Transcript PRINCIPLES OF DISEASE Symbiosis • Relationship between 2 or more species • Mutualism- both benefit,

PRINCIPLES OF DISEASE
Symbiosis
• Relationship between 2 or more species
• Mutualism- both benefit,
Symbiosis
• Commensalism-one benefits and other
unaffected
Parasitism
• One benefits at expense of other
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Pathogen-causes disease
Metabolically unstable relationship
Host dies or eliminates pathogen
Most successful parasites
Parasitism
• Host under continuous pressure from infection
• Battle between host & parasite
• Emergence of new & return of old infectious
diseases
Pathogenicity
• Capacity to produce disease
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Adherence
Multiply on host
Ability to invade host or cause damage
Avoid being damaged by host’ defenses
Depends upon # of organisms
Virulence
• Intensity of disease produced
Terms
• Contamination
• Infection- multiples and invades tissue
• Disease- disrupts state of health
Normal Flora
• 1 x10 13 body cells with 1 X1014 bacterial cell
• Resident flora always present
Normal Flora
• Resident flora
• Transient flora
Opportunists
• Usually cause no disease
• Conditions allow them to cause disease
Opportunists
• Intro of bug into unusual body sites
• Disturbance of normal flora
Advantage of Normal Flora
• Ensures normal development of immune
system
• Prevent over growth of harmful organismmicrobial antagonism
Microbial Antagonism
• Normal flora in colon prevents overgrowth
of C. difficile
• E. coli produces bacteriocins
Disadvantage of Normal Flora
• Potential for spread into sterile parts of
body
• Intestine may perforate
• Skin broken
• Extraction of tooth
• Perianal skin flora enters urinary tract
Etiology
• Cause of disease
• Koch’s postulates-organism causes disease
Frequency of Disease
• Endemic
– Always present in population
• Epidemic
– Occurs in unusually high number of people
• Pandemic– Epidemics world wide
Types of Infectious Diseases
• Acute -develops rapidly but lasts for short
time- influenza
• Chronic disease -develops more slowly and
continues or recurs for long periods -TB,
hepatitis B
• Latent- agent remains inactive for a time
and later becomes active-shingles
Herd Immunity
• Proportion of people in community who are
immune
• Important in cyclic diseases
• If high, disease can only spread among
susceptible people
• Loss of herd can lead to reemergence of
disease
Extent of Disease
• Local infection-limited to small area of
body- boils
• Focal - starts as local infection (sinus or
teeth) then enter blood or lymph and
spreads
• Systemic -organisms or products spread
through out body-measles
• Bacteremia- presence of bacteria in blood
Extent of Disease
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Septicemia-bacteria multiplies in blood
Toxemia-toxins in blood
Viremia-virus in blood
Subclinical (inapparent )- no noticeable
illness-hepatitis A
• Primary disease- initial acute infection
• Secondary infection -opportunistic infection
Stages of Disease
• Incubation period-time between initial
infection and first appearance of S&S
Prodromal Period
• Short period–only in some diseases
Invasive Period
• Period of illness-most acute
• Overt signs and symptoms
• Cough, sore throat
Decline/Convalescence
• S&S subside
• Regain strength and recovery
Epidemiology
• Study of mechanism and factors involved in
the frequency and spread of disease
• Incidence of diseases
• Prevalence of diseases
Chain of Infection
Susceptible
Host
Elderly & Young
Pts w/ Chronic Illness
Diabetic
Use of Invasive Equip
Infecting
Agents
Bacteria
Parasites
Viruses
People Food
Equipment
Entry
Broken Skin
Respiratory System
GI & GU System
Reservoir
Portal of Exit
Direct Contact
Indirect Contact
Transmission
Airborne
Droplet
Respiratory System
GI & GU System
Spread of Disease
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Chain of infection
Agent- pathogen
Reservoir-source/site of organism
Human reservoirs
• Animal reservoirs -zoonoses
Humans
• Sick people
• Carriers
– Incubatory or asymptomatic carriers
• HIV but not AIDS
• Hepatitis C
– Chronic carriers
• Typhoid Mary excreted salmonella for years in feces
• S. pyogenes in throat
Animals
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Domestic and wild
Mammals carry rabies-exposure to saliva
Consume contaminated animals or products
Arthropod borne-West Nile
Zoonoses
– Lyme disease: wild deer and mice
– Hantavirus pulmonary disease: rodents
Environmental Reservoirs
• Able to survive in nonliving reservoirs
• Soil: C. tetani
– Humans produces toxin
– Survives in soil by forming endospores
• Contaminated water
Portal of Exit
• Via body fluid or feces
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Respiratory tract
GI
GU
Nonintact skin-lesions, wounds
Modes of Transmission
• Airborne
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Tiny droplet nuclei vs large droplets
Dust particles
Suspended in air don’t fall
More likely to reach lower resp tract
Resistant to drying
• TB, measles and chicken pox
– Spread rapidly in crowded conditions
Droplet
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Large droplets, short distances
Mucous droplets -coughing , sneezing
Pertussis, influenza, SARS
Talking less transmission
Contact
• Direct- person to person, touching ,sex,
colds
– Horizontal transmission
– Fecal-oral transmission especially if public
health & hygiene lacking
Contact
• Vertical
– Parent to offspring-birth canal, breast milk,
placenta
• Indirect-via fomites-tissues, diapers , door
knobs- hands
– Normal person sheds skin atrr rate of 5 x10 8
per day
• Hep B, C, D, lice, STDs
Vehicle
• Via medium-water, food, blood - Shigella in
water or food, S. aureus
• Vector-arthropod
– Mechanical-passive
– Biological- active
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Portals of Entry
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Respiratory
GI - in food and water
GU-sexually transmitted microbes
Non intact skin- parenteral
Susceptible Host
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Imunocompromised
Old age or young
Not vaccinated
Large inoculum
Healthcare Infections
• Healthcare acquired
– Exogenous
– Endogenous
Consequences
• Serious illness or death
• Prolonged hospital stay
• Need for antimicrobial therapy
• Foci for spreading infection
Controlling Disease Transmission
• Standard precautions-everyone
• Isolation for communicable diseases or bugs
Prevention
• SSIs –prophylactic antibiotics
• Devices- central lines & ventilators
Prevention
• Quarantine
• Immunization- influenza & pneumococcal
• Vector control