Protozoal parasites Flashcards
How are protozoal parasites classified?
Presence or not of inactive cyst stage (usually extracellular)
lost motility
reduced metabolism
no growth of and multiplication.
Usually modified outer wall.
The cyst/ ”spore” resistant and often the infective stage
What are the four types of method of motion for protozoal parasites?
Amoeboid (Sarcomastogophora)
Flagellate (Sarcomastogophora)
Ciliate
Sporozoan- bad ones, filamentous complex at one end. can forms spores and malaria is usually under this group (Apicomplexa)
How do protozoal parasites reproduce?
Homologous recombination machinery is present in most (??all) species- expressed in certain points in the cycle-Host enzymes not required
Suggests meiosis/ sexual division may occur however appears rarer than binary fission
Single haploid cells only observed in some protozoa forms e.g., plasmodia (?? Other forms of recombination without haploid fusion… amoeboid parasites, conjugation (sexual material transfer without reproduction- ciliates)
What are the mitotic forms of division seen in protozoal parasites?
Binary fission: replication of DNA –> cytokinesis –> two identical daughter cells (get image)
Schizogony: cell –> reproduce multiple times to form schizont –> cytokinesis –> merozoites formed
Tell me about Flagellates
How do they reproduce?
What are the most sever flagellates
Mastigophora (flagella)
One or more flagella - sometimes with an undulating membrane (e.g., Trypanosomes)
Often two stages mastigote (flagellate)- (which has 3 sub -forms pro-, epi-, and trypo-) extracellular and amastigote, intracellular stages
Predominantly reproduce by asexual binary fission (do show sexual reproduction, in sense that you see DNA transfer)
Anterior is at flagellar tip end, which acts as a propeller to drag parasite along
No cyst stages (most severe)
- intestinal and urogenital flagellates e.g., Giardia, Trichomonas,
- Blood and tissue flagellates e.g., (haemoflagellates- kinetoplastids) Trypanosoma, Leishmania,
What are Amoeboid’s and whats are their two stages?
Sarcodina (flesh like)
Two stages
- Trophozoite (trope, nourishment + zoon, animal) from moves and capture food via pseudopods, temporary extensions of the cell into which the endoplasm then flow- nutritional stage. Usually non-ciliated (not always)
- Resistant long-lived cysts some multinucleate (Entamoeba histolytica)
How do Amoeboids reproduce?
Asexually via binary fission
What may some amoeboids show, provide an example for this?
Some may show third transient (1-2 hrs) flagellate state!! E.g., Naegleria Fowleri
Naegleria Fowleri brain eating amoeba - primary amoebic meningoencephalitis - ~ 100% lethal – found in tepid stagnant water - used as a model to study changes from amoeboid to flagellated stages- flagellate state for movement and reverts to amoeba
What are Ciliate’s and what are their two stages?
Ciliated protozoa- cilia distributed in rows or patches
Two stages: Cyst and Trophozoite
Tell me about the reproduction of ciliates
They have macronucleus-regulates metabolic activities and micronucleus -storage site for the germline genetic material
Show both sexual conjugation and binary fission
micronucleus gives rise to the macronucleus and is responsible for the genetic reorganization during conjugation
macronucleus organises protein production
diploid nucleus is the store of genetic material that converts to macronucleus
division: miotic stage–> two organisms attach via conjugation –> before that’s finished the micronucleus go through meiosis –> end up with 4 haploid micronuclei –> one of those divides again –> 5 haploid nuclei–> transfer across of the two fused conjugated cells –> 2 haploid micronuclei come together to form diploid micronucleus –> division of cell, reproduction –> old macronucleus is destroyed and replaced by micronuclei that becomes macronucleus
Give an example of a ciliate that is the only human parasite?
Balantidium coli, a giant intestinal parasite of humans and pigs (only human parasite)
Tell me about Sporozoa or Apicomplexa
What stages do they have?
What do they lack?
Tell me about their life cycle
Spore like stages
Lack flagella, cilia, or pseudopodia but capable of gliding movements.
Specialised apical complex secretes enzymes which allow the sporozoite (main infective from) to enter a host cell.
Have complex life cycle with alternating sexual and asexual reproductive phases involving two different hosts (digenetic).
Tell me about the complex reproduction of sporozoa or apicomplexa
asexual schizogony forming many offspring (merogony forming merizoites, and gametogany forming gamete)- which fuse for
sexual sporogony forming sporozoites – infective form for transfer
What are the two classes of sporozoa or apicomplexa and give examples of whats included in the classes?
Coccidian class – Coccidia, Neospora, Toxoplasma
Haematozoan class includes -Plasmodium species
Define Schizogony
Asexual multiple fission comes in a number of forms
Define Sporogony
Sexual and asexual phase in definitive host e.g., mosquito, male and female gametes fuse in the enteric area of the mosquito forming oocyst- undergoes Meiosis now
Tell me about the Schizogony of sporozoa or apicomplexa
Oocyst multiple asexual divisions Schizogony- forming multinucleate cells which split to single nucleate sporozoites- enter salivary glands and passed to secondary host
Define asexual schizogony
Asexual phase in secondary host e.g., mammal utilitising a schizont large multinucleate cell
Define Pre-erythrocytic schizogony (merogony)
Pre-erythrocytic Schizogony (merogony) – sporozoites enter cells (eg liver) and show nuclear replication form a Schizont –– this divides to single nucleate merozoites which are released
What are the two outcomes of erythrocytic schizogony (merogony or gametogany)
- Merozoites enter RBCs and form trophozoites – these show nuclear replication form Schizont– this divide to merozoites – released and repeats (merogony)
OR some merozoites instead undergo meiosis and form gametocytes which are released (gametogany)
- Gametocyte (in some sporozoa these differ in size eg Plasmodia)
Male - microgamete (can be flagellated!)
Female – macrogamete
In some cases with erythrocytic schizogony, there is no schizont, instead what conversion is there?
Trophozoites –> Merozoites directly
What parasites are included under the term flagellates?
Trypanosoma and Leishmania
Tell me about the flagellates main differentiation stages
? primarily insects’ parasites, vertebrates a minor part of biological cycle
Main differentiation stages- different structure, behaviour, and metabolism
- Flagellated Trypomastigote- in mammal, insect gut and transfer organism
Extracellular (some subversions- metacyclic (usually infectious to us), bloodstream, stumpy, procyclic (dividing form in insect))
- Flagellated epimastigote- found in insect tissue, extracellular
- Non-flagellated amastigote- present inside mammalian cells, intracellular- doesn’t need flagella because it is inside the cell
There is a promastigote in Leishmania…
Give an example for a Hemoflagellate
Trypanosoma (for Leishmania- see last year)
Tell me the main differentiation stages of Haemoflagellates
Body Borer
Believed to initially been a parasite of insects (may still be and mammals a minor part of biological cycle)
3 main differentiation stages
Promastigote
Trypomastigote - flagellated, in mammal and transfer organism to and from insect. Extracellular
Epimastigote – flagellated form found in insect tissue
Amstigote
Amastigote – non -flagellated form present inside mammalian cells (show binary fission). Intracellular
Tell me the morphology of the trypanosome…
Variety between species?
Adaptation?
characteristics/ features?
Different species have different morphological forms
Trypanosomes adopt different morphological forms in different hosts
Flagella appears at side in tyropmastigote and epimastigote
At and in promastigote
What are the different forms of the Trypanosome that appear in the life cycle?
Trypomastigote-posterior localization of mitochondrial DNA aggregate, (kinetoplast K), to the nucleus (N). An attached flagellum exits from the flagellar pocket (FP) near the cell posterior.
Epimastigote-kinetoplast is anterior to the nucleus. While the flagellum is still attached to the cell surface, it also has a long, cell-free overhang.
Promastigote-similar arrangement of DNA-containing organelles as epimastigote, but the flagellum is unattached after exiting the FP pocket at the cell anterior. (Seen in Leishmannia – not Trypanosomes)
Amastigote – smaller, spherical, kinetoplast anterior to the nucleus. The flagellum very short and nonmotile, - INTRACELLULAR FORM
Tell me about the Microtubule quartet (MtQ) in trypanosomes
The microtubule quartet (MtQ) has opposite polarity to the other array microtubules- (nucleated near the basal body and grows towards the cell anterior may act as a signal for the formation of the flagella).
The flagellum attachment zone (FAZ) filament interrupts the array and attaches the flagellum to the cell surface.
PFR, para-flagellar rod.
FP- flagellar pocket has unique composition
Classification of trypanosome species: Morphology and genetics show marked difference
Flagellate morphology
Different species have different morphological forms
Trypanosomes adopt different morphological forms in different hosts
Promastigote- Leissmania
Trypomastigote-?
General structure of the trypanosome
Position of flagella changes with nuclei position
Plasma membrane covered in protein coat made of VSG proteins
Give the structure of the trypanosomes
Unicellular eukaryotes
The cell membrane consists of at least three discrete domains: the cell membrane, the flagellar membrane, and the flagellar pocket
Possess a microtubule corset closely opposed to the cell membrane – define the shape of the cell
Have a kinetoplast – a mass of cytoplasmic DNA found at the base of the flagellum and continuous with the (single) mitochondrion.
Possess a paraflagellar rod – only partially characterised with unknown function (attachment to insect host? Aids motility?)
Tell me about the Kinetoplast
Mass of mitochondrial DNA which sits where the flagellar pocket will be at the end of the mitochondria
Kinetoplast splits first, then flagellar then nucleus during division
The kinetoplast is a specialized region of the mitochondria of trypanosomatids that harbors the most complex and unusual mitochondrial DNA found in nature. Kinetoplast DNA (kDNA) is composed of thousands of circular molecules topologically interlocked to form a single network.
What does the paraflagellar rod help with?
Possess a paraflagellar rod – only partially characterised with unknown function (attachment to insect host? Aids motility?)
- Attachment to insect host? Dense hemi-desmosome- like plaques associated with proximal flagellum and unsect cells
- Aids motility?
- Stabilises flagellum
Tell me about Kinetoplasts and their genetic information?
Unique to kinetoplastids (flagellates inc. Tryp and Leish)
Mitochondrial DNA
Mass of circular maxi- and mini- kDNA near flagella polar body
Present at one end of the branched single continuous mitochondria
10-40 copies of the mitochondrial genome (maxicircles)
1000 +copies of guide DNA (minicircles- forms gRNA) – unique correction system of mitochondrial genes akin to CRISPR
Name some significant flagellates (non-human)
- Crithidia
- Phytomonas
Tell me about Crithidia and provide an example
Crithidia – mongenic insect parasites (possible direct ancestor of group)
Only found in choanomastigote form
e.g., C. bombi parasite of bumblebees implicated in decline of wild bee populations
Digenic parasites:
Digenetic parasites are those that need more than one host (usually two) to complete their life cycles.
What is the life cycle of the African Trypanosomiasis?
overtime will end up in CSF in CNS
When present in blood in high amount it goes to Stumpy form
Can show sexual production as evidence for DNA transfer occurring
Cattle can also be infected by T.b.rhodesiense (this is not seen with gambiense form)
Tell me some general features of Tsetse flies
Day feeding
Attracted to smell, movement, and colour (specifically blue) – large animals
Often quite host specific
Very good transmission system – both Mechanical and Biological Transmission, must feed regularly
(Horse flies can act as Mechanical vector for trypanosomes)
The presence of these flies / their parasites is a direct cause of sub-Saharan poverty
– and failure in agriculture
What are the two sub-strains of human T.bucei (that cause sleeping sickness in man)
Tell me some info about each strain
T. b. gambiense is found in Central and West Africa
- More Chronic - ~98% of all ASS
- Limited reservoirs
- Easier to control
T. b. rhodesiense is found primarily in East Africa (Botswana, Ethiopia, Kenya, Malawi, Tanzania, Uganda, Zaire, and Zimbabwe)
- More Acute - ~2% of all ASS
- Wildlife and Livestock infected too
- Harder to control
Why is the VSG varied?
VSG is varied because have genetic recombination and VSG expression site switching in respect to the promotor and position relative the telomere (the most telemetric version is expressed) causes changes in VSG expression
What does the VSG do during immune evasion?
VSG recombination to novel forms
Stripping and replacement of VSG also occurs
?? role of flagellar groove
VSG shedding and attachment on to RBC causes
RBC lysis and anaemia
Recruitment of complement and antibodies away from the parasite
Hypocomplementemia- lower complement levels as they are being used to lyse RBC
What is the infective form of the Trypanosoma?
Tell me about this
The infective form is the stumpy trypomastigotes
Transition from slender (blood) to stumpy (infectious non proliferating) forms caused by a quorum sensing mechanism, stumpy induction factor (SIF) accumulates as parasite numbers increase during parasitaemia. I.e., so non-dividing infectious form only produced when high levels (consider the opposite)
Where the long form is ingested, they die in the fly
What are some new treatments for infection by tryptosoma?
Fexinidazole - 2018, first drug for advanced-stage sleeping sickness in thirty years- Nitroimidazole compound
Acts against both stages if not severe taken orally- taken orally and enters CNS
Parasite nitro reductases reduce fexinidazole to reactive intermediates free radical and superoxide release which are capable of damaging DNA and proteins
What are some preventions that can be done in order to reduce Tsetse fly attack?
Environmental
Map highly effected sites – localised sequential aerosol spaying with plant spread insecticides in severe outbreaks
(Ground treatments not used – residues)
Bush Clearance – ecological issues
Pour on systemic insecticide treatment of animals (East African trypanosomiasis)
Baits and coloured traps (pheromone and insecticide traps)
Human
Long-sleeved shirts / pants of medium-weight material in neutral colours
Inspect vehicles - flies are attracted to the motion and dust from moving vehicles.
Avoid bushes.
Minimise activity during the hottest part of the day.
Together can reduce Tsetse fly attack by >99%
Whats the life cycle of the flagellates (Haemoflagellates) Trypanosome?
Assassin bugs crawls as it can’t fly
Triatomine insect vector- Triatoma, Rhodnius, and Panstrongylus (or “kissing bug”) takes a blood meal and releases trypomastigotes in its faeces at bite wound.
Trypomastigotes enter host through wound or at intact mucosal membranes, eg conjunctiva.
In the mammal host, the trypomastigotes invade cells at site of inoculation, and differentiate into intracellular amastigotes. These multiply by binary fission, differentiate into trypomastigotes, and release into the circulation
Trypomastigotes infect cells in a variety of tissues and transform into intracellular amastigotes in new infection sites->Clinical disease
The bloodstream trypomastigotes do not replicate (cf African trypanosomes). Replication resumes only when the parasites enter another cell or in the “kissing bug” when infected by feeding on mammals that contains circulating parasites.
In insect the ingested trypomastigotes transform into epimastigotes in the vector’s midgut. The parasites multiply and differentiate in the midgut and differentiate into infective metacyclic trypomastigotes (generally taken up by bug when it takes a meal) in the hindgut.
Replicated via binary fission
Distribution of chagas disease
What is the current treatment for chagas disease?
Nifurtimox (see Sleeping Sickness) and Fexinidazole / Benzinidazole. Both administered orally
needs long treatment courses and can’t overcome pathology
~60 clearance of parasite as in cellular niche
Benznidazole - see Fexinidazole (Nitroimidazole) nb this is not a benzimidazole the microtubule inhibitor – see helminth lectures
All severe side effects
