Epidemiology and Disease: Understanding Disease Transmission and Origin

Epidemiology and DiseaseHow 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 DiseaseHow 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 DiseaseHow 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).

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 DiseaseHow 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 • 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 • Vehicle: Transmission by an inanimate reservoir (food, water) • Vector: Arthropods, especially fleas, ticks, and mosquitoes • Mechanical: Arthropod carries pathogen on feet • Biological: Pathogen reproduces in vector

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

The Inanimate Environment Can Facilitate Transmission Xrepresents VRE culture positive sites ~ Contaminated surfaces increase cross-transmission ~ (2001 study)

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

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 Reported to City, County, and CDC Table 14.7

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 iron- binding proteins • Antigenic variation Alter surface proteins

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

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

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: Understanding Disease Transmission and Origin