Download Chapter 14: Infections, Infectious Diseases, and Epidemiology

Chapter 14: Infections, Infectious Diseases, and Epidemiology
Symbiotic Relationships Between Microbes and Their Hosts
Mutualism-
Commensalism-
ParasitismNormal Microbiota in Hosts
-Resident microbiota-Transient microbiotaDuring fetal development, contain no normal microbiota. First microbiota enter
when amniotic sac ruptures during birth. More arrive over the next few months.
How normal microbiota become opportunistic pathogens
1.
2.
3.
Reservoirs of Infectious Diseases in Humans
Animal Reservoirs-
Human Carriers-
Nonliving Reservoirs-
1
The Movement of Microbes: Contamination and Infection
Exposure to Microbes: Contamination and Infection
-Contamination-InfectionPortals of Entry- location of pathogen entry
-Skin-Mucous membranes-Placenta-Parenteral Route-
The Role of Adhesion in Infection
-Adhesion-
-Adhesion factors-
-Host cells usually contain glycoproteins that can bind to adhesion factors.
-Avirulent-Some bacterial pathogens adhere to a surface via a biofilm.
2
The Nature of Infectious Disease
Disease-
MorbidityManifestations of Disease: Symptoms, Signs, and Syndromes
-Symptoms-Signs-Syndrome-Asymptomatic or subclinical infections-
Causation of Disease: Etiology
-Etiology-Using Koch’s Postulates
-used to identify a specific pathogen for a specific disease
-Exceptions to Koch’s Postulates
-some pathogens cannot be cultured in the laboratory
-some diseases are caused by a combination of pathogens,
combination of pathogens and physical factors, or genetic
cofactors.
-ethical consideration prevent applying Koch’s postulates to
diseases and pathogens that occur in humans only.
3
Virulence Factors of Infections Agents
-pathogenicity-virulence-virulence factors-extracellular enzymes-toxins-Exotoxins- destroy host cells or interfere with host metabolism.
Can be three principle types:
-cytotoxins-neurotoxins-enterotoxins-antitoxins-Endotoxins- found in Gram (-) outer membrane, lipid portion of
the lipopolysaccharide.
-Antiphagocytic Factors- virulence factors that evade phygocytosis,
allowing for pathogen to remain in host longer.
-Capsules-Antiphagocytic Chemicals-
4
The Stages of Infection Diseases
-Incubation Period-Prodromal Period-
-Illness-
-Decline-
-Convalescence-
The Movement of Pathogens Out of the Hosts: Portals of Exit
Pathogens typically exit the body in materials that the body secretes or
excretes, ear wax, tears, nasal secretions, saliva, sputum, blood, reproductive
secretions, milk, or bodily wastes.
Modes of Infectious Disease Transmission
Contact Transmission- Can be direct, indirect, or respiratory droplets
-direct contact transmission-
-indirect contact transmission-
-droplet transmission-
5
Vehicle Transmission- the spread of pathogens via air, drinking water, food, or
bodily fluids being handled outside the body.
-airborne transmission-
-waterborne transmission-
-food-borne transmission-
-bodily fluids transmission-
Vector Transmission- vectors are animals that transmit diseases from one host
to another, can be biological or mechanical.
-biological vectors-
-mechanical vectors-
Classification of Infectious Diseases
Diseases may be classified by many characteristics; taxonomy of pathogen,
organ system affected, or effects on populations
-Acute disease-Chronic disease-Subacute disease-Latent disease-
6
-Communicable-Noncommunicable-
Epidemiology of Infectious Diseases
Frequency of Disease
-incidence-prevalence-endemic-sporadic-epidemic-pandemicEpidemiological Studies
-Descriptive epidemiology:
-index case-Analytical epidemiology:
-Experimental epidemiology:
7
Hospital Epidemiology: Healthcare Associated Infections (nosocomial)
-Types of healthcare associated infections
-exogenous-endogenous-iatrogenic-
-Factors influencing healthcare associated infections
 Exposure to many pathogens, some being antimicrobial resistant

Weakened immune systems of patients

Transmission of pathogens among patients, health care workers,
staff, and visitors.
-Control of healthcare associated infections, CDC Universal Precautions:
 Do not sheath used needles, scalpels, or other sharp instruments,
use “sharps” containers.

Use protective barriers to prevent exposure to blood and other
body fluids

Immediately and thoroughly wash hands and other skin surfaces
that are contaminated by blood or other fluids.
8