Epidemiology and Disease Processes
Chapter 17,
examples from Chapter 19
Fields of Microbiology
Epidemiology
-- Population focus
-- disease spread & containment
Microbial pathology
-- Disease focus
-- ‘etiology’ of disease
-- Biology of pathogen & effects on host
John Snow’s classic
search for source of
cholera – London, 1854
Clinical Microbiology
-- Patient focus
-- ID of pathogen and treatment
Germs
Pathology
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Roles of the the CDC
Epidemiological studies
the MMWR
Notafiable diseases
(see tables 15.3 & 15.4)
Recommendations:
antibiotics
drugs
vaccine
The WHO
based in Geneva, Switzerland
Pathology
2
Our bodies sustain diverse microbial ecosystems
Microbiota
= all the species
Microbiome:
= where they live
or all their genes
Over 100 trillion cells
~90% of the cells in our body
~3 – 5 lbs of body weight
1000s of species
- from all domains
~3,000,000 microbial genes
- vs ~25,000 human genes
How does our microbiome
influence our lives?
We are a meta-organism
Mutualistic symbiosis
Microbiome effects our biology
Disruption can lead to disease
-- introduction of pathogens
-- changes in immune tolerance
-- crossing the epithelium
What are the clinical stages of a disease?
Incubation
Prodromal
Invasive
Acme
Decline
Convalescence
Symptom can be:
Acute
Chronic
Latent
Pathology
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What are disease ‘Reservoirs’?
Nonliving (usually noncommunicable, opportunistic)
tetanus
fungi
Living
Animal (‘zoonotic’) (generally noncommunicable)
rabies
anthrax
lyme disease
Human (may be ‘contagious’)
cholera
Pneumonia
HIV
‘Carriers’ (read essay about Typhoid Mary, p 376)
Nosocomial
Pathology
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What are “modes of transmission:”?
The “Five F’s”
A. Contact transmission
Direct Contact transmission
-- includes ‘aerosols’
-- respiratory infections
Indirect Contact transmission
involves ‘fomites’
Haemophilus
B. Vehicular transmission (disseminates)
water, food, dust
cholera, salmonellosis
C. Vector transmission
Reservoirs, Vehicles and Vectors are not the
same!
Pathology
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Entering and exiting the body
Portals of entry
Skin
Mucous epithelia (‘membranes’)
-- respiratory
-- eye
-- reproductive
-- digestive
Placental
Parenteral
Portals of exit
Skin
Feces
Wounds
Aerosols
Vectors
Pathology
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Case study:
Lyme disease
An “Emerging Disease”
New Lyme, Conn, 1982
Borrellia burgdoferi
White-tailed deer & mice
Ixodes
complex life cycle
Pathology
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Lyme disease, con’t
Distibution
Stages of disease
Acute symptoms:
“Bulls-eye rash”
flu-like symptoms
Chronic symptoms:
arthritis
neurological disorders
etc
Treatment
antibiotics (yes and no)
Pathology
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Patterns of disease occurrence
epidemic
pandemic
endemic
sporadic
cyclic
Pathology
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Case study: Tuberculosis
-- A ‘reemerging’ disease
Mycobacterium tuberculosis
Intracellular pathogen
lungs
WBCs
immune response
granulomas
Spread/control linked to clinical
and social factors:
1) Diagnosis and treatment difficult
2) Slow growth
3) Poverty
-- developed & developing nations
4) AIDS
Pathology
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What are the stages of an infection?
Adherence
Colonization
Invasion
1. Adherence
glycocalyx
fimbriae
receptors
Pathology
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Colonization and Invasion
are often coupled
Many ‘strategies’
Enzymes (‘virulence factors’)
collagenase
hemolysin
collagenase
hemolysin
streptokinase
Phagocytosis
Intracellular and extracellular
infections
Penetration
Actin Tails
Pathology
14
What causes the symptoms of infection?
Syphilis lesions in liver
Altered physiology
e.g., fever; lethargy; loss of appetite
-- altered blood chemistry;
-- effects on hypothalamus
Immune responses – some damaging
e.g., many diseases; tuberculosis, leprosy
rheumatic fever, etc
Toxins -- damage to cells, tissues and organs
Exotoxins
Gram-Positive sp.
proteins, Secreted from cells
Highly toxic, specific effects
Endotoxins
Gram-negative lipopolysacchrarides
Less toxic, more general effects
pyrogenic, hypotension
Endotoxins
Enteric Virulence
Pathology
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Some Effects of Exotoxins
1) Cell destruction (hemolysins)
2) Hemorrhaging (anthrax, Streptococus toxins)
3) Effect intestinal function (enterotoxins)
water balance (cholera toxin)
Anthrax lesion
4) Nerve function (botulism & tetanus toxins)
Toxicity of Some Exotoxins
Toxin
Botulism Type D
Tetanus
Shigella Neurotoxin
Diphtheria
Lethal Dose (mg)
0.8 x10-8 (mouse)
4 x10-8 (mouse)
2.3 x10-6 (rabbit)
6 x10-5 (guinea pig)
Toxicity compared with:
Strychnine Snake Venom
3x106 times
3x105 X
6
1x10 X
1x105 X
1x106 X
1x105 X
3
2x10 X
2x102 X
Pathology
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Botulism and Tetanus
Clostridium botulinum vs
obligate anaerobes
C. tetani
Botulism
food borne
flaccid paralysis
Tetanus
soil borne
rigid paralysis
Pathology
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A Botulism Case History
- Food risks
- Antitoxins
Birds, Babies, Botox and Bioweapons…
Pathology
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Case study:
Helicobacter pylori causes peptic ulcers
Only discovered 1982
Dimorphic
causes
60-80% of stomach ulcers
90% doudenal ulcers
Stomach cancers
Immune response plays
important roles
Good news: treatable
Bad news: 25% in U.S. infected
More bad news: antibiotic resistance
is spreading
Pathology
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Gonorrhea
agent Neiserria gonorrhoeae
-- Gram-negative dipplococcus
-- attaches via fimbriae
Endotoxin
Infection in males
“thick, copious & yellowish” pus
Pathology
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Gonorrhea Infection in females
cervix
fallopian tubes
PID
ectopic pregnancy
neonatal prophylaxis
epidemiology
Pathology
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A Souvenir of London
Bought a souvenir in London
got to hide it from my mum.
Can't declare it at the customs,
but I'll have to take it home.
Tried to keep it confidential,
but the news is leaking out.
Got a souvenir of London.
There's a lot of it about.
Yes I've found a bit of London,
and I'd like to lose it quick.
Got to show it to my doctor,
'cos it isn't going to shrink.
Want to keep it confidential,
but the truth is leaking out.
Got a souvenir of London.
There's a lot of it about.
by Procol Harum, 1973
ASoL
Pathology
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What causes the symptoms of Syphilis?
Agent
Treponema pallidum
spirochete
Stages of the infection
Incubation
Primary (1O) syphilis
chancre
(clinical latency)
Secondary (2O) syphilis
immune hypersensitivity
(clinical latency/ recurrent 2O)
Tertiary syphilis
gumma lesions
Pathology
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Syphilis, con’t.
Tertiary syphilis
gumma lesions
Saddle nose
autoimmunity?
Treatment
Congenital syphilis
Notched teeth
Saber shin nose
Pathology
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