ch. 11 - final exam

epidemiology & cycle of microbial disease

epidemiology

is an investigative branch of medicine that deals with the source, cause, & possible control of infectious disease & other public health problems

epidemiologists

are challenged to determine why an outbreak of disease occurs at a particular time &/or particular place

sporadic diseases

occur only occasionally & in an unpredictable fashion (tetanus)

endemic diseases

regularly found at a steady level in a particular location (common cold)

epidemic diseases

sudden increase in morbidity (illness rate) & mortality (death rate) above the norm (plague)

pandemic diseases

epidemics that spread across continents (covid)

common-source epidemics

involve contact with a single contamination source (contaminated water)

propagated epidemics

result from person-to-person contact (syphilis & HIV)

herd immunity

proportion of immunized individuals in a population; can slow the spread of disease

reproduction rate (R0 or R-nought)

mean # of secondary cases, occurring in a susceptible population in the wake of a particular infection

calculating R0

BS/Y

B- transmission rate

S- # of susceptible at start of epidemic

Y- removal rate

cycle of microbial disease

1. pathogen

2. reservoir (source) of pathogen

3. transmission to susceptible host

4. portal entry into susceptible host

5. portal exit out of susceptible host

reservoir is

a site in nature in which microbes survive (& possibly multiply) & from which they may be transmitted

characteristics of reservoirs

• all pathogens have > 1 reservoir

• are prime targets for preventing, minimizing, eliminating existing & potential epidemics

• humans are reservoir for pathogens causing smallpox, gonorrhea, measles, polio

two types of carriers

active & healthy carriers

active carriers are

individuals who have a microbial disease

healthy carriers are

ones who have no symptoms & may unwittingly pass the disease on to others

chronic carriers are

a type of healthy carrier- individuals harbor a pathogen for long periods without becoming ill with the disease but may spread to others (Salmonella, Hepatitis B virus

zoonoses are

disease in which animals serve as reservoirs

nonliving reservoirs

some organisms able to survive & multiply in nonliving environments: soil & water

transmission is

a mechanism by which an infectious agent is spread to a susceptible person

direct transmission

microbes from reservoir (or source) & host

• contact, animal bites, transplacental

indirect transmission

microbes from reservoir (or source), intermediate agent, & host

• vehicle-borne, airborne, vectors

vectors of infectious diseases include

ticks, fleas, mosquitos, louse, kissing bugs, tsetse fly

portal of entry

access into (or onto) the body; important in the outcome of infection

portal of exit

is required for transmission to a new host

hospital environment as a source of nosocomial infections

• ill patients - weakened immune system

• foster development of antibiotic-resistant strains of bacteria

• invasive procedures & insertion of needles, catheters, tubes, etc., facilitate direct transmission of microbes

control measures

all hospitals required to have an infection-control officer & committee to maintain accreditation