidshealth.org/en/kids/ismovie.html?WT.ac=p-ra animation of how the immune system works (direct link: http://bcove.me/zo3d76kb )
See Ted Ed video on Rosalind Franklin: DNA’s unsung hero
https://www.nobelprize.org/prizes/chemistry/2020/press-release/ – during Emmanuelle Charpentier’s studies of Streptococcus pyogenes, one of the bacteria that cause the most harm to humanity, she discovered a previously unknown molecule, tracrRNA. Her work showed that tracrRNA is part of bacteria’s ancient immune system, CRISPR/Cas, that disarms viruses by cleaving their DNA.
Short videos including immune immune system structure and function – overview, non-specific and specific response.
If pathogens get through the body’s first two lines of defense, a third line of defense takes over. This third line of defense involves the immune system. For a cartoon introduction to the immune system, watch this video: http://www.youtube.com/watch?v=WJEc2GDEfz8.
https://www.aai.org/Education/Summer_Teachers/Docs/Archive/2003_Porter_Final.pdf Unit plan on acting out the immune response. Great ideas for extension.
http://pulse.pharmacy.arizona.edu/10th_grade/disease_epidemics/science/handouts/defensive.pdf Unit plan studying the body’s defense mechanisms
https://www.youtube.com/watch?v=CeVtPDjJBPU YouTube video: Your Immune System: Natural Born Killer by Crash Course Biology (advanced)
Analogies of Immune System:
https://prezi.com/bwpdtgswrv61/immune-system-castle-analogy/ Protecting a castle
https://web.archive.org/web/20130502012737/http://www.amnh.org/nationalcenter/infection/ Infection, detection, protection. Series of activities and games focusing on the immune system. These are geared at younger learners but provide good ideas for adapted technology creation.
http://www.amnh.org/ology/features/bacteria_in_the_cafeteria_game/ more aligned with lesson 2, this is a great idea for an interactive game though.
Which type of barrier to pathogens is in your opinion the most effective? Explain why.
Class extension activity: https://www.aai.org/Education/Summer_Teachers/Docs/Archive/2003_Porter_Final.pdf In the class activity “Acting Out the Immune Response” at the URL below, students will act out a nonspecific and then a specific response to an invading pathogen. Each student will have an assigned role in the activity, and props will be used.
Society has battled infectious diseases since the beginning of recorded history. Leading scientists have broken new ground and understood diseases by building a germ theory and then applying good science
Major pandemics, such as the plague and coronavirus or influenza, have been battled with ‘the prepared mind’ (look up what Pasteur said)
1) Pneumonic plague is a variant that
a) Attacked the lungs
b) Caused painful swelling in the groin and armpits
c) Infected the blood
d) Caused 50% of people who caught it to die
2) The scientist who won the Nobel Prize by testing his theory on himself by giving himself a stomach ulcer was
a) Louis Pasteur
b) Robert Koch
c) Barry Marshall
d) Alexander Flemming
3) The scientist who received the Nobel Prize for discovering penicillin was
a) Louis Pasteur
b) Robert Koch
c) Barry Marshall
d) Alexander Flemming
4) Koch’s postulates include
a) The organism must always be present in every case of the disease
b) The organism must be isolated from a host containing the disease and grown in pure culture
c) Samples of the organism taken from pure culture must cause the same disease when given to a healthy susceptible animal
d) All of the above