Natural History of Disease Flashcards
describe the pattern of disease progression
- exposure
- infection
- disease: absent/subclinical, mild, moderate, severe clinical
-ending in: cure, control, disability, or death
describe the chain of infection
- etiologic agent: microorganisms capable of causing disease or illness
-include bacteria, fungi, parasites, prions - reservoir host: place in which infectious agents live, grow, and reproduce
-include people, water, food - portal of exit: ways in which infectious agent leaves the reservoir
-includes blood, secretions, excretions, skin - mode of transmission: ways in which the infectious agent is spread from the reservoir to the susceptible host
-includes: physical contact, droplets, airborne - portal of entry: ways in which the infectious agent enters the susceptible host
-includes: MM, resp and GI tracts, broken skin - susceptible host: individuals may have traits that affect their susceptibility and severity of disease
-traits include: immune deficiency, age, stress
what are 5 ways to prevent transmission/break the chain?
- stop the source
- block the portal of exit
- interrupt mode of transmission
- protect portal of entry
- increase host’s defenses
define infectivity, pathogenicity, and virulence
infectivity:
-ability of organism to multiply in a host
-measured by seroconversion and secondary attack rate
pathogenicity:
-ability of an agent to cause disease
-measured by attack rate
virulence:
-ability of an agent to cause severe disease and/or death
-measured by case fatality
describe reservoirs
- ecological niche where a pathogen lives and multiplies
-generally needed to perpetuate the agent - examples:
-fruit bats, nonhuman primates for ebola
-birds for west nile virus
-bodies of water
-soil
describe carriers
- subclinically infected
- NOT necessary to perpetuate the agent
- examples:
-typhoid mary
-herpesviruses (latent carriers)
describe 8 common routes of transmission
- direct contact: physical contact with body fluids
-touching, sexual contact, contact with oral secretions or body lesions - indirect contact: contact with contaminated objects (fomites) or secretions (sneeze/cough)
- droplet: oral/nasal secretions within 3 meters
- aerosol: through the air
-inhalation of infectious particles less than 100um in diameter - vector: typically invertebrates
-biological: essential to pathogen life cycle (develops/multiplies inside)
-mechanical: not essential to pathogen life cycle (simply carries in between hosts) - vehicle: via inanimate substance
-food, water, air, fomite, blood, bone marrow - horizontal: between hosts of a similar generation
- vertical: from parent to offspring
-transovarial, in utero, via colostrum
describe incubation period
time between exposure to the infectious agent and development of clinical signs
describe latent period
- time between infection and when the infected host can spread the agent to others
-infected host may or may not have symptoms - this time is KEY is determining how quickly the infectious agent spreads
- infected host cannot spread agent during this time
describe infectious period
the time when a host is able to spread the infectious agent to others
describe endemic, epidemic, and sporadic disease
endemic: occurs with predictable regularity
epidemic: occurs when the disease exceeds expectations
sporadic: occurs rarely and without regularity
describe point source, continuous source, and propagated epidemics
point source: short period exposure to a single source of infectious agent results in all susceptible hosts becoming sick within one incubation period
-ex. food poisoning in everyone who ate at a buffet
continuous source: susceptible hosts are exposed to the infectious agent over an extended period of time
-ex. cholera from one water pump
propogated: the infectious agent is spread person to person
-ex. COVID
