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
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
• Locations of normal
microbiota on and in the
human body
Figure 14.2
Normal Microbiota and the Host:
• 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.
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
• Koch's Postulates are used to prove the cause
of an infectious disease.
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. nonviral cancer, heart disease).
Frequency and Occurrence Terminology
Pandemic
May, 2008
Severity or Duration of a 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)
Predisposing Factors
• 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
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.
Transmission of Disease
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
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.
Nosocomial (Hospital-Acquired) Infections
• Are acquired as a result of a hospital stay
• 5-15% of all hospital patients acquire nosocomial
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
Figure 14.7, 9
Relative frequency of Different Nosocomial Infections
(Bloodstream associated infection)
Top Nosocomial Pathogens Causing Hospital Associated Infections
Pseudomonas
aeurginosa (esp.
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 + betalactamase inhibitor, cephalosporin
Escherichia coli
Gram neg.
bacillus
Urinary tract infections, pneumonia, neonatal
meningitis, bacteremia
trimethoprim-sulfamethoxazole,
ciprofloxacin
Gram neg.
coccus
Urinary tract infections,bacteremia, bacterial
endocarditis, diverticulitis, and meningitis
Expensive antibiotics like
quinupristin/dalopristin (Synercid) and
linezolid (Zyvox)
imipenem or quinoloneresistant)
(esp. cephalosporin resistant )
Vancomycin
resistant
enterococci -VRE
(e.g. Enterococcus
faecalis)
Commonly found in stool
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
Gram pos.
coccus
Pneumonia, otitis media in children
Penicillins or cephalosporins,
otherwise vancomycin
Acinetobacter
baumanii
Gram neg.
coccobacilli
Pneumonia
Imipenem, polymixin B
Clostridium difficile
Diarrhea and colitis after a course of antibiotics
(“C. diff”)
Gram neg.
Bacillus;
anaerobic
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
Staphylococcus
aureus, (esp. MRSA methicillin resistant
Staphylococcus aureus)
Streptococcus
pneumoniae (esp..
PRP: penicillin resistant
pneumococci)
The Inanimate Environment Can Facilitate Transmission
X represents VRE culture positive sites
~ Contaminated surfaces increase cross-transmission ~ (2001 study)
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.
The Stages of a Disease
Figure 14.5
Reservoirs of Infection
• 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
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.
Emerging Infectious Diseases
• 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)
Nationally Notifiable Diseases -2010
Anthrax
Arbovira l diseases (West Nile)
Botulism
Brucellosis
Chancroid
Chlamydia trachomatis infection
Cholera
Cryptosporid iosis
Cyclosporiasis
Dengue
Diphtheria
Ehrlichiosis/Anaplasmosis
Giardiasis
Gonorrhea
Haemo philus influenzae
Hansen disease (leprosy)
Hantaviru s pulmonary syndrome
Hepat itis A, B, and C
HIV infection
Influenza-associated pediatric mortality
Legionellosis
Listeriosis
Lyme disease
Malaria
Measles
Meningococcal disease
Mumps
Novel influenza A virus in fections
Pertussis
Reported to City, County, and CDC
Plague
Poliomyelitis, paralytic
Poliovirus infection, nonpar alytic
Psittacosis
Q Fever
Rabies
Rubella
Rubell a, congenital syndrome
Salmonellosis
SARS-CoV disease
Shiga toxin E. coli (STEC)
Shigellosis
Smallpox
Spotted Fever Rickettsiosis
Streptococcal toxic-shock
Streptococcus pneumoniae
Syphilis
Tetanus
Toxic-shock syndrome (other than
Streptococcal)
Trichine llosis (Trichinosis)
Tuberculosis
Tular emia
Typhoi d fever
VISA
VRSA
Varicella (morbidity)
Varicella (deaths only)
Vibriosis
Viral Hemorrha gic Fevers (e.g. Ebola, Lassa)
Yellow fever
Table 14.7
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.
Gaining a Foothold: Mechanisms of Pathogenicity
• Pathogenicity
The ability to cause disease
• Virulence
The extent or degree of pathogenicity
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
Enzymes That Break Down Host Cells
• Coagulase
Coagulate blood
• Kinases
Digest fibrin clots
• Hyaluronidase
Hydrolyses hyaluronic
acid
• Collagenase
Hydrolyzes collagen
• IgA proteases
Destroy IgA antibodies
• Siderophores
Take iron from host ironbinding proteins
• Antigenic variation
Alter surface proteins
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
Endotoxin
Figure 15.4b
Endotoxins Produce Fever, Chills, Weakness, Shock
Figure 15.6
Exotoxin Examples
Source
Metabolic product
Chemistry
Mostly Gram + (e.g. bacteria
causing typhoid fever, meningitis,
urinary tract infections)
By-products of growing cell
Protein
Fever?
No
Neutralized by antitoxin
Yes
LD50
Small
Exotoxins Have Different Effects
Figure 15.4a
Exotoxin Types
• 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
Figure 15.5
Examples of Exotoxins
Exotoxin
Lysogenic
conversion
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
Source
• Corynebacterium diphtheriae
(diptheria)
• 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.
Cytopathic and Pathogenic Properties of Viruses and Fungi
• 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)
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.