Download Disease and Epidemiology

Diseases and
Epidemiology
Epidemiologists—what do they
do?
• They identify a problem, collect data, formulate and
test hypothesis
• Epidemiology is as old as medicine
• Who gets sick, why and when
• John Snow (Broadway pump) can be considered as
the father of Epidemiology
• Determine the problem (outbreak) and implement
control measurements to prevent additional disease
• Often described as “disease detective”
Definitions
Disease: occurs when an infection results in an
abnormal state of health
Pathology: concerned with the cause of disease
Infection: is the invasion or colonization of the
body by pathogenic microorganism
Normal Microbiota
•Animals, including humans, are generally free
of microbes in utero
•At birth, a normal/characteristic microbial
population will begin to establish itself
•The newborn’s first contact with MO is usually
lactobacilli, which multiply rapidly prior birth
•More MO are introduced as the newborn
breathes and feeding begins
Normal Microbiota
•Many usually harmless MO establish
themselves inside other parts of the adult body
& on its surface
•Typical human body contains 1x1013 body
cells, yet harbors 1x1014 bacteria
•Normal flora does not produce disease
•Transient microbiota are present for
days/weeks/or months and then disappear
Normal Microbiota
•Microbial antagonists: once established the
normal biota can benefit the host by preventing
the overgrowth of harmful MO
•It involves competition among MO
Relationship btw the normal
microbiota and the host
•Presence of normal microbiota in the adult
human vagina maintains a local pH of 3.5-4.5 &
prevents overgrowth of the yeast Candida
albicans
•If the bacterial population is eliminated by
antibiotics, excessive douching or deodorants,
the pH of the vagina reverts to neutral and C.
albicans flourishes
Definitions
Symbiosis: living together---relationship btw host
& normal microbiota
Commensalism: one of the organism is
benefiting –the other one is unaffected
Mutualism: is a type of symbiosis that benefits
both organisms I.e. the large intestine has E.coli,
that synthesizes vitamin K and some B vitamins
These vitamins are absorbed into the bloodstream
Opportunists
•Opportunistic pathogens: they do not cause
disease in their normal habitat in a healthy
person, but will in a different environment
•MO that gain access through broken skin or
mucous membranes can cause opportunistic
infections
•Or if the host is already weakened or
compromised by infection (AIDS)
The Etiology of Infectious
Diseases
•Some disease—polio/Lyme disease or TB
have a well known etiology
•The etiology of Alzheimer’s disease is
unknown
•Hemophilia is an inherited disease
•Osteroarthritis are degenerative diseases
Koch’s postulates
•In 1877 he published some early papers on
anthrax, a disease of cattle that can occur in
humans
•He demonstrated that Bacillus anthracis, were
always present in the blood of animals that had
the disease and were not present in healthy
animals
•Koch showed that a specific infectious disease
(anthrax) is caused by a specific MO that can be
isolated and cultured on artificial media
Koch’s 4 postulates
1. Same pathogen must be present in every
case of the disease
2. Pathogen must be isolated from the diseased
host & grown in pure culture
3. Pathogen from pure culture must cause
disease when it is inoculated in a healthy
animal
4. Pathogen must be isolated from inoculated
animal & must be shown to be the original
MO
Classifying Infectious Diseases
•Symptoms: changes in body function
(pain/malaise)
•Signs: are objective changes the physician can
observe & measure
•Syndrome: specific group of symptoms or
signs
•Communicable disease: disease that spreads
from one host to another, either directly or
indirectly (chickenpox, measles, gentical herpes)
Patterns of Disease
Sporadic Disease : typhoid fever in the US—
disease occurs occasionally
Endemic: a disease constantly common in a
poplulationcommon cold
Epidemic : influenza
Pandemic : an epidemic disease that occurs
worldwide (influenza)
Development of Disease
Reservoir: for a disease to perpetuate itself
there must be a continuous source either living
or an inanimate object that provides the
pathogen with adequate conditions for survival
& multiplication
Classifying Infectious Diseases
Communicable disease: disease spreads from
host to host (TB, typhoid fever, gential herpes)
Noncommunicable diseases: Clostridium tetani
produces disease only when introduced into the
body via abrasions or wounds
Acute disease: develops rapidly but lasts only a
short time (influenza)
Chronic disease: develops more slowly, and the
body’s rx’s may be less severe (Mono, TB and
Hepatitis B)
Primary infection: is an acute infection that
causes initial illness
Secondary infection: is one caused by an
opportunistic pathogen after primary infection
has weakened the body’s defenses
(Pneumocystic pneumonia –AIDS)
3 types of transmission categories
Direct contact: person-to-person (touching,
kissing) (common cold/influenza, measles,
scarlet fever)
Indirect contact (fomites):contaminated
syringes, toys, thermometers (Hep B and tetanus)
Droplet transmission: mucus droplets that travel
short distances (1m)—sneeze contains 20,000
droplets (influenza, pertussis (whooping cough)
5 types of vehicle transmission
Waterborne: pathogens are spread by
contaminated H2O or poorly treated sewage
Food-borne: foods that are incompletely
cooked, poorly refrigerated or prepared under
unsanitary conditions
Foodborne: Mother was changing the diapers of her infant and returned
to canning products for the church picnic and the individual purchasing
the last batch of the canned items became sick;
Foodborne infections: Didn't anyone know?
Airborne transmission: spread of agent by
droplet nuclei in dust that travels >1m
Mechanical transmission: passive transport
of the pathogen on the insect’s feet or other
body parts (houseflies can transfer typhoid
fever and bacillary dysentery (shigellosis)
from the feces
Biological transmission: active process/ is
more complex---arthropod (insect) bites an
infected person or animal & ingests some of
the infected blood—(Plague/Lyme disease)
Nosocomial infections: infection acquired whil
staying in the hospital or nursing homes
•Prevention: aseptic techniques such as Lister
and Semmelweis & use of disposable materials
•2 Mio people per year contract nosocomial
infections & nearly 90,000 die as a result
•MO in the hsp environment
Combo of all
•Compromised status of host
3 poses
•Chain of transmission
significant
risk
Four different stages in the
development of disease
1. Compromised host (cancer, surgery, HIV+)
2. Microorganisms in the hospital (antibiotic
resistant ones & higher prevalence due to
environment)
3. Nosocomial infections (urinary tract, surgical
site, lower respiratory, bacteremia & skin
infections)
4. Chain of transmission (direct/indirect contact
w/ medical personel, fomites & ventilation
system)