Microbiology: Parasites Flashcards Preview

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Flashcards in Microbiology: Parasites Deck (11):
1

Intermediate vs. Definitive host

-Definitive host: parasite undergoes sexual reproduction in host
-Intermediate host: parasite undergoes a larval stage, but not sexual reproduction

2

Infection vs. infestation

-Infection: parasite is present in the internal organs or tissues (entry usually oral or skin). Organisms called endoparasites
-Infestation: Parasites are on hair, skin, or clothing. Called ectoparasites

3

Protozoa

-Unicellular eukaryotes found world-wide
-Can be in trophozoites (active) or cyst (less active) stages
-Intestinal: entamoeba, giardia (monkey face), cyptosporidium
-Urogenital: trichomonas vaginalis
-Free-living: naegleria fowleri, acanthamoeba
-Intestinal/tissue: toxoplasma gondii (cats to humans)
-Blood and tissue: hemoflagellates (trypanosoma, leishmania), malaria (plasmodium)

4

Hemoflagellates

-Trypanosoma cruzi causes chagas disease (eventual myocarditis), from America (kissing bug)
-Trypanosoma brucei causes sleeping sickness (eventual meningoencephalitis), from Africa (tset fly)
-Leishmania causes cutaneous and mucocutaneous lesions, transmitted from sand fly

5

Malaria

-Caused by plasmodium species, transmitted by anopheles mosquitoes
-Once injected into human the protozoa replicates in the liver parenchymal cells (1st round of replication)
-Liver cells burst to release merozoites, which infect RBCs and mature into gametocyte or schizont (which contains merozoites and continue the inter-RBC replication)
-Gametocyte taken up by mosquito to be passed on to next host
-Mosquito is definitive host, human is intermediate host

6

Methods for Dx of protozoa

-Intestinal parasite: stool sample analysis (for cysts)
-Intestinal/tissue: ELISA of blood
-Hemoflagellates and malaria: blood smear

7

Helminths

-Can be tapeworms (flat), roundworms (round, nematodes), or flukes (flat)
-Relatively long and often long-lived
-Develop thru egg-> larva-> adult
-Dx is established through demonstration of parasite or its eggs in stool

8

Tapeworms

-Taenia saginata (beef) or solum (pork)
-Saginata is better to have (fewer complications)
-Each segment is an egg (seen in feces)
-Get them from eating undercooked meat that was infected

9

Nematodes

-Includes roundworms, hookworms, pinworm
-Dx is usually through detecting eggs in feces (except pinworm)
-Pinworm is Dx through the scotch tape test: tape against anus to grab some of the eggs or worms
-Female pinworms migrate out of anus at night and deposit eggs on perianal skin

10

Flukes

-Includes hermaphroditic flukes and bisexual (blood flukes or schistosoma)
-Schistosoma lay eggs in lumen of blood vessels, eggs disseminate and can cause granulomas in liver (contributes to obstruction of portal circulation)
-Chronic hyper-responsiveness to egg Ags leads to clay pipestem fibrosis: fibrosis of portal vein
-This is the third stage in the lifecycle of schistosoma, after the two sexes have mated and the eggs have been laid

11

Rx for parasitic worms

-Use Praziquantel, which disrupts tegument of skin on the worm
-Will kill living worms but do nothing for damage already done/eggs left deposited or in circulation
-Killing all worms at once can result in hypersensitivity rxn (must know worm burden)