Principles of Disease and Epidemiology

1
Principles of Disease and Epidemiology

• How do we know you are sick let alone that its an
  epidemic?

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Defining Some Terms

• Pathology Study of disease
• Etiology Study of the cause of a disease
• Pathogenesis Development of disease
• Infection Colonization of the body by
  pathogens
• Disease An abnormal state in which the body
  is not functionally normally

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Symbiosis

• Symbiosis is the relationship between organisms
  living together
• Commensalism
• one organism is benefited
• the other is unaffected.
• Mutualism
• both organisms benefit.
• Parasitism
• one organism is benefited at the expense of the
  other.

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You as Ecosystem

• Transient microbiota may be present for days,
  weeks, or months
• Normal microbiota permanently colonize the host
• 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

Figure 14.2
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Normal Microbiota and the Host

• 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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Some Normal Flora
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Kochs Postulates

• Koch's Postulates are used to prove the cause of
  an infectious disease.

Figure 14.3.1
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Kochs Postulates

• Koch's Postulates are used to prove the cause of
  an infectious disease.

Figure 14.3.2
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Classifying Infectious Diseases

• Symptom A change in body function
  that is
  felt by a patient as a result of diisease
• 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 spread from one host to
  another.
• Contagious disease easily spread from one
  host to another.
• Noncommunicable disease 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.

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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 infective

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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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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 8
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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
Figure 14.6b, c
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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

Figure 14.7, 9
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Relative frequency of nosocomial infections
Figure 14.10
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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
• Evolution of new strains
• V. cholerae O139
• Inappropriate use of antibiotics and pesticides
• Antibiotic resistant strains
• Changes in weather patterns
• Hantavirus

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Emerging Infectious Diseases

• Contributing factors
• Modern transportation
• West Nile virus
• Ecological disaster, war, expanding human
  settlement
• Coccidioidomycosis
• Animal control measures
• Lyme disease
• Public Health failure
• Diphtheria

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Epidemiology

• The study of where and when diseases occur

Figure 14.11
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Principles of Disease Surveillance

• www.who.int/emc/slideshows/Survintro/sld001.htm

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Epidemiology
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Methods
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Table 14.7
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Centers for Disease Control and Prevention (CDC)

• Collects and analyzes epidemiological information
  in the U.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
  population in a given time period
• Mortality rate - number of deaths from a
  disease/total population in a given time

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CDC and MMWR

• Centers for Disease Control and Prevention
• Morbidity and Mortality Weekly Report
• Published by the CDC
• Weekly information on reportable diseases