Epidemiology of Zoonotic Diseases: Bacterial Zoonoses Overview

Bacteria Overview and Phylogeny

  • Most bacteria have circular double-stranded DNA.
  • Most bacteria live extracellularly.
  • Some, like chlamydiae, are obligate intracellular pathogens.
  • A pathogen is defined as an organism able to grow, reproduce, and cause disease within the cells of a host.
  • Many bacteria are present as normal flora in the gut of animals.
  • Bacteria are classified by:
    • Morphology
    • Staining
    • Encapsulation
    • Oxygen requirements

Bacteria Cell Anatomy

  • Key components include:
    • Pilus
    • Ribosome
    • Capsule
    • Cell wall
    • Flagellum
    • Nucleoid (DNA)
    • Cell membrane

Bacteria Shapes

  • Spheres (Cocci)
    • Diplococci (e.g., Streptococcus pneumoniae)
    • Streptococci (e.g., Streptococcus pyogenes)
    • Tetrad
    • Staphylococci (e.g., Staphylococcus aureus)
    • Sarcina (e.g., Sarcina ventriculi)
  • Rods (Bacilli)
    • Chain of bacilli (e.g., Bacillus anthracis)
    • Spore-former (e.g., Clostridium botulinum)
  • Spirals
    • Vibrios (e.g., Vibrio cholerae)
    • Flagellate rods (e.g., Salmonella typhi)
    • Spirilla (e.g., Helicobacter pylori)
    • Spirochaetes (e.g., Treponema pallidum)

Gram Staining

  • Gram stain is the most common stain for general bacterial identification.
  • Gram-positive bacteria:
    • Retain crystal violet dye, appearing dark blue.
  • Gram-negative bacteria:
    • Do not retain crystal violet, appearing red/pink.
    • Have an additional outer membrane containing lipopolysaccharide (endotoxin), increasing virulence.

Examples of Gram-Positive and Gram-Negative Bacteria

  • Gram-positive:
    • Staphylococcus aureus
    • Clostridium botulinum
    • Streptococcus pneumoniae
    • Bacillus anthracis
    • Streptococcus pyogenes
    • Corynebacterium diphtheriae
    • Micrococcus luteus
  • Gram-negative:
    • Neisseria meningitidis
    • Spirillum volutans
    • Escherichia coli
    • Neisseria gonorrhoeae
    • Helicobacter pylori
    • Treponema pallidum
    • Streptobacillus moniliformis
    • Vibrio cholerae

Infectious Diseases and Transmission

  • Infectious diseases are disorders caused by organisms like bacteria, viruses, fungi, or parasites.
  • Transmission methods:
    • Person to person (e.g., aerosols)
    • Insect or animal bites
    • Ingesting contaminated food or water
    • Exposure to organisms in the environment
    • Contact with contaminated blood

Overview of Bacterial Infections

  • Bacterial meningitis:
    • Streptococcus pneumoniae
    • Neisseria meningitidis
    • Haemophilus influenzae
    • Streptococcus agalactiae
    • Listeria monocytogenes
  • Otitis media:
    • Streptococcus pneumoniae
  • Pneumonia:
    • Community-acquired:
      • Streptococcus pneumoniae
      • Haemophilus influenzae
      • Staphylococcus aureus
    • Atypical:
      • Mycoplasma pneumoniae
      • Chlamydia pneumoniae
      • Legionella pneumophila
  • Tuberculosis:
    • Mycobacterium tuberculosis
  • Skin infections:
    • Staphylococcus aureus
    • Streptococcus pyogenes
    • Pseudomonas aeruginosa
  • Sexually transmitted diseases:
    • Chlamydia trachomatis
    • Neisseria gonorrhoeae
    • Treponema pallidum
    • Ureaplasma urealyticum
    • Haemophilus ducreyi
  • Eye infections:
    • Staphylococcus aureus
    • Neisseria gonorrhoeae
    • Chlamydia trachomatis
  • Sinusitis:
    • Streptococcus pneumoniae
    • Haemophilus influenzae
  • Upper respiratory tract infection:
    • Streptococcus pyogenes
    • Haemophilus influenzae
  • Gastritis:
    • Helicobacter pylori
  • Food poisoning:
    • Campylobacter jejuni
    • Salmonella
    • Shigella
    • Clostridium
    • Staphylococcus aureus
    • Escherichia coli
  • Urinary tract infections:
    • Escherichia coli
    • Other Enterobacteriaceae
    • Staphylococcus saprophyticus
    • Pseudomonas aeruginosa

Types of Infectious Diseases

  • Nosocomial infection: Acquired in a hospital setting (e.g., Clostridium difficile).
  • Iatrogenic infection: Occurs as a result of a medical procedure (e.g., infection during surgery).
  • Opportunistic infection: Occurs when the host’s normal defenses have been compromised (e.g., vaginal yeast infection).
  • Zoonotic disease: Transmitted from an animal to a human (e.g., COVID-19).

How Bacterial Pathogens Cause Disease

  • Four main steps:
    • Adhesion
    • Invasion
    • Infection
    • Transmission

Adhesion

  • Microbes attach to the host at a portal of entry using special surface molecules called adhesins.

Invasion

  • Invasion describes the spreading of a pathogen throughout the tissues or body systems of the host. Example: Helicobacter pylori invading epithelial cells.

Bacterial Toxins

  • Toxins are biological poisons that improve a pathogen’s ability to invade their host and cause damage.
  • Endotoxins:
    • Lipopolysaccharide found in the outer membrane of Gram-negative bacteria.
    • Released when cells divide or die.
    • Produce general inflammation.
  • Exotoxins:
    • Proteins produced mostly by Gram-positive bacteria.
    • Produced as part of metabolism.
    • Produce specific damage to host cells.

AB-Type Toxins

  • AB toxins have two components:
    • A component: Usually the "active" portion.
    • B component: Usually the "binding" portion.

Examples of Exotoxins

ToxinSpeciesMechanism of Action
Cholera ToxinVibrio choleraeCauses secretion of fluids and electrolytes from intestinal cells
Tetanus ToxinClostridium tetaniInhibits neurotransmitters and causes paralysis
StreptolysinStreptococcus pneumoniaeDisrupts host cell membrane by creating pores

Infection

  • Infection results from a successful invasion and multiplication of the pathogen.
  • Extent of infections:
    • Local: Pathogen is limited to a small area of the body (e.g., toenail fungus).
    • Systemic: Pathogen or its products are spread throughout the body by the circulatory or lymphatic system (e.g., septicemia).

Transmission

  • Pathogens leave the body through specific portals of exit.
    1. Respiratory (coughing, sneezing, or talking)
    2. Gastrointestinal (feces or saliva)
    3. Genitourinary secretions
    4. Skin (wound drainage or insect bites)

Classifying Disease by Communicability

  • Noncommunicable: Cannot be transmitted between hosts.
  • Communicable: Can be transmitted between hosts.
  • Contagious: Can be transmitted rapidly and easily between hosts.

Reservoirs of Infection

  • Disease can be transmitted from a living organism or inanimate source.
  • Living Reservoir:
    • Humans (both affected and carriers -- asymptomatic).
    • Wild and domestic animals (e.g., insects or mammals).
  • Nonliving Reservoir:
    • Soil (e.g., Clostridium botulinum).
    • Water (e.g., Escherichia coli).

Disease Transmission: Types of Vector Transmission

  • Vectors are animals that carry pathogens from one host to another.
  • The most common vectors for human diseases are insects.
  • Biological Transmission: Pathogen is transmitted actively when an insect carrying a pathogen acquired from one host bites another host.
  • Mechanical Transmission: Pathogen is transmitted passively via contact with the insect’s body parts.

Zoonotic Diseases

  • Zoonotic diseases are spread between animals and people.

Zoonoses

  • Most of the emerging infectious diseases of humans are zoonotic, being transmitted from non-human vertebrates to humans via direct transmission, environmental deposition, fomites, or arthropod vectors.
  • Mammals are the primary sources of zoonotic pathogens, and rodents are the most prevalent reservoir hosts worldwide.

Top 8 Zoonotic Diseases of National Concern in the U.S. for One Health Collaboration

  1. Zoonotic influenza
  2. Salmonellosis
  3. West Nile virus
  4. Plague
  5. Emerging coronaviruses (SARS, MERS)
  6. Rabies
  7. Brucellosis
  8. Lyme disease

Zoonotic Diseases - Examples (Bacterium, Reservoir, Transmission, Disease)

  • Bacillus anthracis
    • Gram-positive rods
    • Main Reservoir: Domestic animals
    • Mode of Transmission: Direct contact
    • Disease: Anthrax
  • Listeria monocytogenes
    • Gram-positive rods
    • Main Reservoir: Domestic animals
    • Mode of Transmission: Ingestion of unpasteurized milk products
    • Disease: Sepsis in neonate or mother
  • Erysipelothrix rhusiopathiae
    • Gram-positive rods
    • Main Reservoir: Fish
    • Mode of Transmission: Direct contact
    • Disease: Erysipeloid
  • Bartonella henselae
    • Gram-negative rods
    • Main Reservoir: Cats
    • Mode of Transmission: Skin scratch
    • Disease: Cat-scratch disease
  • Brucella species
    • Gram-negative rods
    • Main Reservoir: Domestic animals
    • Mode of Transmission: Ingestion of unpasteurized milk products; contact with animal tissues
    • Disease: Brucellosis
  • Campylobacter jejuni
    • Gram-negative rods
    • Main Reservoir: Domestic animals
    • Mode of Transmission: Ingestion of contaminated meat
    • Disease: Diarrhea
  • Escherichia coli O157:H7
    • Gram-negative rods
    • Main Reservoir: Cattle
    • Mode of Transmission: Fecal-oral
    • Disease: Hemorrhagic colitis
  • Francisella tularensis
    • Gram-negative rods
    • Main Reservoir: Many animals, especially rabbits
    • Mode of Transmission: Tick bite and direct contact
    • Disease: Tularemia
  • Pasteurella multocida
    • Gram-negative rods
    • Main Reservoir: Cats
    • Mode of Transmission: Cat bite
    • Disease: Cellulitis
  • Salmonella enteritidis
    • Gram-negative rods
    • Main Reservoir: Poultry, eggs, and cattle
    • Mode of Transmission: Fecal-oral
    • Disease: Diarrhea
  • Yersinia enterocolitica
    • Gram-negative rods
    • Main Reservoir: Domestic animals
    • Mode of Transmission: Fecal-oral
    • Disease: Diarrhea
  • Yersinia pestis
    • Gram-negative rods
    • Main Reservoir: Rodents, especially rats and prairie dogs
    • Mode of Transmission: Rat flea bite
    • Disease: Sepsis
  • Mycobacterium bovis
    • Mycobacteria
    • Main Reservoir: Cows
    • Mode of Transmission: Ingestion of unpasteurized milk products
    • Disease: Intestinal tuberculosis
  • Borrelia burgdorferi
    • Spirochetes
    • Main Reservoir: Mice
    • Mode of Transmission: Tick bite (Ixodes)
    • Disease: Lyme disease
  • Leptospira interrogans
    • Spirochetes
    • Main Reservoir: Rats and dogs
    • Mode of Transmission: Urine
    • Disease: Leptospirosis
  • Chlamydia psittaci
    • Chlamydiae
    • Main Reservoir: Psittacine birds
    • Mode of Transmission: Inhalation of aerosols
    • Disease: Psittacosis
  • Rickettsia rickettsii
    • Rickettsiae
    • Main Reservoir: Rats and dogs
    • Mode of Transmission: Tick bite (Dermacentor)
    • Disease: Rocky Mountain spotted fever
  • Coxiella burnetii
    • Rickettsiae
    • Main Reservoir: Sheep
    • Mode of Transmission: Inhalation of aerosols of amniotic fluid
    • Disease: Q fever
  • Ehrlichia chaffeensis
    • Rickettsiae
    • Main Reservoir: Dogs
    • Mode of Transmission: Tick bite (Dermacentor)
    • Disease: Ehrlichiosis

Factors Influencing Emergence and Reemergence of Zoonotic Diseases

  • Anthropogenic activities:
    1. Population growth
    2. Poverty and migration
    3. Sociopolitical issues
    4. Food habit changes
    5. Poor health care
  • Natural Changes/Perturbations:
    1. Climate Change
    2. Temperature shifts
    3. Geological anomalies
    4. Biodiversity shifts including vectors
    5. Evolution of infectious agents
    6. Pathogen adaptation
  • Occupational:
    1. Agricultural practice changes
    2. Trade in Zoonotic fauna
    3. Medical research

Case Studies Overview

  • Anthrax, Lyme Disease, E. coli O157:H7
  • Aspects covered for each disease:
    • Organism
    • History
    • Epidemiology
    • Transmission
    • Disease in Humans
    • Disease in Animals
    • Prevention and Control

What You Need to Know For Each Disease

  • Cause of the disease (etiology).
  • General properties of the microbe.
  • Course of the disease.
  • Mode of transmission.
  • Pathogenesis, including virulence factors.

Bacillus Species

  • Sporogenous Bacilli
    • Aerobic Bacilli
      • Bacillus simplex
      • Bacillus cereus
      • Bacillus anthracis
    • Anaerobic Clostridia
      • Cl. perfringens
      • Cl. tetani
      • Cl. difficile
      • Cl. botulinum

Anthrax

  • Causative agent: Bacillus anthracis
    • Gram-positive, non-motile, aerobic, cylindrical shape, capsulated
    • Saprophyte: able to survive in soil, air, water, and vegetation.
    • Spores are located in the center of the nonmotile cells
    • Anthrax spores occur naturally in soil and may lie dormant for years before ingested by domestic animals; horses, cows and sheep as examples.
    • Can be transmitted by direct contact with contaminated wool, hides or tissues or through inhalation.
    • 20k – 100k cases of infection

History of Anthrax

  • 700 BC: Ancient origins of anthrax
  • 1752: First clinical descriptions of anthrax
  • 1877: Robert Koch uses anthrax to develop Koch Postulates
  • 1881: Louis Pasteur creates the first vaccine for anthrax.
  • 1900s: First uses of anthrax as act of aggression.
  • 1937: Anthrax vaccine for animals reduces human cases.
  • 1960s: Global concern about the use of bioweapons.
  • 1979: Deadly anthrax outbreak in Sverdlovsk, USSR.
  • 2001: Anthrax attack on America.
  • 2010: Doctors find a new form of anthrax.

Bacillus anthracis Significance

  • First pathogenic bacteria to be observed under microscope
  • First bacilli to be isolated in pure culture
  • First bacilli in which spores were demonstrated
  • First bacterium used for preparation of attenuated vaccine
  • First bacterium to be shown as cause of disease
  • First bacterium to be used a weapon in bioterrorism

Koch's Postulates

(Refer to lecture slides for details on Koch's Postulates)

B. Anthracis Identification

  • Colonies are round and have a “cut glass” appearance
  • Growth in gelatine stabs resembles an inverted fir tree

Epidemiology of Anthrax

  • Soil is contaminated with spores from the carcasses of dead animals
  • Spores remain viable for decades and germinate in soil at specific pH and moisture content
  • Grazing animals infected through injured mucous membranes serve to perpetuate the chain of infection

Infection and Symptoms

  • Primarily a zoonotic disease (mostly goats, sheep, cattle, horses)
  • Other animals (e.g. rats and birds) are relatively resistant to infection
  • Humans become infected incidentally by contact with infected animals of their products
  • Symptoms: Initial symptoms may resemble a common cold. After several days, the symptoms may progress to severe breathing problems and shock. Inhalation anthrax is often fatal.
  • If untreated: 90% fatal
  • 8,000 to 10,000 spores required
  • Incubates: Sick in 1-5 days; sickness lasts 3-5 days (usually fatal)
  • Treatment: Protective vaccine.

Four Modes of Transmission

  • Cutaneous: Through cuts or sores in skin. Those who handle meat or hides and game animals. (95%)
  • Gastrointestinal: Eating infected meat and through mucous membranes (<1%)
  • Inhalation (pulmonary): Inhaling spores. Deadliest form and often fatal even with treatment. (5%)
  • Injection: Identified in Europe with those injecting illegal drugs from regions where naturally occurring anthrax is common. (very rare)

Cutaneous Anthrax

  • Most common but least dangerous
  • Lesions typically are 1-3cm in diameter and have a characteristic central black eschar
  • Bumps/blisters over body
  • Marked edema/swelling apparent
  • Lymphangitis and symptoms of fever, malaise and headache

GI Anthrax

  • Rarely deadly if treated
  • Body swelling especially neck region
  • Nausea/vomiting/severe aches
  • Diarrhea and stomach swelling

Inhalation Anthrax

  • Most deadly
  • Fever and chills
  • Chest discomfort
  • Nausea, vomiting, stomach pains
  • Pleural effusion
  • Death

Anthrax Virulence Factors

  • B. anthracis has three main virulence factors:
    • A poly-D-glutamic acid capsule which protects itself from phagocytosis
      *Note: B. anthracis that does not produce a capsule is not virulent and does not induce anthrax in test animals
    • Three proteins that combine into two protein exotoxins:
      • Edema Factor (EF)
      • Lethal Factor (LF)
      • Protective antigen (PA)
        • PA + EF → Edema Toxin → Edema
        • PA + LF → Lethal Toxin → Tissue damage and shock

Anthrax Virulence Factors Detailed

  • EF inhibits

    • T-cells
    • neutrophils
    • platelets
    • endothelial cells

  • monocytes EF & PA (ET) inhibit

    • phagocytosis

  • lethal toxin (LT)

  • extracellular space

  • edema toxin (ET)

  • cytosol

    • A lethal factor (LF)
    • protective antigen (PA) PA63
    • edema factor (EF)
    • anthrax toxin receptor (ATR)
    • anti-PA antitoxin
    • adenosine triphosphate (ATP)
    • cyclic adenosine monophosphate (CAMP)
    • mitogen-activated protein kinase (MAPKK)
    • N-terminus
    • cleavage

  • LF affects

    • cell proliferation
    • immune modulation
    • survival of toxic insults LF & PA (LT)
    • +cytokine expression
    • +chemokine expression
    • macrophage spore clearance
    • + macrophage apoptosis

Anthrax Summary

  • Causative agent: Bacillus anthracis, Gram +ve bacterium
  • Spores can lie dormant in soil for decades
  • Zoonotic disease spread from mostly large herbivorous mammals
  • 4 modes of transmission (Cutaneous, GI, Inhalation, Injection)
  • Virulence factors: protective capsule, Edema Factor, Lethal Factor, Protective Antigen

Ecology and Epidemiology of Lyme Disease

Lyme Disease Statistics

  • One of the fastest-growing infections in Europe (2nd only to HIV/Aids).
    • Recently a 14% increase in Europe.
  • In America, Lyme disease has tripled in the last 30 years.
    • Previously exclusively upstate NY but now Lyme disease reported in all 50 states (CDC).
  • Costs >USD 1B per year
  • NOT a well researched infection

Lyme Disease: Borrelia and Ixodes

  • 1977 -1st recognised clinically in Lyme, Connecticut by Dr. A Steere
    • Diagnosis of juvenile rheumatoid arthritis
  • 1980s etiology of disease (Borrelia spirochete tick vector) recognised by Dr. W. Burgdorfer
  • Borrelia genus: Relapsing fever and Lyme disease borreliae
  • Borrelia burgdorferi sensu lato complex: >15 species globally; 3 species associated with the majority of Lyme disease
RegionLyme Disease AgentTick Vector
North AmericaBorrelia Burgdorferi sensu strictoIxodes scapularis (E Coast); Ixodes pacificus (W Coast)
EuropeB. garinii; B. afzeliiIxodes ricinus
AsiaB. garinii; B. afzeliiIxodes persulcatus

Erythema Migrans

  • Pathognomonic Bull’s eye rash
  • 3-30 days after the bite
  • May not be circular
  • May be multiple
  • 1 in 3 recall tick-bite
  • 65% notice EM rash
  • Confused with other conditions

Transmission of Lyme Disease

  • Ixodes adult females lay eggs
  • Ixodes eggs hatch and molt into larvae
  • Ixodes larvae feed on infected first host
  • Infected Ixodes larvae molt to nymph stage
  • Infected Ixodes nymph feeds on second host
  • Infected nymph molts to adult Ixodes
  • Ixodes adult feeds on third host
  • Humans, dogs: incidental hosts
  • Important note: A vector borne disease, which means it cannot be transferred from person to person

Life Cycle of Ixodes scapularis (Blacklegged Ticks)

  • 2-year life cycle
  • Eggs hatch in Spring
  • First blood feed in Summer
  • Second blood feed following Spring/Summer
    • Humans at most risk here
  • Third blood feed Fall/Winter of second year

Ixodes Tick Feeding Strategies

  • Risk zones:
    • Woods
    • Long grass
    • Undergrowth
    • Moors & Heathland
  • Across the UK: Town and Country!
  • Tick bites are painless and can go unnoticed
  • Ticks carry & transmit other pathogens eg Anaplasma, Rickettsiae, Viruses etc.

Tick Anatomy

  • Key features:
    • Hypostome
    • Palp
    • Porose Area of Basis Capituli
    • Scutum/Shield

Tick Feeding Process

  • Animation demonstrates how a hard tick (Ixodes) feeds on a host (a person or animal).
  • The tick pumps saliva into the skin, which has special properties:
    • Numbing the bite area so the host doesn't feel the tick feeding
    • Keeping the blood from clotting so the tick can continue to feed for a number of days until it is full
  • Disease-causing organisms from the tick's salivary glands and intestines are introduced during saliva introduction or if the tick regurgitates due to compression or irritation during tick removal.
  • Lyme disease (Borreliosis) can transmit to a person or animal during this process.

Female Blacklegged Tick (Ixodes scapularis) Size Comparison Once Feeding

Visual representation of tick size at different feeding intervals (0 hours to 7 days).

Lyme Disease Epidemiology

  • Lyme disease – most common form of tick-borne infection in both USA and Europe with cases increasing each year
  • 2001: 17k cases reported to CDC
  • 2019: 40k cases reported to CDC
  • However, many cases are not reported, and the CDC estimates nearly 0.5M cases

Lyme Disease Case Distribution (United States, 2019)

Visual representation of cases broken down by age group indicating highest incidence in children ages 5-14 and adults ages 45-69

Lyme Disease in UK

  • Occurs throughout the UK
    • Approximately 10-15% acquired abroad
  • Occurs at any age
  • Under-reported
  • True incidence (x10-20?)

Number of Lyme Disease Cases in Europe

*Visual representation of reported cases from 1990 to 2010 indicating increase in incidents over time.

Climate Change and Health - Lyme Disease

  • Environmental & Institutional Factors
    Ecosystem changes
    *Landscape Changes
  • Climate Drivers
    High/Low temperatures, weather patterns
    Earlier tick activity
    Social Behavioral Context
  • Geographic location proximity*
  • Health outcomes - Illnesses carried by ticks

Lyme Disease Summary

  • Causative agent: Borrelia burgdorferi, spirochete bacterium
  • Primary arthropod vector: Black-legged ticks, Ixodes sp.
  • Vector-borne zoonotic disease
  • Pathology: Erythema migrans – bull’s eye rash.
  • Reservoir in small mammals, especially rodents and mice
  • Increases in incidence around the world due to multiple factors (climate and socio-economic factors)

Escherichia coli O157:H7

E. coli O157:H7 Outbreaks in the United States

*Visual representation of outbreaks from 1982 to 2002.

  • Significant events noted:
    • E. coli O157 became nationally notifiable
    • Large western states outbreak
    • PulseNet for E. coli O157

Escherichia coli (O157:H7) Characteristics

  • Gram-negative, non-spore former, short rod to ovoid shape
  • Grows optimally at 37°C, facultative anaerobe
  • Metabolically very versatile; can ferment lactose to acid
  • Common resident of the GIT of most warm-blooded animals
  • Used extensively in research
  • Some strains very pathogenic, dependent on the set of genes
  • Serotyping:
    • O antigen – LPS
    • K antigen – capsule
    • H antigen – flagella
  • Pathotype is based on specific virulence factors

Clinical Manifestations of Enterohaemorrhagic E. coli (EHEC)

  • EHEC derived from warm blooded mammals most importantly farm animals.
  • The most important source is cattle (asymptomatic carriers)
  • EHEC transmitted by food and water (Hamburger bug).
  • 50+ serotypes but most outbreaks most commonly associated with O157:H7

Cattle: Main Animal Reservoir

  • Summertime is seasonal peak
  • Asymptomatic and transient carriers
  • 10210^2 – 10510^5 CFU/g faeces
  • Immature animals (<2 yrs) more likely infected

Linking O157:H7 Infection Rates to Dairy and Feedlot Cattle

Visual representation suggesting higher rates in feedlots, but not directly correlated with human cases

Transmission of Pathogens from Environment to Human Hosts - CDC Model, 1984

  • MEAT → HUMAN

How O157:H7 Circulates in the Environment – from Farm to Plate

  • Model of transmission is much more complicated
    • Cows -> Manure, hides, abattoirs -> Runoff + meat -> Food + water -> Person to Person

E. coli O104:H4 2011 Outbreak

  • Huge outbreak of Shiga Toxin-producing E. coli infections linked to fenugreek sprouts
  • 3950 cases
  • 53 deaths
  • 800 cases of hemolytic uremic syndrome – kidney failure

Timeline of E. coli Infection

  • E. coli O157:H7 ingested
  • Abdominal cramps, non-bloody diarrhea (3-4 days).
  • Bloody diarrhea (1-2 days).
  • Resolution in 95% of cases or HUS in 5% of cases (5-7 days).

How Does E. coli O157:H7 Interact with Host Cells?

  • A number of virulence factors
    • Plasmid (pO157), carries the Locus of Enterocyte Effacement PAI, intimin, and expresses Shiga toxins.
    • The LEE locus encodes a TTSS and TTSS effector proteins.
    • One of the T3SS proteins, E. coli Secreted Protein (Esp) A, forms a filament that serves to translocate TTSS effector proteins from the bacterium into the host cell by way of a pore created by EspB and EspD.
    • Effector - Tir serves as the receptor for the major adhesin, intimin, and thus allows adherence of the bacterium to the host cell.

Controlling E. coli O157:H7

*Cattle farm management and husbandry effects
*Preharvest Control
Organic vs. Natural Beef
*Manure management
*Feed and supplements (Probiotics and Vaccination)

Does O157:H7 Dependent on Cattle Management

  • There does not appear to be differences in shedding rates of E. coli O157:H7 dependent on cattle management

Enterohaemorrhagic E. coli Summary

  • Causative agent: E. coli O157:H7, Gram -ve bacterium
  • Zoonotic foodborne disease spread from mostly large herbivorous mammals (main reservoir cattle)
  • Factors that influence cattle shedding: pen environment and gut environment
  • E. coli outbreaks in fresh produce, especially those eaten raw
  • Virulence factors include Locus of Enterocyte Effacement PAI
  • Shiga Toxin AB-type toxin, related to Shigella dysenteriae