Microbe-Human Interactions:
Infection & Disease
I. Introduction
A. Recall _______
Koch’s Postulates (experimental steps to establish the
microbe that causes a disease)
1. isolate a pathogen from a diseased host & grow pathogen in pure
culture
2. inoculate a healthy organism with the cultured pathogen
3. organism must get the same disease
4. isolate the same pathogen from the new host
B. Exceptions to Koch’s postulates
1. Microbes that can’t be grown on artificial media
examples: Viruses
Rickettsia
Treponema
2. More than one microbe produces the same disease
examples:
meningitis
pneumonia
3. One microbe that causes multiple diseases
examples: Streptococcus pyogenes
4. Strictly human diseases with no animal model
examples:
Rubella (German measles)
Strep throat
Scarlet fever
smallpox
Normal Flora (microbes that normally live in/on the body w/o harm)
II. ____________
A. _______
Resident vs _________
Transient flora
(always there)
(only present for a short time or on and off)
Colonization
B. Establishment of Normal Flora = __________
1. Newborns are free of flora, but established as infant is exposed to
organisms from _______,
food etc.
vagina _____,
air ______
2. Colonization is a selective process due to physiological conditions in
the body such as _____,
O2 ________,
temperature ____,
nutrients etc.
pH ___________,
12-18 months to fully establish normal flora
3. Takes about ____________
Symbioses (different organisms living together)
C. __________
1. __________
Mutualism (both partners benefit)
bacteriocins
E. coli: produces vitamins K & some B, and ___________
(chemicals that ward off harmful species)
Commensalism (one partner benefits, other is neutral)
2. ___________
skin organisms live off of secretions/sloughed cells
Parasitism (one partner benefits while the other is harmed) many
3. _________
bacteria, fungi, protozoans, worms and even viruses
parasite
host
D. Opportunistic
____________ organisms (organisms that are usually nonpathogenic,
but that can become pathogenic under certain circumstances)
1. when host health is compromised
2. when there is a reduction of normal flora
habitat (part of the body)
3. if an organism gets in a different_______
E. coli from gut to urinary tract
Klebsiella pneumoniae from gut to respiratory
Pathogenesis (disease development)
III. Mechanisms of ____________
A. Production of disease is actually a process of steps
Transmission to a susceptible host
1. ____________
Adherence to appropriate target tissue(s)
2. ___________
Invasion
3. ________
Colonization
4. __________
Damage to host while evading defenses
5. ________
Exit from body
6. _____
Survival outside long enough to be transmitted to another host
7. _________
B. Transmission must be to the correct “portal of entry”
mucous
1. typically to exposed surfaces such as ______
skin or _______
membranes (which is not an easy thing to do!)
punctures
bites cuts
abrasions _________etc.
2. entry aided by _____,
____, ________,
food water
a. Gastrointestinal tract (via ______,
_____)
bacteria, especially Gram- _______
enteric bacilli
viruses such as polio and Hepatitis A
protozoans such as Entamoeba and Giardia
b. Respiratory tract (via ____)
air
bacteria that cause strep throat, diphtheria, pertussis
viruses such as influenza, measles, mumps, rubella, chickenpox
and the common cold
fungi such as Histoplasma and Pneumocystis
c. Urogenital tract (most are _____)
STDs (or misplaced opportunists)
bacteria such as Neisseria, Treponema, and Chlamydia
viruses such as papilloma and herpes
protozoans such as Trichomonas
fungi such as Candida
3. Infectious
________ ____
dose = minimum number of microbes necessary to insure
infection (ex: only 10-100 Shigella but 1,000,000 Salmonella)
C. Adherence (attachment)
Ligands (projections of microbe that match host receptors)
_________
1. pili tips, surface proteins, etc. (can change b/c of mutations so
previous Ab don’t recognize them!)
2. same organism can have different ligands to adhere to different
Pink eye
parts of the body (ex: Haemophilus influenzae)
Middle ear
3. some ligand genes on plasmids can spread like antibiotic resistance!
4. why people don’t get a lot of other animal diseases and vice versa
D. Invasion (in order to establish infection)
1. high concentrations, more likely to invade successfully
Bacteremia = presence of bacteria in the blood
2. ___________
Viremia = presence of viruses in the blood
________
E. Colonization (when conditions are such that invading microbes are
reproduce
successful enough to _________)
Septicemia = blood infection where bacteria are reproducing
__________
phagocytosis
F. Evade host defenses (mainly by avoiding ____________)
1. Capsules
________ (Streptococcus, Salmonella, Neisseria)
Leukocidins are substances that are toxic to WBCs
2. __________
3. _________
Catalase breaks down H2O2 produced by phagocytes, preventing
digestion of the engulfed microbe
& Cause Damage/Disease
Toxins (poisonous substances) (________
Toxemia when in the blood)
4. _______
Exo- toxic soluble proteins secreted (botulism, tetanus)
a. _____:
___________
Hemolysins cause lysis of RBC’s
b. Endo_____: cell wall components released when cell dies, toxic to
host (lipopolysaccharides in Gram-negative cell walls)
*Can lead to Septic shock
5. ____________
Exoenzymes (act on host cells/tissues)
a. __________
Coagulase activates prothrombin to coagulate fibrinogen in
plasma, forming a fibrin clot that “hides” the microbe from
phagocytosis
Fibrinase
b. ___________
breaks down blood clots in order to spread
Hyaluronidase “spreading factor” breaks down hyaluronic acid
c. _____________
(loose connective tissue), allowing organism to invade tissues
The effects of Hyaluronidase can be drastic!
Late stage necrosis of epidermis, subcutaneous layers, fascia, and
musculature of upper lateral leg. Necrosed peripheral nervous tissue
results in no perception of pain at wound site!
G. Development of Disease
Incubation period (between infection and 1st signs/symptoms)
1. __________
Depends on dose of microbes, which microbes, virulence, host health
a. typhoid fever 10-14 days
b. AIDS 10 years! (allows more spreading!)
Prodromal period of 1-2 days follows incubation in some
(2). _________
malaise _______,
fatigue
diseases (= early, mild signs/symptoms such as _______,
muscle aches etc. )
____________,
Death
3. Illness
______ period when the disease is acute and ______most
likely
Chills
a. _______/______
Fever
Leukocytes (> 10,000/ml)
b.  numbers of ___________
nodes
c. swollen lymph
_____ _____
d. Nausea/diarrhea
______________
Rashes/lesions
e. ____________
pain
f. severe ____
4. Recovery
Decline period (1-few days) when signs/symptoms are subsiding
________
BUT most susceptible to secondary, Opportunistic
___________ infections
Convalescent period needed to regain strength
____________
H. Disease Terminology
Local infection (limited to point of entry)
1. _____
boil wart
Vs
Focal infection (spreads to a new location) rabies Hepatitis A
_____
Vs
appendicitis
tonsillitis
Systemic
________ (infection that spreads to several sites and the blood)
syphilis
Acute diseases develop fast but for a short duration influenza
2. ______
cold
Tooth abscess
measles
chickenpox
Vs
Chronic diseases develop slow but for a long duration TB leprosy
_______
Vs
______ diseases may be inactive for long periods of time Cold sores
Latent
Genital herpes
3. Diagnosis
________ (identification) of a disease is dependent upon:
Symptoms
_________ of a disease are subjective changes in body function
sore throat
Vs
pain
aches
malaise
_____ of a disease are objective (measurable) changes
Signs
fever
rash
lesions
edema
inflammation
A _________
Syndrome is a group of symptoms/signs characteristic of a
certain disease. Rubella syndrome
A Subclinical
_________ infection is asymptomatic,
but patient is still infectious
(more common in children)
I. Exit by means of
1. Sneeze
______/_______
Cough
Insect bites
Diarrhea
2. ________
4. ____________
Sex!
Pus /_______
3. ____
5. _____
Blood
J. Survival outside long enough to gain entry into a new host
1. Some can also live in the environment Clostridium tetani
2. Some are hardy and can survive for as long as several weeks
before a new host comes along Mycobacterium tuberculosis
reservoirs Rabies, RMSF
3. Some hang out in animal__________
4. Some require direct contact b/c they are fragile Treponema
pallidum
K. Pathogenesis depends on many factors
1. Genetics, both species and individual
2. state of host health
3. age (_______&
less capable immune systems)
Elderly
Infants ________have
4. ________
Stress (causes  corticosteroids that are immunosuppressive)
Epidemiology: The study of Disease in
Populations
Epidemiology = study of frequency and distribution of disease in
IV. ___________
order to set guidelines for disease prevention and control.
= like detective work to determine the cause, reservoirs, transmission,
portals of entry/exit, etc.
Case reporting is essential to make predictions
A. ____________
Centers for Disease Control & Prevention (CDC)
1. National ________________________
located in Atlanta, Georgia
& Mortality Weekly Report (MMWR) tracks over
2. Morbidity
_______________________________
50 diseases carefully b/c hospitals, Drs., coroners, etc. REPORT
them: AIDS, STDs (such as gonorrhea, syphilis, Herpes), measles,
tetanus, TB, hepatitis, rabies, chicken pox, malaria, etc.
www.cdc.gov/mmwr/
Health Organization (WHO) plans which diseases will
3. World
_______________________
be targeted for eradication (such as smallpox, accomplished in 1979,
and polio, targeted for 2009).
B. Epidemiologic Statistics: Frequency of Cases
1. __________
Prevalence = total number of existing cases with respect to the
entire population (usually expressed as a __________);
percentage
a “snapshot” to help assess the overall impact of a disease
example: 100 people have a disease…………..
a. out of 500,000 people (0.02%) not a big deal, but
b. out of 500 people (20%) is a big deal
Incidence # of ____
new cases in a specific time period compared
2. _________
with the general healthy population (usually expressed as # cases
per 100,000 people)
risk of infection
a. indicates both the _____
rate and ____
Disease rate
Morbidity rate or ________
b. also called the__________
A class of 50 students w/o influenza (P & I both 0 because 0/50 have
influenza) becomes exposed to influenza
1st week, 5 students become ill.
2nd week 5 more students become ill
2nd week 5 more students become ill
w/ 1st 5 students recovered
1 in 10
% and I = __
P = 10
____
1 in 10
20% and I = __
P = ____
1 in 10
10% and I = __
P = ____
Incidence of pneumococcal disease (per 100,000 people)
3. _________
Mortality rate = percentage of people who die from a disease
4. Terms that describe disease frequency
Endemic = a disease that is always present in a population
a. _________
(steady frequency) common cold
b. Sporadic
________ = a disease that only pops up occasionally at irregular
intervals in random locales Typhoid fever
diphtheria
Epidemic = a lot of people get a disease in a short time
c. _________
(increasing frequency) Chlamydia
Gonorrhea
Pandemic = a worldwide epidemic influenza AIDS
d. _________
C. Investigative Strategies of the Epidemiologist
1. Determining Reservoirs
________ (= continual ______
source of infectious organisms)
a.Carriers
________ are asymptomatic people that can spread disease
Gonorrhea (50% of infected females are asymptomatic!)
(1). _________
Typhoid Mary
(2). ________
*precautions can be taken:
*if humans are the only reservoir, it should be easier to control
3. _________
Mortality rate = percentage of people who die from a disease
4. Terms that describe disease frequency
Endemic = a disease that is always present in a population
a. _________
(steady frequency) common cold
b. Sporadic
________ = a disease that only pops up occasionally at irregular
intervals in random locales Typhoid fever
diphtheria
Epidemic = a lot of people get a disease in a short time
c. _________
(increasing frequency) Chlamydia
Gonorrhea
Pandemic = a worldwide epidemic influenza AIDS
d. _________
C. Investigative Strategies of the Epidemiologist
1. Determining Reservoirs
________ (= continual ______
source of infectious organisms)
Carriers are asymptomatic people that can spread disease
a. ________
Gonorrhea (50% of infected females are asymptomatic!)
(1). _________
Typhoid Mary
(2). ________
*precautions can be taken:
Don’t go out
Don’t kiss
Don’t drink after Don’t have sex!
*if humans are the only reservoir, it should be easier to control
b. Nonhuman animals
biological vector (part of the pathogen’s life cycle) mosquitoes
(1) ________
mechanical vector (just carriers) cockroaches
(2) _________
houseflies
Zoonosis = an animal disease we can get
(3) _________
rabies
anthrax
plague
RMSF
A fly walked on
the agar surface!
Environmental (soil, water, food)
c. ____________
tetanus cholera
Salmonella
2. Terms for transmission of infectious agents
a. Communicable
___________ diseases are spread from one person to another
Herpes
measles
Common cold
Contagious if easily spread
b. Communicable diseases are called _________
Chickenpox
c. Noncommunicable
______________ diseases (you cannot get them from another
person)
tetanus
botulism
3. Patterns of communicable disease transmission
Direct
a. _______(Physical,
person-to-person) “A portal of exit meets a
portal of entry!” touch kiss sex Respiratory droplets/sneeze,
 1 meter (close proximity) common in crowds, elevators
cough
Vertical spread (mother to fetus/infant) Rubella, STDs
(1) _______
Horizontal spread (anybody else to anybody else)
(2) _________
Indirect
b. ________
Fomites (inanimate objects) toys
(1) _______
used kleenex
eating utensils
needles
Door knobs
Toilet seats
food
(2) ______/______
water (especially GI parasites) (This transmission
Preparation fecal-oral)
Source or from __________;
can be from the ________
Salmonella eggs/chicken
Typhoid Mary
(3) _______
Droplet nuclei (small, dried up on dust, carried by air currents)
*
*
*
*
good ventilation helpful (dilutes)
air filters help trap
pressurized air (out of operating rooms)
damp mops better than brooms
D. Areas of Epidemiology
1. _________
Descriptive epidemiology occurs after disease outbreak and
describes the characteristics of ill people
age
a. ____
sex
b. _____
race
c. ____
d. _________
occupation
lifestyle Smoker? Drug use? Sexual activity?
e. ________
Home location (to help figure out reservoirs)
f. ___________
Timing
g. ______
#
#
* Common Source Epidemic
* Propagated Epidemic
c
a
s
e
s
time
c
a
s
e
s
time
Analytical epidemiology then determines which risk factors
2. _________
[identified by descriptive studies] are actually relevant by
comparing those with the disease to those without the disease
_________