Principals of Disease and Epidemiology
- Pathogenicity - ability of organisms to cause disease >
- Transmission
• infectious dose (ID50) - number of organisms to • direct - person to person, animal, environment,
colonize 50% of hosts vertical
- varies between organisms, dependent on host • indirect - airborne, vehicle, vector
factors • communicable - spread between hosts
- lesser ID, more pathogenic - noncommunicable: typically acquired from
>
virulance - severity of disease caused by organism environment (tetanus, botulism, cholera)
• lethal dose (LD50) - number of organisms to kill • contagious - easily spread between hosts
50% of hosts (respiratory infections)
- highly ID50 not necessarily LD50 • zoonotic diseases - animal to human
- lesser LD, more virulent - bites, consuming, handling contaminated products
>
- pathogen types - rabies, beef tapeworm
• opportunistic - cause disease in weakened hosts > stages of infectious disease
- immunocompromised, extremes of age, taking • incubation - between infection and development of
antibiotics, gain access to sterile body sites, iatrogenic symptoms
infections • prodromal - early symptoms develop
• true - cause disease in healthy individuals • acute phase - peak of disease
- associated with specific disease, have pro-virulence • decline - replication agent brought under control,
factors: adherence, cause tissue damaged, exo/ symptoms start to resolve
endotoxins • convalescent - patient recovers
>
- dysbiosis - disruption of normal commensals - epidemiology - to describe, explain, predict, prevent
• reduce local competition, allow pathogens to flourish • describe 5 W's (what, who, where, when, why)
• normal flora are killed off - sever diarrhea, antibiotic • host - who
use
> occurence of disease - organisms exposed to and harboring disease, may
or may not be "sick"
• sporadic - occasional in population (polio, ebola)
• agent - what
• endemic - routinely in population or region (common
cold, gonorrhea) - what causes disease: bacteria, virus, fungi,
protozoa, helminths/parasites, algae
• epidemic - widespread in given area in short time
(influenza) • environment - where
• pandemic - epidemic spreading to numerous - favorable surroundings and conditions that allow
disease to be transmitted (dirty water, blood, warm
countries (AIDS, COVID-19) temp, seasons)
>
- disease tterminology
• vehicle of transmission - where/how
• emerging pathogens - newly identified agents,
pathogens that previously only caused sporadic cases - how host and agent interact in environment
• reemerging pathogen - was under control but is not - vector: mosquito, tick
resurfacing - famine: doorknob, tabletop, medical equipment
> sources >
- health outcomes
• exogenous • morbidity - occurrence of illness, disability, injury in
- environmental: contaminated food, medical population
equipment, soil, water • mortality - occurrence of death in population
- animals, humans >
- herd immunity - most of population is vaccinated
• endogenous > ethics in epidemiology
- misplaced normal microbiota: harmless skin • informed consent, study laws, genetic
bacteria can enter surgical incisions discrimination l
- disrupted microbiota, opportunistic pathogens
- Pathogenicity - ability of organisms to cause disease >
- Transmission
• infectious dose (ID50) - number of organisms to • direct - person to person, animal, environment,
colonize 50% of hosts vertical
- varies between organisms, dependent on host • indirect - airborne, vehicle, vector
factors • communicable - spread between hosts
- lesser ID, more pathogenic - noncommunicable: typically acquired from
>
virulance - severity of disease caused by organism environment (tetanus, botulism, cholera)
• lethal dose (LD50) - number of organisms to kill • contagious - easily spread between hosts
50% of hosts (respiratory infections)
- highly ID50 not necessarily LD50 • zoonotic diseases - animal to human
- lesser LD, more virulent - bites, consuming, handling contaminated products
>
- pathogen types - rabies, beef tapeworm
• opportunistic - cause disease in weakened hosts > stages of infectious disease
- immunocompromised, extremes of age, taking • incubation - between infection and development of
antibiotics, gain access to sterile body sites, iatrogenic symptoms
infections • prodromal - early symptoms develop
• true - cause disease in healthy individuals • acute phase - peak of disease
- associated with specific disease, have pro-virulence • decline - replication agent brought under control,
factors: adherence, cause tissue damaged, exo/ symptoms start to resolve
endotoxins • convalescent - patient recovers
>
- dysbiosis - disruption of normal commensals - epidemiology - to describe, explain, predict, prevent
• reduce local competition, allow pathogens to flourish • describe 5 W's (what, who, where, when, why)
• normal flora are killed off - sever diarrhea, antibiotic • host - who
use
> occurence of disease - organisms exposed to and harboring disease, may
or may not be "sick"
• sporadic - occasional in population (polio, ebola)
• agent - what
• endemic - routinely in population or region (common
cold, gonorrhea) - what causes disease: bacteria, virus, fungi,
protozoa, helminths/parasites, algae
• epidemic - widespread in given area in short time
(influenza) • environment - where
• pandemic - epidemic spreading to numerous - favorable surroundings and conditions that allow
disease to be transmitted (dirty water, blood, warm
countries (AIDS, COVID-19) temp, seasons)
>
- disease tterminology
• vehicle of transmission - where/how
• emerging pathogens - newly identified agents,
pathogens that previously only caused sporadic cases - how host and agent interact in environment
• reemerging pathogen - was under control but is not - vector: mosquito, tick
resurfacing - famine: doorknob, tabletop, medical equipment
> sources >
- health outcomes
• exogenous • morbidity - occurrence of illness, disability, injury in
- environmental: contaminated food, medical population
equipment, soil, water • mortality - occurrence of death in population
- animals, humans >
- herd immunity - most of population is vaccinated
• endogenous > ethics in epidemiology
- misplaced normal microbiota: harmless skin • informed consent, study laws, genetic
bacteria can enter surgical incisions discrimination l
- disrupted microbiota, opportunistic pathogens
