Lecture 3 8/28/24 Flashcards
How can a case be defined?
based on signs, symptoms, epidemiology, and/or performance
How are disease patterns described in populations?
by animal characteristic, in space, over time
What are the two most common ways of depicting spatial distribution?
-area maps
-simple spot/dot maps
Why is it important to characterize disease in populations?
-to describe the current status of the population, as well as changes over time
-to make comparisons between groups over time
-to establish cause and identify possible preventive measures
What are the different patterns of disease?
-sporadic
-endemic
-outbreak/epidemic
-pandemic
What is a sporadic disease?
occurs infrequently with no discernable pattern
What is an endemic disease?
occurs with a predictable pattern and has a constant presence
What is an epidemic disease?
significantly more disease than usual, with no predictable pattern
What is a pandemic disease?
epidemic affecting a number of countries
What does a sporadic disease pattern potentially suggest about the causative agent?
-causative agent infrequently infects the host
-causative agent is usually present, but other factors are required for clinical disease to develop
What is endemic disease the result of?
a predictable and often long-term balance between agent and host
Why is the word outbreak used instead of epidemic?
-outbreak draws less media attention and is perceived as less frightening
-often used with food related illnesses
How does an outbreak differ from an epidemic?
-outbreak is any occurrence of disease at a higher rate than expected, but is relative
-epidemic is occurrence of disease in which the frequency of disease during a time interval is clearly in excess of expected frequency
What is an epidemic curve?
graph of the number of new cases over time, which provides information about how disease is spreading in the population
Which two values are key to the construction of an epidemic curve?
-time of disease
-frequency of disease
Which factors impact the shape of an epidemic curve?
-incubation period
-infectivity
-proportion of susceptible hosts in the population
What is a minimum/threshold density?
the number of susceptible animals required to allow contact-transmitted epidemic to commence
What is a point source epidemic?
epidemic in which there is a rapid onset of disease cases, indicating a common source
What is a propagated epidemic?
epidemic in which there is a slower onset of cases with a build up over time, indicating animal-to-animal transmission
What are the characteristics of a point source epidemic?
-common source
-usually needs a vehicle
-skews epidemic curve to the right
What are the characteristics of a propagating epidemic?
-animal to animal transmission
-usually spread by hosts and/or vectors
-epidemic curve skews to the left
What are the defining characteristics of a pandemic?
-epidemic affecting multiple countries
-disease must be infectious
What are the components of the WHO definition of a human pandemic?
-emergence of disease new to a population
-agent infects humans and causes serious illness
-agent spreads easily and sustainably among humans
How does the pattern of disease change with time and a stable environment?
starts as epidemic before transitioning to endemic and eventually sporadic
