infectious agents and transmission (PH exam 2)

burden of diseases

more common in low- and middle income countries

pathogens definitiion

disease-causing microorganisms that grow in or on the body, damaging the tissue, inducing inflammation and triggering signs/symptoms

virulent

ability to cause disease

communicable

able to be transmitted

what is involved in the epidemiologic triad

host, agent, environment, and vector

host

• the “who” organism harboring the pathogen or microbe

• what features of host will foster the onset or transmission of disease

agent

• the “what”; mircobe that causes the disease

• what features of the agent will foster the onset or transmission of disease

• reservoir- source of an infectous agent

environment

• the “where” external factors that cause or allow transmission

• what features of environment will foster the onset or transmission of disease

• anything about environment that will change transmission

vector

• living agent that carries and transmits the infectious pathogen

• communicable disease are those with human vectors

what do we want to know to prevent spread of an infectious disease

when and for how long is someone contagious

infectious period: period of contagion

• time interval when an infected host can transmit to susceptible hosts

• highly variable across different diseases

• known as infective period, communicability period, contagious

latent period

time period from infection to onset of infectious period

testing is usually inaccurate

subclinical infectious period

time from start of infectious to onset of symptoms

• is infectious but doesn’t have symptoms

• might start screening

preclinical phase

incubation period in infectious disease natural history terminology

• interval from infection to onset of sign/symptoms

transmission

horizontal vs vertical

horizontal transmission

transmission from reservoir to susceptible human- can be direct or indirect

vertical transmission

transmission from one generation to the next (infected mothers to newborns)

direct transmission

individual is infected through direct contact with reservoir

indirect transmission

pathogen can live outside host (sometimes on fomites which can be contaminated) before infecting another individual

fomite

contaminated inanimate object (drinking fountain)

nosocomial infections

• infections that are hospital-aqquired

• pathogens can be from:

  • patient

  • healthcare staff

  • infected instruments or needles

  • environment

epidemic

normal frequency of disease with respect to time population, and geographic area

sporadic

occasional disease that is unexpected but does not prompt further cases

epidemic

occurrence of disease in excess of normal expectancy with respect to time, population, and geographic area

pandemic

worldwide epidemic, only world health can declare

WHOs pandemic definition

• when diseases growth is exponential

• when daily new cases grow more than they did day prior

• covers a wide area and crosses international borders

• leads to large-scale social disruption, economic loss, etc

international health regulation

legally binding agreement of 196 countries; require all countries to have ability to detect, assess, report and respond to PH events