Epidemiology and Disease How are diseases transmitted and acquired? Microbial interactions Microbial...

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:

• CDC, WHO

• Koch's Postulates are used to prove the cause of an infectious disease.

Koch’s Postulates

Good exam question

• CDC, WHO

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).

Frequency and Occurrence Terminology

May, 2008

Pandemic

• 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

• Frequency and occurrence terminology

• CDC, WHO

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

• CDC, WHO

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

Relative frequency of Different Nosocomial Infections

(Bloodstream associated infection)

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

• CDC, WHO

The Stages of a Disease

Figure 14.5

• 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

• 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

Table 14.7Reported to City, County, and CDC

Nationally Notifiable Diseases -2010

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

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 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

Exotoxins Have Different Effects

Figure 15.4a

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.

• CDC, WHO

• 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...

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