introduction to parasitology

Question 1

where did the term parasite originate from?

Answer 1

ancient greece

“parasito”
—- “para” = on, at, beside
—- “sitos” = food
——— originally meant someone who looked after sacrificial meal for the gods, an honoured role

Question 2

what does the work parasite mean? what do we study in parasitology?

Answer 2

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

Question 3

in parasitology, how are species organized?

Answer 3

protozoan (single celled)

metazoan (multicellular)
—- helminths (worm-like)
—- arthropods (insects)

Question 4

what are the advantages to a parasitic lifestyle? correlated disadvantages?

Answer 4

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

Question 5

describe the life cycle of giardia duodenalis

Answer 5

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

Question 6

what are facultative parasites?

Answer 6

don’t need host

Question 7

what are obligate parasites?

Answer 7

requires host

Question 8

what are endoparasites?

Answer 8

lives inside host

Question 9

what are ectoparasites?

Answer 9

lives on host’s surface

Question 10

what type of parasite is naegleria fowleri?

Answer 10

endoparasite

facultative parasite
—– lives in bodies of water and in humans too

“brain-eating” amoeba, effects similar to meningitis

Question 11

what type of parasite is plasmodium falciparum?

Answer 11

endoparasite

obligate parasite
—– host/vector

causes malaria

Question 12

what type of parasite is head louse?

Answer 12

lice

ectoparasite

obligate parasite

Question 13

how many parasitic protozoans have we identified?

Answer 13

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

Question 14

what are the conventional classifications based on mechanism of motility? name and describe them

Answer 14

flagellates
—– uses flagella

amoeboids
—– uses protoplasm, the flow of fluid to move

apicomplexans
—– glides

ciliates
—– uses cilia

Question 15

how is modern classification for protozoans done?

Answer 15

consider motility, metabolism, and DNA genotyping

used to be just mechanism of motility

Question 16

what are the mechanisms of entry?

Answer 16

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)

Question 17

what are the types of parasite hosts? describe them

Answer 17

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

Question 18

what are the types of parasites (based on how many hosts they have)?

Answer 18

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

Question 19

what is antigenic variation?

Answer 19

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

Question 20

what is molecular mimicry?

Answer 20

parasite has molecules that resemble host to trick it and think it’s not foreign

Question 21

what is immune modulation?

Answer 21

parasite releases things that suppress or modulate the immune system

Question 22

what is intracellular inhabitation?

Answer 22

parasite resides in cells, hiding from immune system

Question 23

what is encapsulation?

Answer 23

cyst/capsid protects parasite

Question 24

what is protease secretion?

Answer 24

parasite releases proteases that destroy host proteins and disrupts junctions

Question 25

what is toxin production?

Answer 25

parasite’s metabolic byproduct can be toxic to host

Question 26

who is antonie van leeuwenhoek in regards to parasitology?

Answer 26

took a sample of his stool and used his invention of the microscope to examine

first to observe protozoans
—– giardial cysts and giardial trophozoites

Question 27

describe giardial dueodenalis

Answer 27

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

Question 28

differentiate between the trophozoite and cyst morphology of giardial duodenalis

Answer 28

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

Question 29

where, geographically, is giardial duodenalis more common?

Answer 29

Northern West

—– cysts survive longer in cool, moist environments

it is distributed worldwide tho

Question 30

how does giardial trophozoites affect the small intestine?

Answer 30

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

Question 31

describe the diagnosis for giardial duodenalis

Answer 31

antigen-capture ELISA or direct fluorescent antibody test (DFA)
—– rapid testing

nucleic acid amplification tests (NATTs)

Question 32

describe the treatment for giardial duodenalis

Answer 32

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