1. Infectious Diseases
Copyright PEER.tamu.edu

2. Think about it: What infectious disease have you had?
Can you name an infectious disease that causes people to die?
What is an infectious disease that has been in the news recently?
Answers will vary:
1. The cold, flu, stomach virus, strep throat, bronchitis, ear infection, chicken pox….
2. AIDS, pneumonia, H1N1 virus, yellow fever, malaria….
3. H1N1, SARS …..

3. Epidemiology
The branch of medical science dealing with the transmission and control of disease.
There are human physicians that study epidemiology and also veterinarians that study animal epidemiology.

4. Infectious Diseases are Caused by Microbes
What’s a microbe?

5. You have to have a microscope to see microbes!
What is a Microbe?
Microbes are microscopic organisms that can exist almost anywhere. Different microbes have different habitat preferences, ranging from extreme heat to extreme cold. Some microbes need oxygen and some do not.
Most microbes can survive in a large variety of habitats, but they can only thrive in a few habitats.
We even have microbes in our bodies--some help us out and some hurt us.
This slide gives some of the abiotic factors that affect microbes.
It is useful in a class discussion to compare microbes with cells in multicellular organisms. See “Cells Are Us” in the Web curriculum at peer.tamu.edu
You have to have a microscope to see microbes!

6. Microbes Can Multiply Fast
Microbes Can Multiply Fast! Typical growth curve of an undisturbed population of microbes at normal temperatures (about 40 – 100 degrees F)
This graph shows the number of cells on the y-axis (expressed in log) and the time on the x-axis. The point of this is to show that after a brief lag time, the cells multiply exponentially. At a point, the growth becomes stationary, and then they begin to die.

7. Biotic and Abiotic Factors in the Environment:
Microbes require several biotic (living) and abiotic (non-living) factors to be present in the environment to be able to survive.
Can you name one biotic factor bacteria require?
Can you name two abiotic factors bacteria require?
Biotic Factor: Some may utilize a host- i.e. human, dog, cat
Abiotic Factors: Energy (lightning bolt), Temperature (thermometer), water (faucet), nutrients (food), some require oxygen and some do not

8. Using what you know about biotic and abiotic factors, Can You Explain:
Growth becomes stationary because the population saturates its environment. Nutrient supply, water, build-up of wastes, etc. limit multiplication
As their environment deteriorates, many of the individuals don’t have enough nutrients or water to stay alive. Also, they may be killed by build-up of toxic wastes. Finally, there may be an issue of “metabolic aging,” which hasn’t been studied very much.
For an animated tutorial go to :
Why growth becomes stationary?
Why the microbes eventually die?

9. Common Types of Microbes
Viruses*
Bacteria
Protozoa
Prion*
There is some controversy at this time on the classification of Prion and Viruses. Although they are infectious agents, they are technically not considered to be living (more discussion on this later in the presentation). Scientists disagree on whether to classify them as microbe even though they are frequently included in microbiology texts. This is an excellent opportunity to encourage a discussion about classification of organisms.
Fungi
*See slide notes

10. Infectious agents are microbes that can cause disease.
Microbes and Disease
Some microbes cause disease and some don’t.
Microbes that cause disease are called infectious agents, we commonly call them “germs” or “bugs.”
Infectious agents are microbes that can cause disease.

11. Bacteria can look like spheres, rods, or spirals.
Let’s go over the types of Microbes:
Bacteria
Bacteria are unicellular (one-celled) and prokaryotic (they don’t have a nucleus).
Bacteria are heterotrophic (they must consume substances to get energy to survive).
They are in the Domain Eubacteria and the Kingdom Eubacteria.
There are countless numbers of bacteria on the Earth but less than 1% of them cause disease in humans.
Bacteria can live in a vast range of places, but need energy sources to thrive.
Bacteria can look like spheres, rods, or spirals.
It is useful in a class discussion to compare microbes with cells in multicellular organisms. See “Cells Are Us” in the Web curriculum at peer.tamu.edu
An exercise: ask students how many kinds of bacteria can they name (anthrax, brucellosis, tetanus, diphteria, E. coli, salmonella, and a few others are among those that many students should have heard about).
Source: NSF.gov

12. Prions
A prion is an infectious particle (not a cell) made from an abnormally folded protein found on the surfaces of nerve cells. They are not classified into a Domain or Kingdom of living organisms. There is controversy over whether to classify them as microbes, but they are infectious agents.
Prions are highly resistant to heat, radiation, and disinfectants.
The best known prion forms holes in brain tissue, making the brain look like Swiss cheese. The prion causes mad-cow disease and may cause some forms of Alzheimer's Disease.
Mad Cow Disease Resource:
Alzheimer's Disease Resource:
Prion Resource:
Brain picture from:

13. Viruses
A virus is a microbe that consists of a piece of genetic material (RNA) housed within a protective coat. Viruses are not made of cells. They are not classified into a Domain or Kingdom of living organisms.
The virus reproduces by hijacking the cell of another organism (host) and getting the host cell to reproduce more viruses.
Most viruses cause disease and are specific as to which type of cell they will attack.
Viruses are neither heterotrophic nor autotrophic. They use the cell that they infect to get energy from. Currently, they are not considered living organisms, but there is debate among the scientific community on this topic.
At this age of student, it is not important that they know all the names in the drawing. Just that they see the general structure of the virus.

14. Break Time Discuss: What is the difference between living and non living?
At this point a class discussion about what constitutes living and non living organisms would be appropriate. Again, a discussion about the classification of Prion and Viruses would be appropriate here.
For a few websites on this, see Teacher Resources in the Lesson Plan

15. Protozoa found in human stool sample
Protozoa are unicellular (one- celled) eukaryotic (have a nucleus) microbes that can be parasites or predators of other microbes.
Most need a moist environment to live. They are heterotrophic (they must consume substances to get energy to survive).
They are in the Domain Eukaryota and Kingdom Protista
Usually cause disease in humans.
Protozoa can be helpful to other animals
Yuck!
Protozoa found in human stool sample
Fish and Whales use protozoa as food, making them an important part of the marine food web.
Giardia (pictured) is a common cause of food poisoning.
Giardia

16. Fungi
A multi-cellular (many- celled) eukaryote (has a nucleus in cells) microbe that is much larger than the other microbes.
They are heterotrophic (they must consume substances to get energy to survive).
They belong to the Domain Eukarya and Kingdom Fungi.
Only about 1/2 of all fungi cause disease in humans.
Yeast is a fungus that is used to make bread and cheese for us!
An exercise: ask students how many kinds of fungi can they name (ringworm and “jock itch” are ones they may know about). Tell them how they can recognize ringworm in their pet. (round red spot without much hair)

17. Quick Check #1: What is a microbe? Name five kinds of microbes.
How are these five kinds of microbes alike?
How are these five kinds of microbes different?
A microscopic organism
Bacteria, viruses, fungi, protozoa, prions
The all have the ability to cause infectious diseases. They are very tiny, even microscopic.
Some are made of cells, some are not. Some have a nucleus, some do not. They belong to different Domains and Kingdoms.
They cause diseases in different ways.

18. How Can an Infectious Agent Attack Me?
Infectious agents can enter through air, food, water, sexual interactions, skin contact, blood transfusions, etc.
The body’s reaction to an infection can vary from a mild discomfort to death.
Infectious
Agent
This link is to the PEER curriculum on the Body’s Defenses. It explains in much more detail about how the body reacts to infectious agents.
For more on bodily reaction, if you have a live Internet connection, show the class a few pages of the PEER Web curriculum materials on bodily defenses in the Organ Systems module at peer.tamu.edu.
For more on the immune system, click here

19. viruses and hantavirus.
Species Specificity
I can transmit
Brucellosis
Some infectious diseases of animals can be transferred to humans.
These are called zoonotic diseases.
All mammals can transmit rabies but raccoons and skunks are the most common carriers.
We can transmit lots
of infectious agents
including arena
viruses and hantavirus.
I can transmit
Ebola virus!
Some carrier species are eventually killed by the organism, but can spread it to other species before they die. Other carrier species seem to co-exist without much damage from their infectious agents. As humans encroach on the habitats of wild animals, they get exposed to diseases that have not been a problem before to humans.

20. Where are those microbes?
Think about it: Where Do Infectious Agents Hide When Not Infecting You?
Where are those microbes?
The soil
Bodies of water
Surfaces like desks and tables
People’s skin
In the air
On certain animals
Infectious agents can live on surfaces like a desk for hours or even days, like the cold virus.
This is why sanitary practices are needed to help prevent infections.

21. Do you know the difference between “infectious” and “contagious?”
Infectious: microbe can invade the body
Contagious: microbe can be spread from one person to another.
Explain it if they don’t know. The difference between infectious and contagious is that you can be infected without being contagious, but you cannot be contagious without being infected. Being infected may or may not produce symptoms of the disease.

22. Quick Check #2 How can microbes get in the body to cause infection?
What is an infectious disease that can be transmitted from an animal to a human called?
Where are microbes commonly found?
What’s the difference between being infected and being contagious?
Infectious agents can enter through air, food, water, sexual interactions, skin contact, blood transfusions, etc.
A Zoonotic Disease.
2. In the soil and on most surfaces.
3. Infected means the organisms has entered your cells but you may not show signs of the disease. Contagious means you can spread the organisms to others. You can be infected but not contagious. You cannot be contagious unless you are infected.

23. What are the Main Types of Infectious Diseases?
Digestive Diseases
Respiratory Diseases
Liver Diseases
Sexually Transmitted Diseases
But of course, any body tissue or system can be infected.
Skin Diseases

24. Some Types of Infectious Diseases:
Type of Disease
What Microbe Usually Causes It
A Few of the Known Symptoms
Common Types
Respiratory
Diseases
Bacteria and Viruses
Coughing, congestion, fluid in lungs
Bronchitis, Pneumonia, Cold, Flu
Digestive Diseases
Viruses, Bacteria and Protozoa
Nausea, vomiting, diarrhea, cramps or pains
Botulism (food poisoning)
Stomach “flu” (gastroenteritis)
Liver Diseases
Viruses
Fatigue, poor appetite, jaundice
Hepatitis
Sexually Transmitted Diseases
Viruses and Bacteria
Can vary, from mild rash to death
Chlamydia, Herpes, AIDS
Skin Diseases
Fungi and bacteria
Rash, itching, redness
Athletes foot, acne

25. Food Poisoning is a Disease Caused by Infectious Agents
Prevent food poisoning by stopping microbes from reproducing: keep hot foods hot and cold foods cold.

26. Food Poisoning See also our curriculum on the Digestive System
Botulism- collapse, respiratory failure, and death. (Caused by improper canning methods)
Classical food poisoning can be prevented by better food storage and handling techniques.
Outbreaks usually occur at picnics, school cafeterias, or anywhere where the food is not handled properly or not kept refrigerated.
Symptoms
nausea
vomiting
abdominal cramps
fever
diarrhea
A good example of a food poisoning problem can be found in the Egypt adventure in the Integrated PEER curriculum. See also module on digestion in the Organ Systems Web-based curriculum at peer.tamu.edu. If you have a live Internet connection show them a few pages.
See also our curriculum on the Digestive System

27. Which Foods Are a Problem?
Almost all foods can carry infectious agents.
Hamburgers, potato salad, cold cuts, hot dogs, soft cheeses, eggs, and any raw meat are favorite places where microbes can grow and become likely to infect.

28. Infectious Agents Can Be Deadly
Infectious diseases cause more deaths worldwide than any other single cause.
Infectious diseases account for over 56% of deaths in developing countries.
However, these diseases account for only 8% of deaths in rich countries.
An exercise: ask students why they think that poor countries have more problems with infectious disease. The answers should relate to availability of clean food and water sources, the ability to make vaccines and medicines, sanitation practices, nutrition and general health.
As a practice on reading graphs, ask students to tell the numbers of people killed by each type of disease.

29. Not all infectious disease are deadly; Acne is an Infectious Disease!
The pimples are infections of the skin.
The skin makes oil from sebaceous glands in the skin. Too much of this oil clogs pores and allows bacteria to grow and multiply.
White blood cells rush to fight the infection. The blood cells die and become pus.
Acne is not contagious, but it is infectious

30. But for any disease, there are three key steps for dealing with it.
Different infectious diseases require different approaches for prevention and control.
But for any disease, there are three key steps for dealing with it.
Knowledge

31. Three Key Steps reak the cycle of transmission
ill the infectious agent
Break the cycle: Cover your mouth when you cough or sneeze, stay home when you are sick, wash your hands often…
People and animals that live/work in large groups or herds easily pass diseases from one to another. This is a key point in the follow-up activity.
Kill the Infectious Agent: Use antibiotics as directed, use hand sanitizers, spray surfaces with antibacterial/antifungal products….
Increase host resistance: Get vaccinations, eat right, exercise, get plenty of sleep…
ncrease host resistance
Do you have some ideas on how to do these three things?

32. Quick Check #3 List the main types of infectious diseases.
Give an example of a deadly infectious disease.
Give an example of an infectious disease that is not deadly.
What are the three key steps for dealing with infectious disease?
digestive, respiratory, liver, sexually transmitted diseases, skin.
Flu, AIDS/HIV, malaria…answers may vary
Acne, gastroenteritis…answers may vary
Break the cycle of transmission, kill the organism, increase host resistance

33. Activity Time Model on spread of disease.
See the notes in the Presentation Plan

34. Some Current Research
Over-use of antibiotics has led to some bacteria developing resistance. It’s a big problem.
Scientists search for antibiotics that can replace current ones to which bacteria have evolved resistance.
In the old days, scientists took soil samples to find fungi that killed bacteria

35. One New Strategy
Forcing antibiotics to grow with another kind of bacterium might cause them to start secreting an antibiotic to kill off the competition.
If your class has the sufficient biology background, this is a good place to talk about gene regulation. In this case, “alien” chemicals in the background produced by the competing bacteria have activated (or de-repressed) silent genes in the other bacterial strain.
Many bacteria have genes that can make products, like toxins —even antibiotics against other bacteria.