exam 1 Flashcards
what is disease
any impairment that interferes with or modifies the performance of normal functions
vector
living organisms that can transmit infectious pathogens between humans, or from animals to humans
parasite
organisms that live on or in another organisms and depend on this host to complete their life cycle
pathogen
a microorganism that causes damage to a host
infectious disease
can be transmitted to/from another person or organism as a result of transmission of a biological agent
infectious disease agents
living agents that cause harm while living in or on a host (viruses, bacteria, fungi, protozoa, helminths, arthropods)
noninfectious disease
not transmitted directly, and instead are a result of a combination of environment and genetics
noninfectious disease agents
nonliving agents (chemicals, toxicants, poisons), physical agents (cold, heat, trauma), nutrient deficiency (vitamin c, minerals, salts)
zoonosis
disease caused by an infectious agent that can transferred naturally from wildlife to humans and back to wildlife
what percent of emerging infectious disease in humans are zoonotic
60 - 75
intrinsic causes of disease
genetic defects, degeneration
extrinsic causes of disease
infectious/non infectious agents, noninfectious transmissible agents (prions)
spillover
transmission of a pathogen from one host species to another
amplifier
a host, within which, a pathogen replicates or is transmitted at rapid abundance or rate
spillback
transmission of a pathogen from a spillover host back into the reservoir host from which it originated
etiology
study or theory of the factors that cause disease
cause
that which brings about a condition or produces any effect
koch’s postulates
- agent present in every case of the disease, not others
- isolate agent, grown in pure culture
- inoculate experimental animals with culture, develop disease
- must recover the same agent from inoculated/infected animals
exceptions to koch’s postulates
noninfectious diseases
mixed infections - tough to separate agents, know which is causing which part
carrier state - agent present, no disease
opportunistic agents - agents present and do not cause disease
chronic disease - the cause is gone before the disease appears
emerging infectious disease
a disease that either has appeared and is affecting a population for the first time or has existed previously but is rapidly spreading in incidence or space
incidence
rate of cases occurring during a particular time period
web of causation
epidemiologic model that strongly emphasizes the concept of multiple causation while de-emphasizing the role of agents in explaining illness
epidemiological triad
a simple model where the agent is not central focus causation includes interaction among host, agent, environment
applies to disease emergence and re-emergence
what causes emergence
host - susceptibility
pathogen - infectivity, virulence
environment - stressors of conditions influencing hosts, pathogens, vectors, etc
two strategies of detection
- detecting the pathogen/parasite itself - microparasites, macroparasites
- detecting disease - mainly searching for evidence of an immune response (blood/serum test), impairment of function, or clinical signs
three steps of conducting a good study
- state the question/hypothesis of interest clearly
- these shape what data needs to be collected and hence the type of study
- develop an appropriate plan for sampling
the goal of sampling is to…
answer a research question in a way that is minimally biased and fairly precise
population of interest
the complete collection of sample units of interest within a defined area (the sample frame)
ex. individuals within a defined population or plots within a defined area
sample
some fraction of the units within the population of interest are randomly selected
data from the sample are used to estimate some parameter(s) of interest from the target population
parameter
a quantitative measure that describes a characteristic of a population
fixed quantity in a population; usually unknown
ex. mean, sd, variance
estimator
a formula, or function of the sample data used to estimate some parameter
estimate
the value you calculate from the sample to estimate the parameter
often denoted by a caret or hat (^) over the symbol
bias
describes how far the average value of the estimator is from the true population value
measures of quality of an estimate include
precision and prevalence
precision
refers to the closeness of repeated measurements of the same quantity
standard deviation (SD), standard error (SE), and coefficient of variation are all measures of precision
ALWAYS report a measure of precision along with a parameter estimate (e.g., a confidence interval or SE on the parameter estimate)
prevalence
proportion of hosts infected
# currently infected / # in population
types of random selection sampling
simple random and stratified random
simple random sampling
every possible sample unit in the study area/sampling frame has an equal chance of being sampled during each sampling event; typically done without replacement - enumerate all possible sample units and take a random sample from the list
stratified random sampling
the sampling frame is divided into mutually exclusive and exhausted strata (subgroups) and a simple random sample is taken from each stratum
benefits of stratified random sampling
increased precision because variation among units within a stratum is < variation among units across strata
allows for unique estimation of mean/variance for each strata
allows for different numbers of sample units by strata
