Protozoan and Helminth Parasites Flashcards
What are obligate parasites?
required to spend at least part of their life cycle in a parasitic relationship
What are facultative parasites?
generally free living but can become parasitic if they enter a suitable host
What is a definitive host?
the host in which the parasite reaches sexual maturity
What is an intermediate host?
a host that is required for parasite development but no sexual development takes place
What is an incidental host?
a host that can be infected but does not play a role in the parasite’s life cycle
often a ‘dead-end’ host
What is a paratenic host?
no development takes place but the parasite remains alive and infective to another host
How do parasites typically enter a host?
through broken skin, mouth or elsewhere
Arthropod vectors (mosquito, tsetse fly…)
What are helminths?
term used to refer to parasitic worms
- nematodes (roundworms)
- cestodes (tapeworms)
- trematodes (flukes)
What type of disease is malaria?
an acute disease
Severe anaemia
Coma
Hypoglycaemia
Acidosis
Organ failure
Respiratory distress
Pregnancy complications
after multiple infections severity usually decreases
What is the causative agent of malaria?
Plasmodium spp.
What are apicomplexan parasites?
parasites that contain an apical complex, a specialised structure consisting of various organelles that allow for invasion of host cells
use gliding motility to infect host cells
Substrate dependent as doesn’t involve flagella or shape shifting
eg plasmodium falciparum moves in corkscrew fashion to move into host cell
(Other eg: Cryptosporidium spp, Toxoplamsma gondii)
What is African Trypanosomiasis?
transmitted by tsetse fly (definitive host)
causative agent of sleeping sickness in humans and nagan in domestic livestock
proliferates extracellularly in the host bloodstream
moves into the nervous system at lager stages of infection
parasites are coated in variant surface glycoprotein (VSG)
shields parasite by hiding invariant proteins
these proteins are hidden in pockets that antibodies cannot easily reach
What type of organism is Plasmodium?
a protozoan parasite
What is PfEMP1?
allows infected red blood cells and other uninfected red blood cells to stick to blood vessel walls and each other
this is to avoid being filtered out by the spleen
but creates blockage in the blood vessel
present in Plasmodium
Why are African Trypanosomes so hard to get rid of?
1500-2000 VSG genes in trypanosome genome
~15 expression sites in the genome
only 1 expression site is active at a time
when immune system combats 1 VSG it switches to another
trypanosomes have an inexhaustible repertoire of antigenic variants
→ can establish long term chronic infection
What mechanisms do African Trypanosomes use to switch between different VSGs?
- gene conversion
- segmental gene conversion
- telomere switch
- transcriptional switch
Pathology of intestinal helminths?
Abdominal pain
Diarrhoea
Malnutrition
Protein deficiency
Iron deficiency
Growth reduction
Neurological problems
Susceptibility to other infections
Challenges of combatting helminth infections?
Good at evading and suppressing host immunity
-large size makes them difficult to kill/dislodge
-takes decades to develop immunity and protective memory
-long lived (can live 3-10yrs in host)
Helminth Co evolved with humans for long time, good at manipulating immune system
Hygiene hypothesis?
Low or absent helminth burden present in westernised populations
Lack of helminths to suppress immune system
Increased immune responses from helminth vacuum (more allergies)
What is cysticercosis?
Taenia solium - species of tapeworm
Eggs ingested
Develop into larvae in gut, penetrate into intestinal wall and encyst in muscle and CNS
Can cause brain and spinal cord pathologies (dizziness, seizures, epilepsy)
What is Schistosoma spp.?
Trematode
Kinetoplastid parasites?
Human African trypanosomes
Trypanosoma cruzi
Leishmania spp
Vector borne with insect definitive hosts
Can be intra or extracellular
Advantages and disadvantages of trypanosomes proliferating in bloodstream?
Adv:
Glucose and nutrient rich
Readily accessible to insect vector
Disadv:
Fully exposed to immune system
Proliferative stages cannot survive in tsetse fly gut (stumpy form can tho)
Advantages and disadvantages of intracellular life in a blood cell?
A:
Nutrients from host cell
Shield from immune system
Erythrocyte host cells readily available and accessible to mosquito vector - transmission efficient
D:
Parasite needs to convert terminally differentiated erythrocytes into cells with nutrient uptake systems
Remodelling of membrane by parasite increases cell rigidity- may be detected and removed by spleen
Parasitaemia?
Detectable levels of parasite in blood (like viraemia)
How do trypanosome parasites avoid antibody action?
Variant surface glycoproteins cover surface and shield invariable proteins from antibody binding (eg flagella components)
Highly variable N terminal sequence
Conserved C terminus anchored in PM
What happens at high trypanosome density?
Slender form proliferates until high density
Increase in parasitaemia
Increases concentration of sif (stumpy induction factor)
Causes some parasites to differentiate into non-replicating transmissible stumpy forms
Example of Quorum Sensing to maximise transmission opportunities while maintaining infection
Downside of stumpy form?
Not replicating
No new production of different VSG types
Host immune system can catch up to them (that’s why only some differentiate from replicating slender forms)
