Protozoan biology L18 Flashcards
protozoans in host
once in the host, parasites my live extracellularly, or hide inside cells
plasmodium spp force their way into cells
trypanosoma brucei lives in blood stream extracellular
challenges encountered by protozoal parasites
infecting host an sometimes specific host cells - may involve migration and parasite motility
undergoing transmission
gaining nutrients - may need to adapt to different environments at different life cycle stages
avoiding being killed by host
maintaining balance between proliferation, forming long term infection and undergoing transmission
malaria is an acute disease
causes flu-like illness that can rapidly develop into a life-threatening condition with severe anaemia, coma, acidosis, organ failure, respiratory distress
Toxoplasmosis; the disease
in healthy hosts
- initial infection causes mild flu-like symptoms
- chronic infection is asymptomatic
infection during pregnancy can lead to foetal encepthalitis
in immuno-compromised people - can cause severe disease and neuropathology;
- headache, confusion, poor coordination, seizures, lung problems
caused by opportunistic infection, blurred vision caused by severe
inflammation of the retina (ocular toxoplasmosis)
What are key challenges protozoan parasites face during transmission between hosts and vectors?
Surviving immune responses
Withstanding temperature & pH changes
Finding and invading specific host cells
Avoiding digestion in the GI tract (if oral route)
Timing life cycle stages with host/vector presence
How do protozoan parasites establish themselves in host environments?
Evolve surface proteins for immune evasion
Use host cell receptors for targeted entry
Modify host cell function or evade phagolysosome fusion
Form cysts to survive harsh conditions
Example of antigenic variation in protozoa?
Trypanosoma brucei constantly switches its surface glycoproteins to avoid immune detection.
Example of host cell manipulation?
Toxoplasma gondii forms a parasitophorous vacuole to avoid lysosomal degradation.
Example of cyst formation?
Giardia lamblia and Entamoeba histolytica form cysts to survive outside the host.
What motility structure do amoebae use?
Pseudopodia (e.g. Entamoeba histolytica)
What motility structure do flagellates use?
Flagella (e.g. Trypanosoma, Giardia)
What motility structure do ciliates use?
Cilia (e.g. Balantidium coli)
How do apicomplexans move without visible structures?
Use gliding motility via actin-myosin motors (e.g. Plasmodium, Toxoplasma)
What is differentiation in protozoan parasites?
Transformation between life stages to adapt to new environments (e.g. sporozoite → merozoite → gametocyte in Plasmodium)
Why is differentiation important for transmission?
Ensures survival, infectivity, and progression of the life cycle across hosts and vectors.
Example of differentiation in T. brucei?
Switches between bloodstream forms in humans and procyclic forms in the tsetse fly.
toxoplasma life cycle and hosts
intermediate hosts can be any mammalian species
definitive hosts are cats as sexually cycle takes place in cat gut
transmission to cats occurs via predation
tranmission occurs via ingestion of contaminated faeces
during chronic infection, parasite forms cysts in tissues
advantages of intracellular life - plasmodium
Advantages
gain nutrients from their host cell
shielded from the host immune system
host cells (erythrocytes) are readily available and are accessible to the mosquito vector
-> transmission is very efficient
disadvantages of intracellular life - plasmodium
Disadvantages
parasite must convert terminally-differentiated erythrocytes into cells with nutrient uptake systems
remodelling of the red cell membrane by the parasite results in increased red cell rigidity
-> infected erythrocytes may be detected and removed by
the spleen
Apicomplexan parasites use gliding motility to invade host cells
used by motile stages of the lifecycle to migrate to their host cell and actively propel themselves into the host cell
substrate-dependent cell motility - does not involve flagella or cilia (swimming) or shape-shifting (amoeboid crawling)
advtanges of extracellular life - African trypanosomes
Advantages:
glucose and nutrient-rich environment
readily accessible to insect vector
disadvantages of extracellular life - trypanosomes
Disadvantages:
fully exposed to the host immune system
proliferative stages cannot survive in the Tsetse fly gut
VSG coat
variant surface glycoprotein, shield parasite surface by hiding invariant proteins
can switch these for antigenic variation to evade immune system
slender form of Trypanosoma brucei
proliferative - dividing in blood stream
not transmissible
expresses VSG for immune evasion
function - keep infection going and evade immune system
eventually transform into stumpy form when parasite density is high
