Epidemiology and Disease Transmission Flashcards
- The word comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of.
*is the study of the distribution and determinants of health- related states or events in specified populations, and the application of this study to the control of health problems - Study of interrelationship of factors in particular areas in the field of health, and the application of the results of such studies to influence such factors to achieve a given outcome.
- Study of ecology of health and disease, and the application of knowledge gained to promote health and control diseases.
EPIDEMIOLOGY
- Traditional epidemiologic triad model holds that infectious diseases result from the interaction of agent, host, and environment.
- Transmission occurs when the agent leaves its reservoir or host through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host.
CHAIN OF INFECTION
- Any element, substance, or force whether living or non-living, the presence or absence which can initiate or perpetuate a disease process.
- Could be physical and mechanical in nature
- Chemicals
- Exogenous
- Endogenous
AGENT
Physical features, biologic requirements, chemical make-up, viability, and resistance.
Inherent Characteristics
o Pathogenicity measures the ability of an agent when lodged in the body to set-up a specific reaction, local or general, clinical or sub-trial.
o Virulence- refers to the severity of the reaction produced and is usually measured in terms of fatality.
o Antigenicity- the ability to stimulate the host to produce antibodies
Characteristics directly related to man
o Refers to the reservoir and sources of infection and
o Modes of transmission.
Characteristics in relation to the environment
- The habitat in which the agent normally lives, grows, and multiplies.
- Includes humans, animals and the environment
- The reservoir may or may not be the source from which an agent is transferred to a host.
RESERVOIR
o Many common infectious diseases have.
o Sexually transmitted diseases, measles, mumps, streptococcal infection, and many respiratory pathogens.
HUMAN RESERVOIRS
o Many of these diseases are transmitted from animal to animal, with humans as incidental hosts.
o Zoonosis- refers to an infectious disease that is transmissible under natural conditions from vertebrate animals to humans
ANIMAL RESERVOIR
o Plants, soil, and water in the environment are also reservoirs for some infectious agents.
o Many fungal agents, such as those that cause histoplasmosis, live and multiply in the soil.
ENVIRONMENTAL RESERVOIR
- is the path by which a pathogen leaves its host.
- The portal of exit usually corresponds to the site where the pathogen is localized.
Portal of Exit
o Occurs through skin- to-skin contact, kissing, and sexual intercourse.
o Direct contact also refers to contact with soil or vegetation harboring infectious organisms.
Direct transmission
o Refers to spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking.
o Droplet spread is classified as direct because transmission is by direct spray over a few feet, before the droplets fall to the ground.
Droplet spread
o Refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors).
Indirect transmission
Occurs when infectious agents are carried by dust or droplet nuclei suspended in air.
Airborne dust includes material that has settled on surfaces and become re suspended by air currents as well as infectious particles blown from the soil by the wind.
o Airborne transmission
may indirectly transmit an infectious agent include food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels). A vehicle may passively carry a pathogen - as food or water may carry hepatitis A virus.
Vehicle-borne
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-borne
- The portal of entry refers to the manner in which a pathogen enters a susceptible host.
- The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act.
Portal of Entry
- The final link in the chain of infection is a susceptible host.
- Susceptibility of 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.
- An individual’s genetic makeup may either increase or decrease susceptibility.
Host
- Knowledge of the portals of exit and entry and modes of transmission provides a basis for determining appropriate control measures.
- In general, control measures are usually directed against the segment in the infection chain that is most susceptible to intervention, unless practical issues dictate otherwise.
- Interventions are directed at:
Implications for Public Health
Implications for Public Health Interventions are directed at:
o Controlling or eliminating agent at source of transmission
o Protecting portals of entry
o Increasing host’s defenses
refers to the severity of the reaction produced and is usually measured in terms of fatality.
Virulence
the ability to stimulate the host to produce antibodies
Antigenicity
