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8/8/2019 PRINCIPLES OF DISEASES AND EPIDEMIOLOGY
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Disease andEpidemiology
Pathology Study of disease Etiology Study of the cause of a disease
Pathogenesis Development of disease
Infection Colonization of the body bypathogens
Disease An abnormal state in which thebody is not functionally normally
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Transient microbiota may be present for days, weeks,
or months
Normal microbiota permanently colonize the host
Symbiosis is the relationship between normalmicrobiota and the host
Normal Microbiota and the Host
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In commensalism, one organism is benefited and the
other is unaffected. In mutualism, both organisms benefit.
In parasitism, one organism is benefited at theexpense of the other.
Some normal microbiota are opportunistic pathogens.
Normal Microbiota and the Host:
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.2
Locations of normal
microbiota on and in
the human body
Normal Microbiota and the Host:
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Microbial antagonism is competition betweenmicrobes.
Normal microbiota protect the host by: occupying niches that pathogens might occupy
producing acids
producing bacteriocins
Probiotics are live microbes applied to or ingested intothe body, intended to exert a beneficial effect.
Normal Microbiota and the Host:
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Koch's Postulatesare used to provethe cause of aninfectious disease.
Koch¶s Postulates
Figure 14.3.1
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Koch's Postulatesare used to provethe cause of aninfectious disease.
Koch¶s Postulates
Figure 14.3.2
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Classifying Infectious Diseases
Symptom A change in body function that isfelt by a patient as a result of disease
Sign A change in a body that can bemeasured or observed as a resultof disease.
Syndrome A specific group of signs andsymptoms that accompany adisease.
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Classifying Infectious Diseases
Communicable disease A disease that is easilyspread from one host toanother.
Contagious disease A disease that is easilyspread from one host toanother.
Noncommunicable disease A disease that is nottransmitted from one hostto another.
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Incidence Fraction of a population that
contracts a disease during aspecific time.
Prevalence Fraction of a population havinga specific disease at a given time.
Sporadic disease Disease that occursoccasionally in a population.
Endemic disease Disease constantly present in apopulation.
Epidemic disease Disease acquired by manyhosts in a given area in a shorttime.
Pandemic disease Worldwide epidemic.
Herd immunity Immunity in most of a population.
Occurrence of Disease
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Acute disease Symptoms develop rapidly
Chronic disease Disease develops slowly
Subacute disease Symptoms between acute andchronic
Latent disease Disease with a period of no
symptoms when the patient isinactive
Severity or Duration of a Disease
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Local infection Pathogens limited to a small areaof the body
Systemic infection An infection throughout the body
Focal infection Systemic infection that began asa local infection
Bacteremia Bacteria in the blood
Septicemia Growth of bacteria in the blood
Extent of Host Involvement
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Toxemia Toxins in the blood
Viremia Viruses in the blood
Primary infection Acute infection that causes theinitial illness
Secondary infection Opportunistic infection after aprimary (predisposing) infection
Subclinical disease No noticeable signs or symptoms(inapparent infection)
Extent of Host Involvement
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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
Predisposing Factors
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The Stages of a Disease
Figure 14.5
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Reservoirs of infection are continual sources of infection.
Human ² AIDS, gonorrhea
Carriers may have inapparent infections or latentdiseases
Animal ² Rabies, Lyme disease
Some zoonoses may be transmitted to humans
Nonliving ² Botulism, tetanus
Soil
Reservoirs of Infection
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Contact
Direct Requires close association betweeninfected and susceptible host
Indirect Spread by fomites
DropletT
ransmission via airborne droplets
Transmission of Disease
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Transmission of Disease
Figure 14.6a & 8
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Vehicle Transmission by an inanimate reservoir (food, water)
Vectors Arthropods, especially fleas, ticks, andmosquitoes
Mechanical Arthropod carries pathogen on feet
Biological Pathogen reproduces in vector
Transmission of Disease
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Transmission of Disease
Figure 14.6b, c
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.7, 9
Are acquired as a result of a hospital stay
5-15% of all hospital patients acquire nosocomialinfections
Nosocomial (Hospital-Acquired) Infections
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.10
Relative frequency of nosocomial infections
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Common Causes of Nosocomial Infections
Percentage of nosocomial infections
Percentage resistant toantibiotics
Gram + cocci 34% 28%-87%
Gram ± rods 32% 3-34%
Clostridium difficile 17%
Fungi 10%
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Diseases that are new, increasing in incidence, or showing a potential to increase in the near future.
Contributing factors:
Evolution of new strains V. cholerae O139
Inappropriate use of antibiotics and pesticides
Antibiotic resistant strains Changes in weather patterns
H antavirus
Emerging Infectious Diseases
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Contributing factors:
Modern transportation
West Nile virus
Ecological disaster, war, expanding human settlement
Coccidioidomycosis
Animal control measures
Lyme disease Public Health failure
Diphtheria
Emerging Infectious Diseases
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The study of whereand when diseasesoccur
Epidemiology
Figure 14.11
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Epidemiology
John Snow 1848-1849 Mapped the occurrence of cholera in London
Ignaz Semmelweis 1846-1848 Showed the hand washingdecreased the incidence of puerperal fever
Florence Nightingale 1858 Showed that improvedsanitation decreased the
incidence of epidemic typhus
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Descriptive Collection and analysis of dataregarding occurrence of disease
Snow
Analytical Comparison of a diseased groupand a healthy group
Nightingale
Experimental Study of a disease using controlledexperiments
Semmelweis
Case reporting Health care workers report specifieddisease to local, state, and national
offices Nationally Notifiable
DiseasesPhysicians are required to reportoccurrence
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Table 14.7
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Collects and analyzes epidemiological information in theU.S.
Publishes Morbidity and Mortality Weekly Report(MMWR) www.cdc.gov
Morbidity: incidence of a specific notifiable disease
Mortality: deaths from notifiable diseases
Morbidity rate = number of people affected/total populationin a given time period
Mortality rate - number of deaths from a disease/totalpopulation in a given time
Centers for Disease Control and Prevention (CDC)