36: Protozoa Flashcards
true parasites
eukaryotic organisms living on another eukaryotic organism
protozoa
single-cellular parasites that can be intracellular or extracellular
what type of parasite is malaria?
intracellular protozoan parasite
what type of parasite is leishmania?
intracellular
what type of parasite is toxoplasma?
intracellular
what type of parasite is giardia?
extracellular
what type of parasite is trypanosomia brucei?
extracellular
helminths
multicellular parasitic worms that can be metres long and live in hosts
giardia lamblia
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
trypanosoma brucei
blood-dwelling trypanosomes transmitted between hosts via tsetse fly vector
- sleeping sickness
main response is IgG
zoonosis from cows
giardia lamblia statistics
200M symptomatic infections annually
- even more asymptomatic
- up to 90% of infections are asymptomatic
almost no mortality
- considered primarily a zoonosis
giardia transmission
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
giardia animal reservoir
beaver as the main animal reservoir in the US
other animal species can also carry giardia
- cats and dogs can be reservoir
trypanosoma brucei transmission
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
immune response to trypanosomes
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
antigenic variation of trypanosoma brucei with VSGs
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
leishmania chagasi
infects macrophages and is transmitted by sandflies
zoonotic and non-zoonotic species
toxoplasma gondii
lives in muscle and neurons as cysts
leishmania life cycle
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
leishmania infects macrophages
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
leishmania triggered disease
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
leishmania infections present a spectrum of clinical disease
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
toxoplasma gondii animal life cycle
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
