Lecture 1 - Principals of Parasitism Flashcards
Significant costs of parasitism
- lost of agricultral & human productivity
- human/animal suffering & premature mortality
- rational efforts of parasitism control depend on understanding of parasitism
Independent evolution is at least _____ times among the nematodes that infect vertebrates
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definition of parasite
an organism that is metabolically dependent and survives at the expense of another organism
commensalism vs. parasitism
host not harmed nor helped vs. survives @ expense of host
What do parasites depend on the host for
Metabolic dependency- sustenance (nutrition), survival, maturation, reproduction
Shelter- stable environment and protection for competition and predation by other organisms
What effect can parasites have on the host
hematocrit, fecundity, BCS, feed efficiency, time to conception
T/F disease resulting from parasitism is secondary
TRUE; parasites exist to perpetuate the species
How are parasites subject to fitness of evolutionary biology?
parasites that kill their host must find way to adapt and overcome the fitness cost
Fitness is characterized by parasites ability to
- colonize
- ability to resist environmental stresses
- survive host defenses
- reproduce and disseminate its progeny
What environmental stressors must parasites overcome
drug resistance & seasonal climatic extremes (hard freeze)
What host defenses must parasites overcome
immunomodulation and immune avoidance
Parasites have ability to alter their ____________________ to enhance the odds for survival and reproduction
biologic functions
Parasite populations are ________and _______
plastic and dynamic
Parasites have the capacity to respond to a variety of conditions and stimuli
(selection pressures) by ________________
permanent alterations of their genetic composition
How do parasites respond to selection pressures by alterations of their genetic composition?
hypobiosis, vertical transmission of developmental stages, shorter or abbreviated lifecycle development
hypobiosis
arrested development
How are parasite populations dynamic?
- permanent alterations of their genetic composition
- drug resistance
- ability to colonize new hosts/sites within hosts
Why are puppies born with roundworms?
cross placenta @ 42 days gestation
Most animals eventually develop some degree of
___________________ to parasitic infections
aquired immunity
acquired immunity with parasitsm
mechanisms to mitigate associated disease
Parasitic diseases in domestic livestock and companion animal populations is generally a consequence of __________-
management
1 cause of death in whitetail deer
lead poisoning
Parasitic disease is usually related to the
number of parasites infecting the host
What is it called when their is a large number of parasites in a living/grazing environments
hyper-contamination
What is it called when the host dies by depletion of host resourses
hyper-infection
How we can control parasitism and mitigate disease
- disrupt transmission between parasites and their host
- development of host immunity
- changes in management/modification of environment
How can we enhance host immunity?
vaccination and low levels of exposure
What is premunition
low levels of exposure
How can we disrrupt transmission between parasites and their host population?
breaking the life cycle of infection and reinfection RARELY achieved by meds alone
How can we modify environment to mitigate parasites
- protected environment for neonates
- reduced environmental contamination with infective stages
- selective breeding
- better nutrition
How do we create a protected environment for neonates
clean pasture for babies with no established immunity
How does better nutrition mitigate parasites
avoid the effects of parasitic disease
How can parasites cause disease?
- suck blood
- feed on solid tissues directly or after liquifying
- compete with host for ingested food
- traumatic injury by mechanical obstructions
- destroy host cells by growing in them
- production of toxic substances
- cause various host reactions
- stimulate cancerous growth
- carry additional diseases (parasites, viruses, bacteria)
- reduce host resistance to other diseases and parasites
What parasites suck blood
mosquitos, hookworms
What parasites suck lymph
midges
What parasites are exudates
lungworms
What parasites feed on solid tissues directly
giant kidney worms, liver flukes
What parasites feed on solid tissues after lysing and liquifying them
chiggers, amoebas
What parasites ingest intestinal contents
ascarids
What parasites absorb contens through the body wall
tapeworms
What parasites obstruct the intestines
ascarids
What parasites obstruct bile ducts
ascarids, fringed tapeworm
What parasites obstruct blood vessels
dog heartworm
What parasites obstruct lymph channels
filariids
What parasites obstruct bronchi
lungworms
How do hydatid cysts harm the hosts
pressure atrophy against body organs
What parasites destroy host cells by growing in them
coccidia, malaria
What toxic substances can parasites produce to aid their ability to enter host tissues, feed, reproduce
hemolysis, histolysins, anticoagulants
What host reactions can parasites cause
allergic, inflammatory, hypertrophy, hyperplasia, and nodule formation
What parasite stimulates the development of cancerous cell growth
Spirocerca lupi
What diseases do the following parasites carry?
Mosquitos
lungworms
flukes
mosquitos- heartworm and malaria, lungworms- swine influenza, flukes- salmon poisoning
What is an obligatory parasite
cannot complete its life cycle without spending part of all of its time on or within host
What is a facultative parasite
not normally parasitic by become so when eaten or
opportunisitically enter a host through and orifice or
wound
Example of facultative parasite
– Naegleria fowleri causative agent of Primary Amoebic
Meningoencephalitis (PAM) “Brain eating amoebae”
– Halicephalobus a causative agent of encephalitis in
horses
How does Naegleria fowleri cause disease
warm water->nasal passage->brain
Where does Halicephalobus enter
brain and kidney
ndoparasite
Organisms living within a host environment
Ectoparasite
– Organisms living on host (external environment)
Abberant parasite
Organisms found in locations where they do not
normally occur
Example of Abberant parasites
“Ectopic infections”
* Toxocara larvae in the eye of its host,
* Dirofilaria immitis in the brain of a tiger
* Paragonimus in the liver
How do parasites cause disease in their
host?
They feed on host resources and
impact the host physically and
immunologically
Accidental or Incidental parasite
Parasitic organisms that enter or attach to host species that are different from the one(s) with which they are normally associated
Why may accidental parasites not be able to survive in host?
often elicits a major pathological response from the host.
Repeated successful colonization of an accidental host can cause
host switching, development of new host association
Pseudoparasite
Diagnostic parasite stages or other artifacts (plant pollen, fungi,
arthropods) that superficially resemble protozoan cysts or helminth eggs in the feces, blood, or urine of an examined animal
Why is pseudoparasite a misnomer
“pseudo‐parasite products” are not associated with
a true host‐parasite association
Example of pseudoparasite
Eimeria oocysts passed in dog feces, various pollen mistakenly attributed to parasitic species infecting a host
Hyperparasite
When a parasitic organism is host to another parasite species
Examples of hyperparasite
-Mosquito that is host to Plasmodium sp. or Dirofilaria immitis
-Flea that is host to Dipylidium caninum
Definitive Host
Where a parasite attains reproductive maturity
What is definitive host evidenced by
circulation or passage (in feces or other host tissues) of progeny capable of colonizing additional host species
Intermediate Host
in which a larval or intermediate stage parasite must
undergo development to become infective for the
“definitive or final host
Paratenic Host
A facultative host used by a larval or intermediate stage
parasite to facilitate transmission to the “definitive or final
host, DO NOT undergo development
What is the distinguishing factor between paratenic and intermediate hosts?
parasites do not undergo development in paratenic hosts
What often bridges an ecological gap between passage of
infective stages and successful transmission and
establishment in a new host for completion of a lifecycle
and perpetuation of the parasite population?
paratenic host
reservoir hosts
Maintain a parasite in the population at sufficient levels to
facilitate its transmission between susceptible hosts
reservoir host for zoonotic parasites and infectious diseases
animals (Lyme disease deer, white-footed mouse)
Reservoir hosts for Dirofilaria immitis
coyotes, and stray/unprotected canines
Reservoir hosts may be …..
- definitive (adult parasites)
- intermediate (obligate developmental stages)
- Paratentic (facultative developmental stages)
Reservoir hosts are a _________ parameter rather than a _________ parameter
population; individual
vectors
Organisms that facilitate transmission of infective
parasite stages between different individuals of a
host population
Biological Vectors assume the existence of an
___________________________ for successful transmission and
maintenance of the parasite species in the host
population
obligate relationship
vectors often also play a role as _____________
intermediate/paratenic hosts
Which vectors have an obligate relationship
biological
2 types of vectors
biological and mechanical
example of mechanical vectors
flying syringe, transport on feet
Direct life cycle
parasites infect host directly
Direct Lifecycle
– Parasites infect host directly
– Stages passed from host in
feces/other tissues
– Infective to another “Definitive
host” (dog to dog)
– May require period of
development to infective stage
* Larval development ____________
* Free living larval stages in
_____
- w/in eggs
- environment
obligate indirect life cycle require intervention of an
intermediate host
obligate indirect life cycle is infective to the
intermediate host
obligate indirect life cycle have obligate requirement for development to
infective stage
obligate indirect life cycle have indirect transmission to
definitive host
obligate indirect life cycle may involve
paratenic host
facultative indirect lifecycle indirect transmission to
definitive host
facultative indirect lifecycle optional intervention of an
intermediate or paratenic host
facultative indirect lifecycle stages passed from host in
feces/other tissues
facultative indirect lifecycle infective to
definitive host or the “optional host”
horizontal transmission
-Parasites colonize susceptible individuals by usual routes
– Infection across different generations of host population not required
vertical transmission
-Transmission of parasites from mother to offspring by transplacental or lactogenic routes
– Trans‐generational requirement
– Prenatal or perinatal
2 types of host specificity
monospecific and heterospecific
monospecfic host
- limited number of hosts capable of completing lifecycle
- Pinworms in primate hosts
heterospecific
- wide variety of species capable of hosting parasite
- Typical of intermediate and paratentic hosts
- Toxoplasma gondii, Baylisascaris procyonis
zoonotic
animal to human
anthroponotic
human to animal
endemic (enzootic)
The normal or usual distribution of parasites in a host population or
geographic area (Eimeria sp. is endemic in Tennessee cattle)
Epidemic (epizootic)
- An excess number of parasite cases, far exceeding the normal or usual distribution in a host population
- Temporal and Spatial characteristics
- “ 50% of last years kid crop were aborted in an epizootic of
toxoplasmosis “
prevalance
The occurrence of a parasite in a population defined by time &
space
Incidence
The rate at which new cases are added to a host population defined
by time & space
