Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC (Atlanta, GA), WHO of the UN (Geneva, Switzerland)
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
Important Definitions
• Pathology Study of disease
• Etiology Study of the cause of a disease
• Pathogenesis Development of disease
• Infection Colonization of the body by pathogens
• Disease An abnormal state in which the body is not functionally
normally
Figure 14.2
• Locations of normal microbiota on and in the human body
Normal Microbiota and the Host:
• Transient microbiota may be present for days, weeks, or months
• Normal microbiota permanently colonize the host
• Symbiosis is the relationship between normal microbiota and the host
• Commensalism is when the bacteria benefit but the host (us) neighter benefits or is harmed
• Microbial antagonism is competition between microbes.
• Normal microbiota protect the host by:
• occupying niches that pathogens might occupy
• producing acids
• producing bacteriocins
• Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect.
Normal Microbiota and the Host:
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC, WHO
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
• Koch's Postulates are used to prove the cause of an infectious disease.
Koch’s Postulates
Good exam question
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC, WHO
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
Classifying Infectious Diseases
• Symptom A change in body function that is felt by a patient as a result of disease (e.g. pain)
• Sign A change in a body that can be measured or observed as a result of disease (e.g. body temperature).
• Syndrome A specific group of signs and symptoms that accompany a disease (e.g. AIDS, SARS).
Classifying Infectious Diseases
• Communicable disease A disease that can be spread from one host to another (e.g. measles).
• Contagious disease A disease that is easily spread from one host to another (e.g. colds).
• Noncommunicable disease A disease that is not transmissable from one host to another (e.g. non-viral cancer, heart
disease).
• Acute disease Symptoms develop rapidly (e.g. influenza)
• Chronic disease Disease develops slowly or is ongoing (e.g. bacterial vaginitis, atherosclerosis)
• Latent disease Disease with a period of no symptoms (e.g. AIDS)
Severity or Duration of a Disease
• Make the body more susceptible to disease
• Short urethra in females
• Inherited traits (e.g. sickle-cell gene)
• Climate and weather
• Fatigue
• Age
• Lifestyle
• Chemotherapy
Predisposing Factors
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Frequency and occurrence terminology
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC, WHO
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
1. Contact Transmission
• Direct: Requires close association between infected and susceptible host
• Indirect: Spread by fomites (inanimate objects)
• Droplet:Transmission via airborne droplets
Transmission of Disease
2. Vehicle: Transmission by an inanimate reservoir (food, water)
3. Vector: Arthropods, especially fleas, ticks, and mosquitoes
4. Mechanical: Arthropod carries pathogen on feet
5. Biological: Pathogen reproduces in vector
Transmission of Disease
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC, WHO
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
Figure 14.7, 9
• Are acquired as a result of a hospital stay
• 5-15% of all hospital patients acquire nosocomial infections
Nosocomial (Hospital-Acquired) Infections
• Although acquired in the hospital, infection may appear after discharge• Some infections occur in outbreaks or clusters (10%) but the majority are endemic• Can result from diagnostic or therapeutic procedures: catheters in bladder or blood vessel, surgery • Correlated with length of stay
Top Nosocomial Pathogens Causing Hospital Associated Infections
Pseudomonas aeurginosa (esp. imipenem or quinolone-resistant)
Gram neg. bacillus
Urinary tract infections, respiratory infections, bacteremia, bone and joint infections, gastrointestinal infections and sepsis with severe burns and in cancer and AIDS patients.
Penecillins, penecillins + beta-lactamase inhibitor, cephalosporin
Escherichia coli (esp. cephalosporin -resistant )
Gram neg. bacillus
Urinary tract infections, pneumonia, neonatal meningitis, bacteremia
trimethoprim-sulfamethoxazole, ciprofloxacin
Vancomycin resistant enterococci -VRE (e.g. Enterococcus faecalis)
Gram neg. coccus
Urinary tract infections,bacteremia, bacterial endocarditis, diverticulitis, and meningitis
Commonly found in stool
Expensive antibiotics like quinupristin/dalopristin (Synercid) and linezolid (Zyvox)
Staphylococcus aureus, (esp. MRSA - methicillin resistant Staphylococcus aureus)
Gram pos. coccus
Skin infections, endocarditis, pneumonia and toxic shock syndrome
Vancomycin, and very expensive quinupristin/dalopristin (Synercid) and linezolid (Zyvox) if vanco fails. Follwed by a course of minocycline, trimethoprim-sulfamethoxazole, clindamycin, and rifampin
Streptococcus pneumoniae (esp.. PRP: penicillin resistant pneumococci)
Gram pos. coccus
Pneumonia, otitis media in children Penicillins or cephalosporins, otherwise vancomycin
Acinetobacter baumanii
Gram neg. coccobacilli
Pneumonia Imipenem, polymixin B
Clostridium difficile (“C. diff”)
Gram neg. Bacillus; anaerobic
Diarrhea and colitis after a course of antibiotics Metronidazole (Flagyl) -relatively cheap - which becomes toxic because this bacterium (and Enamoeba, Giardia, and Trichomonas) all share a fermentation enzyme; DNA damage results
Candida albicans yeast Blood-stream infections: candidiasis Clotrimazole, miconazole, ketoconazole, amphotericin B
The Inanimate Environment Can Facilitate Transmission
~ Contaminated surfaces increase cross-transmission ~ (2001 study)
X represents VRE culture positive sites
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC, WHO
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
• Reservoirs of infection are continual sources of infection.
• Human — AIDS, gonorrhea
• Carriers may have inapparent infections or latent diseases
• Animal — Rabies, Lyme disease
• Some zoonoses may be transmitted to humans
• Nonliving — Botulism, tetanus
• Soil
Reservoirs of Infection
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC (Atlanta, GA), WHO of the UN (Geneva, Switzerland)
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
• Diseases that are new, increasing in incidence, or showing a potential to increase in the near future.
• Contributing factors:
• Evolution of new strains: V. cholerae O139; E. coli O157:H7
• Resistance: inappropriate use of antibiotics and pesticides:
• Changes in weather patterns:Hantavirus
• Modern transportation: West Nile virus
• Chaotic environment (ecological disaster, war, expanding human settlement): cholera
• Vector or Animal control measures: Lyme disease
• Public Health failure: Diphtheria (failure in diagnosis, immunization, immediate hospitalization in some countries)
Emerging Infectious Diseases
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC (Atlanta, GA), WHO of the UN (Geneva, Switzerland)
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
1. Portal of Entry: Skin, mucus membranes, parenteral route
• ID50: Infectious dose for 50% of the test population
2. Adhesion: Binding to host cells
3. Penetrating Host Defenses
• Enzymes break down cells and cell connections
• Toxins: Endo- and Exotoxins (cytocidal)
• LD50: Lethal dose (of a toxin) for 50% of the test population
Gaining a Foothold: Mechanisms of Pathogenicity
• Pathogenicity The ability to cause disease
• Virulence The extent or degree of pathogenicity
• Coagulase Coagulate blood
• Kinases Digest fibrin clots
• Hyaluronidase Hydrolyses hyaluronic acid
• Collagenase Hydrolyzes collagen
• IgA proteases Destroy IgA antibodies
• Siderophores Take iron from host iron- binding proteins
• Antigenic variation Alter surface proteins
Enzymes That Break Down Host Cells
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC (Atlanta, GA), WHO of the UN (Geneva, Switzerland)
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
Toxins: Two Types
• Toxin Substances that contribute to pathogenicity (endo- and exotoxins)
• Toxigenicity Ability to produce a toxin
• Toxemia Presence of toxin the host's blood
• Toxoid Inactivated toxin used in a vaccine
• Antitoxin Antibodies against a specific toxin
Exotoxin Examples
Source Mostly Gram + (e.g. bacteria causing typhoid fever, meningitis,
urinary tract infections)Metabolic product By-products of growing cell
Chemistry Protein
Fever? No
Neutralized by antitoxin Yes
LD50Small
Exotoxin Types
Figure 15.5
• Superantigens or type I toxins
• Cause an intense immune response due to release of cytokines from host cells
• Fever, nausea, vomiting, diarrhea, shock, death (e.g. SA enterotoxin)
• Membrane-disrupting toxins or type II toxins
• Lyse host’s cells by:
• Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins)
• Disrupting phospholipid bilayer
Examples of Exotoxins
Source Exotoxin Lysogenic conversion
• Corynebacterium diphtheriae (diptheria)
A-B toxin. Inhibits protein synthesis. +
• Streptococcus pyogenes (strep throat)
Membrane-disrupting. Hemolytic. +
• Clostridium botulinum (botulism) A-B toxin. Neurotoxin +
• C. tetani (tetanus) A-B toxin. Neurotoxin
• Vibrio cholerae (cholera) A-B toxin. Enterotoxin +
• Staphylococcus aureus (toxic shock) Superantigen. Enterotoxin.
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC, WHO
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.
• Viral Cytopathic Effects
• Extra bodies and parts within attacked cells (inclusion bodies)
• Fused cells (polykaryocytes)
• Fungal Pathogenic Effects
• Allergic response over time from fungal waste prolducts
• Evasion from being eaten by macrophages
• Some fungal products:
• Block protein production
• Destroy cell proteins (e.g.Candida, Trichophyton)
• Cause hallucinations (LSD-like symptoms ergotoxin produced by Claviceps ergot fungus)
Cytopathic and Pathogenic Properties of Viruses and Fungi
Epidemiology and Disease How are diseases transmitted and acquired?
• Microbial interactions
• Microbial antagonism
• Opportunistic infections
• Proving the cause (etiology) of a disease
• Koch’s Postulates
• Classifying Disease
• Symptoms and signs
• Communicable and contagious
• Incidence, sporadic, endemic, epidemic, pandemic
• Acute/chronic, local vs systemic, bacteremia/septicemia/viremia
• The Spread of Infection
• Contact Transmission: direct vs indirect
• Vehicle Transmission
• Vectors (live non-human carriers)
• Nosocomial infections; protection
• The Course of a Disease
• Incubation, prodromal, illness, decline, convalescence periods
• Tracking diseases: Epidemiology
• CDC (Atlanta, GA), WHO of the UN (Geneva, Switzerland)
• Mechanisms of Pathogenicity: Disease Stages, Toxins, Cytopathic Effects
The study of disease transmission and origin is called epidemiology and it seeks to determine the index case.