Pathogenicity and Epidemiology

pathogenicity

an organism’s ability to cause disease

virulence

the degree of pathogenicity

virulence factors

needed for virulence, but not for viability

examples of virulence factors

toxins, enzymes, adhesion, motility, capsules

exotoxins

released from living organisms - usually protein, very potent, doesn’t cause fever, destroyed by heat

endotoxins

part of a gram negative bacterial cell wall that is released upon death, LPS - less potent, heat stable, causes inflammation and fever

adherence factors (adhesins)

fimbriae, capsule, lectin

epidemiology

the study of factors and mechanisms for the spread of disease

epidemic

many infections at one time in one population

pandemic

many infections at one time worldwide

endemic

always present in a population

sporadic

occasional cases spread out in time and space (typically not communicable)

acute

develops rapidly, typically short-lived

chronic

develops slowly, long-lived

sub-acute

in-between acute and chronic

latent

stays inactive for a long time

LD50

lethal dose for 50% of the population

ID50

infective dose for 50% of the population

contaminated

host has received exposure

infected

host has been colonized

illness

host has disease

local infection

infection is confined to a limited area

systemic infection/disseminated disease

infection throughout the body

bacteremia

bacteria in the blood

septicemia

bacteria growing in the blood

viremia

virus in the blood

toxemia

toxins in the blood

primary infection

acute initial illness

secondary infection

a second agent causes greater disease in someone who is already sick

opportunistic pathogen

wouldn’t necessarily get you sick unless you already have a weakened immune system

subclinical infection

no noticeable illness, but the person is still infected

mortality

the number or rate of deaths

morbidity

the number of cases of the illness

etiology

the cause/history of disease or outbreak

nosocomial 

acquired in a healthcare setting

symptoms

what the patient feels

signs

what the physicians sees or measures

asymptomatic

no symptoms

communicable

can spread from host to host

contagious

easily spread from host to host

noncommunicable

not spread from host to host

exposure/contamination

infection

incubation period

the period before signs and symptoms show

prodromal period

signs and symptoms are not yet developed enough for diagnosis

period of illness

period during which signs and symptoms are present

period of decline (convalescence)

illness declines, patient begins to feel better

common reservoirs

humans, animals, soil, water, food

portals of entry

skin, mucus membranes, nose/mouth/eyes, placenta, parenteral (injections)

portals of exit

bodily fluids, feces, urine, coughing or sneezing

transmission through direct contact

shaking hands, kisses, sexual contact, touching a lesion

transmission through indirect contact

touching doorknobs (fomites), sneezing, coughing

fomites

inanimate objects that spread disease

vehicle definition

many people become ill from the same source

common vehicles of transmission

airborne, waterborne, foodborne

biological vectors of transmission

mosquitos, ticks, etc - insects that move the pathogen from one host to another