Week 5: Platyhelminths Flashcards
1
Q
4 classes
A
- Turbellaria: free living
- Monogenea: ectoparasites on a single host, primarily fish
- Trematoda
- Cestoda
2
Q
Cestoda
A
- tapeworms
- intestinal parasites of vertebrates
- polyzoic: bodies have multiple parts
- has scolex (anchors into the host) and many proglottids (repeating body parts)
- loss of gut and mouth
- all have definitive host and single intermediate host
- transmitted through ingestion
3
Q
Trematoda
A
- endoparasites with 2 or more hosts
- endoparasites of the gut, liver, and blood
- have a ventral sucker, mouth sucker, and highly branched gut
at least two hosts: - definitive host is a vertebrate
- molluscs are 1st intermediate host, usually have 2
- mostly monoecious (hermaphrodites)
4
Q
Bauplan and Morphology
A
- flat on top and bottom
- bilaterally symmetrical
- acoelomate (blind gut): animal that has no internal, fluid-filled body cavity separating its body wall from its digestive tract
- complex reproduction
5
Q
scolex
A
- tapeworm (cestoda) adaptation
- specialized attachment structure
- at anterior pole
- contains sensory organs, knows where it is in the host
- allows it to stick into the intestinal wall
6
Q
proglottids
A
- repeating units found after the scolex
- each one is exactly the same
- as each new one is made, pushes the other down the worm
- as they move back, they mature
- when it gets to the end of the worm, it is full of embryonated eggs
- each is a giant reproductive system
- start immature, then mature sexually, become gravid (full of eggs), when it gets to the very end, it breaks off and the proglottid full of eggs is deposited in the feces
7
Q
reproduction of tapeworms (cestoda)
A
- have very low success rate
- hermaphrodites
- very long lived and huge so they can make lots of eggs
8
Q
feeding of tapeworms (cestoda)
A
- have no mouth or gut
- have a syncytial tegument: continuous, multinucleated layer that covers the entire surface of the parasite (on the outside of the proglottid)
- lacks cell boundaries, meaning that nuclei are embedded within a shared cytoplasm without individual cell membranes separating them (lots of nuclei)
- covered with microvilli, increase the surface area available for absorption
- absorbs nutrients directly from the host’s intestine
9
Q
neurocysticercosis
A
- if you accidentally eat the eggs of cysticerci, instead of the cysticerci itself (tapeworm), you can end up with it in your tissues
- it ends up in the brain
- essentially eats your brain
- most common parasitic infection in the CNS
- leading cause of acquired epilepsy
- cysts actively suppress the host immune system through secreted proteins
- dead cysts no longer suppress the inflammation and the immune system comes in to clean yp which causes damage to the brain
10
Q
immunomodulation
A
- alteration or regulation of the immune system
- ways these organisms can influence the host’s immune responses
11
Q
worm immunomodulation
A
- induce immune cell apoptosis (programmed cell death of immune cells)
- interfere with PRR activation and downstream signaling, allowing them to evade the host immune system, reduce inflammation, and prolong their survival within the host
- modulation of TH1 and TH2 cells and their associated cytokines
- promote a Th2-biased immune response while suppressing the Th1 pathway, which helps them evade the more aggressive, cell-mediated immune responses that could harm them
12
Q
we have evolved alongside worm parasites for a long time, what effects has this had on our immune systems
A
immune tolerance:
- human immune system has developed regulatory mechanisms to prevent excessive inflammation and tissue damage
TH2 skewing:
- likely favoured individuals with more controlled, Th2-dominant immune responses that were effective in managing these chronic infections while avoiding excessive damage
Dampening of inflammatory response:
- worms promote a more anti-inflammatory state, helps worms evade destruction by the immune system but also reduces the risk of excessive inflammation that could cause tissue damage to the host
13
Q
why is it so difficult to design worm vaccines?
A
- multiple life stages in multiple niches (different parts of your body)
- has different antigens at the different life stages
- they are complex organisms that immunomodulate the host
- complex surface with lots of potential antigens
14
Q
schistosomes
A
- abnormal fluke (trematoda)
- dioecious (distinct males and females)
- live in the bloodstream and feed on blood
- eggs still need to get out in the feces, need to make there way to the gut
- sometimes end up lodged in the CNS, muscle or liver
- causes tissue damage
- reinfection is very common
15
Q
who is getting infected by schistosomes
A
- people who come into contact with infected water
- it is a neglected tropical disease, the underprivileged
- children in hot climates who swim
- women doing domestic chores
- people who work in freshwater (fishermen and car washers)
