PUBHLT 2015 Lesson 1: Pathogens, Infectious Diseases, and the Microbiome

Fill in the blanks in the disease triangle.

1. Pathogen

2. Host

3. Environment

Fill in the blanks in the disease triangle.

1. Virulence

2. Susceptibility

3. Severity

What disease do prions cause in sheep?

Scrapie

What disease do prions cause in cattle?

Mad Cow Disease

What disease do prions cause in humans?

New-Variant Creutzfeld-Jakob Disease (nvCJD)

How do prions cause neurodegenerative diseases?

Improper folding

Through what methods are individual proteins transmitted?

Ingestion, transfusion

What does the blue oval represent?

The conditions where humans live comfortably (between 0^oF - 130^oF, and 30%-80% humidity)

What does the yellow oval represent?

The region where vectors (such as mosquitos or ticks) transmit diseasesW

What does the orange oval represent?

Where the host of a virus or bacteria lives and multiplies when it is not infecting humans

What does the grey circle represent?

Where the actual germ can survive, without the host

What types of changes in disease patterns can occur?

1. Changes in pathogen

2. Changes in the environment

3. Changes in the reservoir or vector range

What types of changes in pathogens can occur?

Adaptation, genetic change

What types of changes in the environment can occur?

Altering niche overlap, through seasonal, climatic, and anthropogenic means

What types of changes in reservoir or vector range can occur?

Emerging infections

What is the Chain of Infection?

An epidemiological model showing how infectious diseases spread; breaking any single link stops transmission

What is the pathogen in this context?

The germ causing diseases

What is the reservoir in this context?

Where the germ lives and multiplies

What is the portal of exit in this context?

How the germ leaves the reservoir

What is the mode of transmission in this context?

How the germ travels

What is the portal of entry in this context?

How the germ enters the new host

What is the susceptible host in this context?

The vulnerable person who gets sick

What are some ways to break the chain of infection?

Washing hands, vaccines

Give examples of pathogens.

Viruses, bacteria, parasites

Give examples of reservoirs.

Humans, animals, and the environment

Give examples of the portal of exit.

Coughing, feces, blood

Give examples of modes of transmission.

Direct contact, airborne droplets, vectors

Give examples of portals of entry.

Inhalation, ingestion, broken skin

Give examples of why a host may be susceptible.

Low immunity, lack of vaccines

Which method does Tanzania use to forecast malaria outbreaks?

Predictive climatology

What methods does Tanzania use to prevent wide-spread malaria outbreaks?

Community-based interventions, reducing pesticide use by increasing natural predators

Endogenous

Microbes inhabit our bodies

Exogenous

Microbes exist outside our bodies

What are the types of interactions?

Parasitic, symbiotic, and commensal

Parasitic

One organism benefits at the expense of another

What are some examples of parasitic organisms?

TB, HIV, measles

Symbiotic

Both organisms benefit

What are some examples of symbiotic relationships?

Some gut bacteria produce micronutrients

Commensal

Only one organism benefits, but the other does not suffer

What bacteria is an example of a commensal relationship?

Propionibacterium acnes

What are the stages of infection?

Contamination, colonization, infection, disease

Contamination

Organisms are present, but are not actively growing

Colonization

Microbes are growing on the body’s surface, gut mucosa, etc

Infection

Microbes have entered the body and are actively replicating and beginning to stimulate the immune system

Disease

The infection is starting to cause signs and symptoms

What are some examples of infections which always cause disease symptoms?

Measles, chickenpox, rabies

What are some examples of infections that are usually asymptomatic or inapparent?

90% of polio cases

Give some examples of infections which cause a spectrum of severity, ranging from mild to severe

Measles only rarely causes encephalitis, polio rarely causes paralysis

Plague of Athens (430 B.C.E.)

70,000 people killed probably by typhus

Antonine Plague (166 C.E.)

Up to 7,000,000 people killed throughout the Roman Empire, may have been smallpox

Barbarian Boils (160 C.E. China)

Bubonic plague lead to the collapse of the Eastern Han empire

Black Death (1346-1350 Europe)

1/3 of the population was killed

New World Epidemics (1492 - 1567)

Within 75 years, the indigenous population of Mexico fell by 95%

Louis Pasteur (1822-1895)

Disproved the old theory of spontaneous generation and established germ theory of disease transmission

Robert Koch (1943 - 1910)

Introduced several postulates to establish causal relationships for infectious agents

Golden Age

When the etiology of many diseases was discovered

What are Koch’s Postulates?

• The organism can be regularly isolated from cases of the disease

• The organism can be isolated in pure culture on artificial media

• Inoculation of the cultured organism produces a similar disease in experimental animals

• The organism can be recovered from the diseased animal and will cause the same disease when introduced into another animal

What are some 20th century advances?

• The discovery of viruses in plants and animals

• Koch’s postulates often are hard to prove for viruses

• The ability to isolate and grow viruses in cell culture (1950s) gave rise to the Golden Age of virolgy

• The development of antibiotics

• Impact of biotechnology in the past 30 years

• The eradication of smallpox

What is the mircobiome?

The bacteria, viruses, and eukaryotic organisms that inhabit each of us

How many cells vs bacteria are there in the human body?

Human body - 10¹³ cells
Bacteria - 10¹⁴

How many genes are in the human genome vs the microbiome?

Human genome - 23,000 genes
Microbiome - 3,000,000

How much does each person’s microbiome weigh?

2 lbs

Do all pathogens benefit at the extent of the host?

Yes

Extracellular Pathogens

Living inside the host, but outside the host cells, the pathogen is free to move and colonize the entire body, but is constantly exposed to the host immune system

What is an example of an extracellular pathogen?

Cholera

Intracellular Pathogens

Invades the host cells, better proteching from immune response, but must leave one cell in order to infect another

What are some examples of intracellular pathogens?

Viruses and and some small bacteria

What are the symptoms of cholera?

Severe diarrhea, massive fluid loss, death within 2-3 days

Cholera

• Waterborne pathogen often found in brackish coastal waters

• Infection is usually by drinking water contaminated by other cholera sufferers

• Can sometimes be directly acquired

How does cholera infection occur?

• Most ingested V. cholerae are killed by stomach acids

• Infectious dose is approximately 100,000,000 bacteria

• Surviving bacteria enter small intestine and swim into the mucus layer

• Detach the flagellum, losing ability to swim

• Being secreting the toxins that cause the disease