Pathogenesis and Host Resistance Flashcards
Define pathogen.
Organism that typically causes disease.
Define opportunistic pathogen.
Organism that typically causes disease in immunocompromised people.
Define nonpathogen.
Organism that typically does not cause disease.
Define avirulent organism.
Organism that does not cause disease.
Define virulence.
Quantitative measure of pathogenicity.
What does ID50 mean in terms of virulence? What is the amount needed for shigella? For salmonella?
The number of organisms needed to infect 50% of hosts
Shigella <100; Salmonella~10^5
Define infection.
Pathogenic organism present and multiplying in host.
Define infectious disease.
Pathogenic organism causes damage to host or host tissues.
What’s the difference between a communicable disease and a contagious disease?
Communicable disease is transmissible by infection directly or through the agency of a vector while a contagious disease is a very communicable disease (spreads directly or indirectly).
What outweighs what in a host when infectious diseases occur?
When the infectious organism outweighs the host defenses
Dose, Virulence > Innate, Acquired defenses
???
What’s the difference between local infection and systemic infection?
Local occurs in a certain area of the host, while systemic occurs across all organs/systems of the host.
What’s the difference between acute and chronic infections?
Acute is abrupt and short lived; chronic is long lived.
What’s the difference between subclinical infections and asymptomatic infections?
Subclinical infections are not apparent by clinical examinations. Asymptomatic Infections do not show any symptoms.
Define latent infections.
An asymptomatic infection capable of manifesting symptoms under particular circumstances or if activated.
What are the stages of pathogenesis?
- Transmission
- Evasion of primary host defenses
- Adherence/Colonization
- Disease symptoms caused by invasion or toxin production
- Host response (during 3 & 4)
- Progression or resolution of infection
What’s the difference between an exogenous infection and an endogenous infection?
Exogenous is transmitted by an external source. Endogenous is transmitted by one’s own normal flora.
What are 3 ways for exogenous infections for humans?
From other humans, animals and organisms in the environment.
Soil – Clostridium
Water – Legionella
What is the term for new infections often found in patients after being admitted to hospitals?
Nosocomial infections.
What are a few ways for direct human to human infections?
Sexual contact (HIV, syphilis)
Skin/urine/blood
Tranplacental (rubella, cytomegalovirus)
At birth (Hep. B, HIV)
How about indirect human to human infections?
Airborne respiratory droplets.
Fecal contamination of food/water.
Vectors.
Define reservoir.
Host/carrier that harbors pathogenic organisms without injury to self and serves as a source from which others can be infected.
Define vector.
The mechanism that transmits pathogenic organisms FROM reservoir TO source.
In Malaria (indirect human to human) what is the vector and what is the reservoir?
Humans are the reservoir.
Mosquitos are the vectors.
In what way is infection directly transmitted from animal to humans?
Biting.
In what way is infection indirectly transmitted from animal to humans?
Airborne respiratory droplets.
Fecal contamination of food/water.
Vectors.
In Bubonic plague, reservoir + vector?
Rats are reservoir. Fleas are vectors.
In Lyme disease, reservoir + vector?
Mice are reservoir. Ticks are vectors.
During the colonization/adherence stage, organisms must evade what 2 types of immune defenses?
Innate (non-specific early defense with no memory) and acquired defenses (highly specific, delayed with long term memory).
What physical barriers act as our innate defense?
Skin, ciliated mucous membranes, stomach pH and normal flora.
What cellular components act as our innate defense?
Phagocytes, complements, lysozymes.
List a few ways that organisms evade our immune defenses.
- IgA protease
- Surface structures that prevent phagocytosis (capsules, protein A, M protein)
- Antigenic Variation
- Intracellular state
- Colonization of foreign bodies (artificial heart valves)
What do organisms need to do first in order to multiply and cause disease?
They need to adhere to the host’s cell surfaces.
How do organisms attach to cell surfaces?
Adherence factors such as pili, cell wall components (teichoic acid), slime layer (glycocalyx) in Strep. Mutans.
What happens after adherence, basically how do organisms cause disease?
- Inflammation (organs presence and produce enzymes that degrade tissue – collagenase, hyaluronidase, coagulase, lecithinase, hemolysins)
- Toxin production (exo/endotoxin) and
- Immunopathogenesis (Ab’s against infectious agent damage normal tissue)
What organism causes Gas Gangrene? How does it cause this?
Clostridium perfringens, produces many enzymes (proteases, lipases); lecithinase, degrades the host cell membranes.
What are the pros and cons of acute inflammation?
Defensive response that fundamentally protects host, but can be responsible for clinical manifestations of an infection.
What initiates the inflammatory response in acute inflammation?
Presence of foreign bodies including microorganisms.
What cells are involved in acute inflammation?
Macrophages and neutrophils (PMNs).
What mediators are involved in acute inflammation?
Cytokines, chemokines, histamine, bradykinin.
What are the two types of toxins produced by bacteria? What type of bacteria (gram stain) produces each toxin?
Endotoxin: Part of cell wall of gram (-) bacteria with LPS in outer membrane
Exotoxin: Produced by both gram (+/-) and secretes proteins
Which toxin has a high toxicity
Exotoxin
Are there any vaccines for endotoxins?
No
What are the effects of endotoxin?
IL-1 Fever. Tumor Necrosis Factor. Nitric Oxide (vasodilation, hypotension). Hageman Factor (DIC). Complement (alternative pathway).
What toxin and mediator causes septic shock? What organism? What’s the fatality rate? Cases/year?
Endotoxin by Tumor Necrosis Factor. Meningococcal meningitis; 30-50% fatality; 500,000 cases/year
How do exotoxins produce their toxicity?
Through proteins (polypeptides) consisting of 2 subunits (A and B).
Through proteins (polypeptides) consisting of 2 subunits (A and B).
A: Toxic activity
B: Binds to cell target, delivers toxin
Through what process do exotoxins act?
ADP-ribosylation of target protein
What is an exotoxin of neurological cells called? Of the stomach cells? Of skin cells?
Neurological = Neurotoxins Stomach = Enterotoxins Skin = Exfoliatins
What type of vaccine is there for exotoxins?
Toxoid vaccine
What causes choleragen?
Vibrio cholera
What causes toxic shock syndrome toxin?
Staphylococcus aureus
What causes tetanus toxin?
Clostridium tetani
What causes botulinum toxin?
Clostridium botulinum
What causes diphtheria toxin?
Corynebacterium diphtheriae
How does acute rheumatic fever occur?
Antibodies that cross react with joint, heart, and brain tissues.
How does acute glomerulonephritis occur?
Antigen-antibody complexes form that activate complement and cause inflammation.
What are the stages of an infectious disease?
- Incubation period - time between acquisition of organism and the beginning of symptoms.
- Prodrome period - time of non-specific symptoms such as fever, malaise, anorexia.
- Specific illness period - characteristic signs, symptoms of disease.
- Recovery period - illness abates
Name Koch’s postulates
- The organism must be isolated from every patient who has the disease.
- The organism must be grown in pure culture.
- The pure organism must cause disease in a healthy susceptible animal.
- The organism must be recovered from the inoculated animal.
Which postulates are problematic with today’s knowledge of science?
Some organisms can’t be grown in pure culture, and did the organism actually cause the disease?
What are the two types of vaccinations? Describe each.
Active: developed because the organisms immune system has produced antibodies after an infection or inoculation
Passive: Immunity acquired by the transfer from another animal of antibody or sensitized lymphocytes
What are 3 ways to induce active immunization?
- Toxoid vaccines (Tetanus, diphtheria)
- Subunit vaccines (Capsular - H. influenzae, S. pneumoniae)
- Whole bacteria - not in use much, original pertussis vaccine
How is passive immunization produced?
Neutralize toxins
What are 3 major strategies for disease prevention?
- Public health sanitation.
- Immunization.
- Sterilization/antisepsis.
