EPIDEMIOLOGY AND DISEASE TRANSMISSION PART 2 Flashcards
transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or
animate intermediaries (vectors)
indirect Transmission
a host depends on genetic or constitutional
factors, specific immunity, and nonspecific factors that affect an individual’s ability to resist infection or to limit pathogenicity
Susceptibility
The final link in the chain of infection
host
occurs when infectious agents are
carried by dust or droplet nuclei suspended in air
Airborne transmission
dried residue of less than 5 microns in
size, it may remain suspended in the air for long periods of time and may be blown over great distances
Droplet Nuclei
material that has settled on surfaces and
become resuspended by air currents as well as infectious particles blown from the soil by the wind
Airborne Dust
such as mosquitoes, fleas, and ticks may carry an infectious agent through purely mechanical means or may support growth or changes in the agent
Vector
the causative agent of malaria or
guinea worm disease undergoes maturation in an intermediate host before it can be transmitted to humans
Biologic transmission
are flies carrying Shigella on
their appendages and fleas carrying Yersinia pestis, the causative agent of plague, in their gut.
Mechanical transmission
transmission in food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels)
Vehicle transmission
the manner in which a pathogen enters a susceptible host
Portal of Entry
what causes many pathogens follow a so called “fecal- oral” route because they exit the source host in feces, are carried on inadequately washed hands to a vehicle such as food, water, or utensil, and enter a new host through the mouth
gastroenteritis
Other portals of entry include the skin
hookworm, syphilis, hepatitis B human
immunodeficiency virus
protective antibodies that are directed
against a specific agent
Specific immunity
Nonspecific factors that defend against infection includes:
skin, mucous membranes, gastric acidity, cilia in the respiratory tract, the cough reflex, and nonspecific immune response
Factors that may increase susceptibility to infection by disrupting host defenses includes:
malnutrition, alcoholism, and disease or therapy that impairs the nonspecific immune response
level of disease that amount of a particular disease that is usually present in a community
baseline or endemic level of the disease
level of disease may continue to occur at this level indefinitely
observed level
disease that occurs infrequently and irregularly
Sporadic
persistent, high levels of disease
occurrence
Hyperendemic
constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area
Endemic
carries the same definition of epidemic, but is often used for a more limited geographic area
outbreak
an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known
Cluster
an epidemic that has spread over several
countries or continents, usually affecting a large number of people
pandemic
