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Flashcards in Parasitology Deck (24):

Define parasite

-organisms that live on or within other living organisms (the host) for a significant period of its life and obtains nourishment from it


Give broad examples of parasite categories and be sure to name which 2 are the most common

-All viruses, some bacteria, some fungi
-arthropods: biting insects (lice, mites); important as vectors for other diseases


Compare protozoa and helminths

-P: unicellular, multiply in host, short life cycles, acute/chronic infections
-H: multicellular, do not multiple (lay eggs), long life cycles, chronic infections


4 main parasite portals of entry

1. ingestion
2. arthopod bite
3. transplacental penetration
4. organism-directed penetration


Describe the structure and reproduction of protozoa

-single celled, eukaryotic organisms with NO CELL WALL
-usually reproduce by binary fission
-often produce cysts to survive harsh conditions--aid transmission


How do protozoa obtain nutrients from the host?

-via diffusion or pinocytosis


4 types of protozoa

1. amoeba
2. Sporozoites
3. Flagellates
4. Coccidia: non-motile


We covered 7 protozoa in lecture, belonging to 3 categories based off of location. Name them.

1. GI protozoa: entamoeba histolytica, Giardia lamblia, Cryptosporidium
2. GU protozoa: trichomonas vaginalis
3. Blood and tissue protozoa: toxoplasma gondii, falciparum (malaria), naegleria fowleri


How is Entamoeba histolytica spread?

-fecal oral route after ingestion of a cyst


What is the growing/active form of Entamoeba histolytica called?



What about the Entamoeba histolytica cysts make them useful in diagnosis?

-they have multiple (4) nuclei


Where to Entamoeba histolytica invade?

-colonic epithelium


Both the Entamoeba histolytica cysts and trophozoites are excreted, but the _______ die quickly and it is the __________ that spread the infection.

-trophozoites die quickly
-cysts spread infection


What is the characteristic pattern associated with Entamoeba histolytica?

-flask-shaped ulcers


Describe the life cycle of Entamoeba histolytica

1. fecal oral transmission of cyst
2. acid in stomach converts to trophozoite
3. invasion and division in colon wall- lyses epithelial cells
4. forms flask-shaped ulcerations
5. division and excretion of cysts (and trophozoites) and spread of infection


Entamoeba histolytica epidemiology

-found world-wide, especially in areas with poor sanitation where attach rates can be 10-50% of the population
-many patients are asymptomatic and the infection is cleared
-symptoms will depend on level of infectious dose
-millions of cysts shed in stool per day


3 outcomes of Entamoeba histolytica infections

1. asymptomatic infection
2. intestinal amebiasis (amebic dysentery)
3. extraintestinal amebiasis


If carriers of E. histolyticas, how long do their infections usually last?

-1-2 years


Clinical manifestations of intestinal amebiasis

- related to destruction of colonic epithelial cells
-cramping, diarrhea (not absorbing water well), pain, bloody stools with mucus


Clinical manifestations of extraintestinal amebiasis

-fever and rigors
-liver is primary target and can lead to abscess formation in liver
-immunosuppressed individuals are at greater risk of this


What are the 3 general factors that determine severity of E. histolytica

1. virulence of strain
2. inoculum
3. immune status


How does one diagnose E. histolytica?

-detection of trophozoites and cysts (multiple nuclei) in stool
-serology can be useful, but not in endemic areas since most people will be seropositive


What is the treatment of E. histolytica?

-Metronidazole (flagyl) followed by iodoquinol


What is the ultimate effect of metronidazole? Is it active in its ingested form or must it be activated?

-fragmentation of DNA
-must be reduced inside of bacterium (by ferrodoxin) to be active, and then it leads to fragmentation of DNA