Disease and
Epidemiology
What is Disease?
 Any condition that jeopardizes
the survival of an organism in
a particular environment
What is epidemiology?
The study of the causes,
distribution, and control of disease
in populations.
Some Characteristics of
Disease
 Change of normal appearance,
behavior, or movement
 Fever
 Dull, inflamed eyes
 Rough-soiled hair, fur or
feathers
 Difficulty walking or running
 Abnormal lumps
 Discoloration/lesions of skin
Disease causing entities
 Any agent that may bring abnormal
condition to any or all of the tissues of
the body via eggs, contact, food or a
vector
 2 Types of disease causing entities:
 Infectious agents – caused by a
pathogen (bacteria, virus, parasites etc),
invade the body and multiply there.
 Noninfectious agents –caused by
something other than pathogens.
(carcinogens, environmental, etc.)
Infectious Agents
-pathogen – an infectious
disease causing agent
 Bacteria
 Viruses
 Parasites
 Prions (Mad
Cow
Disease)
Noninfectious agents
 Injuries
 Mutations, genetic
 Poisons and
chemicals
 Poor nutrition
For disease to occur and spread
certain conditions must be met
Chain of infection
To grow and spread,
most microorganisms
prefer
 Warm, dark
environment
 Moisture
 Source of food
 Human body fits the
criteria!
2. Reservoir
 A place the pathogen
can live
 Human body
 Animals
 Environment
 Fomites:
contaminated
inanimate objects-
3.Portal of Exit
 Way of leaving the
reservoir in which it
has been growing:
 Blood
 Tears
 Feces
 Urine
 Saliva
 Draining wounds
4. Means of Transmission Needs to be
transported to another
reservoir
Direct person to person
contact- contaminated
hands most common
Indirect contactcoming in contact with
contaminated
equipment, food,
insect bite
5. Portal of Entry
 Breaks in skin
 Breaks in mucous
membranes
 Respiratory tract
 Digestive tract
 Circulatory system
 Genitourinary tract
How your body fights off a
causative agent








Mucous membranes-trap
Cilia – transport.
Coughing and sneezing-- expel
Hydrochloric acid in the stomach-- destroy
Tears in the eyes-bacteriocidal
Fever-destroy
Inflammation-white cells
Immune response-antibodies
Antibodies and antigens
6. Susceptible host
 Large numbers of
pathogens.
 Body defenses are
weak
Results in susceptible
host, or a person
likely to get an
infection or disease
Chain of infection can
be broken at any
point
The spread of infectious diseases
1.
2.
3.
4.
DIRECT CONTACT: touching or other direct contact with
bodily discharges, secretions or waste, an open wound,
bandage, soiled objects or infected surface; STD, blood
borne
FECAL-ORAL – eating or…….
ASYMPTOMATIC CARRIER – an infected person such
as“Typhoid Mary”
VEHICLE An inanimate object which serves to
communicate disease. For example, a glass of water
containing microbes, or a dirty rag, etc.
5. VECTORS (such as arthropods – “bugs”) VECTOR – A
live organism that serves to communicate disease. For
example, mosquitoes and other arthropods.
6. Airborne/droplet
two types of vectors: mechanical and biological.
Microbes do not multiply within mechanical vectors
- only physically transport microbes from host to
host. In contrast, microbes must propagate within a
biological vector before it can transmit the
microbes.
 mosquito (malaria, St. Louis encephalitis, dengue
fever, yellow fever, West Nile virus)
 flea (bubonic plague)
 tick (Lyme disease, rocky mountain spotted fever,
tick-borne encephalitis)
 deer mouse (hantavirus)
 kissing bug (Triatominae) (Chagas Disease)
 bat(Rabies)
 “Typhoid Mary” Mallon -- was a cook in the New York
City in the 1900s
 she infected 22 people with typhoid fever, one of whom
died. Eventually estimates ran as high as 50 deaths
attributed to her.
 Dr. George Soper interviewed Mary, and suggested
there might be a connection between the dishes she
served and the outbreaks of typhoid.
 After forcibly obtaining urine and stool samples, it was
revealed she was an asymptomatic carrier of typhoid
salmonella
 In 1915, a serious epidemic of typhoid erupted among
the staff of New York's Sloan Hospital for Women, with
twenty five cases and two deaths. City health authorities
investigated.
 Mary was quarantined for life on North Brother Island.
She became something of a celebrity, and was
interviewed by journalists (who were forbidden to accept
as much as a glass of water from her.) She died in 1938
of pneumonia.
Charting the Spread of a
Disease
*Investigator must
work backwards to try
and determine
the index case
*The mode of
transmission/vector
*The “waves” of
infection
Incubation Period
Time period before signs
and symptoms appear
The delay is used for the
pathogen to multiply
Varies with each
disease:
Colds about 7 days
HIV can be 10 years
Infectious Disease
Causing Agents
 Pathogen - a disease causing agent (example:
bacteria, viruses)
 Virulence – ability of a pathogen to overcome
the body’s defense & produce a disease
 Host – any organism serving as a residence for
a pathogen
 Vector – agent/entity that delivers a pathogen
to a host, intermittent host
Bacteria
 Smallest & simplest
form of life
 prokaryotic
 Single-celled
 Have a cell wall
 Vary in size & shape
 Many are beneficial
 decompose and
recycle nutrients
 Foods – yogurt, wines,
cheese
 Aid in digestion
Bacteria Characteristics
1. Two Domains:
Archaebacteria – live in
extreme conditions
Eubacteria – all other bacteria
Distinguishing
Characteristics
of Bacteria
 2. Oxygen need
 No oxygen (anaerobic)
– such as botulism,
tetanus
 Oxygen required
(aerobic)
 Facultative anaerobic –
prefers oxygen, but can
survive in anaerobic
conditions
3. Prokaryotic
No membrane
bound
organelles
such as a
nucleus or
mitochondria
Microscopic How big are bacteria?
4. ________________
http://www.cellsalive.com/howbig.htm
5. Where do they live?
Archaebacteria - live in extreme harsh environments – hot
temperatures, extreme salinity for example and include halophiles,
methanogens, thermophiles, sulfophilic strains
Eubacteria - bacteria we encounter on a daily basis – E. coli for
example
6. Shape:
Spherical - cocci
Helical or Spiral
b.
a.
Rod - bacillus
Vibrio– comma shaped
c.
7.
Staphylococcus
Streptococcus
8. Have Cell Walls -Some are rigid, Some flexible
9. Form Endospores in Harsh Conditions
Distinguishing
Characteristics of
Bacteria
 Cell wall absorb “gram’s stain”?
 Gram positive – retain stain in cell walls
 Gram negative – characteristic of many
pathogenic strains, may not always respond
to anitbiotics
 Ability to release toxins – waste products
from metabolism
 http://www.microbelibrary.org/microbelibrary/files/ccIma
ges/Articleimages/keen/Gramstainkeen.htm
Bacteria release
toxins…………not good!!
1. Chemical substances harmful to the normal
functioning of cells
- Endotoxins – parts of bacterial cells
- Exotoxins – wastes from bacterial cells
Neurotoxins
2. _______________- disrupt the transmission of
nerve impulses.
Bacteria divide by Binary Fission
Bacteria exchange genetic information by
conjugation
-- no new cells are created
-- leads to exchange of antibiotic genes
http://www.hhmi.org/biointeractive/animations/conjugation/conj_frames.htm
Bacterial Diseases
1. Anthrax respiratory infection initially presents
with cold or flu-like symptoms for
several days, followed by severe
(and often fatal) respiratory collapse
Cutaneous
Inhalation
2. Tuberculosis
3. Typhoid fever - caused by the bacterium
Salmonella Typhi. Common worldwide, it is transmitted by ingestion of
food or water contaminated with feces from an infected person.
4. Diphtheria an
upper respiratory tract illness
5. Botulism
6. Tetanus
7. Gonorrhea
STD
8. Syphilis
STD
9. Chlamydia
STD
Bacterial Disease
Treatments
b. products of fungus or competing bacteria
-- Ex: Penicillin, erythromycin, kanamycin,
tetracycline……
mutate
a. Bacteria can _______________to become
resistant to antibiotics
ANTIBIOTICS
a. Inhibit growth of some bacteria – may disrupt cell
walls, or other metabolism
Helpful Bacteria
Make milk into yogurt!
Make antibiotics!
Treat Wastewater!
Aid Digestion!
Pesticide Control!
Also--
© Eric MacDicken
Decomposers/ Natural Cycle!
Bioremediation!
Food/Preservatives!
VIRUSES
Viruses
 Microscopic in size – smaller than
bacteria
 Not considered to be living
 Can cause serious, contagious
disease
 Classified by




type of tissue they invade,
appearance,
host they normally infect
Type of genetic material – DNA or RNA
Virus Characteristics
DNA
inside
Chicken Pox
Human Influenza
Rabies Virus
HIV
Viruses – Structure
 Protein coat
 geometric shapes
 Receptor proteins to match virus with
specific host cell
 Genetic element
 Either DNA or RNA strand
Two Types of Viruses
a. Lytic (virulent)
b. Lysogenic (temporal) –
“dormant”
http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter17/an
imation_quiz_2.html
http://www.cfoxscience.com/mrfox/apbio/Lectures/lys
ogenic_pathway.swf
LYTIC CYCLE
 Viral genetic element (DNA or RNA)
becomes part of host cell DNA
 Host cell produces new viruses
 Cell lyses (is destroyed) thereby
releasing viruses to invade other host
cells
a. Virulent
--Causes disease immediately
Lytic Cycle of a Virulent Virus
Infectious Diseases:
Viral Infection
http://www.bio.cmu.edu/Courses/03121/moovies/Lytic.mov
Virus Reproduction Process
a.Absorption
b.Entry
c. Replication
d.Release
b. Temporal
--Does not cause disease
immediately
Lysogenic Cycle of a Temperate Virus
Remains in cell
Activated to produce
new viruses
http://www.bio.cmu.edu/Courses/03121/moovies/Lysogenic.mov
LYSOGENIC CYCLE
 Considered to be “dormant”
 Is replicated via host cell’s mitotic
cycle
 May become lytic if induced by a
stimulus (such as a chemical
imbalance or environmental stress)
Retrovirus
 http://www.whfreeman.com/kuby/content/an
m/kb03an01.htm
 http://www.pbs.org/wgbh/evolution/library
/10/4/l_104_05.html
Dr. Stephen O'Brien's work with HIV led to a discovery that
could one day help scientists treat or prevent HIV infection:
People from some European populations carry a genetic
mutation that prevents HIV from entering their white blood
cells. O'Brien hypothesizes that this mutation, dating back 700
years, may have been a selective advantage during the
bubonic plague, as it is today, with the onslaught of HIV. From
Evolution: "Evolutionary Arms
Are viruses living?
What are all living things made of?
-- don’t have complete cell parts
What do all living things need?
-- need energy from host cell
How does environment affect living things?
-- do not respond to a stimulus
How do living things reproduce?
-- need host cell to replicate
Viral Diseases
Common Cold
1. ___________________
* 200 kinds of Viruses
Symptoms include nasal discharge, obstruction of nasal
breathing, swelling of the sinus membranes, sneezing, sore
throat, cough, and headache.
Polio
2. ________________
•Poliomyelitis is a crippling disease of
spinal nerve cells caused by poliovirus
infection.
•The disease can strike non-immune
persons of any age but affects mainly
children under the age of three, and
causes paralysis in one case of every
200 to 1000 infections.
•Preventable by vaccination.
Tobacco Mosaic
3. ______________________
Symptoms induced can include mosaic,
mottling, necrosis, stunting, leaf curling, and
yellowing of plant tissues.
AIDS
4. ___________
STD
Acquired immunodeficiency syndrome, is caused by the
human immunodeficiency virus, or HIV.
HIV destroys the body's ability to fight infections by
attacking cells of the immune system.
Rabies
5. ______________
The vast majority of cases
reported to the Centers for
Disease Control and
Prevention (CDC) each
year occur in wild animals
like raccoons, skunks,
bats, and foxes.
Infects the central nervous
system, causing
encephalopathy and
ultimately death.
Cold Sore
6. ______________
(Herpes simplex )
STD
potential
Between 50 - 80% of all people possess this virus and is spread
through direct contact with an infected individual.
Once the virus has entered the body, it cannot be removed.
Only 10% of HSV1 infected people ever develop a sore.
Shingles
7. _____________
An acute infection
caused by a activation of
the varicella zoster virus,
which also causes
chicken pox.
It usually occurs during adulthood after exposure to
chicken pox in childhood. The chicken pox virus
remains dormant in the body.
Measles
8. _____________
Most infected children will have a
rash, high fever, cough, runny nose,
and watery eyes.
For every 1,000 children who get it,
1 or 2 will die from it
Spreads so easily that any child
who is not immunized will probably
get it, either now or later in life.
Warts
9. ___________
STD
Non-cancerous skin
growths caused by a
viral infection in the top
layer of the skin. Viruses
that cause them are
called human
papillomavirus (HPV).
STD
Herpes
10. _______________
HSV-2 usually produces only mild
symptoms or signs or no symptoms at
all.
However, HSV-2 can cause recurrent
painful genital sores in many adults, and
HSV-2 infection can be severe in people
with suppressed immune systems.
Regardless of severity of symptoms,
genital herpes frequently causes
psychological distress in people who
know they are infected.
Hepatitis B
11. _____________
The most common serious liver infection in the world.
It is caused by the HBV virus that attacks the liver.
HBV is 100 times more infectious than the AIDS virus. Yet, can be
prevented with a safe and effective vaccine.
Treatment, Prevention
AND Defense
1. First Level of Response: skin, mucous
linings of respiratory tract
Treatment/Prevention/Defense
(cont’d)
2. Vaccine
Vaccine Given
Anitbodies Produced
3. Interferon – special proteins
produced as immune response
which in turn induce immune
response cells to attack the
antigens (viruses and bacteria)
Guard/Fight Real
Disease
4. Fever – elevated body temperature enhances
immune response
5. Antigen – foreign
substance that induces
immune response
6. Immunity
http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/phag
ocyt.html
http://highered.mcgrawhill.com/sites/0072495855/student_view
0/chapter2/animation__phagocytosis.ht
ml
7. Phagocytosis – the
digestion of an
antigen by an
immune response
cell
http://www.sp.uconn.edu/~terry
/Common/phago053.html
Other causes of disease…
 Parasites –
--Organism living
on, in, or at the
expense of
another living
organism
Types of parasites
 Protozoa
 Single celled
 Helminths (worm parasites)
 Multi-cellular
 Tape worms, Round worms, leeches (segmented
worm) – most roundworms are GOOD!!
 Arthropods – ticks, fleas, bed bugs, flies,
mosquitoes
 Act as vectors (carriers of disease)
 Fungi
Six arthropods that affect
mammals
 Flies
•Mosquitos
•Ticks
•Fleas
•Lice
•Mites