Glossary of Microbiology: Chapter 37

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Define Prevalence
Prevalence is the number of cases at a given time/population unit
Define morbidity
Morbidity is the number of new cases/time period/population unit
Define mortality
Mortality is the number of deaths/number with disease
Define outbreak
An outbreak is a small, localized increase in the occurence of a disease
Define index case
An index case is the first disease case in an epidemic within a give population
Define endemic
Endemic is the basal level of a disease (if the endemic is high it is refered to as hyperendemic)
Define epidemic
An epidemic is a significant increase in the frequency of a disease
Define pandemic
A pandemic is a global epidemic (crosses continents)
Differentiate between signs and symptoms of an infectious diseas.
Signs of an infectious disease are objective changes that can be observed/measured (fever, rash, weight loss), while symptoms are subjective changes experienced by the patient (pain, nausea).
What are the five stages of a typical infectious disease?
The five stages of a typical infectious disease are 1) Incubation, 2) Prodromal, 3) Acute, 4) Decline, and 5)Convalescent periods.
During which stage is a disease usually contagious?
A disease is most usually contagious during the prodromal and acute periods, although it is sometimes contagious in incubation and decline periods.
What is a syndrome?
A syndrome is a typical or diagnostic set of signs and symptoms.
What are Koch's postulates?
How do the kinetics of propagated spread differ from common source epidemics?
A propagated spread has a slow rise and a slow decline, while a common source epidemic has a sharp rise and a sharp decline.
What is threshold density and what happens when the level is reached in a propagated epidemic?
Threshold density is the minimum number of individuals necessary to continue propagating the disease. When threshold density is reached in a propagated epidemic the incidence of new cases ceases because the pathogen can not propagate itself.
What are sources and reservoirs?
A source is a location from which the etiologic agent is transmitted to the host. A reservoir is a habitat where the organism can reproduce and be a source for subsequent infections.
What are examples of animate and inanimate reservoirs?
An examples of animate reservoirs are animals (carriers). Examples of inanimate reservoirs are soil, water, etc.
What is a carrier?
A carrier is an infected individual that acts as a source.
When is a disease a zoonose?
A disease is a zoonose when it is carried by an animal and transmitted to humans.
What constitutes airborne transmission?
For transmission to be considered airborne the pathogen must travel in the air at least one meter.
What are droplet nuclei?
Droplet nuclei are small particles that represent what is left from evaporation of larger particles called droplets (they are airborne).
What are examples of direct contact transmission?
Examples of direct contact transmission (person to person) are sex and rabies (animal bite).
What are fomites?
Fomites are inanimate objects that transmit to host.
Whay are aerosols listed under contact rather than airborne?
Aerosols are listed under contact rather than airborne because they travel less than one meter.
What are examples of "common vehicles"?
"Common vehicles" are common inanimate intermediaries in the indirect transmission of an agent that carries the agent from a reservoir to a susceptible host. Two examples are food and water.
Differentiate between mechanical and biological vectors.
In mechanical vector transmission carriage of the pathogen is passive, which no growth during transmission (ex: flies). In biological vector transmission the vector acts as a reservoir where the pathogen grows (ex: mosquito).
What is the apparent relationship between transmission rates and changes in virulence?
There are two possible relationships between transmission rates and changes in virulence: Decreasing transmission rates favors decreased virulence-this appears true for cholera and bacillary dysentary, and
Increasing transmission rates favor increased virulence-this is hypothesized for the flu epidemic of 1918.
Give an example of how a pathogen can be induced to evolve increased virulence.
A pathogen can be induced to evolve increased virulence if the spread of the disease is independent of host health/survival (ex: colds/gonorrhoea, syphillis)
Give an example of how a pathogen can be induced to evolve decreased virulence.
A pathogen can be induced to evolve decreased virulence if the spread of the disease is dependent upon host health/survival (ex: arthropod-borne diseases/diphtheria, tuberculosis)
How do changes in transportation and the disruption of ecosystems contribute to the emergence of new diseases?
What are the three types of measures we use to control epidemics? Cite a couple examples for each.
Three types of measures we use to control epidemics are 1)reducing or eliminating the source/reservoir (ex:quarantine, treatment of waste, destruction of animal reserve), 2) breaking the connection (ex: chlorination of water, pasteurization, destruction of vectors), and 3) increasing the herd immunity (ex: active and passive immunization).
Why are biological agents effective for terrorists?
Biological agents are effective for terrorists because they have small mass, are inexpensive, there is a delay from release to effect, the manufacture and dispersal can be low tech, and they have a strong psychological impact.
What are the bacteria, viruses, and toxins most commonly associated with biowarfare?
Some of the bacteria, viruses, and toxins that are most commonly associated with biowarfare are: Bacillus anthracisis, Yersinia pestis, Hemorrhagic viruses, Variola (smallpox virus), Botulinum toxin, and Staph. enterotoxin.
What are three general strategies employed in defense against bilogical agents?
Three general strategies employed in defense against biological agents are vaccines, drugs, and detection/intelligence.

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