Exam 4 Ch 18 Flashcards
Zoonotic transfer
Spread of a infectious agent from its natural animal host to a human
vector-borne transmission
Spread of an infectious agent from an infected individual to another organism such as an insect that then transmits the infectious agent to a different susceptible host
reservoir host
Natural host that supports replication of a pathogen
Epidimieology
study of patterns of disease within populations
morbidity rate
Rate of disease
mortality rate
Rate of death associated with disease
incidence
Number of new cases of a disease appearing in a population during a specific time period
prevalence
Total number of cases of a disease in a population at a particular time or during a particular time period
endemic disease
Disease that is normally present in a population
epidemic
Significant rise in incidence of a disease above that normally expected in a population
Outbreak
Cluster of cases appearing within a short period of time in a localized population
pandemic
Global epidemic, usually on more than one continent
primary pathogen
Microbe that causes disease in otherwise healthy hosts
opportunistic pathogen
Microbe that causes disease only when a host has been compromised
virulence
Degree of severity of disease a pathogen is capable of causing
Pathogenecity
Relative measurement of the ability of a microbe to cause disease
Virulence vs pathogenicity
Virulence describes directly how harmful a pathogen (SEVERITY) it is. Pathogenicity describes the overall process of infection such as transmission (ABILITY TO INFECT)
Case-to-infection (CI) ratio
The proportion of infected individuals who develop the disease. Used to measure pathogenicity
pathogenesis
Process by which a pathogen causes disease
symptom
Subjective disease state, such as muscle aches
sign
Objective disease state that can be readily observed or measured, such as a rash or fever
symptom vs sign
symptom is subjective and sign is objective
virulence factor
Product made by a pathogen that enhances its ability to cause disease
antigenic variation
Change in molecules on the surface of a pathogen to which the immune system responds; can allow pathogen to avoid immune detection
latent infection
Infection characterized by a delay or cessation of disease; in viral disease, characterized by limited transcription of the viral genome; results in reduced immune response; see also latency
autophagy
Intracellular degradation in which materials to be destroyed are encased in a membrane and sent to the lysosome
toxin
Substance of biological origin that damages a host
apoptosis
Cell death accomplished through a highly ordered and tightly controlled cascade of chemical-signaling events within the cell that results in its destruction without the release of damaging cell constituents or triggering of inflammation
necrosis
Cell death that occurs through chemical or physical cell injury or loss of oxygen supply; results in cell rupture and the release of toxic cellular contents and cytokines to the surrounding tissues, producing further cell death and triggering inflammation
fomite
Inanimate object via which pathogens may be transferred to a susceptible host aka water or food
Indirect trasmission
Spread of an infectious agent from one individual to another via an object, like a contaminated inanimate object, water, food, or an insect
Direct transmission
Spread of an infectious agent via physical contact between an infected individual and a susceptible individual
Koch’s postulates
Guideline for demonstrating that a specific microbe causes a specific disease:
- The suspected microbe should exist in every individual with the disease and account for the signs and symptoms of the disease.
- The microbe should not be fortuitously associated with other diseases as a non-pathogen.
- After being isolated and grown in a pure culture, the microbe should cause the same disease following inoculation of a healthy host.
A fourth postulate, stating that the suspected microbe then should be re-isolated from an experimentally inoculated host, often has been added to this original list.
Molecular Koch’s postulates
Guideline using molecular tools to demonstrate that a specific microbial product is a virulence factor:
- The virulence factor gene should be present and expressed in pathogenic strains of the microbe.
- Experimental inactivation of the virulence factor gene should lead to a decrease in virulence.
- Experimental reversion of this inactivating change should result in a restoration of virulence.
- The virulence factor gene should be expressed during an infection.
Resistance to the virulence factor must provide protection.
prevalence vs incidence
prevalence is the total number of cases over a period of time or at a specific time. Incidence is the number of new cases over a period of time.
Ex:
There were 500 cases of the flu during November. 400 started in November. The 500 cases are the prevalence, and the 400 new ones are the incidence.
horizontal trasmission
Spread of an infectious agent between members of a species that are not parent and offspring
vertical trasnmission
Spread of an infectious agent from parent to child
pathogenic islands and their role in making new pathogenic microbes through horizontal gene transfer
Region of a chromosome containing multiple virulence factor genes. They are sometimes transferred to non-pathogenic bacteria creating new pathogens
Be familiar with horizontal gene transfer mechanisms: transduction, transformation,
conjugation.
Transduction: the process by which DNA is transferred from one bacterium to another by a virus.
Transformation: a process where bacteria can uptake foreign extra-cellular DNA
conjugation: DNA is transferred from a donor to a recipient bacterium by direct contact
Steps of a microbe causing disease
- Gain entry into host
- Attach to target organism/cells
- Evade host defenses
- Obtain nutrients from the host
- Exit the host
How does attachment occur
Most commonly through protein-to-protein interactions: viruses tend to bind to specific host cell receptors
Less commonly attachment occurs through generalized interactions: rice blast fungus attaching to hydrophobic surfaces like cells
How do microbes evade host defenses
Antigenic variation, latency, capsules, phage evasion, or phage defense
exotoxins
produced by bacteria that cause immune responses
endotoxins
part of the microbial itself
