Chapter 7 Principles of Disease and Epidemiology.
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Transcript of Chapter 7 Principles of Disease and Epidemiology.
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Chapter 7
Principles of Disease and Epidemiology
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Principles of Disease and Epidemiology
• 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
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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.
Figure 14.1c
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Symbiosis
• In commensalism, one organism is benefited and the other is unaffected.
• In mutualism, both organisms benefit.
• In parasitism, one organism is benefited at the expense of the other.
• Some normal microbiota are opportunistic pathogens.
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Normal Microbiota and the Host
• Locations of normal microbiota on and in the human body.
Table 14.1c
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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 are live microbes applied to or ingested into the body, intended to exert a beneficial effect.
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Koch’s Postulates
• Koch's postulates are used to prove the cause of an infectious disease.
Figure 14.3 (1 of 2)
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Koch’s Postulates
• Koch's postulates are used to prove the cause of an infectious disease.
Figure 14.3 (2 of 2)
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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.
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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.
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Occurrence of 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.• 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.
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Figure 14.4
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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 patient is inactive.
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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.
• Bacteremia: Bacteria in the blood.• Septicemia: Growth of bacteria in the blood.
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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).
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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
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The Stages of a Disease
Figure 14.5
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Reservoirs of Infection• Reservoirs of infection are 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
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Transmission of Disease
• Contact– Direct: Requires close association between
infected and susceptible host.– Indirect: Spread by fomites.– Droplet: Transmission via airborne droplets.
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Transmission of Disease
Figure 14.6a, d
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Transmission of Disease• Vehicle: Transmission by an inanimate reservoir
(food, water).• Vectors: Arthropods, especially fleas, ticks, and
mosquitoes.• Mechanical: Arthropod carries pathogen on feet
.• Biological: Pathogen reproduces in vector.
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Transmission of Disease
Figures 14.7b, 14.8
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Nosocomial (Hospital-Acquired) Infections
• Are acquired as a result of a hospital stay.
• 5-15% of all hospital patients acquire nosocomial infections.
Figures 14.6b, 14.9
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Relative Frequency of Nosocomial Infections
Table 14.5
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Percentage of Nosocomial Infections
Percentage Resistant to Antibiotics
Gram + cocci 51% 29%-89%
Gram – rods 30% 3-32%
Clostridium difficile
13%
Fungi 6%
Common Causes of Nosocomial Infections
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Emerging Infectious Diseases• Diseases that are new, increasing in
incidence, or showing a potential to increase in the near future.
• Contributing factors– Genetic recombination
• E. coli 0157, Avian influenza (H5N1)
– Evolution of new strains• V. cholerae 0139
– Inapproriate use of antibiotics and pesticides• Antibiotic resistant strains
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Emerging Infectious Diseases• Changes in weather patterns
– Hantavirus
• Modern Transportation– West Nile virus
• Ecological disaster, war, and expanding human settlement– Coccidioidomycosis
• Animal control measures– Lyme disease
• Public Health failure– Diphtheria
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Crossing the Species Barrier
UN 13.3
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Epidemiology
• The study of where and when diseases occur
Figure 14.10
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John Snow 1848-1849 Mapped the occurrence of cholera in London
Ignaz Semmelweis 1846-1848 Showed that hand washing decreased the incidence of puerperal fever
Florence Nightingale 1858 Showed that improved sanitation decreased the incidence of epidemic typhus
Epidemiology
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Descriptive Collection and analysis of data regarding occurrence of disease
Snow
Analytical Comparison of a diseased group and a healthy group
Nightingale
Experimental Study of a disease using controlled experiments
Semmelweis
Case reporting Health care workers report specified disease to local, state, and national offices
Nationally notifiable diseases
Physicians are required to report occurrence
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Table 14.7 (1 of 2)
“AIDS” to “Gonorrhea”; “Pertussis” to “Streptococcal Toxic Shock Syndrome”
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Table 14.7 (2 of 2)
“Haemophilus influenzae” to “Mumps”; “Streptococcus pneumonaie” to “Yellow Fever”
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Centers for Disease Control and Prevention (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.
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• Collects and analyzes epidemiological information in the United States.
• Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov
Centers for Disease Control and Prevention (CDC)