introduction to parasitology Flashcards
where did the term parasite originate from?
ancient greece
“parasito”
—- “para” = on, at, beside
—- “sitos” = food
——— originally meant someone who looked after sacrificial meal for the gods, an honoured role
what does the work parasite mean? what do we study in parasitology?
any organism that derives metabolic benefits by living on or inside a host of a different species (heterospecific!)
includes animals, plants, fungi, bacteria, and viruses, which live as host-dependent guests
in parasitology, we study parasitic eukaryotes (specifically, protozoans and metazoans) and hosts and the interactions between them
in parasitology, how are species organized?
protozoan (single celled)
metazoan (multicellular)
—- helminths (worm-like)
—- arthropods (insects)
what are the advantages to a parasitic lifestyle? correlated disadvantages?
once host located no need for further search
—– but extreme host specificity can increase vulnerability to extinction (if host dies, needs another of the host species to proliferate)
must reside at optimal site in host to insure food/survival
—– food permanently available
—– limited requires for complicated food capturing mechanism and reduced need for food processing (simply absorbs nutrients as broken down by the host)
if endoparasitic, protection from environmental extremes
—– must adapt to host’s internal physiological environment
protection from predators and diseases
—– must overcome host’s immune defenses
reduced need for dispersal because host/vector carries the parasite
—– spread limited by host’s geographic range
can devote larger proportion of energy intake to reproductive output than a free-living organism
—– transmission can be extremely risky, and most offspring die before establishing in a new host
describe the life cycle of giardia duodenalis
human being ingests cyst (tetranucleated) and it goes down to the stomach
low pH and bile triggers excystation – cyst opens up and 2 trophozoite emerges
trophozoite adheres to villi in small intestine and takes residence here
trophozoite multiplies (asexual reproduction)
some can become cyst to be transmitted into environment (sexual reproduction? parasexual? look up)
— note trophozoite form can’t survive in the environment
what are facultative parasites?
don’t need host
what are obligate parasites?
requires host
what are endoparasites?
lives inside host
what are ectoparasites?
lives on host’s surface
what type of parasite is naegleria fowleri?
endoparasite
facultative parasite
—– lives in bodies of water and in humans too
“brain-eating” amoeba, effects similar to meningitis
what type of parasite is plasmodium falciparum?
endoparasite
obligate parasite
—– host/vector
causes malaria
what type of parasite is head louse?
lice
ectoparasite
obligate parasite
how many parasitic protozoans have we identified?
over 200,000
—– 35,000 currently living
—– many discovered in fossils
10,000 have adapted for life as parasites
—– parasitic protozoans infect a wide spectrum of vertebrate and invertebrate life
—– approximately 70 different protozoan parasitic species have been isolated from humans - can’t inhabit humans
what are the conventional classifications based on mechanism of motility? name and describe them
flagellates
—– uses flagella
amoeboids
—– uses protoplasm, the flow of fluid to move
apicomplexans
—– glides
ciliates
—– uses cilia
how is modern classification for protozoans done?
consider motility, metabolism, and DNA genotyping
used to be just mechanism of motility
what are the mechanisms of entry?
oral
—– giardia duodenalis
sexual
—– trichomonas vaginalis (sensitive to environment so other routes aren’t as effective)
inhalation
—– taxoplasma gondii (from cat poop)
direct contact
—– trypanosoma cruzi (from fly poop that can enter thru mucosa)
arthropod vectors
—– plasmodium falciuparum (malaria)
what are the types of parasite hosts? describe them
definitive (final)
—– where parasite reaches sexual maturity and undergoes sexual reproduction OR
—– undergoes most crucial stage of lifecycle
intermediate
—– where parasite undergoes asexual reproduction OR
—– develops into its next stage (DOES NOT REACH SEXUAL MATURITY HERE)
reservoir
—– harbours the parasite and serves as a source of infection for other hosts
—– may be asymptomatic
what are the types of parasites (based on how many hosts they have)?
monoxenous
—– 1 hosts
diheteroxenous
—– 2 hosts
—– sexual reproduction occurs in final host and asexual or phase change in first host
triheteroxenous
—– 3 hosts
—– sexual reproduction occurs in final host and asexual or phase change in prior hosts
what is antigenic variation?
parasite expresses different certain surface proteins and changes them frequently and presents those different antigens to immune system
—– host will send immune cells targeting those antigens but then they can’t find those antigens because they have changed
helps them hide from immune system
what is molecular mimicry?
parasite has molecules that resemble host to trick it and think it’s not foreign
what is immune modulation?
parasite releases things that suppress or modulate the immune system
what is intracellular inhabitation?
parasite resides in cells, hiding from immune system
what is encapsulation?
cyst/capsid protects parasite
what is protease secretion?
parasite releases proteases that destroy host proteins and disrupts junctions
what is toxin production?
parasite’s metabolic byproduct can be toxic to host
who is antonie van leeuwenhoek in regards to parasitology?
took a sample of his stool and used his invention of the microscope to examine
first to observe protozoans
—– giardial cysts and giardial trophozoites
describe giardial dueodenalis
most prevalence protozoan in human intestine
—– inhabits upper small intestine of vertebral hosts
binucleated
—– both nuclei are transcriptionally active
obligate parasite and monoxenous (1 host in lifecycle)
has 2 morphologies
—– trophozoite
—– cyst
aerotolerant anaerobe
—– no mitochondria
transmitted to hosts thru the fecal oral route
differentiate between the trophozoite and cyst morphology of giardial duodenalis
trophozoite
—– adapted for survival within small intestine
—– binucleate, both nuclei are transcriptionally active
—– 4 pairs of flagella (8 flagella)
—– adhesive disc to stick to the villi of the small intestine
—– mitosomes, similar to the mitochondria but with reduced genome because it doesn’t need some structures (e.g. golgi body) to survive within the host
cysts
—– used to transmit into environment and to another host
—– cyst wall makes it environmentally stable
—– tetranucleate (4 diploid nuclei) which facilitates transmission
—– metabolic rate is only 10-20% of trophozoite. the reduced rate is to survive the potentially long transmission
where, geographically, is giardial duodenalis more common?
Northern West
—– cysts survive longer in cool, moist environments
it is distributed worldwide tho
how does giardial trophozoites affect the small intestine?
its adherance results in atrophy and flattening of the villi
making it harder for us to absorb nutrients (malabsorption), resulting in diarrhea and weight loss
describe the diagnosis for giardial duodenalis
antigen-capture ELISA or direct fluorescent antibody test (DFA)
—– rapid testing
nucleic acid amplification tests (NATTs)
describe the treatment for giardial duodenalis
nitroimidazoles (e.g. metronidazole) are primary drugs used for treatment
—– antibacterials that targets anaerobes (doesn’t harm us)
—– damages DNA so they can’t replicate
