PATHOGENESIS OF
INFECTIOUS
DISEASES
Chapter 14Learning objectives
• After studying this chapter, you should be able to:
• Cite four reasons why an individual might not develop an infectious disease after
exposure t
...
PATHOGENESIS OF
INFECTIOUS
DISEASES
Chapter 14Learning objectives
• After studying this chapter, you should be able to:
• Cite four reasons why an individual might not develop an infectious disease after
exposure to a pathogen
• Discuss the four periods or phases in the course of an infectious disease
• Differentiate between localized and systemic infections
• Explain how acute diseases differ from subacute and chronic diseases
• Differentiate between “symptoms” and “signs” of a disease and cite several examples
of each
• Cite several examples of latent infections
• Differentiate between primary and secondary infections
• List six steps in the pathogenesis of an infectious disease
• Define virulence and virulence factors
• List six bacterial structures that serve as virulence factors
• List six bacterial exoenzymes that serve as virulence factors
• Differentiate between endotoxins and exotoxins
• List six bacterial exotoxins and the diseases they cause
• Describe three mechanisms by which pathogens escape the immune response
2Pathogenesis of infectious diseases
• The prefix “path-” means disease
• Pathogenicity – ability to cause disease
• Pathogenesis – the steps or mechanisms involved in the
development of a disease
• An infectious disease/infection is the disease caused
by a microbe
• Microbes that cause the disease are known as pathogens
• Microbiologists use the word infection to mean
colonization by a pathogen
• Pathogen may or may not cause a disease in the person
• Therefore a person can be infected with a pathogen
and not have the infectious disease caused by it
3Why infection does not always occur
• Wrong anatomic site
• Lack of appropriate receptors
• Presence of antibacterial factors
• Ex: lysozyme
• Presence of indigenous microflora
• Microbial antagonism
• Bacteriocins
• Good health of host
• Host humoral immunity
• Previously infected by it/vaccinated
• Host cellular immunity
4Four Phases of Infectious Disease
I. Incubation period
• Time between arrival of pathogen and onset of symptoms
II. Prodromal period
• Patient feels “out of it”
III. Acute phase (period of illness)
• Patient experiences the typical symptoms associated with the
disease
• Communicable diseases transmit easily during this phase
IV. Convalescent phase
• Patient is recovering
• Damage can be permanent
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