1.2 Introduction to Disease

Merriam Webster

condition of the living body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs/symptoms

signs

changes that can be observed by a health practitioner and are objective (ex. fever, swelling, lesions)

symptoms

changes in body function that are subjective and not observable (ex. pain, discomfort, nausea)

subclinical

clinical signs/symptoms are absent

acute

sudden onset but brief duration

chronic/persistent

long-term condition, disease, or infection

subacute

intermediate of acute and chronic disease

fulminant

occurs rapidly and severe intensity

primary

clinically apparent disease with specific known cause

secondary

microbial invasion right after primary infection

recurrent

multiple acute episodes of same infection

opportunistic

infectious disease caused by transient or normal flora bacteria when host resistance is depressed

contagious

easily transmissible disease or highly communicable period of infection

latent/dormant

subclinical carrier state that is typically not considered transmissible

localized

confined to a small area of the body

systemic

disseminated/spread throughout many parts of the body

incidence rate

number of new cases arising in a defined population over a specified period of time (ex. 100 new cases per day)

prevalence

number of individuals who have a disease at any one time (ex. 100 million Americans have had)

attack rate

frequency of active cases of disease/number of people exposed (ex. 4/60 → 4 sick, 60 exposed)

Ro

basic reproduction rate, expected number of new cases one infected individual will generate (how easily transmissible)

mobidity

incidence rate or prevalence

mortality

quantification of deaths or death rate

sporadic

occurs in single or scattered instances

cluster

aggregation of cases within a limited geographical area and time

endemic

constantly present in a population

hyperendemic

an endemic disease with comparatively persistent high levels

outbreak

incidence rate substantially exceeds what is “expected” based on recent experience

epidemic

an outbreak that spreads rapidly to many people

pandemic

an epidemic that spreads internationally, can only be declared by world health organization

epidemiology

study of who, what, when, where, and why of diseases

reservoir

continual source of the disease organisms that provides an ongoing opportunity for transmission

carriers

human reservoirs that harbor pathogens but don’t show signs of illness or become ill

zoonoses

animal reservoirs that have a disease able to be transmitted to humans

non living reservoirs

usually consists of water or soil, typically a result of lack of proper sanitation

nosocomial infection

hospital acquired infection

transmission

movement of a pathogen from one source to another

contact transmission

direct contact/interaction (also includes coughing, sneezing)

airborne transmission

infectious droplet nuclei, protection includes minimum gas mask

vehicle transmission

fomites (non living carriers/interaction), such as doorhandles or food borne

vector transmission

carried by another organism

biological vector transmission

disease needs a specific vector

mechanical vector transmission

vector is just carrying disease, not specifically needed

ID50

infectious dose for 50% of a sample population; may vary based upon pathogen, portal of entry, or age of host

incubation period

time between introduction of microbe into host and first appearance of signs/symptoms

prodromal pahse

short period following the incubation period characterized by early and mild symptoms such as malaise and fever

illness/invasive phase

disease is the most acute with apparent signs, if the immune system is ineffective during this period then the patient dies

decline phase

signs and symptoms begin to diminish, length of time varies, most susceptible to secondary infection during this period

convalescence period

return of the body to normal state, may still be infectious

acute self-limited infection

follows developmental curve

persistent infection with shedding

microbe persists after recovery in infectious form with continuous or intermittent shedding

persistent latent infection

microbe persists in latent non-infectious form until reactivation with microbial growth and shedding

persistent slow infection following acute infection

microbe slow grows until final disease after the initial recovery

persistent slow infection (no acute stage)

continual slow microbial growth until final disease

factors that influence outcome of infection

genetic/biological factors, social/political/economic factors, ecological factors, physical environmental factors