Download Microbiology - Imperial Valley College

Chapter 14
Principles of
Disease
and Epidemiology
© 2013 Pearson Education, Inc.
Copyright © 2013 Pearson Education, Inc.
Lectures prepared by Christine L. Case
Lectures prepared by Christine L. Case
© 2013 Pearson Education, Inc.
Pathology, Infection, and Disease





Pathology: the study of disease
Etiology: the study of the cause of a disease
Pathogenesis: the development of disease
Infection: colonization of the body by pathogens
Disease: an abnormal state in which the body is
not functioning normally
© 2013 Pearson Education, Inc.
Normal Microbiota and the Host
 Transient microbiota may be present for days,
weeks, or months
 Normal microbiota permanently colonize the host
 Symbiosis is the relationship between normal
microbiota and the host
© 2013 Pearson Education, Inc.
Figure 14.1 Representative normal microbiota for different regions of the body.
Bacteria (orange
spheres) on the surface of
the nasal epithelium
© 2013 Pearson Education, Inc.
Bacteria (brown)
on the lining of the stomach
Bacteria (orange)
in the small intestine
Symbiosis
 In commensalism, one organism benefits, and the
other is unaffected
 In mutualism, both organisms benefit
 In parasitism, one organism benefits at the
expense of the other
 Some normal microbiota are opportunistic
pathogens
© 2013 Pearson Education, Inc.
Table 14.1 Normal Microbiota on the Human Body
Eyes (conjunctiva)
Nose and throat
(upper respiratory
system)
Mouth
Skin
Large intestine
Urinary and
reproductive
systems (lower
urethra in both
sexes and vagina
in females)
© 2013 Pearson Education, Inc.
Normal Microbiota and the Host
 Microbial antagonism is a competition between
microbes
 Normal microbiota protect the host by
 Occupying niches that pathogens might occupy
 Producing acids
 Producing bacteriocins
 Probiotics: live microbes applied to or ingested
into the body, intended to exert a beneficial effect
© 2013 Pearson Education, Inc.
Koch’s Postulates
1. The same pathogen must be present in every
case of the disease.
2. The pathogen must be isolated from the diseased
host and grown in pure culture.
3. The pathogen from the pure culture must cause
the disease when it is inoculated into a healthy,
susceptible laboratory animal.
4. The pathogen must be isolated from the
inoculated animal and must be shown to be the
original organism.
© 2013 Pearson Education, Inc.
Figure 14.3 Koch’s Postulates: Understanding Disease.
1 Microorganisms are
isolated from a diseased
or dead animal.
2a The microorganisms are
grown in pure culture.
3 The microorganisms
are injected into a healthy
laboratory animal.
Colony
2b The microorganisms
are identified.
4 Disease is reproduced
in a laboratory animal.
5a The microorganisms are
isolated from this animal
and grown in pure culture.
5b Microorganisms
are identified.
The microorganism from the
diseased host caused the same
disease in a laboratory host.
© 2013 Pearson Education, Inc.
Koch’s Postulates
 Koch’s postulates are used to prove the cause of
an infectious disease
 Some pathogens can cause several disease conditions
 Some pathogens cause disease only in humans
© 2013 Pearson Education, Inc.
Classifying Infectious Diseases
 Symptom: a change in body function that is felt by
a patient as a result of disease
 Sign: a change in a body that can be measured or
observed as a result of disease
 Syndrome: a specific group of signs and
symptoms that accompany a disease
© 2013 Pearson Education, Inc.
Classifying Infectious Diseases
 Communicable disease: a disease that is spread
from one host to another
 Contagious disease: a disease that is easily
spread from one host to another
 Noncommunicable disease: a disease that is not
transmitted from one host to another
ANIMATION Epidemiology: Overview
© 2013 Pearson Education, Inc.
Occurrence of a Disease
 Incidence: fraction of a population that contracts a
disease during a specific time
 Prevalence: fraction of a population having a
specific disease at a given time
 Sporadic disease: disease that occurs
occasionally in a population
ANIMATION Epidemiology: Occurrence of Diseases
© 2013 Pearson Education, Inc.
Occurrence of a Disease
 Endemic disease: disease constantly present in a
population
 Epidemic disease: disease acquired by many
hosts in a given area in a short time
 Pandemic disease: worldwide epidemic
 Herd immunity: immunity in most of a population
© 2013 Pearson Education, Inc.
Figure 14.4 Reported AIDS cases in the United States.
Number of cases
120,000
Second
250,000
cases
First 250,000 cases
Third
250,000
cases
Fourth
250,000
Cases
100,000
80,000
Expansion of
surveillance
case definition
60,000
40,000
20,000
0
1979
1983
1987
1991
1995
Year
© 2013 Pearson Education, Inc.
1999
2003
2007
Severity or Duration of a Disease
 Acute disease: symptoms develop rapidly
 Chronic disease: disease develops slowly
 Subacute disease: symptoms between acute
and chronic
 Latent disease: disease with a period of no
symptoms when the causative agent is inactive
© 2013 Pearson Education, Inc.
Extent of Host Involvement
 Local infection: pathogens are limited to a small
area of the body
 Systemic infection: an infection throughout the
body
 Focal infection: systemic infection that began as a
local infection
© 2013 Pearson Education, Inc.
Extent of Host Involvement
 Sepsis: toxic inflammatory condition arising from
the spread of microbes, especially bacteria or their
toxins, from a focus of infection
 Bacteremia: bacteria in the blood
 Septicemia: growth of bacteria in the blood
© 2013 Pearson Education, Inc.
Extent of Host Involvement
 Toxemia: toxins in the blood
 Viremia: viruses in the blood
 Primary infection: acute infection that causes the
initial illness
 Secondary infection: opportunistic infection after a
primary (predisposing) infection
 Subclinical disease: no noticeable signs or
symptoms (inapparent infection)
© 2013 Pearson Education, Inc.
Predisposing Factors
 Make the body more susceptible to disease







Short urethra in females
Inherited traits, such as the sickle cell gene
Climate and weather
Fatigue
Age
Lifestyle
Chemotherapy
© 2013 Pearson Education, Inc.
Time
© 2013 Pearson Education, Inc.
Period of
illness
Period of
decline
Most severe signs
and symptoms
Signs and
symptoms
Period of convalescence
Prodromal period (mild signs or symptoms)
Incubation period (no signs or symptoms)
Number of microbes
Figure 14.5 The stages of a disease.
Reservoirs of Infection
 Continual sources of infection
 Human: AIDS, gonorrhea
 Carriers may have inapparent infections
or latent diseases
 Animal: rabies, Lyme disease
 Some zoonoses may be transmitted to humans
 Nonliving: botulism, tetanus
 Soil
© 2013 Pearson Education, Inc.
Transmission of Disease
 Contact
 Direct: requires close association between infected and
susceptible host
 Indirect: spread by fomites
 Droplet: transmission via airborne droplets
© 2013 Pearson Education, Inc.
Figure 14.6ad Contact transmission.
Direct contact transmission
Droplet transmission
© 2013 Pearson Education, Inc.
Vehicle Transmission
 Transmission by an inanimate reservoir
(food, water, air)
© 2013 Pearson Education, Inc.
Figure 14.7 Vehicle transmission.
Water
© 2013 Pearson Education, Inc.
Food
Air
Vectors
 Arthropods, especially fleas, ticks, and mosquitoes
 Transmit disease by two general methods:
 Mechanical transmission: arthropod carries pathogen
on feet
 Biological transmission: pathogen reproduces in vector
© 2013 Pearson Education, Inc.
Figure 14.8 Mechanical transmission.
© 2013 Pearson Education, Inc.
Figure 12.31 Mosquito.
© 2013 Pearson Education, Inc.
Nosocomial Infections
 Are acquired as a result of a hospital stay
 Affect 5–15% of all hospital patients
© 2013 Pearson Education, Inc.
Figure 14.6b Contact transmission.
Preventing direct contact transmission through the use of gloves, masks, and face
shields
© 2013 Pearson Education, Inc.
Figure 14.9 Nosocomial infections.
Microorganisms
in hospital
environment
Compromised
host
Nosocomial
infection
Chain of transmission
© 2013 Pearson Education, Inc.
© 2013 Pearson Education, Inc.
Common Causes of Nosocomial
Infections
Coagulase-negative
staphylococci
S. aureus
15%
Percentage
Resistant to
Antibiotics
89%
15%
80%
Enterococcus
10%
4–71%
15–25%
3–32%
13%
Not reported
Percentage of
Total Infections
Gram-negative rods
C. difficile
© 2013 Pearson Education, Inc.
MRSA
 USA100: 92% of health care strains
 USA300: 89% of community-acquired strains
© 2013 Pearson Education, Inc.
Clinical Focus 14.1 Nosocomial Infections
© 2013 Pearson Education, Inc.
Figure A The gram-positive cocci grown on mannitol-salt agar.
Clinical Focus 14.1 Nosocomial Infections
© 2013 Pearson Education, Inc.
Emerging Infectious Diseases
 Diseases that are new, increasing in incidence, or
showing a potential to increase in the near future
© 2013 Pearson Education, Inc.
Emerging Infectious Diseases
 Contributing factors
 Genetic recombination
 E. coli O157, avian influenza (H5N1)
 Evolution of new strains
 V. cholerae O139
 Inappropriate use of antibiotics and pesticides
 Antibiotic-resistant strains
 Changes in weather patterns
 Hantavirus
© 2013 Pearson Education, Inc.
Emerging Infectious Diseases
 Modern transportation
 West Nile virus
 Ecological disaster, war, and expanding human
settlement
 Coccidioidomycosis
 Animal control measures
 Lyme disease
 Public health failure
 Diphtheria
© 2013 Pearson Education, Inc.
Clinical Focus 13.1 Influenza: Crossing the Species Barrier
Avian
gene pool
1918 H1N1
Human H3N2
North American swine
Triple reassortment
H1N2
Eurasian
swine H1N1
2009 H1N1 pandemic
© 2013 Pearson Education, Inc.
Epidemiology
 The study of where and when diseases occur
 Centers for Disease Control and Prevention
(CDC)
 Collects and analyzes epidemiological information in the
United States
 Publishes Morbidity and Mortality Weekly Report
(MMWR)
 www.cdc.gov
© 2013 Pearson Education, Inc.
Epidemiology
John Snow
1848–1849
Mapped the occurrence of
cholera in London
Ignaz Semmelweis 1846–1848
Showed that handwashing
decreased the incidence of
puerperal fever
Florence
Nightingale
Showed that improved
sanitation decreased the
incidence of epidemic
typhus
© 2013 Pearson Education, Inc.
1858
Epidemiology
 Descriptive: collection and analysis of data
 Snow
 Analytical: comparison of a diseased group and a
healthy group
 Nightingale
 Experimental: controlled experiments
 Semmelweis
© 2013 Pearson Education, Inc.
Epidemiology
 Case reporting: health care workers report
specified disease to local, state, and national
offices
 Nationally notifiable diseases: physicians are
required to report occurrence
© 2013 Pearson Education, Inc.
The CDC
 Morbidity: incidence of a specific notifiable disease
 Mortality: deaths from notifiable diseases
 Morbidity rate: number of people affected in
relation to the total population in a given time period
 Mortality rate: number of deaths from a disease in
relation to the population in a given time
© 2013 Pearson Education, Inc.
Figure 14.10 a & b Epidemiological graphs.
40,000
Number of reported cases
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
1999
2000
2001
2002
2003
2004
2005
Apr
May
Jun
Jul
Month
2006
2007
2008
2009
2010
(a) Lyme disease cases, 1999–2010
600
Reported cases per
100,000 people
500
400
300
200
100
0
Jan
Feb
(b) Lyme disease by month, 2009
© 2013 Pearson Education, Inc.
Mar
Aug
Sep
Oct
Nov
Dec
Figure 14.10c Epidemiological graphs.
Reported cases per
100,000 people
120
100
80
60
40
20
0
1948
1958
1968
1978
Year
Reported tuberculosis cases, 1948–2010
© 2013 Pearson Education, Inc.
1988
1998
2008