Principles of Disease and Epidemiology

Chapter 14

Principles of Disease and Epidemiology: Normal Microbiota and Infectious Disease

• Etiology – Study of cause of disease

• Pathology – Branch of science that tries to determine etiology

• Infection – Invasion of the body by pathogenic organisms

• Disease – Any change from a state of health– Example: HIV infection versus AIDS

• Normal microbiota –organisms that permanently colonize the human body but do not cause disease under normal conditions– Figure 14.1 & Table 14.1

Figure 14.1 - Overview

Representative normal microbiota from skin, tongue, and esophagus

Table 14.1 (1 of 4)

Table 14.1 (2 of 4)

Table 14.1 (3 of 4)

Table 14.1 (4 of 4)

Principles of Disease and Epidemiology:Normal and Opportunistic Microorganisms

• Commensalism vs. Parasitism– Commensalism: one organism benefits, the other is

unaffected.– Parasitism: one organism benefits and the other is

harmed.

• Normal flora vs. opportunistic microorganisms– Opportunistic organisms ordinarily do not cause

disease in their normal habitat in a healthy person.• Example: E. coli in the gut versus a urinary tract infection.

– Or, if the host is weakened or compromised, microbes that are usually harmless can cause disease.

• Example: AIDS often accompanied by opportunistic infection, such as Pneumocystis jiroveci

Principles of Disease and Epidemiology:

Normal and Opportunistic Microorganisms

Principles of Disease and Epidemiology: Etiology of infectious disease

• A Koch’s postulates (4 observable requirements)

1 The same disease organism 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 inoculated into a healthy, susceptible animal.

4 The pathogen must be again isolated from the animal and must be shown to be the same pathogen as the original.

Principles of Disease and Epidemiology:Etiology of infectious disease

• A. Koch’s Postulates – Dr. G’s I. A. version

– 1 Isolate in All

– 2 In Another

– 3 Identical Ailment

– 4 Isolate Again

Figure 14.3 - Overview

Application of Koch’s postulates

Principles of Disease and Epidemiology:Etiology of infectious disease

• Emerging Infectious Diseases: new or increasing infectious diseases – See Emerging Infectious Disease Journal online:

• http//www.cdc.gov/ncidod/EID/index.htm

Principles of Disease and Epidemiology:Etiology of infectious disease

• 8 Probable reasons for emerging infectious diseases. p 238-440

1. Genetic recombination and evolutionary changes:

• Example: Avian flu

2. Unwarranted or wide spread use of antibiotics and pesticides:

• Example: Antibiotics in animal feed

3. Environmental changes:

• Example: Global warming and malaria expansion

4. Modern transportation of existing disease:

• Example: West Nile Virus

5. Infections of humans due to expansion of human settlements, war, natural disaster:

• Examples: Malaria, ebola, Valley Fever (coccidioidomycosis)

6. Animal control measures affect the incidence of disease:

• Example: Deer populations vs. Lyme disease

7. Failure of public health measures

• Example: Missed vaccine events, e.g. diphtheria

8. Genetically engineered bioterrorism

• None as of yet, but should be concern

Table 14.6 (1 of 3)

Table 14.6 (2 of 3)

Table 14.6 (3 of 3)

Principles of Disease and Epidemiology: Other Important Concepts

• A Stages of Disease

Principles of Disease and Epidemiology: Other Important Concepts

• B. Transmission of disease

– 1. Contact: Direct, indirect (fomite), droplet

Principles of Disease and Epidemiology: Other Important Concepts

• B. Transmission of disease

– 2. Vehicle transmission: e.g. food, water, air

Principles of Disease and Epidemiology: Other Important Concepts

• B. Transmission of disease

– 3. Vectors: mechanical vs. biological

Mechanical Transmission

Table 14.3

Principles of Disease and Epidemiology: Other Important Concepts

• C. Reservoir of infection: human carriers, animal, nonliving (soil, water)

Table 14.2 (1 of 3)

Table 14.2 (3 of 3)

Principles of Disease and Epidemiology: Other Important Concepts

• D. Nosocomial (Hospital-Acquired) Infections

Principles of Disease and Epidemiology: Other Important Concepts

• D. Nosocomial (Hospital-Acquired) Infections

Principles of Disease and Epidemiology: Other Important Concepts

• D. Nosocomial (Hospital-Acquired) Infections

Principles of Disease and Epidemiology: Other Important Concepts

• E. Compromised host: broken skin and invasive procedures, depressed immune system, antibiotic use

• F. Epidemiology: when, where, how

Principles of Disease and Epidemiology: Other Important Concepts

• G. Morbidity, mortality, and notifiable disease (case reporting). See MMWR online: http://www.cdc.gov/mmwr/

Table 14.7 (2 of 2)