Diagnostic Parasitology Flashcards
Techniques in the diagnosis of parasitic infections
Diagnostic parasitology
Formula for 10% formalin
10/100 * 1000
Common Reagents
Carbol Fuchsin
Formalin (5% and 10%)
Lugol’s Solution
SAF
An acid-fast stain
Carbol Fuchsin
Reagent used for Cryptosporidium spp. and in general for Coccidian parasite (group)
Carbol Fuchsin
Reagent used for preservation of protozoan CYST
For all-purpose use
5% Formalin
Reagent used for helminth eggs, larvae and adult stage
10% formalin
Stain for parasite
the first stain to be developed
Lugol’s solution
Regaent used as substitute for Schaudinn’s solution
Does not have mercuric chloride
Sodium acetate-acetic acid formalin fixative
Also called routine fecal analysis
Direct fecal smear
simplest and easiest technique to facilitate detection of intestinal parasites
Direct Fecal smear / Routine fecal analysis
Detects the presence of intestinal protozoans (trophozoites or cyst) or helminth eggs can be observed directly with a light microscope
DFS / routine fecal smear
vegetative, motile, and labile stage of parastie
Trophozoite
Labile means easily killed
Trophozoites are processed within
30mins - 1hr
Trophozoites are usually found in what type of stool
Water stool
Nonmotile and resistant stage of parasite
Cyst
Stage of parasite that can survive in harsh environment
Cystr
Cyst is seen in what type of stool
Formed stool
In preparation of DFS
small amount of fresh feces is mixed with either
Saline (NSS) - to detect protozoan motility
Lugol’s/Iodine solution - to reveal the parasite structure
- however no live parasite can be seen here as it is toxic
Reagent that is toxic for parasite and only used to reveal structure/morphology
Lugol’s solution/iodine solution
Seen when using Saline preparation
Motile trophozoites and larvae
RBCs (must be reported)
Leukocytes
Charcot Leyden crystals (reported)
Seen when using Iodine preparation
Cysts of protozoa
DFS PREPARATION
Place 1 drop of NSS and 1 drop of Lugol’s/iodine on separate places
Take 2mg of fecal specimen (by poking the specimen with applicator stick)
Emulsify in the drop of saline
next using different stick 2mg of stool emulsify in drop of iodine (which will kill any organisms present)
Place a coverslip there should be no air bubbles
Reading DFS slide
Systematic reading should be enforced
read the whole cover slip
Disadvantage of DFS
has lower sensitivity
can’t detect parasites most of the time especially if the person has low parasitemia or parasitic infection
technique used for monitoring large-scale treatment programmes implemented for the control of soil-transmitted helminth infections
Kato Katz Technique
o Commonly used in the community to determine if the treatment was successful
Kato katz
Parasites acquired from the soil
soil-transmitted helminths
what are the soil-transmitted helminths
Ascaris lumbricoides
Trichuris trichiura
Hookworm
Threadworm
o Quantify eggs and establishes burden of intestinal infection (worm burden)
Kato katz
A quantitative technique
KAto katz
can quantify the number of eggs
How many / the concentration of parasites in the body
Manner of reporting in kato katz
Eggs per gram stool (epg)
Technique that can Quantify eggs and establishes burden of intestinal infection
Kato katz
Materials and reagents for kato katz
Wooden applicator stick Screen Template Plastic spatula Microscope slides Hydrophilic cellophane Flat bottom jar with lid Newspaper, absorbent tissue Glycerol-malachite green
Kato katz template
Used to measure the stool
9mm on a 1mm thick template : 50mg
6mm on a 1.5mm thick template : 41.7mg
6.5 on a 0.5mm thick template : 20mg
Glycerol-malachite green reagent
Glycerol = clearing agent
Malachite green = stain
Where hydrophilic cellophane is soaked
Hydrophilic cellophane
soaked in glycerol-malachite green
used as the cover slip
Screen
Used to sieve the stool
KATO KATZ technique can be used for
Parasites with thick eggshell EXCEPT for hookworm
because hookworm eggs are cleared rapidly due to think eggshell which is why important to read slide immediately
EXCEPT for hookworm how many hours should kato katz slides be stored
1 or more hours
To speed up the clearing and examination, slide can be plced in a 40 degrees incubator or kept in direct sunlight for several minutes
A. Lumbricoides and T. trichiura in Kato katz technoque
since they have thick eggshells, slides can remain visible for many monts
Hookworm eggs in Kato katz technique
since they have thin eggshells they can only remain visible for 30-60mins
Schistosome eggs (Blood fluke) OR Cercaria (Infective stage) in Kato katz
recognizable for up to several months bUT is recommended to be examined within 24 hours
Technique used for Enterobius vermicularis (pinworm) and Taenia solium/Taenia saginata
Cellophane swab
Extreme itchiness of the perianal area
enterobiasis
Pork tapeworm
Taenia solium
Beef tapeworm
Taenia Saginata
Time of collection for cellophane swab (Enterobius vermicularis)
Early in the morning before the person washes or defecates
Caused by tapeworm - Taenia solium / Taenia saginata
Taeniasis
How many negative tests to rule out pinworm infection
5 times negative (Daily)
Pinworm becomes infective for how many hours
4-6 hours
Mode of transmission of Enterobius vermicularis
INHALATION
The egg of enterobius vermicularis is usually
D-shaped
REagent to apply after using cellophane swab
Toluol or I2 in xylol
procedures allow for the detection of parasitic
elements (eggs, larvae, oocysts, and cysts) that may be missed when examining only a direct wet smear.
More sensitive than DFS HOWEVER there will be no live parasites because will be killed by formalin
Concentration technique
More stool = more sensitive
(under concentration technique) parasite will sink; parasite found at the bottom
Sedimentation
(under concentration technique) parasite will float; parasite at the top
Floatation
Also called concentration technique
Formalin-ethyl acetate sedimentation concentration
Formalin = preservative Ethyl-acetate = dissolve fats
recommended as being the easiest to perform
and the least subject to technical error, allowing recovery of
the broadest range of parasitic elements.
The specimen can
be fresh or fixed stool.
Formalin-ethyl acetate sedimentation concentration
This technique is not recommended for eggs of
Fasciola spp. and larvae of Strongyloides stercoralis
Formalin-ethyl acetate sedimentation concentration
This procedure leads to recovery of all protozoan cysts and
oocysts, helminth eggs and larvae present in the stool
specimen;
Formalin-ethyl acetate sedimentation concentration
separation of parasitic
elements from the coarsest organic debris, using a high
specific density flotation solution.
concentration by floatation
most widely used flotation solution
zinc sulfate solution and sodium chloride
