Written Exam 3 Slide groups 1-3 Flashcards
What is immunodiagnosis?
Using antibody-antigen interactions to identify pathogens and diagnose infection
What is an in vitro diagnostic test of serum
Serological test
What is plasma with all clotting factors removed; the blood fraction that contains antibodies?
Serum
How are serological tests used to identify antibodies in sample?
- Patients serum antibody content unknown is taken and placed on a slide
- A prepared known antigen is added to the serum
- A positive Ab-Agn interaction is usually evident as some visible sign, such as a color change or clumping
How are serological tests used to identify antigen in a sample?
- Isolated colony identify unknown from an agar plate and then placed on a slide
- Antibodies of known identity added to the slide with the unknown colony
- A positive Ab-Agn interaction is usually evident as some visible sign, such as a color change or clumping
Explain the Latex agglutination test
Pathogen-specific antibody cross-links antigen-coated latex particles, forming complexes that settle out and form visible clumps
**When more concentrated serum is added, there are more agglutinated particles since the antigen-coated particles are bound to the antibody -> creating a clump
Explain Hemagglutination Inhibition Test
- Uses red blood cells (RBC) as indicators instead of latex particles
- Some viruses bind to antigen on RBCs and agglutinate RBCs
- Mumps, measles, influenza
- Antibodies to the virus will block the virus’ ability to agglutinate RBCs
- Inhibition of agglutination indicates the presence of antibodies to the virus
Explain Labeled Antibody Tests and list examples
Uses antibody molecules that are linked to some molecular “label” that enables them to be easily detected
- Used to detect either antigens or antibodies
Examples:
- Fluorescent antibody tests (immunofluorescence)
- ELIZA
- Western blot to detect proteins
Explain Immunofluorescence and describe the steps
- Antigen is attached to slide and flooded with patient’s serum (serum includes IgG from patient)
- Fluorescent-labeled anti-IgG antiglobulin is added
- Fluorescent label is attached to the anti-IgG (antiglobulin)
- Allowing it to fluoresce
- Fluorescent label is attached to the anti-IgG (antiglobulin)
What does ELISA stand for?
Enzyme Linked Immunosorbent Assay
Explain the process of ELISA
- A patient’s _antibodies bind to known antigen_ that is attached to a well in 96 well plate
- Patients antibodies are detected by a secondary antibody that is labeled with an enzyme
- When substrate is added, the enzyme-antibody complex hydrolyzes the substrate, which releases a dye
- Wells that develop color are positive for the antibody; colorless wells are negative
Explain how ELISA is used to detect an antigen
- Specimen is coated with antibodies, NOT ANTIGEN
- Antigen washed over the sample and antigen binds to the antibodies
- Secondary antiviral antibody binds and the Antiimmunoglobuilin enzyme is then added and bound to the second antiviral antibody
- Enzyme-antibody complex hydrolyzes the substrate and releases a die.
When using ELISA, what is used to detect HIV?
p24 Antigen (colored wells indicate reactivity)
Explain Western blots and how the work
- Used to identify presence of antigen
- Run gel electrophoresis on proteins isolated from a clinical sample
- Transfer proteins to a nitrocellulose membrane
- Incubate membrane with primary antibody
- Primary antibody binds to its antigen protein
- Add secondary antibody that is labeled with an enzyme
- Visualize the protein
Explain Immunochromatography tests and how they work
**Rapid diagnostic tests
- Prepared antigen extracted from patient (in beaker)
- Movement of fluid containing complexes of antibodies bound to antigen
- Anti-antibodies stop movement of antibody-antigen complexes. Color becomes visible because of density of complexes
What is a major example (common) of immunochromatography tests?
Pregnancy tests (at home method) = Rapid diagnostic tests
Explain the relationship between Normal Microbiota and the Host
- Microbiota (aka normal flora): The microorganisms that normally colonize various sites on/within the body without causing disease
What is the difference between resident and transient microbiota?
- Resident Microbiota = inhabit sites for extended periods
- Transient microbiota = inhabit temporarily
What is the ability of a microbe to stay affixed to a body surface and replicate? and how is this achieved?
Colonization
Achieved by:
- Adhesins
- Environmental factors
- susceptibility to pathogens
Where do the normal microbiota colonize in the host?
- Conjunctiva, Nasal mucosa, Oral mucosa, Pharynx, Skin, Large intestine (colon), Rectum, Urethra, Vagina
What spots in the body are normally free of microbes (sterile)?
Blood, CSF and internal organs
What does our microbiota do?
- Part of our first line of defense against infection – competitively exclude pathogens
- Covering of blinding sites prevents attachment
- Consumption of available nutrients
- Production of compounds toxic to other bacteria
- Aid in digestion, in vitamin production, drug metabolism
- Many other functions that are just now learning about (the Human microbiome project)
How do we acquire the microbes that make up our normal microbiota?
- From mother to baby
- Oral (pre-mastication of food)
- Mammary, through breastfeeding (selection)
- Cutaneous (contact with skin)
- Vaginal (passage through birth canal)
- Mom’s oral hygiene is important as it influences the baby oral microbiota
What can perturb the normal microbiome of a person?
- By age three, a child’s microbiome looks a lot like an adult’s, and it becomes much more stable
- It continues to change in response to events like illness, disease, antibiotic treatment, fever, stress, injury, and changes in diet
Explain the difference between an opportunistic and true pathogen
-
Opportunistic pathogen:
- Can be a member of the normal microbiota (endogenous microbes) or common in environment (exogenous microbes)
- When a normal microbe that is commonly exposed to becomes a pathogen that attacks host (human) during an immunocompromised state/certain conditions
- “true” pathogen:
- microorganisms that infect and cause disease even in healthy individuals with normal immune system (have mechanism to become pathogenic)
- Able to breach defenses of a healthy host
- Are never part of the normal microbiota
- microorganisms that infect and cause disease even in healthy individuals with normal immune system (have mechanism to become pathogenic)
Explain the relationship between host and microbiota?
Delicate balance; some can cause disease should opportunity arise
Explain opportunistic conditions and when a weak immune system may arise
- Changes in composition of the normal microbiota (ie. Taking antibiotics)
- Displacement of normal microbiota to another site in the body (ex. IV touches skin of patient, skin bacterium then inserted into blood stream)
- Weakened immune system
- Immune suppression (chemotherapy, organ transplants)
- Immunodeficiency (AIDS)
- Old age or stress or other diseases
What is the normal microbiota
endogenous microbes
What is a microbe that is common in the environtment
exogenous microbes
Explain the difference between an infection and an infectious disease:
-
Infection:
- Refers to successful colonization (multiplication) with or without invasion of microorganisms within a host with or without the manifestation of disease (may not be associated with a disease)
- Extracellular pathogen: replicate outside of cells within the host
- Intracellular pathogens: replicate inside cells within the host (obligate or facultative)
- Refers to successful colonization (multiplication) with or without invasion of microorganisms within a host with or without the manifestation of disease (may not be associated with a disease)
-
Infectious disease:
- A microorganism or its products cause damage to host cells/tissue resulting in signs and symptoms
***You can have an infection without disease = asymptomatic***
What are the possible outcomes of an infection?
- Infection without disease (asymptomatic or subclinical infection)
- Infection with disease (symptomatic) and then recovery
- Infection, disease, and then death
What is the term that describes the ability to cause disease
Pathogenicity
Describe virulence
the quantitative ability of a pathogen to cause disease
- Pathogens differ in their degree of virulence
- Pathogens use various strategies to establish virulence
- Highly virulent pathogens are MORE LIKELY to cause severe disease
Describe virulence factors
Proteins and other molecules that contribute to the pathogen’s ability to establish itself in a host or cause host damage
Explain how Virulence is measured:
- Virulence can be estimated from experimental studies of the LD50 (lethal dose50)
- LD50= The number of microbes that kills 50% of an experimental group of animal hosts
In the attached example: Streptococcus pneumonia is much more virulent because it has a MUCH lower LD50
Explain the concept of an Infectious Dose (ID):
- Infectious Dose (ID) is a minimum number of microbes required to be taken in the body to cause infection
- ID50 = the number of microbes that will cause infection in approximately 50% of an experimental group of hosts
Explain the Generalized Events in the Establishment of an Infectious disease:
- Entry into the host, with evasion of host primary defenses
- Adhesion of the microorganism to host cell
- Invasion of the host
- Propagation (growth of the organism
- Damage to host cell by bacterial toxins or immune response of the host (own immune response may cause the damage -> results in infectious disease)
- Progression or resolution of the disease Either treated via antimicrobial therapy or kills person by taking over)
Explain the types of Portal of Entry for bacteria into the body
- Fecal-oral = through mucosal surfaces of gastrointestinal track
- Skin = through traumatized epithelial surfaces (can be very small like paper cut)
- Respiratory = through mucosal surfaces of respiratory tract (inhalation)
- Urogenital = through mucosal surfaces of genital and urinary tracts (STI’s or UTI)
- Parenteral = through injection into the bloodstream (ex. Insect bites or needle sticks)
- Placenta = crossing also is a big one that is not mentioned on slide…
E. all of the above
Recall:
A. Spread from cell to cell without ever having to leave the cell = antibodies
B. Frequently change the structure of their surface antigens = step ahead of antibody response (not allowing for recognition)
C. Mimic host molecules on their surface (coat w/host type structure)
D. Replicate within a host cell (similar to antibodies in response A above)
Explain the measures as to how a microbe can concur the EVASION OF HOST DEFENSES
- Mimic host molecules: cover surface with molecules similar to those found in host cell, appears to be “self”
-
Hide within a host cell:
- Spread without ever having to enter the extracellular space where they can be attacked by immune cells, complement or antibodies
- Avoid recognition by phagocytes (anti-phagocytic)
- Avoid death inside a phagocyte (anti-phagocytic)
Name and describe the main types of anti-phagocytic mechanisms:
- Inhibit recognition by phagocyte (ie. Using a capsule, allow the ability to hide from phagocyte) [streptococcus pneumonia]
- Inhibit lysosomal fusion (phagosome fails to fuse with lysosome, do not break a part and allows them to escape from the phagolysosome and grow in the cytoplasm) [M. tuberculosis]
- Block activation by interferon gamma (Resist antibacterial lysosomal action and multiply within cell)
What are other ways to evade host defenses that were listed?
- Destroy antibodies and/or complement by bacterial proteases
- Antigenic variation: alter structure of surface antigens, stay ahead of antibody production
- Superantigens cause excessive stimulation of immune cells in a nonproductive way (activates lots of T-cells that are NOT specific for that pathogen -> excess inflammation)
Step 2 of the bacterial/pathogen attack is what? explain
Step 2 : Adhesion
-
Adhesins – general term for any microbial factors that promote attachment
- Tip of fimbriae
- Glycocalyx
- Cell wall
- Biofilms
Step 3 of the bacterial/pathogen attack is what? explain
STEP 3 = INVASION
- The process whereby a microorganism enters host cell or tissues and spread to the body
- A pathogen that is highly invasive can penetrate and rapidly spread through tissue (ie. Streptococcus pyogenes = flesh-eating bacteria)
How do pathogens penetrate the skin and mucosal membranes?
-
Skin:
- Difficult barrier to penetrate; bacteria rely on injuries and abrasion
- S. aureus = via cut or wound
- Malarial parasite injected by mosquitoes (bite)
- Difficult barrier to penetrate; bacteria rely on injuries and abrasion
-
Mucosal membranes
- Two general mechanisms
- Direct uptake into small membrane-enclosed vacuoles (engulf and carry across membrane)
-
Exploitation of antigen sampling
- Dendritic or mucosal M cells that are constantly taking up antigens and if they produce a virulence factor, can be carried across the membrane
- Two general mechanisms
Step 4 of bacterial/pathogen attack is what? explain
Step 4: Colonization and Growth (replication)
- New organisms must compete with established organisms for nutrients and space
- Pathogens may grow locally at the site of invasion or may spread throughout the body (systemic)
Step 5 of the bacterial/pathogen attack is what? explain
Step 5: Damage to Host
- In order to cause disease, pathogens must CAUSE DAMAGE TO HOST CELLS which produces SIGNS AND SYMPTOMS
- Damage facilitates dispersal of organism
- Diarrhea, coughing, etc
- Damage can be direct** result of pathogen, such as a TOXIN PRODUCTION, or **indirect via IMMUNE RESPONSE
- Damage facilitates dispersal of organism
Now going in to the types of TOXINS the microbes can produce, What are the types and briefly describe the types of bacteria effected AND their mechanism for release
-
Exotoxins:
- Produced by G+ or G-
- Produced as they grow and metabolize.
- They are released into the surrounding medium
-
Endotoxin:
- Produced by G- ONLY
- Part of the outer membrane = Lipid A
- Are released when bacteria die and cell wall breaks down
Where are most of the genes for exotoxins carried?
on PLASMIDS OR PHAGES
Name and describe the types of Exotoxins
- Most genes for exotoxins are carried on plasmids or phages
- 3 Major Categories:
-
Cytolytic toxins:
- Work by degrading cytoplasmic membrane integrity, causing cell lysis and death (work on SPECIFIC cell types and degrade cell membrane)
- Toxins that lyse red blood cells are called HEMOLYSINS
- Work by degrading cytoplasmic membrane integrity, causing cell lysis and death (work on SPECIFIC cell types and degrade cell membrane)
-
AB toxins:
- Consist of two subunits, A and B.
- B subunit binds host cell receptor and transfers subunit A (the toxic part) across the membrane
- Consist of two subunits, A and B.
-
Superantigen toxins:
- Activate non specifically CD4+ T cells which leads to an excessive inflammatory response
- ***NON SPECIFIC => HUGE INFLAMMATION
- Activate non specifically CD4+ T cells which leads to an excessive inflammatory response
-
Cytolytic toxins:
Explain the mechanism for Cytolytic toxin (exotoxin category #1)
-
Cytolytic toxins:
- Work by degrading cytoplasmic membrane integrity, causing cell lysis and death (work on SPECIFIC cell types and degrade cell membrane)
- Toxins that lyse red blood cells are called HEMOLYSINS
- Work by degrading cytoplasmic membrane integrity, causing cell lysis and death (work on SPECIFIC cell types and degrade cell membrane)
Explain the mechanism for AB toxin (exotoxin category #2)
-
AB toxins:
- Consist of two subunits, A and B.
- B subunit binds host cell receptor and transfers subunit A (the toxic part) across the membrane
- Consist of two subunits, A and B.
Explain the mechanism for Superantigen toxin (exotoxin category #3)
-
Superantigen toxins:
- Activate non specifically CD4+ T cells which leads to an excessive inflammatory response
- ***NON SPECIFIC => HUGE INFLAMMATION
- Activate non specifically CD4+ T cells which leads to an excessive inflammatory response
Explain the mechanism for Endotoxin:
- ONLY G – BACTERIA => OUTER MEMBRANE
- Lipid A = TOXIC PART
- When LPS* gets into the circulation, it can *trigger a massive inflammatory response
- Excessive release of cytokines from host (ie. “Cytokine storm”)
- Induces inflammatory trauma throughout the entire body
- Fever, shock, disseminated intravascular coagulation, and death (clotting dysfunctional)
What are the mechanisms of Bacterial Pathogenesis?
-
Produce toxins that are ingested (exotoxin consumption -> food poisoning, bacteria not causing the disease)
- Eg. C. botulinum, S. aureus
-
Colonize mucous membrane, produce toxin (Toxin crosses membrane not the bacteria)
- Eg. V. cholera, C. diphtheria
-
Invade host tissues, avoid defenses (bacteria crosses and invades -> replication disrupts function of cell)
- Eg. M. tuberculosis, Y. pestis, Salmonella enterica
- NOT A TOXIN
- Eg. M. tuberculosis, Y. pestis, Salmonella enterica
-
Invade host tissues, produce toxins (Cross membrane, invade cell and produce toxin)
- Eg. Shigella dysenteriae, Clostridium tetani)
What is it when Toxins released by pathogens get into the blood circulation to produce systemic disease, but the infection itself remains localized at the portal of entry
Toxemia
What is it when Bacteria present in the blood
Bacteremia
What is it when microbe spread via the circulation to affect other body tissues/organs (ie. Checken pox)
Systemic
What is it when a Virus is present in the blood
Viremia
What is it when a microbe enters the body and remains confined to a specific tissue (ie. A skin wart)
Localized
What is it when there is an acute, life-threatening illness caused by infectious agents or produces in bloodstream; can progress to septic shock which involves low blood pressure and multi-organ failure
Sepsis
What are the three areas of epidemiology and how are they defined?
-
Descriptive epidemiology = Distribution
- Frequency of health events
- By person, time and place
-
Analytic epidemiology = Determinants
- Seach for causes or risk factors
- Design studies to investigate a hypothesis based on descriptive epidemiology
-
Applied epidemiology = Application
- Outbreak control
- Prevention
What is an epidemic investigation and what type of epidemiological area is this?
Epidemic investigation: “Descriptive epidemiology” = who, what, when where, transmission?
- Undertaken when the number of cases of a disease increases over what is considered to be the norm
- The study of the extent, characteristics, mode of transmission and etiology of a cluster of cases of a specific disease
What is it when disease consistently present in a population (normal rate)
endemic
What is it when an epidemic occurring on several continents and usually affecting an exceptionally high proportion of the global population (HIV/AIDS)
Pandemic
What is it when occasional (spontaneous) cases are reported at irregular intervals
Sporadic
What is an epidemic?
Epidemic – Occurrence of more cases of disease than expected in a given area over a particular period of time (“outbreak”)
What is a Case Definition:
- Set of uniform criteria used to define a disease for public health surveillance
- May include criteria for person, place, time, clinical features, and lab criteria
- Case definitions enable public health to classify and count cases consistently across
Describe an Epidemic (Epi) Curve
Epidemic (Epi) Curves: (Histogram)
- Graph that illustrates the time of onset of disease in each case and can determine a trend from the data
How is disease frequency measured?
- Used to characterize the occurrence of disease in a population
-
Incidence:
- NUMBER OF NEW cases of disease that develop in a population during a DEFINED PERIOD OF TIME
- Individuals who CHANGE IN DISEASE status over a specific period of time
-
Prevalence:
- NUMBER OF EXISTING cases of disease in a population during a defined period of time
- Individuals with outcome of interest, REGARDLESS OF WHEN diagnosed
** For example: Incidence of aids has decreased (not as many new cases) but the Prevalence (number existing) has increased due to better prognosis and treatment so people are living longer with AIDS
What is another term for ILLNESS (not including death).
How is it usually determined?
Morbidity
Prevalence is often used to determine the level of morbidity in a population
What is the term used to describe when a proportion of people who become ill in a population after exposure to an infectious agent (Special type of morbidity rate)
Attack rate
What is the term used to describe the incidence of death due to a disease during a particular time period
Mortality rate
What is the term used to describe mortality rate/ incidence rate
Case fatality rate
What is the difference between an Infectious disease and a communicable disease
-
Infectious disease: Illness caused by an infectious agent (bacteria, viruses, fungi, parasites)
- How infectious a disease is refers to how many pathogens are needed to infect an exposed individual
- May or may not be communicable ie. Passed on
-
Communicable Disease: an infectious disease that is CONTAGIOUS and which can be TRANSMITTED FROM ONE SOURCE TO ANOTHER by infectious microorganisms
- Not all infectious diseases are contagious (ie. Food poisoning)
- How contagious a disease is reflected by how many people an infected source can spread the disease to
Explain the concept of the reproductive number
The Reproductive Number (Ro) of a pathogen
- The number of people that one sick person will infect (on average) is called Ro. H
- Measles = highly contagious and Ebola = not contagious
What are analytical epidemiologic studies and what do they test
- Test hypotheses about exposure – outcome relationships
- Investigate association between an exposure and a disease outcome to identify determinants
- Include a comparison group
What are kinds of analytic epidemiologic studies (name and describe)
-
Experimental study designs
- The researcher intervenes and put individuals in an experimental or controlled trial (involves placebo)
- Randomized controlled trial
-
Observational study designs:
- Rely on “natural” allocation of individuals to exposed or non-exposed groups (Researcher NOT controlling group)
- Cohort studies = common characteristics, exposure or experiences (exposure = self-selected and outcome disease/non disease is followed over time)
- Case controlled studies = identify cases with disease and match this to a control group similar and Look BACK and assess exposure history
Describe a cohort study
- Cohort studies = common characteristics, exposure or experiences (exposure = self-selected and outcome disease/non disease is followed over time)
Describe a Case-Control Study
- Case controlled studies = identify cases with disease and match this to a control group similar and Look BACK and assess exposure history
What are the components of the Chain of infection:
What are the components of the Chain of infection: (Want to break the chain!)
- Reservoir
- Portal of exit
- Mode of transmission
- Portal of entry
- Susceptible host
- Infectious agent
What are types of contact transmission, Name and describe
-
Direct:
- Skin-skin
- Mucous-mucous (sexually transmitted)
- Across placenta (vertical)
- Through breast milk (vertical)
-
Indirect:
- Droplets: close range (ie. Respiratory droplets inhaled by someone close by = couch, sneeze and inhale)
- Fomites: Inanimate objects that transmit pathogens, ie doorknobs (touching)
What are types of vehicle transmission
-
Air-borne
- Aerosols = inhalation
- Droplet nuclei inhaled by those over a long distance (coughing or sneezing where evaporates and leaves dust particles that remain in the room)
- Food-borne
- Water-borne
What is vector transmission
- Living organisms that can carry pathogens
- Arthropods: insects (mosquitos, flies) and arachnids (mites, ticks, spiders)
What are Reservoirs
- Where microorganisms can live, accumulate or persist outside of the host of interest
- Serves as a source of infection for other host organisms
- Human reservoir
- Animal reservoir
- Non-living reservoir
What is zoonoses?
- Infections acquired from animals (Endemic in animal host)
- Acquired through various routes
- Humans are usually dead-end hosts to zoonotic pathogens
- ***Cannot do human to human!!!
Descirbe the course of infectious disease
**Pathogens communicable status differs per type in which area it is most transmitted
Describe Asymptomatic carriers
- For some pathogens, transmission may occur in asymptomatic individuals or during the incubation period before symptoms occur
- A well known example is the typhoid disease outbreak in 1900’s
- Healthy carrier of salmonella typhi
- She continued to work as a cook and infected numerous people until she was quarantined for life against her will
Explain the terms the describe the duraction of symptoms
- Acute = Symptoms have rapid onset and lasts only short time
- Chronic = symptoms develop slowly and persist (could last for decades)
- Latent = Infection never completely eliminated (dormant phase). Pathogen is not replicating in the latent phase but may reactivate (Herpes)
Infectious disease surveillance is done how?
-
Public health departments
- States have the authority to mandate which diseases must be reported by health care providers
- Notifiable disease
-
CDC publishes the morbidity and mortality weekly report (MMWR)
- Tracks over 50 diseases reported by hospitals, HCWs, coroners, etc.
Describe a nosocomial infection
Nosocomial infectious (HAI = hospital associated infection)
- Diseases that are acquired or developed during a hospital stay
- ~10% of hospital patients develop HAIs (1/3 completely preventable)
- Source of the infection is somewhere in the hospital
- The source can be identified by asking:
- Are all strains of the organism identical?
- Did any hospital staff have access to all the patients?
- Did all the patients use a particular medical device?
- Were standard infection control measures enforced?
What are typical nosocomial infections that were discussed?
Risk factors for UTI: indwelling catherters, immunocompromised hosts
How are outbreaks managed?
- Identify the index case (SOURCE IS A PERSON)*** and all people who contact with the individual ***(CONTACT TRACING)
- Immunization and treatment of identified cases to prevent further spread
- Isolation and quarantine if necessary
What is an index case?
if the course is a person
Describe the difference of Isolation vs. Quarantine:
- Isolation = separation of people who HAVE A DISEASE
- Quarantine = separation of people who HAVE BEEN EXPOSED to a disease
Describe the difference between eradication and elimination of a disease
-
Eradication: termination of all transmission of infection by the extermination of the infectious agent through surveillance and containment (COMPLETELY REMOVING)
-
***EASY IF HUMAN IS THE ONLY RESERVOR” (only eradicated small pox, polio may be next)
- Easier to eradicate disease whose signs and symptoms are obvious and therefore can isolate the person
-
***EASY IF HUMAN IS THE ONLY RESERVOR” (only eradicated small pox, polio may be next)
- Elimination: sometimes used to describe eradication of a disease from A LARGE GEOGRAPHIC REGION. Disease which are amenable to elimination in the mean time are polio, measles and diphtheria
