4.4 The Chain of Infection and Disease Transmission

most (but not all) infectious diseases are…

communicable disease

what is a communicable disease

illnesses spread between hosts by either direct or indirect contact with a pathogen

the theory of how communicable diseases spread between hosts is called the…

chain of infection

if we can break the links in the chain, we can…

prevent the spread of infection

the first link is the…

presence of an infectious microbe in the environment

most chains of infection occur in the place where a microbe is…

endemic

what does endemic mean

the area where a microbe is found under normal circumstances and infection regularly occurs

an epidemic is an…

unusually rapid spread or growth of infections, beyond the endemic region

pandemic spread is an epidemic in which growth of infections is…

uncontrolled + spread across international borders

within the environment, a microbe must have one or more…

reservoirs

what is a reservoir

the place or host a microbe grows/reproduces

typically, the reservoir is also a…

source of infectionw

what does source mean

the site from which a microbe is transmitted to a new host

EX: hookworm reservoir is human hosts but the source of infection is…

contaminated soil

human reservoirs: human hosts are people who…

have active infections

reproduction of the microbe within the host…

causes active diseasec

carriers are people who…

harbor pathogenic bacteria in their bodies without disease

carriers include:

• people with asymptomatic infections

• people with latent infections

• people who carry pathogens in the normal microbiota

animal reservoirs: diseases with animal reservoirs are called…

zoonotic diseases

animal reservoirs…

may or may not experience disease due to infection

environmental reservoirs: some pathogens can grow and survive in…

soil and water

when growing within a human or animal reservoir, there must be a…

way for the pathogen to leave the body of the reservoir

there must be a way for the pathogen to leave the body of the reservoir.. this is called

portal of exit

nearly all pathogens exit the body…

within some sort of bodily fluid

enviromental reservoirs…

DO NOT have portals of exit

what is otic?

discharge from ear infections that contain pathogenic organisms

mucus secretions naturally…

trap pathogenic organisms

coughing/sneezing can make…

fine mists of mucus called respiratory droplets

the GI tract produces…

saliva, feces & bule

pathogens can be harbored in…

urine and sexual secretions

what is ocular

eye infections will cause tears to harbor pathogenic organisms

discharge from skin infections typically contains both…

immune cells and pathogenic organisms

during many infections, other bodily fluids may become…

contaminated with blood

blood itself can exit directly through…

wounds or during withdrawal during medical procedures

once the pathogen has left the reservoir, it must be…

passed to new host

the way that this happens is the pathogen’s…

mode of transmission

transmission is typically closely tied to a pathogen’s..

portal of exit

a single pathogen may have…

multiple modes of transmission

transmission will always be some kind of…

contact with the pathogen itself

direct contact types of transmission occur when there is…

contact between the source of the pathogen and the new host

1. person to person contact

2. animal contact

3. environmental contact

4. vertical transmission

what is person to person contact

contact with an ill person via skin or mucus membranes

person to person contact varies by portal of exit but includes:

skin to skin contact, kissing, etc.

person to person contact can also happen with…

contact with the bodily fluids or waster of an ill person

PTP contact varies by portal of exit but includes:

blood saliva, feces, urine

respiratory droplets are made by..

cough, sneezing, talking, and singing

what is animal contact

contact with an ill animal via touching or bites

what is enviromental contact

contact with pathogens in water or soil

some pathogens naturally have…

water or soil reservoirs

must be able to…

survive for an extended time outside of a hosts

EX: bacillus anthracis is an…

endospore forming bacteria in soil

• most commonly where grazing live-stock are found

what is vertical transmission

transmission of pathogens from parent to offspring through the placenta, childbirth, or breast feeding

newborn babies can contract…

pink eye with the normal microbiota of the vag

newborns in hospitals are typically treated with…

antibiotic eye drops on a routine basis for prevention

indirect contact types of transmission occur when…

hosts comes into contact with the pathogen without contracting the source

what is an airborne transmission

contact with air containing air born particles with pathogens

the distinction between this and person-to-person contact is that…

airborne droplets travels away from the original source

respiratory droplets are small enough to…

travel on air currents

aerosoilzed pathogens due to…

air condition or heating

• EX: legionnaire’s disease (pontiac fever)