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Disease causing micro-organisms
Microbes
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Microbes are not the enemy!
Less then 1% can directly make us ill
Microbes that cause disease are called pathogens
When pathogenic microbes enter the body and reproduce this is an infection
When the infection cause damage to an organisms function or systems then this is referred
to as disease
- You can have an infection without a disease

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However many microbes can cause other secondary disease such as;
Gastric cancer (Helicobacter pylori – bacteria),
Cervical cancer (human papilloma virus),
Liver cancer (hep C - virus)
Myocarditis and pericarditis (bacteria or virus causing the heart or surrounding tissue to
swell)

History
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Pre 1800’s: Widely accepted that disease was caused by supernatural forces
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J
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The microorganism must be found in abundance in all organisms suffering from the disease, but
should not be found in healthy organisms
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The microorganism must be isolated from a diseased organism and grown in pure culture
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The cultured microorganism should cause disease when introduced into a healthy organism
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The microorganism must be re-isolated from the inoculated, diseased experimental host and
identified as being identical to the original specific causative agent
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Isolate germ
2
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Inject it
4
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The study of the essential nature of diseases and especially of the structural and functional changes
produced by them
Infectious / Contagious / Communicable Diseases → Antigens
Micro-organisms
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Viruses
Bacteria
Fungi
Protozoa
Algae (blue/green)
Worms
Insects (ticks, lice, etc
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Coli

Staphylococci

Campylobacter

Clostridium
botulinum

Vibrio cholerae

Heliobacter pylori

Description
Diarrhoea, fever, vomiting, abdominal cramps 12 to 72 hours after infection
Dehydration
Self-limiting gastrointestinal disease
Severe cases: Salmonella from intestines to bloodstream (typhoid fever)
Most E
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pylori in upper gastrointestinal tract
Less than 20% of infected individuals are symptomatic
Stomach pains, nausea, bloating, belching, vomiting, black stools in rare cases
Infected individuals: higher risk of peptic ulcers and stomach cancer
New evidence suggests it may play a role in immune modulation of stomach environment

Common diseases caused by viruses in our society
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Influenza: Orthomyxoviridae (influenza virus)
Measles: Paramyxoviridae family of viruses
Common cold: Rhinoviruses, Coronaviruses
Hepatitis: Picornavirus, Hepadnavirus, Hepacivirus, Deltavirus, Hepevirus
Herpes: Herpes simplex virus 1 and 2 (HSV-1 and HSV-2)
AIDS: Human immunodeficiency virus

Fungus?
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Fungi obtains its nutrients from other complex organic substances
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Most fungi are multicellular organisms, however some can be singled celled organisms such
as yeast
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Note the
optically empty vacuoles in both neuronal perikarya (cell bodies) (black arrows), occasionally
containing membranous debris, and also the neuropil (network of axons and glial branchings) (red
arrows)
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Bar = 50 μm

Creutzfeldt–Jakob Disease (CJD)
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Incidence of approximately 1 case per million population per year
Psychiatric / behavioural / dementia-like symptoms
Gerstmann–Sträussler–Scheinker syndrome
Fatal Familial Insomnia
Kuru: possibly transmitted through cannibalism in Papua New Guinea

Pathogenic Protozoans
Amoebic dysentery (Entamoeba histolytica)
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Amoebiasis, AKA entamoebiasis
Contaminated food and water with faeces of infected individuals
Many infected individuals are completely asymptomatic
Frequent symptoms: abdominal pain, mild diarrhoea, bloody diarrhoea, severe colitis
If parasite reaches bloodstream, lodges in liver (amoebic liver abscesses)
Estimated 50,000 to 200,000 deaths / year (primary and secondary causes)

Giardia lamblia, Giardia intestinalis, duodenalis
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Giardiasis (beaver fever)
Zoonotic parasitic (direct contact infected animals)
Also contaminated drinking & untreated water, oral-oral, faecal-oral routes
Frequent symptoms: weakness, loss of appetite, watery stools, stomach cramps, vomiting,
bloating, sulphurous burping (hydrogen sulfide (H2S) sulfur-containing proteins)
Often self-limiting
Antibiotics
estimated prevalence of 3–7% in US population

Infection
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For infection to occur the microbes must enter the body:
Respiratory tract
digestive tract
Urinal tract
genital tracts
Cuts or breaks in the skin
Once inside the body they must survive and reproduce!

Virulence: ability to infect
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“strength” of a pathogen to overcome the immune defenses
Relates to structure of invader and its ability to enter
Length of exposure
Individual’s health

Toxin:
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Poisonous / toxic
Harmful substance
Living or dead
Cause disease

Infection
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The growth of a disease-causing organism in the host
Depends upon:
Person’s health (their immunity)
Number of infective entities
Environmental conditions

How does the body fight infection/foreign invaders?
Three main lines of defence
1
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Nonspecific Immune Response
3
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from leukocytes

Immunity
“The ability of the body to fight infection and/or foreign invaders by producing antibodies or killing
infected cells”
Immune System
“The system in the body responsible for maintaining homeostasis by recognizing harmful from nonharmful organisms and producing an appropriate response”
Antigens
“any substance (as an immunogen or a hapten) foreign to the body that evokes an immune response
either alone or after forming a complex with a larger molecule (as a protein) and that is capable of
binding with a product (as an antibody or T cell) of the immune response”
Identification structures and toxins that pathogens exhibit that can cause harm to an organism
Evokes the immune system to respond through a immune reaction (antibody production)
Specific immune response
Response to a specific pathogen / antigen
Involves the creation of specific Antibodies
Antibody attaches to Antigen on foreign body

Passive & active immunity
1
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2
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It only lasts for a short
period of time
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Maternal antibodies are passed through the placenta to the foetus during pregnancy
2
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Human or animal blood plasma or serum
2
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Monoclonal antibody therapy



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