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Infectious Diseases. General Principles. Slide Index. Click on a Subject to Go Directly to That Topic. Overview of Microbes Bacteria — Prions — Fungi Viruses — Protozoa Overview of Infectious Agents and Disease Food Poisoning — Respiratory Disease Liver Disease — STD’s

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infectious diseases

Infectious Diseases

General Principles

slide index
Slide Index

Click on a Subject to Go Directly to That Topic

  • Overview of Microbes
    • Bacteria — Prions — Fungi
    • Viruses — Protozoa
  • Overview of Infectious Agents and Disease
    • Food Poisoning — Respiratory Disease
    • Liver Disease — STD’s
  • Break the Transmission Cycle
  • Kill the Infectious Agent
  • Increase Host Resistance
    • Active and Passive Immunization
    • Vaccines
  • Case Studies: More Information on Specific Diseases
what is a microbe
What is a Microbe?
  • Microbes are microscopic organisms that can live 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 live 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.

You have to have a microscope to see microbes!

where can microbes live
Where can microbes live?

In plants

In animals

In the dirt

All of these





microbes and disease
Microbes and Disease
  • Most microbes belong to one of five categories: bacteria, viruses, prions, protozoa, or fungi.
  • Some microbes cause disease and some don’t.
  • Microbes that cause disease are called infectious agents, commonly called “germs” or “bugs.”

Infectious agents are microbes that

can cause disease.

what do they look like

Campylobacter jejuni

E. coli

Source: NASA


Hepatitis C Virus

Source: Amgen, Inc;

What Do They Look Like?

Infectious agents look different, depending on what class of agent they are

Dutch Elm Fungus


HIV Virus

Ciliated Protozoa


Source:; Wilhelm Foissner

  • Bacteria are prokaryotic, unicellular microbes.
  • They have their own metabolism.
  • 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.
  • Some bacteria produce toxins that can harm us.

Bacteria can look like balls, rods, or spirals.


  • A virus is a microbe that consists of a nucleic acid housed within a protective coat.
  • The virus reproduces by hijacking the host cell’s metabolic machinery to replicate its own DNA or RNA.
  • Most viruses cause disease and are specific as to which type of cell they will attack.


  • A prion is an infectious particle made from an abnormally folded protein found on the surfaces of neurons.
  • Prions are highly resistant to heat, UV 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.
  • One celled microbes that can be parasites or predators.
  • Can live in a variety of places, but prefer moist habitats.
  • Usually cause disease in humans.
  • Protozoa are sometimes helpful to other animals. They are a food source for whales and help cows as well as termites digest their food!

Protozoa found in human stool samples


  • A multi-cellular microbe that is much larger than the other microbes.
  • Only about 1/2 of all fungi causes disease in humans.
  • A fungal disease is called a mycose.
  • Yeast is a fungus that is used to make bread and cheese for us!

What Am I?

Click on the Buttons to quiz yourself on the various microbes!

Word Bank

how can an infectious agent attack me
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.



species specificity
Species Specificity

I can transmit

Brucellosis and


  • 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 arenaviruses

and hantavirus.

I can transmit

Ebola virus!

where else are infectious agents
Where Else Are Infectious Agents?
  • Bacteria, protozoa, and fungi all reside in the soil.
  • Other infectious agents can live on surfaces for hours or even days, like the cold virus.
life cycle of infectious agents
Life Cycle of Infectious Agents
  • Once a few microbes enter the body, it may take a few hours or days for the agent to reproduce enough to become infectious for others or to cause disease.
infectious agents are deadly
Infectious Agents are 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.

Why do more people die from infectious diseases in undeveloped, poor countries than in developed, rich countries?


Poorer countries do not have good vaccination programs.

Poorer countries are mostly located in the southern hemisphere where warm temperatures are perfect for infectious agents.



None of these.

what are the main types of infectious disease
What are the Main Types of Infectious Disease?

Food Poisoning

Respiratory Diseases

Liver Diseases

Sexually Transmitted Diseases

food poisoning is a disease caused by infectious agents
Classical food poisoning is poisoning from foods contaminated with enterotoxins.

Bacterial food poisoning is caused by the bacteria itself, not the toxin it produces.

Both bacterial and classical food poisoning have similar symptoms.

Food Poisoning is a Disease Caused by Infectious Agents

Why do you think there was a picture of a hamburger on the previous slide?


Because hamburgers are unhealthy and have lots of fat which poisons us.

Because hamburgers are a common place for food poisoning to occur.

Because we are talking about food safety so there is a picture of some food.



food poisoning
Food Poisoning
  • 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 stored unrefrigerated for a long period of time.


  • nausea
  • vomiting
  • abdominal cramps
  • fever
  • diarrhea
  • Botulism-neurologic collapse, respiratory failure, and death. (Caused by improper canning methods)
which foods are problem foods
Which Foods are Problem Foods?
  • 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.
respiratory diseases
Respiratory Diseases
  • Many infectious agents attack the respiratory tract.
  • The most common respiratory disease is the cold, but others include bronchitis, influenza, SARS, and pneumonia.
liver diseases
Liver Diseases
  • Most liver diseases are caused by a variety of viruses collectively known as hepacivirus.
  • These viruses cause hepatitis (inflammation of the liver)
  • You were probably vaccinated for Hepatitis A virus when you were young.


A liver with varying stages of hepatitis. The cells on the left are normal liver cells.


In the previous slide you learned that many viruses cause hepatitis (aka: inflammation of the liver). What does the “itis” mean?

Move your mouse around if an input box does not appear.

sexually transmitted diseases







Chlamydia trachomatis

Treponema pallidum


Herpes Simplex Virus

Sexually Transmitted Diseases
  • STD’s are a result of various viral and bacterial infections that are transmitted through sexual interaction or blood/serum exchange.
  • There are more than 20 STD’s identified.
  • The most common are:
acne is an infectious disease
Acne is an Infectious Disease!
  • The pimples are dead white blood cells that were attacking bacteria in the skin’s pores.
  • The sebaceous glands in your skin make an oily substance called sebum. Too much sebum can clog up the hair follicle. This allows bacteria to grow and multiply.
  • White blood cells rush to the rescue to fight the infection.

Acne is not contagious or transferable

different infectious diseases require different approaches for prevention and control

Different infectious diseases require different approaches for prevention and control.

Here are some ideas that apply to most infectious diseases.

three key steps
Three Key Steps

reak the cycle of transmission

ill the infectious agent

ncrease host resistance

reak the cycle of transmission
reak the Cycle of Transmission
  • Control animals and other biological disease carriers (e.g. insects, rats).
  • Control air, dust, or dirt that may harbor infectious agents.
  • Use sanitary practices.
    • Good personal hygiene
    • Proper food-handling procedures
    • Use of protective clothing
    • Avoid water, foods, animals, and insects likely to transmit disease
  • Detect disease early and start treatment.
  • Isolate or limit exposure to infected people.
  • Use aseptic technique in the management of patients and their excretions and secretions.
controlling disease carriers
Controlling Disease Carriers
  • Sterile males can be used to control insect populations.
  • Cleaning regularly and picking up trash can keep rodents away.
  • Sometimes the only way to stop a disease transmission is to kill the carriers.


Source: USDA

Why does introducing sterile males into a population of insects reduce the transmission of infectious agents?

It prevents non-sterile males from surviving and reproducing.

It indirectly reduces carrier population numbers.

Sterile males cannot carry diseases.




Infection occurs when you have the infectious agent in or on you and it is injuring you in some way.

Contamination occurs when you have the infectious agent in or on you but it is not injuring you. However, it does have the potential to injure others.




are the natural bacteria in your large intestine contaminating you or infecting you
Are the natural bacteria in your large intestine contaminating you or infecting you?



Which is an example of a contaminated person that is not infected?

A nauseated doctor (who had her flu vaccine) that had previously helped a man with the flu.


A healthy nurse (who had her flu vaccine) that had previously helped a man with the flu.


good sanitary practices prevent the spread of infection
Good Sanitary Practices Prevent the Spread of Infection
  • Wash your hands regularly!
  • Always keep your area clean and neat!
  • Be careful around people with infections
why does keeping your area clean and neat help prevent the spread of infection
Why does keeping your area clean and neat help prevent the spread of infection?

It helps keep potential disease carriers, like rodents and flies, away.

A neat and clean environment is not the best habitat for germs.

It helps keep germs from multiplying and creating large populations.

All of the Above





cleanliness healthiness
Cleanliness = Healthiness
  • Scrubbing with soap and water eliminates dirt and kills most germs.
  • Using disinfectant provides an extra margin of safety.
  • The biggest place for germs to reside in your house is in the kitchen.

Click on a button to see the best places for infectious agents to reside!

The cafeteria is a great place for germs to hide. The food that sits out for hours unheated or cooled is a perfect breeding ground for bacteria.

The cafeteria is a great place for germs to hide. The food that sits out for hours unheated or cooled is a perfect breeding ground for bacteria.

The cafeteria is a great place for germs to hide. The food that sits out for hours unheated or cooled is a perfect breeding ground for bacteria.



Teacher’s Desk


Germs absolutely love the bathroom! Many diseases are spread through human feces. Always wash your hands!!!

Germs absolutely love the bathroom! Many diseases are spread through human feces. Always wash your hands!!!

Germs absolutely love the bathroom! Many diseases are spread through human feces. Always wash your hands!!!


The playground isn’t just a fun place for you! Infectious agents can live in the soil and on the bars. Any germs on your hands will transfer to the bars and to the next person who plays on them.

The playground isn’t just a fun place for you! Infectious agents can live in the soil and on the bars. Any germs on your hands will transfer to the bars and to the next person who plays on them.

what are the best disinfectants
What are the Best Disinfectants

Disinfectant Strength Enveloped Non-Enveloped Bacteria FungiViruses Viruses

Low Good Good Good Good

Chlorox Bleach





Low Good Fair Good Good

Low Good Good Fair Good

Low Poor Good Fair Good

Low Poor Good Fair Fair

All of these are low level in strength but anything higher is not necessary for everyday use.


Based upon the previous slide, which disinfectant is the best one to use?

Chlorox Bleach




Quaternary Ammonia

washing your hands
Washing Your Hands

Fun Statistics About Washing Your Hands:

1. A study of 305 Detroit students found that washing their hands 4 times a day reduced their sick days due to respiratory illnesses by 24% and stomach flues by 51%.

2. 1 out of every 3 people do not wash their hands after using the bathroom.

  • Washing your hands is the most important thing you can do to keep from getting sick!
  • You pick up germs and infect yourself by touching your nose, eyes, and mouth.
  • The spread of the cold, hepatitis A, meningitis, and diarrhea can all be prevented by washing your hands.


how long should you scrub your hands when washing them
How long should you scrub your hands when washing them?

0-10 seconds

15-30 seconds

1-2 minutes





Why does touching your nose, eyes, and mouth get you sick if you haven’t washed your hands?

Because your nose, eyes, and mouth have mucous membranes that easily transfer infectious agents from your hands to the rest of your body.

Because your nose, eyes, and mouth have no resistance to infectious agents so infection is a sure thing.



food preparation
Food Preparation
  • Many deadly infectious agents live in our food.
  • Always clean your area before and after cooking, especially when cooking raw meat.
  • Always cook food well and keep foods refrigerated.
the all important refrigerator
The All Important Refrigerator
  • Keeping foods cold is even more important than cooking them.
  • Cold temperatures keep infectious agents from multiplying and growing.
  • Always refrigerate foods within two hours of cooking.
  • Keep foods at or below 40°F.

Why does cooking food help prevent infectious disease?


Cooking food prevents infectious agents from growing and multiplying

Cooking food kills infectious agents


isolate the disease
Isolate the Disease
  • The key to blocking the transmission of infection is to isolate the disease.
  • Volunteer isolation and quarantine are the best ways to prevent the spread of disease.
  • Public authorities must act quickly to prevent outbreaks from becoming epidemics.

This card was posted outside the house of a person who had scarlet fever. The authorities quarantined him to prevent the spread of infection.

Source: National Library of Medicine

problems with isolation
Problems with Isolation
  • Most people do not want to voluntarily quarantine themselves.
  • Mass transit allows an easy route for an infectious disease to spread.
k ill the infectious agent
Kill the Infectious Agent
  • Heat
    • Usually 150°F or above
    • Cook chicken/turkey to 165 °F
  • Cold
    • Foods should be refrigerated at or below 40 °F.
    • Cooling may only slow infectious organisms’ growth, not kill the organism.
  • Chemical sterilization (e.g. chlorinate water supplies and sewage)

Organisms that form spores may survive heat, cold, and chemical sterilization. Prions are unaffected by these methods.

i ncrease host resistance
Increase Host Resistance
  • Use vaccines and toxoids for active immunization and immunoglobulins for passive immunization.
  • Improve general health - proper nutrition, exercise, healthy lifestyle, etc.
active vs passive immunization

Occurs when a person is exposed to an infectious agent, contracts the disease, and develops antibodies against that infectious agent.

Vaccines are artificial active immunization because they cause the immune response without causing the disease (usually!)


Occurs when a person is injected with antibodies, such as immunoglobulins.

This is a short term immunity since it does not stimulate the immune system to make it’s own antibodies.

Unlike active immunization, passive immunization will never cause the disease.

Active vs. Passive Immunization

If a person is infected by an infectious agent, contracts a disease, and lives through it, has he acquired passive or active immunization?



  • Vaccines are very important preventative medicine.
  • Vaccines consist of killed or weakened microbes that stimulate the immune system against that microbe.
  • Some infectious agents can change their genetic makeup making it difficult to produce a vaccine.
  • Texas’ required immunizations include: Polio, Haemophilus Influenza B, Diphtheria, Tetanus, Pertussis, Hepatitis A, Chickenpox, Measles, Mumps, Rubella, and Hepatitis B.
types of vaccines
Types of Vaccines
  • Inactivated Vaccines
  • Live, Weakened Vaccines
  • Toxoids
  • Conjugate Vaccines
  • Subunit Vaccines
  • Recombinant Vector Vaccines

Click Me to Visit the PEER web site and review your knowledge of the Immune System!

inactivated vaccines
Inactivated Vaccines
  • These vaccines are produced by killing the infectious agent.



  • They do not have to be refrigerated.
  • They will never come back to life and cause the disease.
  • They usually require booster shots because they only weakly stimulate the immune system to make antibodies.

Weakened Vaccines

  • These vaccines are produced by weakening a live vaccine or removing it’s disease causing ability.



  • They emit a large immune system response so you only have to receive the vaccine once or twice.
  • They have to be kept in special conditions, like refrigeration.
  • They can mutate and cause the disease.


  • Toxoids are produced by inactivating the toxin that some infectious agents create.
  • Toxoids are used against Tetanus and Diphtheria.



  • You only have to have the vaccine once or twice.
  • They will never be reactivated and cause the disease.
  • They have to be refrigerated.

Conjugate Vaccines

  • Immature immune systems, like those found in children, cannot recognize some infectious agents.
  • Conjugate vaccines are produced by attaching a protein or toxin from a microbe that young immune systems can recognize to an infectious microbe that these immune systems can’t recognize.
  • The Hib vaccine is a conjugate vaccine.

Subunit Vaccines

  • These vaccines are produced by taking apart an infectious agent and only using the antigen part (the part that stimulates an immune response).
  • The vaccines for Hepatitis B and Streptococcus pneumoniae are subunit vaccines.



  • They are more difficult to make and require new, expensive technology.
  • They cannot cause the disease.

Recombinant Vector Vaccines

  • These vaccines are produced by inserting the harmless genetic material of an infectious agent into a different, weakened or killed, infectious agent.
  • Scientists have not been able to make vaccines for all infectious agents. They are hoping that inserting the genetic material from these infectious agents into another vaccine will evoke an immune system response against these infectious agents.

Test Your Knowledge!!

Word Bank

The questions will keep repeating until you get them all correct!! Each word is used only once.

how vaccines are made
How Vaccines are Made
  • The microbes grow on an agar or tissue graft such as calf fetal serum, chick serum/egg, or monkey serum/egg.
  • The microbes are purified and the vaccine is produced.
  • Allergic reactions to a vaccine can occur when the purification process does not eliminate all of the serum.

When a person has an allergic reaction to the vaccine, what is that person really allergic to?


He is allergic to the weakened or dead microbe.

He is allergic to the serum used to grow the microbes.


genetic recombination and bacterial resistance
Genetic Recombination and Bacterial Resistance
  • Many infectious agents can change their genetic makeup to become stronger, more virulent microbes.
  • These microbes are unaffected by vaccines or antibiotics that previously killed that species of microbe.
  • Genome sequencing of these microbes helps scientists identify drug targets for the microbes and understand their resistance abilities.
healthy lifestyle the best preventative maintenance
Healthy Lifestyle--The Best Preventative Maintenance
  • Eating healthy food, taking vitamins, and regular exercise stimulates the immune system.
  • Good sanitation practices also limits an infectious agent’s ability to spread to you and others.
influenza virus
Influenza Virus
  • Infects the nose, throat, and lungs causing the flu.
  • Symptoms: fever, muscle ache, chills, sweating, sore throat.
  • This virus rapidly changes its RNA to produce more virulent strains and new vaccines have to be made each season.

See the PEER Influenza Supplement for more information.

severe acute respiratory syndrome
Severe Acute Respiratory Syndrome
  • First identified in February, 2003.
  • The virus or viruses cause a form of atypical pneumonia which results in acute respiratory distress and can lead to death.
  • It is unknown what this virus is or how it works. Researchers think it is a type of cornavirus (the same category of the common cold virus).
  • It can be spread from person to person through respiratory droplets, just like the common cold.
  • Symptoms include a fever greater than 100.4°F, cough, and difficulty breathing. Sometimes the person will also feel the same symptoms as those caused by the influenza virus.
clostridium tetani
Clostridium tetani
  • Causes Tetanus or Lockjaw
  • Symptoms: muscle spasms and tetanic seizures that can lead to bone fractures and muscle tears.
  • The bacteria produces a toxin called tetanospasmin which blocks inhibitory nerve transmission from spinal cord to muscles. This causes an over-excitation of the muscles.
  • Without treatment, 1 out of 3 people die.
escherichia coli
Escherichia coli
  • Causes E. coli enteritis, a disease caused by the bacteria itself and/or the toxin it produces.
  • Symptoms: diarrhea, cramps, vomiting
  • Can lead to Hemolytic Uremic Syndrome which is life threatening.

Source: CDC