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9 Cards in this Set
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first, definitions:
definitive host: intermediate host paratenic host: principal host: incidental host: |
definitive host - this is important - it's the host that has the adult/reproducing form of the parasite.
this is in contrast to the intermediate host, which can host some/all of the pre-sexual stage forms of the parasite. this is closely related to the paratenic host - here, the parasite is in suspended animation, waiting for the host to be eaten by something bigger where it can develop more. principal host - where the bug spends most of its time (most common host). incidental host - not the usual (principal) host, but one that the parasite can live inside. |
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can parasites live outside their host?
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some parasites are "facultative" parasites - they can be free or parasitic. Though most are "obligate" parasites.
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Talk about co-evolution between parasites and their host - what does disease present like when the host/pathogen have long evolved together?
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both sides evolve - and the longer they do it (being more highly adapted) means less disease is caused. The bug is less dangerous, and the host can tolerate infection.
with tolerated infection, generally see a bell curve, with most showing NO ACUTE PATHOLOGY, though some will. immune response to well-adapted parasite usually keeps it in check without overreacting and causing inflammation. doesn't erradicate. |
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talk about a parasite infecting a host to which it's not adapted - what does disease look like compared to normal host? what's an example of this?
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may end in stopped life cycle
may be only able to partially continue life cycle - though this is rare (most can't continue in a host they're not used to). disease progress in an uncommon host is hard to predict. could be non existent due to inability to continue life cycle could be less severe, due to attenuated life cycle could be more severe either way, it's all quite different. heartworms are an example - in dogs, lots of surviving/replicating progeny, bad disease state. in cats, it's a dead end - only a few survive, maybe live in pulmonary vessels, but generally little disease. INCIDENTAL HOSTS usually have usually mount MORE EXTREME immune response to parasites, can be bad. |
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what is the result of the fact that lots of parasites have several life stages?
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the different stages can cause differential pathology. also, these varried stages and trasnforming between them allow for several therapy targets.
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how can parasites bet passed?
how do parasites eat? reproduction? |
direct contact, ingestion, congenitally, vectors (both arthropods and vertebrates)
parasites get food may compete for nutrients, steal them, or get them passively. reproduction can be sexual or asexual division - some parasites can do both. |
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do parasites grow exponentially out of control?
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no - they have self limiting properties. Can control how fast they mature, how fast they reproduce - and can pick up on host signals to regulate all of this.
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Compare parasites to bacteria in terms of immune response, and talk about the different responses for different parasites? long term immunity?
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parasites tend to be immunologically complex and have LOTS of antigens.
both TH1 and TH2 responses important: protozoans tend to be all about TH1 responses (need cell mediated) Helminths are all about TH2 responses (don't forget that although eosinophils are cells, they're part of the TH2 response - and eosinophils are required for fighting off helminths). NOTE - positive eosinophelia means only that the parasite is MIGRATING. tend to see that big parasites result in eosinophelia, little parasites don't. different life stages = different immune response. LONG TERM IMMUNITY - usually don't get it - though it can be partial (people re-infected with malaria do better than those with primary infection). |
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so overall, what does pathogenicity depend on?
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parasite burden (infected number).
ability to replicate in host (protozoans can replicate in hosts, helminths can't - so it really depends on how many helminths you eat). immune response regulation. mechanical effects (eating gut parts) toxins (round worm kinds score lower on tests) invasion/destruction of cells inflammatory response loss of nutrients to parasite. |
