-
parasitism
one organism (parasite) gains benefit while the other (host) is harmed
-
commensalism
one organism benefits and the other is not affected
-
mutualism
both organisms gain benefit
-
parasite
organism dependent on another organism for its existence
-
host
the organims the parasite depends on
-
infection
establishment of a host-parasite relationship by growth and multiplication of the parasite in or on the host
-
disease
an injury or abnormal finding in a living organism which results in recognizable effects
-
epidemiology
the study of the distribution and determinants of disease in a population
-
infectious disease
one that results from an infection with an organism causing morbidity
-
non-infectious disease
one that does not involve infection with an organism
-
reservoir
host or place where the parasitic organism usually lives and mulitiplies
-
3 main reservoirs for organisms that cause disease in humans
-
soil organims
- saprophytes - free-living
- utilize dead organic materials for nutrients
- only become parasitic on occasion
-
animals
- always parasitic
- organisms are called zoophilic
- different species of animals will be hosts for different microorganisms
- diseases caused by these organisms are called zoonoses
-
humans
- only found in humans
- organisms are always parasitic
-
portal of entry
- place where the parasitic organism enters the host
- mouth for GI tract infections
- nose and mouth for respiratory tract infections
-
portal of exit
place where microorganism leaves host
-
transmission
- the way in which an organism gets from its reservoir to its host
- may or mat not involve intermediate vehicle
-
vector
- arthropod that carries organism from reservoir to host
- biological - multiplication in vector
- mechanical - no mulitiplcation in vector
-
fomites
inanimate objects that carry organisms from reservoir to host
-
4 main routes of transmission
- respiratory route or droplet infection
- fecal-oral route
- blood-borne route
- contact route
-
respiratory route
- reservoir - humans or animals
- portal of entry - respiratory tract
- port of exit - respiratory tract (droplets produced through sneezing and coughing)
- fomites (hands) often involved
-
fecal-oral route
- reservoir - humans or animals
- portal of entry - mouth
- portal of exit - anus and mouth (in feces and vomit)
- often spread through contaminated food and water
- fomites frequently involved
-
blood-borne route
- reservoir - humans or animals
- portal of entry - broken skin, insect bite
- portal of exit - broken skin, insect bite
- intermediate vehicles essential - arthropod vectors, needles, blood transfusions
- - not needed when transmitted through sexual contact
-
contact route
- reservoir - humans, animals, soil
- portal of entry - abrasion, mucous membrane
- portal of exit - lesion, sore, contaminated secretion (none for soil organisms)
- fomites can be involved
- sexual transmission is through contact route unless blood-borne
-
communicability
the ability of an infective organism to pass from one host to another
-
communicable disease
- one which can be transmitted from one human or animal to another (contagious)
- most diseases
-
non-communicable disease
- those which cannot be transmitted
- diseases caused by soil organisms
- - each human must acqurie anew
-
endemic
a disease that is constantly present in an area but invovles relatively few persons
-
sporadic
a disease that occurs only occasionally and involves only a few individuals
-
epidemic
a disease taht involves a large number of persons for a limited period of time
-
pandemic
describes a series of epidemics that involve a large part of the world
-
emerging infectious diseases
an infectious disease whose incidence has increased recently or has been newly discovered
-
4 types of emergin infectious diseases
- new disease, new organism
- old disease, newly discovered to have infectious origin
- new manifestation of known organism
- re-emergin - once common, decreased in prevalence, now coming back strong
-
transiency
in or on host, no multiplication
-
colonization
- multiplication in host without causing any reaction from host
- - balanced relationship
- - situation fro normal flora
-
subclinical/asyptomatic
multiplication in host eliciting immune reaction, but no disease
-
clinical/symptomatic
multiplication in host with clinically evident disease
-
iceberg concept of infection
- what you see above water is just a small part of the whole
- most get exposure but no infection or infection but no symptoms
-
pathogen
an organism that is capable of causing disease
-
non-pathogen
an organism that is not capable of causing disease
-
opportunist
an organism that only causes disease when the host is compromised
-
what determines the outcome of an imbalance in the host-parasite relationship?
- exposure dose - how many individual microogranisms is the host exposed to
- properties of microorganism
- - pathogenicity = ability to cause disease
- - virulence = extent of disease
-
invasiveness
- ability to invade through host tissues and reach secondary sites
- - can be through direct extension
- - or via the blood and lymph systems
-
septicemia
microorganisms in the blood
-
strategies of invasiveness
- antiphagocytic (interfering with phagocytosis)
- extracellular substances break down tissue
- alternation of surface to avoid immune system
- genetic integration - lysogenic viruses
- flagella (motility) and pili (attachment)
-
toxigenicity
ability ot produce potent toxic substances
-
toxins
- potent poisons produced by microorganisms
- - destroy host cells
- - interfere with normal function
- 2 types = exotoxins and endotoxins
- many toxins are phage encoded
- - lysogenic conversion = when an avirulent strain becomes virulent in this manner
-
exotoxin vs. endotoxin
- exotoxin:
- gram-postive and gram-negative species
- synthesized in the cytoplasm, may or may not be secreted
- protein
- can generally form toxoid
- inactivated by heat
- generally very potent
- endotoxin:
- gram-negative species only
- component of the outer membrane
- lipopolysaccharide
- cannot form a toxoid
- heat-stable
- not very toxix
-
immune response
- necessary to control and clear infections
- many disease manifestations are immune mediated
-
host factors
- genetics
- age
- nutritional status
- hormonal balance
- integrity of organ system
- integrity of immune system
- immune status
-
evolution of host-parasite relationship
- parasite does not want to kill host
- better to cause minor or no disease
- endogenous flora are highly adapted parasites
-
advantageous adaptations of parasites
- survive longer between hosts
- use a vector for transmission
- use alternative hosts
- develop long incubation period
- increase virulence
- decrease virulence
-
host adaptation
exposure to infectious disease will select for human hosts that are more resistant
-
history of host-parasite relationship
- orignal humans hunters/gatherers
- european colonization successful due to infectious diseases
- diseases originate from hunter/gatherers - HIV, Ebola
|
|