1. Chapter 19
Infection and Disease

2. Figure 19.02: Infectious Disease Deaths Worldwide.
19.1 The Host and Microbe Form an Intimate Relationship in Health and Disease
The human body maintains a symbiosis with its microbiota
Infection refers to:
The multiplication of a microbe in a host.
It produces inflammation in infected tissue
If the host loses the competition, disease occurs.
It leads to tissue or organ damage or dysfunction
Figure 19.02: Infectious Disease Deaths Worldwide.

3. Microbiome is the population of microbes that reside in the body without causing disease (in symbiosis).
In mutualism, both host and microbe benefit.
In commensalism, the microbe benefits and the host is unaffected.
Antibiotics can injure the gut microbota
Probiotics may restore microbiota after taking antibiotics
Figure 19.03: A Sampling of the Indigenous Microbiota of the Human Body.

4. The human microbiome begins at birth
In the womb a healthy fetus is sterile
By adulthood, the body contains 10 times more microbial cells than human cells
Figure 19.04: Bacterial colonization of the neonate.
Graphs modified from Development of the Human Infant Intestinal Microbiota, Palmer C., Bik E.M., DiGiulio D.B., Relman D.A., and Brown P.O., PLoS Biology Vol. 5, No. 7, el77 doi: /journal.pbio

5. Pathogens differ in their ability to cause disease.
Figure 19.10A: Invasion by Listeria.
Reproduced from Trends in Microbiology, Vol. 1, Tilney, L.G. and Tilney, M.S., The wily ways of a parasite: induction of actin assembly by Listeria, pp , © 1993, with permission from Elsevier. [
In parasitism, pathogens cause damage and disease in the host.
Pathogenicity refers to a microbe’s ability to enter a host and cause disease.
Virulence is the degree of pathogenicity.
Pathogenicity islands refers to gene clusters responsible for virulence.
Figure 19.10B: Invasion by Listeria.

6. Figure 19.05: Progression and Outcomes of Infection and Disease.
Several events must occur for disease to develop in the host.
An exogenous infection occurs if a pathogen breaches the host’s external defense and enters sterile tissue.
An endogenous infection occurs if normal microbiota enter sterile tissue.
Opportunistic infections occur when commensals take advantage of a change in the body’s environment that favors the microbe.
Figure 19.05: Progression and Outcomes of Infection and Disease.

7. Figure 19.08: Chain of events leading to sepsis and septic shock.
Primary infections occur in otherwise healthy bodies.
Secondary infections occur in a body weakened by a primary infection.
Local diseases are restricted to a single area.
Systemic diseases disseminate to organs and systems.
Figure 19.08: Chain of events leading to sepsis and septic shock.
Adapted from: Telford, Barocchi, Margarit, Rappuoli, and Grandi (2006). Nature REviews/Microbiology 4:

8. 19.2 Establishment of Infection and Disease Involves host and pathogen
Diseases progress through a series of stages.
The incubation period is the time between entry of the microbe and symptom appearance.
The prodromal phase is a time of mild signs or symptoms.
The acme period (climax) is when signs and symptoms are most intense.
As signs and symptoms subside, a period of decline occurs.
The body systems return to normal during convalescence.
Figure 19.06: The Course of an Infectious Disease, as Typified by the Flu.

9. Figure MF 19.02: Public health.
Signs (measurable), symptoms (feelings), and syndromes (progression) characterize diseases.
Acute diseases develop rapidly, cause severe symptoms, and fade quickly.
Chronic diseases linger for long periods of time, and are slower to develop and recede.
Figure MF 19.02: Public health.
© Comstock Images/Jupiterimages

10. Pathogen entry into the host depends on cell adhesion and the infectious dose.
The portal of entry is the route an exogenous pathogen uses to enter the body.
Inhalation
Fecal-oral
STD
Parenteral (through skin)
The infectious dose is the number of microbes entering the body.
Figure 19.07: The Generalized Events in the Establishment of a Local Disease.

11. Figure 19.08: Pathogen Adhesion to a Host Cell.
Many pathogens have adhesins that allow them to adhere to specific tissues.
Capsules
Flagella
Pili
Figure 19.08: Pathogen Adhesion to a Host Cell.
Adapted from: Telford, Barocchi, Margarit, Rappuoli, and Grandi (2006). Nature REviews/Microbiology 4:

12. Figure 19.09: Macrophages undergoing phagocytosis.
Breaching the host barriers can establish infection and disease.
Invasiveness is the ability of a pathogen to penetrate tissues and spread.
Many pathogens use phagocytosis by body cells to enter cells or pass through defenses undetected.
Figure 19.09: Macrophages undergoing phagocytosis.
© Dr. K. G. Murti/Visuals Unlimited

13. Figure 19.11A: Enzyme virulence factors.
Successful invasiveness requires pathogens to have virulence factors.
Pathogens have to adapt to a new environment when they enter a host.
Enzymes can help pathogens resist body defenses.
Some staphylococci produce coagulase to form a blood clot that protects them from phagocytosis.
Others produce streptokinase, which dissolves fibrin clots and allows dissemination of the bacteria.
Figure 19.11A: Enzyme virulence factors.

14. Figure 19.11B: Enzyme virulence factors.
Other enzymes are:
Hyaluronidase enhances pathogen penetration through tissues.
Leukocidins disintegrate neutrophils and macrophages.
Hemolysins dissolve red blood cells.
Virulence can be enhanced in biofilms because immune cells cannot reach bacterial cells.
Figure 19.11B: Enzyme virulence factors.

15. Toxigenicity is the ability of pathogens to produce toxins (poisons)
Toxemia is the presence of toxins in the blood.
Exotoxins are proteins produced during bacterial metabolism.
Cytotoxins kill cells , ex) leukocidens, hemolysin
Neurotoxins act on the nervous system, ex) tetanus.
Enterotoxins act on the gastrointestinal tract.
Antitoxins are produced by the host body and neutralize toxins.

16. Toxoids are toxins whose toxicity has been destroyed but still elicit an immune response.
Endotoxins are released upon disintegration of gram-negative cells (LPS).
They cause blood coagulation and fever.
Endotoxin shock may occur with antibiotic treatment of diseases caused by gram-negative bacilli.

17. Figure 19.12: Six different portals of exit from the body.
Pathogens must be able to leave the host to spread disease.
Pathogens or toxins leave the host through a portal of exit.
Figure 19.12: Six different portals of exit from the body.

18. Figure 19.13: Infectious Disease Elements.
19.3 Infectious Disease Epidemiology includes frequency and spread of disease
Epidemiologists often have to identify the reservoir of an infectious disease.
Reservoirs are places in the environment where a pathogen can be found.
Zoonosis is spread from an animal to human
Dead end host can’t pass on a disease
Carriers have recovered from the disease but continue to shed the disease agents.
Nonliving in soil or water
Figure 19.13: Infectious Disease Elements.

19. Figure 19.15: Droplet transmission.
Epidemiologists have several terms that apply to the infectious disease process.
Communicable diseases are contagious.
They are transmittable among hosts in a population.
Noncommunicable diseases are not easily transmitted to another host.
They are acquired directly from the environment., ex) Tetanus
Figure 19.15: Droplet transmission.
© John Lund/age fotostock

20. Figure 19.14A: Transmission of Microorganisms and Viruses.
Infectious diseases can be transmitted in several ways.
Direct contact methods involve close or personal contact with an infected person.
Horizontal transmission, ex) kissing
Respiratory droplets
Vertical transmission from mother to child
Figure 19.14A: Transmission of Microorganisms and Viruses.

21. Indirect contact methods can involve non-living objects
fomites ex) doorknobs
Vehicle transmission through contaminated food or water
Aerosols, small particles suspended on air currents
Vectors are living organisms carrying disease
Mechanical – transported on feet, ex) flies
Biological – have a life cycle in arthropod, ex) mosquitoes

22. Diseases are also described by how they occur within a population.
An endemic disease is habitually present at a low level in a certain geographic area.
An epidemic disease occurs in a region in excess of what is normally found in that population.
An outbreak is a more contained epidemic.
A pandemic is a worldwide epidemic.
Figure MI19C: Lyme Disease.
Source: CDC.

23. Involve a compromised host associated with hospitals.
Figure 19.16: Nosocomial Infection Elements.
Nosocomial infections are serious health threats within the health care system.
Health care-associated infections (HAIs) occur as a result of receiving treatment for another condition.
Involve a compromised host
associated with hospitals.
Caused by opportunistic agents
Figure 19.17: Sites of Nosocomial Infections.
Source: CDC. Division of Healthcare Quality Promotion (2010).

24. used by healthcare team can stop the chain of transmission
Finding the Chain of Transmission is key to reducing nosocomial infections
Standard precautions
used by healthcare team can stop the chain of transmission
Figure 19.18: Microbe Transmission in a Hospital and Standard Precautions.

25. Figure 19.19: Spreading the Flu.
Infectious diseases continue to challenge public health organizations.
Globalization means that diseases emerging anywhere in the world can be spread globally.
Emerging Infectious Diseases by newly identified pathogens or in a new place
Reemerging (resurgent) diseases show increased resistance
Figure 19.19: Spreading the Flu.
Reproduced from N Engl J Med Jul 9;361(2): Printed with permission from the Massachusetts Medical Society.

26. Figure 19.20: The Global Occurrence of Emerging and Re-Emerging Diseases.
Modified from American College of Microbiology. Clinical Microbiology in the 21st Century: Keeping the Pace. ASM Press, 2008, Washington, D.C., Reprinted with permission of the American College of Microbiology

27. Figure 19.21: Diversity of Emerging/resurgent Diseases.
Disease emergence and reemergence are related to:
Changes in land use or agriculture practices
Changes in human demographics
Poor population health
Pathogen evolution
Contamination of food sources and water supplies
International travel
Failure of public health systems
International trade
Climate change
Figure 19.21: Diversity of Emerging/resurgent Diseases.
Modified from: Woolhouse, M.E.J. (2008). Nature 451: 898–899.