Exam 2: Ch 11: Interactions btwn Humans and Microbes Flashcards
Host
any organism that harbors another organism or particle
Symbiosis
association btwn 2 species
Mutualism
both members benefit
Parasitism
one member benefits, one member (host) is harmed
Commensalism
one member benefits, one member is not benefited or harmed
Resident microflora
microbes always present in/on body
Transient microflora
microbes present for shorter periods of time (minutes to months)
Microbial antagonism
chemical/physiological environment created by resident biota is hostile to other bacteria
normal biota unlikely to be displaced by incoming microbes b/c there are limited # of attachment site
Normal biota
beneficial or commensal to a host in good health w/a functioning immune system
- Contact
microbes are present
doesnt usually lead to infection and disease
- Colonization
presence of bacteria on body surface w/out causing disease
- Infection
multiplication of microbes; microbes penetrate host defenses → enter tissue → multiply
- Disease
disturbance in normal homeostasis
True pathogen
causes disease in healthy individuals;
associated w/ a specific and recognizable disease
Opportunistic pathogen
causes disease in immune compromised host
gain access (injury) to sterile regions
cause disease when “opportunity” arises
Conditions for opportunistic pathogens to flourish:
- failure of the host’s normal defenses
- intro of the organism into unusual body sites
- disturbances in normal/resident microflora
Pathogen
disease causing agent; etiological agent
Pathogenicity
ability to cause disease
Virulence
the degree of pathogenicity
determined by its ability to: establish itself in a host and cause damage
- Portal of entry
the route that a microbe takes to enter the tissues of the body to initiate an infection
exogenous
endogenous
usually have 1 and if they enter wrong one wont cause infection
occasionally have more than 1 = more pathogenic
Exogenous
microbe from a source outside the body
environment, another person/animal
Endogenous
microbe already existing in/on the body
from normal biota or previously silent infection
Infectious dose
minimum # of microbes necessary to cause an infection to proceed
smaller infectious doses = greater virulence
ex. TB is about 10 cells, typhoid fever is 10,000 cells
- Attachment/adhesion
gain a stable foothold on host tissues
dependent on binding btwn specific molecules on both the host and pathogen
pathogen is limited to only those cells (and organisms) to which it can bind
prereq for causing disease b/c the body has so many mechanisms for flushing microbes from tissues
Structures: pili/fimbriae, hooks, spikes, biofilms
- Surviving host defenses
microbes not established as normal biota will likely encounter the host immune defenses when first entering
phagocytes antiphagocytic factors (leukocidins, slime/capsule)
Phagocytes
cells that engulf and destroy host pathogens
w/ enzymes and antimicrobial chemicals
Antiphagocytic factors
virulence factors that help pathogens avoid phagocytes
can cause death of WBCs
Leukocidins
Slime/capsule
Leukocidins
kill phagocytes
Slime/capsule
makes it difficult for the phagocyte to engulf the pathogen
Virulence factors
adaptations a microbe uses to establish itself in a host
contributes to its ability to establish itself in the host and cause damage (ex. flagella, capsule, structure/chemical/toxin)
- Causing disease
3 ways microbes cause damage to their hosts:
- directly thru the action of enzyme
- directly thru the action of toxins (both endotoxins and exotoxins)
- indirectly by inducing the host’s defenses to respond excessively or inappropriately
virulence factors
exoenzymes (hyaluronidsae, coagulase, streptokinase)
toxins (neurotoxins, enterotoxins, hemotoxins,, nephrotoxins)
exotoxins and endotoxins
Exoenzymes
enzymes secreted by microbes
break down and inflict damage on tissues
often dissolve the host’s defense barriers to promote the spread of disease to other tissues
hyaluronidase: breaks down tight junctions in epithelial tissue so it can go deeper
coagulase: causes clotting of blood or plasma around pathogens
streptokinase: dissolves clots and releases bacteria
Toxin
a specific chemical product of microbes
causes cellular damage in other organisms
named according to their target: neurotoxins, enterotoxins, hemotoxins, nephrotoxins 2 types in pathogenic bacteria: exotoxin endotoxin
Exotoxins
released from the inside; specific cell type is attacked
damage the cell membrane and initiating lysis
ex. hemolysins: disrupt membranes of RBCs to release hemoglobin –> break apart RBCs to digest hemoglobin for energy
Endotoxin
not coming from the inside, but from the outer membrane
causes systematic problems
LPS - part of outer membrane gram (-) cell walls
released when cells die
has variety of systemic effects on tissues and organs
causes fever, inflammation, hemorrhage and diarrhea
pyrogenic = causes FEVER
- Portal of exit
enables pathogen to spread to other hosts
shed thru excretion, secretion, discharge, or sloughed tissue (anything w/access to outisde world)
high # of microbes in these materials increases the likelihood that the pathogen will reach other hosts
usually same as portal of entry; but some pathogens use different route
Pathogenicity
the ability to cause disease depends on pathogen's ability to: 1. enter 2. attach 3. survive host defenses 4. cause disease 5. exit virulence factors allow them to be good at those things
Virulence
intensity of disease produced virulence can be decreased as a pathogen is sub-cultured time after time many virulence factors (weapons) exist to increase pathogen's ability to: 1. enter 2. attach 3. survive host defenses 4. cause disease 5. exit
Localized infection
limited to a specific body part of the body and has local symptoms
Systemic infection
pathogen is distributed throughout the body
Focal infection
localized in a specific part of the body but spreads to other parts of the body
Mixed infection
composed of different species of bacteria
Primary and secondary infections
illness caused by a new microbe becoming established in the wake of an initial (primary) infection
ex. primary urinary infection –> secondary vaginal infection
Acute infection
rapid onset of infection, short course of infection
Chronic infection
long duration of infection
Asymptomatic or subclinical
not noticed by host
Signs
objective/measurable
fever, inflammation
Symptoms
subjective
pain
Syndromes
combo of signs and symptoms that occur together
Latency
dormant state of microbes in certain chronic infectious diseases
Recovery of host doesnt always mean the microbe has been removed or destroyed by host defenses
Viral latency - herpes
Bacterial/protozoan latency - syphilis, TB
Epidemiology
the study of disease within populations
helps us investigate the factors regarding a specific disease:
- what causes a disease
- how its transmitted
- how do we prevent and treat it
- how many people are afflicted
Epidemiologists
“disease detectives”
scientists who study epidemiology
Etiologic agent
the cause of a disease
Morbidity
illness
Mortality
death
Incidence
number of NEW cases within a period of time
Prevalence
TOTAL number of cases within a period of time
prevalence > incidence
Reportable/Notifiable diseases
certain diseases must be reported to authorities
a network of agencies keep track of infectious diseases
Endemic
pathogen continually present in a population
cold, flu
Sporadic
occasional cases are reported at irregular intervals at random locales
Epidemic
an “outbreak” or higher than normal # of cases
Pandemic
spread of an epidemic across continents
Epidemiologic studies
epidemiologists collect data on diseases to help prevent outbreaks in the future
3 types:
descriptive
analytical
experimental
John Snow - first epidemiologic study in 1854, traced the source of cholera epidemic to a certain water pump, proved ppl became infected by fecally contaminated drinking water
Descriptive studies
physical aspects of an existing disease and disease spread
who, what, when, where
records as many details as possible: # of cases, populations affected, locations and time, age, gender, race, SES
Analytical studies
why and how
determine causes and factors that influence the rate of disease
factors include: demographic, biological, behavioral, and environmental influences
Disease groups compared to control groups and data is analyzed for similarities and differences
Experimental studies
designs experiments to test a hypothesis
the “cleanest” studies; considered gold standard
many are performed for pharmaceutical (“clinical trials”) or other treatments
Disease transmission
affected by:
- reservoirs of infection
- portals of entry and exit
- mechanisms of transmission
Reservoir
the natural host or habitat (living or nonliving) of a pathogen
Source (transmitter)
the person or item from which an infection is directly acquired
Carrier vs asymptomatic carrier
organism that harbors infections and can spread them to others
may show symptoms or not
Biological vector
organism transports and plays role in life cycle of pathogen
ex virus inside of mosquito, bacteria inside of tick
Mechanical vector
an organism which only transports a pathogen (fly)
Zoonosis
infectious disease humans can acquire from animals
caused by vectors and animal reservoirs spreading their own infections to humans
70% of all new emerging diseases worldwide
impossible to eradicate w/out also eradicating the animal reservoir
Human reservoirs (source of infection)
symptomatic carrier
asymptomatic carrier
Animal reservoirs (source of infection)
wild animals (rabies), deer mice (hanta virus), insects
Nonliving reservoirs (source of infection)
soil (tetanus), water (giardia), food (e. coli)
Communicable
spread from one host to another
receiving host must become infected
Non-communicable
host gets it but cant transmit to another
from self (compromised individual) - microflora
nonliving reservoir - soil (tetanus)
Contagious
easily communicable
measles, flora
Horizontal transmission
spread thru a population from one infected person to another
ex. kissing, sneezing
Vertical transmission
transmitted from parent to offspring
ex. ovum, placenta, milk
Direct (contact)
kissing, sex
droplets (sneezing)
vertical
vector
Indirect
contaminated materials:
- vehicle: food, water, biological products (blood, semen, tissue)
- fecal/oral
air (more than 3 ft away)
- droplet nuclei
- aerosols
Herd immunity
proportion of people immune to a certain disease
Nosocomial infection
infection acquired in a hospital
5-20% of patients acquire one
contributing factors:
-compromised patients
-collection point of pathogens
-lowered defenses permit normal biota to enter the body
-infections acquired directly or indirectly from fomites, medical equipment, other patients, medical personnel, visitors, air, water
The progress of an infection (5 steps)
pathogen needs to become established by being successful at the following:
- Portals of entry
- Attachment
- Surviving host defenses
- Causing disease
- Portals of exit
if you stop a pathogen from being able to do any of these steps, they will not be able to infect the host
Stages of infectious disease
# of infectious agent x time Incubation period (no signs or symptoms) Prodromal phase (vague symptoms) Disease stage: -invasive phase (most severe signs and symptoms) -acme (peak) -decline phase (declining signs and symptoms) Convalescence period
Sequelae
long term or permanent damage to tissues or organs caused by infectious disease
meningitis –> deafness
lyme disease –> arthritis
polio –> paralysis
John Snow
first epidemiologic study in 1854
Traced the source of cholera epidemic to a certain water pump
Proved ppl became infected by fecally contaminated drinking water
Prevention of disease transmission
sanitation immunization isolation quarantine control vectors education about prevention and treatment
Most common nosocomial infections
Most common infections:
- urinary tract (40%)
- surgical sites (19%)
- respiratory (15%)
- other (meningitis, gastroenteritis) (12%)
- skin (8%)
- septicemia (6%)
Common nosocomial pathogens
Common pathogens:
- E. coli
- S. aureus
- Streptococcus
- Candida
- S. epidermidis
Healthcare processes that lead to nosocomial infections
treatments using reusable instruments (respirators, thermometers) indwelling devices (catheters, prosthetic heart valves, grafts, drainage tubes, tracheostomy tubes) high proportion of hospital population receives antimicrobial drug therapy --> drug resistant microbes are selected for at a much higher rate
Nosocomial infections: prevention and control
more than 1/3 of these infections could be prevented by consistent and rigorous infection control methods
use universal precautions
assume all patients and fomites may harbor pathogens
