Intro to Parasitology

Definitive host – harbors the ___ or ___ reproduction stage of a parasite

adult; sexual

Intermediate host – harbors the ___ or ___ reproduction stage of the parasite

larval; asexual

Accidental host – organism that can serve as a host but doesn’t pass parasite to ___ host; parasite cannot ___ its life cycle.

Ex. a human ingesting a worm egg becomes the accidental intermediate host. Egg hatches in intestine and larvae burrow out of the intestine to the tissue - cannot mature further and immune system destroys it. But if we ingest it as larvae, the larvae will know to attach to intestinal wall and mature into adults to reproduce.

definitive; complete

Sexual reproduction is best for genetic fitness because there's more ___ in gene pool - whereas in intermediate hosts that harbor ___ phases, it's only making ___ - not as genetically fit.

diversity; asexual; copies

Transmission vector – organism that ___ and transmits a parasite to ___ host, typically ___ such as mosquitos and ticks.

carries; another; Arthropods

Environmental reservoir (of a parasite) – environment which a parasite can ___ in and where a host can become ___ (ex. Soil and water)

survive; infected

Cyst – ___ form of protozoan; characterized by ___ protective wall that is ___ to environmental factors.

Infective; thick; resistant

Trophozoite – ___, ___, non-infective (active) form of a protozoan; ___ in host (typically asexually)

feeding; motile; replicates

Parasite - organism that benefits at the ___ of the host; cannot live ___.

expense; independently

Protozoa - ___ (little less complex) eukaryotic organisms with ___ different forms.

unicellular; 2

What are the 2 forms of protozoan parasites?

Cyst and Trophozoite

Which protozoan form causes a majority of symptoms in a host?

Trophozoite

Which protozoan form is typically shed (both can be shed but what is TYPICALLY) in the stool and can contaminant food, water, and surfaces?

Cyst

Helminth - parasitic ___, multicellular: round, tape, or fluke (flat)

worm

___ - protozoan parasite that moves by pseudopodia.

Amoeba

___ - protozoan parasite that moves by cilia around the entire membrane

Ciliates

___ - protozoan parasite that move by flagella (whips back and forth to propel organism)

Flagellates

Arthropods - hard exoskeletons, jointed appendages; will be studies as ___/reservoirs

vectors

Obligate parasites - must be parasitic (need host to live), cannot exist without the aid of another ___.

• not found in ___, only in host

host; environment

Facultative parasites - can have ___ and ___ living (can live in environment) abilities (N. fowleri)

parasitic; free

Endoparasites - live ___ the host

Ectoparasites - live ___ the host’s body (usually bugs - ticks, mosquitos)

inside; outside

When assessing a patient for a parasitic infection, we look at…

1. ___ - help narrow down possibilities of parasite (ex. GI parasite = diarrhea; Blood parasite = intravascular hemolysis, etc)
   
   

2. ___ history - critical to know if patient has been outside of their residence (includes an area within US that is not pt’s normal residence)
   
   

3. ___ with clinical laboratory - provides insight in pt’s history they might have

Symptoms; travel; collaborating

___ ___ (PVA) and 10% ___ are the most common preservative collection tubes for O&P examination.

Polyvinyl alcohol; formalin

PVA is used to make slides that are ___ stained and increases ___ of stool to the slide.

permanently; adhesion

Formalin ___ everything in the sample and ___ parasitic structures.

• used in wet mount of concentration procedures

kills; preserves

Concentration procedures help ___ some background stool material so that parasites can be seen if present.

eliminate

For O&P examination, ___ specimens must be collected within a ___ day period (at least ___ hrs apart).

This is because parasites do not ___ shed.

3; 10; 24; consistently

For O&P examination, the stool must be collected in a clean, dry, waterproof container (does not need to be ___ because it is stool).

sterile

For O&P examination what ratio must be met for PVA and 10% formalin tubes? Remember: it is important to fill to the ___.

3:1 (preservative:feces); line

When submitting samples for O&P examination, it is important to submit as ___ as possible - within ___ hrs of collection, otherwise, parasitic structures may ___.

soon; 2; degrade

When collecting stool for O&P examination, beware of the impact of ___ enema (imaging study), procedures using ___, and antimicrobial ___.

It makes identification difficult because it will show up on ___ and may impact how ___ the preservatives work.

barium; dyes; therapy
microscopy; well

Cary-Blair is not ___ for an O&P exam as it only preserves bacteriology. May be able to use for ___ testing! (ex. GI multiplex PCR panel - do not need parasitic structures intact - just need to know if parasitic DNA is present!)

acceptable; molecular

For macroscopic evaluation of formed stool, examine within ___ to 3 hours of passage if held at room temp; within ___ hrs if refrigerated (not ___, going to have some degradation but is not cause for auto reject)>

A portion of sample should be put in preservatives for later testing (PVA and formalin).

2; 24; ideal

Never ___ stool! Causes bacteria to metabolize ___ and will destroy any parasitic structures.

incubate; faster

By knowing the ___ of a stool specimen, we know what we should ___ to see more of in terms of cysts or trophs.

consistency; expect

Cysts are mostly found in ___ and soft stool.

Trophs are mostly found in ___ stool (makes sense because it is the active form that causes symptoms!)

formed; liquid

Brown stool is ___.
Black indicates bleeding in ___ GI tract.
Visible blood indicates bleeding in ___ portion of intestinal tract.

Visible blood AND ___ should be selected for wet mount prep and preserved. (could be indicative of ___ caused by certain amoeba)

normal; upper; lower; mucous; dysentery

Microscopic examination of fecal specimens look for anything ___.

• Direct ___ mount examination (stained + unstained) of fresh stool specimens

• ___ procedures with wet mount examination of the concentrate

• Preparation of ___ stained smears

suspicious; wet; concentration; permanently