1. Chapter 13 – Microbe-Human Interactions

2. Acquisition of resident flora
The human body supports a wide range of habitats
Wide range of microbes can inhabit
Resident flora or microflora
Microbes that inhabit but do not harm the host

3. Locations on the host that harbor normal flora.
Table 13.1 Sites that harbor a normal flora

4. Invasion of normally sterile regions of the body can result in infection and disease.

5. Factors that predispose a person to infections.

6. Exotoxins are released by the bacterium and directly affect different host organs, while endotoxins are released after the bacterium is lysed.

7. Toxins Toxigenicity – ability to make toxins
Toxemia – toxin spread from site of infection by blood
Intoxication – ingestion of toxins (botulism)
Neurotoxins act on nervous system
Enterotoxins act on intestine
Hemotoxins lyse red blood cells
Nephrotoxins damage kidneys

8. Process of Disease Localized infection – warts
Systemic infection – spreads to several sites; measles, AIDS
Focal infection – local infection which can spread, causing local infections in other parts of the body. tuberculosis, strep throat
Primary – initial infection
Secondary – due to altered defenses
Acute vs. Chronic

9. Signs and symptoms
Signs - objective evidence of disease based on observation
Lesions, inflammation, pus
Symptoms – subjective evidence of disease based on the patient
Fatigue, dizziness, nausea
Syndrome – a specific group of signs & symptoms that accompany a particular disease.

10. Epidemiology
Prevalence of disease – number of cases with respect to entire population: usually reported as a %
Incidence – number of new cases over a certain amount of time: usually reported as X per 100,000 people per month, week, year etc.

11. The frequency of a disease in a population can be used to defined endemic, epidemic, sporadic, and pandemic diseases.

12. Reservoirs of Infection
A continual source of the pathogen, such an animal or inanimate object is a reservoir of infection
Living
Sick individuals
Carriers – infected but asymptomatic
Passive carriers – health care workers
Vectors – live animals that transmit infectious agents from host to host

13. Vectors Biological Participates in the pathogen’s life cycle
Infected with the pathogen
Transmit by bites, defecation
Mechanical
Not part of pathogen’s life cycle
Not infected with the pathogen

14. A mosquito is a biological vector and the common house fly is a mechanical vector.
Fig Two types of vectors.

15. Reservoirs of Infection
Nonliving
Soil
Transmit bacteria, protozoa, helminths, fungi
Transmit spores, cysts, ova, larvae
Water – similar to soil

16. Acquisition and Transmission
Communicable
Non-communicable
Patterns of transmission

17. Communicable
An infected host can transmit the infectious agent to another host and establish infection in that host.

18. Non-communicable
Does NOT arise through transmission of the infectious agent from host to host.
Host acquires infectious agent
From self (compromised individuals can be infected by their own microflora)
Nonliving reservoir – soil e.g., tetanus

19. Patterns of transmission
Horizontal
Vertical
Direct (contact)
Indirect

20. Horizontal
Disease is spread through a population from one infected person to another
Kissing, sneezing

21. Vertical The disease is transmitted from parent to offspring
Ovum, sperm, placenta, milk

22. Direct (contact)
Some type of contact must occur between skin or mucous membranes of the infected person and that of the new contact
Kissing, sex
Droplets
Vertical
Vector

23. Indirect Contaminated materials Air
Food, water, biological products (blood, serum, tissue), fomites (door knobs, toilet seats, etc.)
Oral-fecal
Air
Droplet nuclei (dried microscopic residue)
Aerosols (dust or moisture particles)

24. Communicable diseases are acquired by contact and indirect transfer.

25. A sneeze can release enormous amounts of moist droplets, and the dry droplets form droplet nuclei.

26. Nosocomial Infections
Infectious diseases that are acquired or developed from a hospital stay
Urinary tract infections
Respiratory infections
Surgical incisions

27. The most common nosocomial infections.

28. Koch’s postulates Method used to determine the etiologic agent
Ex. Toxic shock syndrome, AIDS, Lyme disease, Legionnaires

29. Steps associated with Koch’s postulates.
Fig Koch’s postulates: Is this the etiologic agent?