Lecture 7 BIOL2410 PDF

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Lecture 7 - Parasitism...

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Lecture 7 – Parasitism Parasitism (symbiotic way of life)  Symbiosis (one or more organisms enter into a partnership)  Parasite: gains benefit from interaction  Host is harmed by parasite (but not killed)  Host=parasite's ecosystem. How many parasites are there? 4 taxonomic groups Protists: single celled eukaryotic organisms Microparasites: Giardia dudenalis (parasite of gastrointestinal tract)  Causes diarrohea Macroparasites: worms Ectoparasites:  Invertebrates that prey on other organisms (eg mosquito, sandfly etc) Life cycles   

Direct life cycle Indirect life cycle Vector-borne life cycle

Parasite depends on host for everything (from habitat, nutrition, resources, transport etc). Parasites goal (once it gets into the host) - undergo its life cycle-to produce infective stagesthat will then passed in some way to another host. Direct life cycle example: Parasite: Cryptosporidium fayeri, cryptosporidium macropodum: primarily formed in marsupials Rock wallaby excretes the parasite in its feces. This parasite is transmissable via direct contact  Fecal material  Ingestion of contaminated food or water Rock wallaby is infected-> passes the parasite to environment-> individuals of the same species ingest the parasite Indirect life cycle, a parasite goes from definitive host (where sexual reproduction takes place) to intermediate host Eg: toxoplasma  Cat excretes, oocysts are released from feces  Ingested by prey of cats  Once the parasite gets into the dormant tissue system  When the cats go out foraging and ingests the prey (it also ingests the parasite)  Cat goes on to produce infective stages

Ectoparasites Parasites themselves Acts as vector or transmission carriers (to get parasites from one host to next) Eg:plasmodium (causes malaria) Host-parasite ecosystem Host, parasite and environment- need to have the right characters to overlap Parasites evolved traits and behaviours to align themselves to the behaviour and ecology of host. According to michelle power, endemic also plays a part. Niches (habitats) 2 broad habitats hosts can provide  Ectoparasite and endoparasite Ecto: outer  Parasites that live within host surface  Eg tick,headlice Endoparasite:  Live within the host  Parasites live inside the host Eg roundworm, tapeworm Hosts provide diverse micro habitats -> parasites (many) have preferred locations within their host Plants have two types of parasites  Micro-organisms  Fungi, hyphae, yeast, bacteria  Occurs on the foliage  (Nematodes can penetrate and invade the roots) Parasitic plants:  Stem parasites  Mistletoe  Root parasites  Endoparasites Parasite transmission stage: Protective outer walls prevent the parasites from drying out in their environmental stages and waiting for a host to come along and ingest them For a parasite to find its host, it needs to overcome physical and physiological barriers to get through the host Once the parasite comes from the environment and enters the host, it experiences:  Temperature change  pH  O2 will vary  Nutrients change

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Emergence signals

They also go through other stages with host The host does not want the parasite there The body will mount an innate response There will be parasite of same species, different species that it will encounter. Parasite entry portals are limited They will either be ingested or come via the skin Once they get in, they find a preferred site Summary (PART:A) Parasites have direct, indirect and vector borne life cycle (robust stages: passed from one host to another). An intermediate host is involved (often, intermediate host is food item) Epidemiology: Study of how parasites move between hosts, their patterns and interactions within populations and individuals. Microparasites  Multiplies in the host  Short generation time  Variable stages and generation present  Hard to quantify Macroparasites  Generally do not multiply in host  Disease often correlated with number of parasites  Low parasites-not much harm, high parasites-greater harm Parasites usually have aggregated distribution Many hosts will have a few parasites and few harbour large number of parasites If many parasites cause disease in population, that population is severely fragmented. Fitness and survival are impacted. Parasite does not want to kill its host Parasite wants to proliferate, move out of this environment and get a new host Cuz if host dies, so does parasite...