2. 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
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3. Etiology of Infectious Diseases
Diseases can be caused by many factors:
infection, genetics, degeneration, and others.
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4. Koch’s Postulates
Developed by Robert Koch in 1877 to establish cause of infectious diseases: anthrax and TB. Experimental Requirements: 1. Same pathogen must be present in every case of the disease. 2. Pathogen must be isolated in pure culture.

5. 3. Pathogen from pure culture must cause the same disease when inoculated in healthy, susceptible laboratory animal. 4. Pathogen must be re isolated from inoculated laboratory animal and shown to be the original organism
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6. Koch’s Postulates for Infectious Diseases
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7. Exceptions to Koch’s Postulates
1. Some microbes cannot be cultured in artificial media.
Treponema pallidum (syphillis)
Mycobacterium leprae (leprosy)
Ricketsias , chlamydias, and viruses only multiply within cells.
2. One disease may involve several different pathogens.
Diarrhea
Pneumonia
Meningitis
Peritonitis
Nephritis
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8. 3. Some pathogens may cause several different diseases.
Streptococcus pyogenes: Scarlet fever, sore throat, skin infections, bone infections, etc.
Mycobacterium tuberculosis: Causes disease of lungs, skin, bones, and internal organs
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9. Classifying Infectious Diseases
Diseases alter normal body function and/or structure.
Evidences of Diseases:
Symptoms: Subjective feelings not obvious to an observer.
Example: Pain and malaise.
Signs: Objective changes that can be measured.
Example: Fever, redness, swelling, paralysis.
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10. Syndrome: A specific group of signs and symptoms that are associated with a specific disease.
Example: AIDS (Acquired Immune Deficiency)
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11. Classifying Infectious Diseases
Classification based on the behavior within a host and within a given population:
Communicable Diseases:
Spread from one host to another, directly or indirectly.
Example: Tuberculosis, herpes, flu, AIDS,
chickenpox, mumps, polio, and hepatitis.
Contagious Diseases:
Spread easily from one person to another.
Example: Chickenpox and measles.
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12. Non communicable Diseases: Not spread from one host to another
Non communicable Diseases: Not spread from one host to another. Caused by microbes that live outside the body or by opportunistic pathogens that live inside the body.
Example: Tetanus, botulism, and yeast infections
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13. Disease Occurrence Disease Incidence : Disease Prevalence:
Percentage of population that contracts a disease in a given time period..
Disease Prevalence:
Percentage of population that has the disease during given time period.
Sporadic Disease:
Occurs only occasionally.
Example: Polio in U.S.
Endemic Disease:
Constantly present in the population.
Example: Common cold or ear infections.
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14. Epidemic Disease: Pandemic Disease:
Many people acquire disease in short time period.
Example: Influenza, gonorrhea, chlamydia, and AIDS.
Pandemic Disease:
Worldwide epidemics.
Example: Influenza and AIDS.
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15. Reported AIDS Cases in the United States
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16. Disease Duration
Acute Disease: Develops rapidly, but lasts a short time.
Examples: Flu and common cold.
Chronic Disease: Develops more slowly, and reactions are less severe. Tend to recur for long periods or to be continual.
Examples: Tuberculosis, hepatitis B, and infection mononucleosis.
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17. Subacute Disease: Intermediate between acute and chronic.
Examples: Subacute bacterial endocarditis (streptococci).
Latent Disease: Causative agent remains inactive for a time, but then becomes active and produces disease symptoms.
Examples: Shingles, genital and oral herpes, AIDS.
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18. Host Resistance Determines Extent of Infection
Primary Infection: Acute infection that causes initial illness.
Example: Common cold.
Secondary Infection: Caused by opportunistic pathogen after primary infection has weakened host immune system.
Example: Pneumonia or bronchitis may develop after the common cold.
Subclinical Infection: Does not cause any noticeable illness in host.
Example: Over 90% of polio infections are asymptomatic.
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19. Spread of Infection Reservoirs of Infection
Human Reservoirs : Infected individuals who may or may not present a disease.
Carriers are infected or individuals without any signs or symptoms of disease (AIDS, polio, gonorrhea).
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20. Nonliving Reservoirs: Two major sources are soil and water.
Animal Reservoirs:
Zoonoses are diseases that occur primarily in wild and domestic animals.
About 150 different zoonoses are known (rabies, anthrax, and Lyme disease).
Nonliving Reservoirs: Two major sources are soil and water.
Soil: Clostridium tetani and botulinum.
Water: Vibrio cholerae and Salmonella
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21. Transmission of Disease
I. Contact Transmission: Spread by direct indirect contact, or droplet transmission contact.
A. Direct Contact Transmission: Person-to-person transmission.
Examples: Touching, kissing, sexual intercourse.
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22. B. Indirect Contact Transmission:
Agent is transferred via a nonliving object.
Examples: Towels, eating utensils, thermometers, stethoscopes, bedding, clothes, money, and syringes.
C. Droplet Transmission:
Microbes are spread in mucus droplets that travel short distances (less than 1 meter).
Examples: Sneezing, coughing, talking, and laughing.
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23. Portals of Exit Site at which microbes leave body.
Most common exit portals are respiratory and gastrointestinal tracts.
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24. Nosocomial (Hospital Acquired) Infections
Any Infections acquired during the course of stay in a hospital, nursing home, or other health care facility.
“Nosocomial” Greek word for hospital.
According to Center for Disease Control (CDC), 5-
15%of all hospital patients acquire N.I.s.
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25. Predisposing Factors Chain of transmission:
Wide variety of microbes in hospital environment
Weakened or immunocompromised patients
Chain of transmission:
Mainly through direct or indirect contact.
From health care workers to patient
From patient to patient
Fomites: Catheters, needles, dressings,
Airborne transmission
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26. Opportunistic , drug –resistant gram-negative the most frequent causes of NCI
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27. Control of Nosocomial Infections
Aseptic techniques.
Frequent and adequate hand washing.
Avoid unnecessary antibiotic prescriptions.
Avoid unnecessary invasive procedures.
Hospital infection control staff members are responsible for overseeing the proper cleaning , storage , and handling of equipment and supplies.
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28. Emerging infectious diseases
New diseases and diseases with increasing incidences are called (EIDs) e.g. Anthrax.
Causes:
Use of antibiotics and pesticides, climate changes , travel , the lack of vaccinations.
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29. Epidemiology
The science that studies when and where disease occur and how they are transmitted in population, incidence and frequency of disease.
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30. Descriptive epidemiology: data about infected people are collected and analyzed.
In analytical epidemiology: a group of infected people is compered with an uninfected group.
In experimental epidemiology : controlled experiments designed to test hypothesis are performed.
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31. Case reporting: provide data on incidence and prevalence to local , state , and national health official.
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32. Prepared by : Microbiology Team