(LE3) Pathogenesis Flashcards
What is a pathogen?
disease-causing organism
What is an infection?
Invasion by pathogens
- pathogen uses host as source of carbon energy
What is an infectious disease?
pathogen growth or toxin production is responsible for disruption of homeostasis
What is commensal symbiosis?
neither organism is harmed or benefited by the relationship
What type of symbiosis describes our normal flora? Define it.
Mutual symbiosis: both organisms benefit from the relationship
What type of relationship describes pathogens? Define it.
Parasitic relation: one organism benefits at the other’s expense
- keeps host alive for benefits
How do commensal organisms (i.e. our normal flora) protect the host from pathogens? What are the two most common clinical pathogens our normal flora protects us from?
Compete with transient or opportunistic microbes for limited resources
- C. diff & MRSA
What are opportunistic infections?
infections caused by pathogens that take advantage of an opportunity not normally available
What are some causes for opportunistic infections?
- immunocompromised host
- Wounds/trauma introduce microbe to a new location
- Alteration of normal flora population
- Organ transplants
What are Koch’s postulates?
- Isolate & identify suspected pathogen in all cases of disease
- Grow pathogen in pure culture
- Upon exposure, the susceptible test animal suffers the same disease
- Re-isolate the same pathogen from the sick/dead test animal
What two pathogens are exemptions to Koch’s postulate, and which exact postulate?
Exemption to second postulate: grow pathogen in pure culture
- Mycobacterium leprae
- viruses
What is a communicable disease? Provide examples
Disease that can spread from one host to another
ex/ HIV, TB
What is a contagious disease? Provide examples
Communicable, but spreads quickly and easily
ex/ common cold, flu and COVID-19
What is a noncommunicable disease? Provide examples
Disease that does not spread from host to host
ex/ Tetanus, Botulism
What is a disease reservoir and what are the different types?
Continuous source of the pathogen
1. Humans with an active infection
2. Animals
3. Non-living reservoir
What pathogens utilize humans as a disease reservoir? What are carriers?
COVID, flu, cold, smallpox
Carriers harbor pathogens and can transmit, but they have no symptoms (asymptomatic)
ex/ Typhoid, walking pneumonia, covid
What is zoonosis? Provide examples
Diseases that can be transmitted from animals to humans
ex/ Rabies, Lyme disease
What are non-living reservoirs? Provide examples
some aspect of the environment (ex/ water or soil)
ex/ Tetanus, Giardiasis
What is a portal of entry?
The way by which a pathogen enters the host to cause an infection
What are the different portals of entry?
- Mucus membranes
- urethra, vagina, anus (STDs)
- placenta or breast milk
- parenteral: via a wound or trauma, broken skin, injection site, etc.
What is a portal of exit?
the way by which the pathogen leaves the host to infect a new host
- may be the same or different than portal of entry
What is the portal of entry and exit for the common cold?
entry and exit are both respiratory tract
What is the portal of entry and exit for Cholera?
Fecal-oral transmission
entry: mouth
exit: fecal matter
What are the different modes of disease transmission?
Contact transmission
Vehicle Transmission
Vector Transmission
What is direct contact transmission?
Form of contact transmission
Bite from an infected animal, sex, touch, etc.
What is indirect contact?
Contact transmission
occurs via fomites (nonliving objects that can harbor pathogens and transmit)
ex/ toe fungus
What are droplets?
Contact transmission (requires close contact)
Saliva from cough, sneeze, or talking
What are the different types of vehicle transmission?
Waterborne: drinking or interacting with water (Cholera)
Airborne: droplets stay in the air. Doesn’t require proximity like droplets. (measles)
Foodborne: pathogen in food (Typhoid, Botulism)
What are the different types of vector transmission?
Mechanical vector: pathogen carried on the body of an animal that is not infected. Ex/ fly “feet” (E. coli)
Biological vector: spread by the bite of an insect (usually) that is not infected
What is the mode(s) of transmission for Lyme disease?
Biological vector transmission
What is the mode(s) of transmission for Gonorrhea?
direct contact
What is the mode(s) of transmission for Cholera?
Waterborne
What is the mode(s) of transmission for Athlete’s foot (fungus)?
indirect fomite transmission
What is the mode(s) of transmission for influenza?
Droplet, contact, or indirect transmission
What is the mode(s) of transmission for Hantavirus?
Airborne
Describe the flow progression of the disease process
What is ID50?
infectious dose that will cause infection in 50%of susceptible test animals. (doesn’t need to cause illness)
What concept of the disease process is pictured? Describe it
Tissue/cell adherence
Ligand on microbe binds receptor on target cell
- specific receptor targets leads to host specificity
What are Ligands mostly composed of?
Mostly glycoproteins
- adhesins
- fimbriae
- capsules
What is virulence?
Severity of a disease
What is virulence factor?
A characteristic of a pathogen that allows it to be virulent
What are two types of virulence factor methods employed by pathogens?
- tissue penetration to help colonize new areas
- evasion/destruction of host’s immune response
What does Hyaluronidase do?
Digests basement membranes
What does collagenase do?
breaks down connective tissues
What do Streptokinase and Staphylokinase do?
Frees pathogen from blood clots
What does Coagulase do?
Specific to S. aureus
- stimulates clot formulation to hide pathogen from immune system
What cytotoxin does Stapylococcus secrete to kill RBCs?
Hemolysins
What cytotoxin produced by Staphylococcus destroys WBCs?
Leukocidins
What is M Protein?
Specific to Streptococcus - super-antigen
- resists phagocytosis, adheres to epithelial tissues, microcolony formation, and invasion of epithelial cells, etc.
What is LD50?
the dose of pathogen /toxin required to kill 50% of susceptible test animals
- measure of virulence
What is often the cause of cell damage to host?
toxins produced by bacteria
- exotoxins
- endotoxins
What are exotoxins?
Mostly in G+ (can be in AF or G-)
Secreted by cell
- specific targets
- cause specific symptoms, e.g. Botulism toxin (flaccid paralysis)
What are endotoxins?
Part of the G- cell wall
- LPS: no target
- all have same general symptoms, e.g. fever, malaise
What is the chemical make-up of an endotoxin vs exotoxin?
Endotoxin: Lipid portion of LPS
Exotoxin: protein
Heat stability of an endotoxin vs exotoxin?
Endotoxin: heat stabile
Exotoxin: Heat labile
Relative toxicity of an endotoxin vs exotoxin?
Endotoxin: Low (high LD50)
Exotoxin: High (low LD50)
Immune response of an endotoxin vs exotoxin?
Endotoxin: weak
- no memory, no vaccines
Exotoxin: strong
- can develop immunity
What are some examples of an endotoxin vs exotoxin?
Endotoxin: Most UTIs, Salmonella
Exotoxin: Tetanus and botulism - neurotoxin
How is cell damage by viruses different from cell damage by bacteria?
Bacteria have toxins that cause damage
Viruses directly kill cell by taking over and reproducing inside cells (cytopathic effects)
What is occurring in the image?
Fibroblasts that usually make fiber protein (collagen) become infected with viruses and stop producing collagen to produce virus cells instead
How do fungi cause cell damage?
Digests cells/tissues
- exoenzymes (digestive enzymes)
- toxins
How do protozoans cause cell damage?
- invade cells and destroy them for reproduction, like viruses (malaria)
or
- ingest tissues/cells (amoebas)
How do worms cause cell damage?
release toxic wastes, eat our food, etc.
What is hypersensitivity in terms of cell damage? Provide an example
Damage occurs due to immune system response (cytokines), not pathogens
e.g., inflammatory reactions in third-stage syphilis cause blindness and deafness
Define signs, symptoms, and syndrome
Signs: objective, observable, measurable presentation of disease
Symptoms: subjective (to the patient)
Syndrome: multiple concurring symptoms
What is an acute disease? Provide an example
Come on quickly and resolve quickly
e.g. cold, flu, covid
What is a chronic disease? Provide an example
Develop slowly and resolve slowly
e.g. TB, Related Hansen’s disease
What is a latent disease? Provide an example
Remains hidden and occasionally arises
e.g. HSV 1 & 2
What are subacute (subclinical) or asymptomatic diseases?
Disease that does not show any signs or symptoms
What is a localized infection? Give an example
Disease is isolated to one spot. Easier to treat.
e.g. anthrax
What is a systemic infection?
Disease is found in several places of the body and may be spreading to other parts
Bacteremia vs. Septicemia
Bacteremia: bacteria spreading in blood, but not growing
Septicemia: bacteria is growing in the blood. (virulence factor)
What is a primary infection?
Initial colonization by pathogen
What is a secondary infection?
Follows primary infection, often when the host is weakened
What is a superinfection? Provide an example
When changes in the environment allow an opportunistic pathogen to thrive and cause disease
e.g. C. diff infection of the bowel following clindamycin treatment
What stage of disease progression is indicated on the chart? What is happening in this stage?
Incubation period
- when infection first occurs
- no S/S
What stage of disease progression is indicated on the chart? What is happening in this stage?
Prodromal phase
- vague symptoms
What stage of disease progression is indicated on the chart? What is happening in this stage?
Invasive phase
- severe signs and symptoms
What stage of disease progression is indicated on the chart? What is happening in this stage?
Acme
- most severe of signs and symptoms
- immune system is catching up to eliminate and expel disease
What stage of disease progression is indicated on the chart? What is happening in this stage?
Decline phase
- declining signs and symptoms
What stage of disease progression is indicated on the chart? What is happening in this stage?
Convalescence period
- no longer exhibiting signs or symptoms
- expelling last of pathogens
During what phase of disease progression is adherence to tissue target occurring?
Incubation phase
During what phase of disease progression are colonization, growth, and immune system avoidance occurring?
Prodromal phase
During what phase of disease progression is damage to host tissue and cells occurring?
Invasive phase
What phase of disease progression are patients most contagious?
Invasive phase
