Disease Transmission Modes

Immune System Big Idea

• The immune system protects the body from infection by pathogens

Section 1 - Infectious Diseases

• This section covers infectious diseases

BIO.3.1.01.087 Learning Objective

• Explain the malfunctioning of biological systems based on hypotheses, such as Koch's postulates.
• Use scientific examples of infectious diseases, their causes, transmission, and treatments, and non-infectious diseases

Learning Outcomes for Infectious Diseases

• Define infectious diseases
• Identify pathogens that cause infectious diseases, including bacteria, viruses, fungi, protozoa and parasites
• Identify ways in which microorganisms can be beneficial
• Explain how Koch proved the germ theory correct
• Analyze how diseases are transmitted
• Discuss the role of reservoirs in disease dispersal
• Recognize that symptoms are caused by the host's immune system response to the invasion of pathogens
• Explain different ways pathogens can cause diseases, including viruses, bacteria and fungi
• Differentiate between disease patterns to include endemic, epidemic and pandemic
• Research a current infectious disease, its cause, transmission, and treatment
• Differentiate between antibiotics and antiviral drugs as treatments for infectious diseases
• Differentiate between bacterial sensitivity and resistance to antibiotics
• Analyze the increase in the occurrence of antibiotic-resistant bacteria

New Vocabulary

• Infectious disease: A disease caused by a pathogen
• Pathogen: An organism that causes disease
• Koch's postulates: Rules for demonstrating that an organism causes a disease
• Reservoir: A place where pathogens can live and reproduce
• Endemic disease: A disease that is always present in a population
• Epidemic: A disease that affects a large number of people in a population at the same time
• Pandemic: A disease that affects people over a large geographic area

What is an Infectious Disease?

• An infectious disease is caused when a pathogen is passed from one organism to another.
• Pathogens are the cause of infectious diseases
• Pathogens include viruses, bacteria, protozoans, fungi and parasites
• A cold and athlete's foot are examples of infectious diseases
• Not all bacteria or viruses are pathogens
• The body benefits from organisms such as bacteria and protozoans.
• These organisms live in the intestinal and reproductive tracts and on the skin.
• The organisms keep pathogens from thriving

Germ Theory

• People thought something passed from a sick person to a healthy person to cause illness, before the microscope was invented
• Louis Pasteur demonstrated that microorganisms from the air are able to grow in nutrient solutions
• Germ theory was developed with the information learned form Pasteur.
• The Germ theory states that some microorganisms are pathogenic, and it wasn't fully demonstrated until Robert Koch developed his postulates

Koch's Experiments

• Robert Koch studied anthrax
• First, he studied a deadly disease that affects cattle, sheep, and people
• Second, Koch isolated bacteria from the blood of cattle that had died from anthrax.
• The bacteria were grown in a laboratory

Koch's Postulates

• These are rules for demonstrating that an organism causes disease
• Postulate 1: The suspected pathogen must be isolated from the diseased host in every case of the disease.
• Postulate 2: The suspected pathogen must be grown in pure culture on artificial media in the laboratory.
• Postulate 3: The suspected pathogen from the pure culture must cause the same disease when placed in a healthy new host.
• Postulate 4: The suspected pathogen must be isolated from the new host, grown again in pure culture, and shown to have the same characteristics as the original pathogen.
• Robert Koch used a pure culture with artificial media containing nutrients

Koch's Postulates Guidelines

• Pathogens should only be in a sick organism
• The pathogen should be isolated and grown in a pure culture
• Introduction of the pathogen to a new host should produce the same disease
• The injected pathogen should be isolated from the second host and be identical to the original pathogen

Koch's Postulate Exceptions

• Some pathogens cannot be grown in pure culture on artificial media, like bacteria that causes syphilis
• Viruses cannot be grown in pure culture because they need cultured cells in order to grow on artificial media

Reservoirs

• Large numbers of microorganisms coexist with humans.
• Only a few microorganisms cause diseases
• Reservoirs of pathogens are sources from which pathogens can spread
• Some cause mild disease such as a cold, and some cause serious diseases such as meningitis

Types of Reservoirs

• Humans can be a reservoir and are the main source of pathogens
• Humans pass these pathogens directly or indirectly
• Many pathogens are passed on to a host before someone knows they are sick.
• Someone that is symptom-free but capable of passing on a pathogen is called a carrier
• Diseases that can be transferred through animals are Influenza and Rabies
• Animal reservoirs are when pathogens are passed to humans from animals
• One animal example is the Bird Flu, which ducks can carry

Animal Reservoirs - Rabies

• Rabies is an animal reservoir found in wild animals
• Bats, foxes, skunks, and raccoons, carry the deadly pathogen
• Rabies passes through animal bites

Other Reservoirs: Soil

• Some bacteria live in the soil and can cause disease in humans
• Tetanus bacteria contaminates a deep wound in the body

Other Reservoirs: Food and Water

• Contaminated water and food can also transmit the pathogen
• The safe disposal of human feces prevents contamination of the water by pathogens.
• Contaminated water in growing or preparing food can transfer the pathogen
• Contaminated food from human contact or insects such as flies can transfer pathogens

Transmission of Pathogens

• There are four classifications of transmission
• Direct Contact with humans, causing Infectious Mononucleosis
• Contact by Air, sneezing or coughing
• Indirect contact by touching contaminated objects that can transfer the pathogens
• Finally, vectors transfer pathogens

Vectors of Pathogens

• Vectors transfer pathogens to a new host
• Vectors are insects that transmit the infectious diseases caused by bacteria, viruses and parasites
• Examples of vectors that can carry pathogens include mosquitoes, ticks and house flies

Vector Examples

• Malaria is a vector of protozoan
• West Nile Virus is a vector of mosquitoes
• House flies transmit E. coli

Symptoms of Diseases

• Symptoms are side effects when the pathogen has invaded host cells
• Viruses ex: Influenza, harm the host because multiple viruses leave through Exocytosis or by the cell bursting
• Bacteria produce harmful chemical toxins.
• The toxins get carried through the body via the bloodstream causing damage

The Effects of Toxins Produced by Pathogens

• Tetanus produces potent toxins that cause spasms.
• Botulism produces toxins that paralyze nerves.
• The Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO) monitor disease patterns
• Disease patterns are observed as outbreaks of a disease spread

Disease Patterns

• Monitor to help with the spread of diseases
• The CDC and WHO published reports for disease pattern incidence
• Endemic diseases are continually found in small quantities, like a cold
• Epidemic are large outbreaks in an area that afflict many
• Pandemic are widespread through a large region

Ways to Fight Diseases

• Drug treatment is one way to fight diseases
• Antibiotics help the body fight infections caused by bacteria
• Antiviral drugs help the body fight infections caused by viruses

Virus vs Bacteria

• Colds and influenza are caused by viruses
• Viruses are non-living particles, contain genetic material, and attack cells to reproduce.
• Viruses cannot be killed with antibiotics
• Bacteria are living organisms, have metabolism and DNA
• Bacteria can be killed with antibiotics because they target bacterial wall production

Fighting Diseases

• Antibiotics can kill or inhibit the growth of microorganisms.
• Some examples of Antibiotics include Penicillin, Erythromycin, Neomycin, Gentamicin
• Chemical agents are used to treat protozoan and fungal diseases.
• Antiviral Drugs are used to treat infections like influenza

What is Penicillin?

• Penicillin is produced from the fungus Penicillium
• It works by killing competing bacteria that grow on the fungus food source

Antibiotic Resistance

• Many bacteria become resistant to antibiotics because of the widespread use of antibiotics.
• Bacteria with the trait to survive antibiotics reproduce quickly and increase antibiotic resistance.
• This has caused staphylococcal disease and made it harder to treat with antibiotics.
• Medical care workers are struggling to medically treat certain diseases because of antibiotic resistance