Terms Flashcards
epidemiologic triad
- an agent
- a susceptible host,
- an environment that brings the host and agent together so that disease occurs.
vehicle
an inanimate object that can carry an agent from a reservoir to a susceptible host (e.g., food, water, blood products, and bedding).
fomite
an inanimate object that can be the vehicle for transmission of an infectious agent (e.g., bedding, towels, or surgical instruments).
infectivity
the ability of an infectious agent to cause infection, measured as the proportion of animals exposed to an infectious agent that become infected.
pathogenicity
the ability of an agent to cause disease after infection, measured as the proportion of animals infected by an agent that then experience clinical disease.
virulence
the ability of an infectious agent to cause severe disease, measured as the proportion of animals with the disease that become severely ill or die.
Herd immunity
the resistance to an infectious agent of an entire group or population (and, in particular, protection of susceptible animals) as a result of a substantial proportion (70-80%) of the population being immune to the agent. Herd immunity is based on having a substantial number of immune animals, thereby reducing the likelihood that an infected animal will come in contact with a susceptible one within the population.
outbreak
the occurrence of more cases of disease, injury, or other health condition than expected in a given area or among a specific group of animals during a specific period. Usually, the cases are presumed to have a common cause or to be related to one another in some way. Sometimes distinguished from an epidemic as more localized, or the term less likely to evoke public panic.
endemic
the constant presence of an agent or health condition within a given geographic area
or population; can also refer to the usual prevalence of an agent or condition.
epidemic
the occurrence of more cases of disease, injury, or other health condition than expected in a given area or among a specific group of animals during a particular period. Usually, the cases are presumed to have a common cause or to be related to one another in some way (see also outbreak).
pandemic
an epidemic occurring over a widespread area (multiple countries or continents) and usually affecting a substantial proportion of the population.
epidemic curve
a histogram that displays the course of an outbreak or epidemic by plotting the number of incident (i.e., new) cases according to time of onset.
attack rate
a form of incidence that measures the proportion of animals in a population that experience an acute health event during a limited period (e.g., during an outbreak), calculated as the number of new cases of a health problem during an outbreak divided by the size of the population at the beginning of the period.
