36: Protozoa

Question 1

true parasites

Answer 1

eukaryotic organisms living on another eukaryotic organism

Question 2

protozoa

Answer 2

single-cellular parasites that can be intracellular or extracellular

Question 3

what type of parasite is malaria?

Answer 3

intracellular protozoan parasite

Question 4

what type of parasite is leishmania?

Answer 4

intracellular

Question 5

what type of parasite is toxoplasma?

Answer 5

intracellular

Question 6

what type of parasite is giardia?

Answer 6

extracellular

Question 7

what type of parasite is trypanosomia brucei?

Answer 7

extracellular

Question 8

helminths

Answer 8

multicellular parasitic worms that can be metres long and live in hosts

Question 9

giardia lamblia

Answer 9

lives in mucosal tissue
- primarily in host intestines
- most common protozoan parasite throughout the world in the US

primarily considered to be zoonosis from beavers

high asymptomatic rate
- stays in intestines so main adaptive immune response is IgA

Question 10

trypanosoma brucei

Answer 10

blood-dwelling trypanosomes transmitted between hosts via tsetse fly vector
- sleeping sickness

main response is IgG

zoonosis from cows

Question 11

giardia lamblia statistics

Answer 11

200M symptomatic infections annually
- even more asymptomatic
- up to 90% of infections are asymptomatic

almost no mortality
- considered primarily a zoonosis

Question 12

giardia transmission

Answer 12

mostly exposure to bodies of water where there is giardia from other animals

cyst form passed in feces
- inert form that survives better outside the body
- non-replicating and has to be activated to become replicating form

parasites attach to mucosal epithelium and can survive for weeks

trophozoite form is replicating form in intestine

Question 13

giardia animal reservoir

Answer 13

beaver as the main animal reservoir in the US

other animal species can also carry giardia
- cats and dogs can be reservoir

Question 14

trypanosoma brucei transmission

Answer 14

live extracellularly and replicate in the blood
- infection normally controlled by IgG but can evade IgG through antigenic variation

spread by the bite of tsetse flies

if parasite escapes antibodies, it can spread to the brain and cause severe disease symptoms

Question 15

immune response to trypanosomes

Answer 15

parasites can constantly replicate and change, so innate immunity doesn’t work and you can activate inflammation but it’s often inhibited

innate immunity
- parasites are hard to eliminate by phagocytosis because of their size

adaptive immunity
- IgG elimination by neutralisation
- antigenic variation since the parasite can change its primary antigen
- variable surface glycoproteins (VSGs) help evade IgG

Question 16

antigenic variation of trypanosoma brucei with VSGs

Answer 16

change in surface antigens allow escape from antibody-mediated responses

unpredictable and we cannot predict which gene cassette will be used
- some parallels with malaria

body has to start over and make new antibodies again and again
- battle between immune system and pathogen

all antibody is IgG and there’s no reason to make IgA because the parasite never leaves the bloodstream

Question 17

leishmania chagasi

Answer 17

infects macrophages and is transmitted by sandflies

zoonotic and non-zoonotic species

Question 18

toxoplasma gondii

Answer 18

lives in muscle and neurons as cysts

Question 19

leishmania life cycle

Answer 19

sandfly comes in and deposits a form that can replicate
- gets taken up by macrophages

escapes lysosomal fusion like TB

animal reservoir for the pathogen is primarily dogs and rodents

Question 20

leishmania infects macrophages

Answer 20

cytokines from T helper cells try to kill parasites but instead macrophages chew up healthy uninfected tissues

mucosal tissue has a lot of macrophages so many to get infected
- infected macrophages cause lesion/damage and not the parasite directly

Question 21

leishmania triggered disease

Answer 21

cutaneous: skin lesion
- macrophages in the skin causing infection, damage and inflammation

mucocutaneous
- starts in the skin around the mucosal tract on the nose

visceral
- spreads all over the body especially in the liver

Question 22

leishmania infections present a spectrum of clinical disease

Answer 22

when you have mucocutaneous, too much immune response

when you have visceral, too little immune response
- fluid from inflammation happening in the inner organs

when you have it just right, cutaneous or asymptomatic

Question 23

toxoplasma gondii animal life cycle

Answer 23

felines as the only definitive host
- mice are a common intermediate host but many other species are also intermediate hosts

cats have the adult forms of the parasites so oocysts are passed in cats’ feces

cysts are in the muscle and brains of chickens, cows and mice which get eaten by the definitive host

humans are considered a dead-end host