PARASITOLOGY SECTION Flashcards
• Parasite - organism completely depending on another
organism (host) for shelter and nourishment.
Medically Important Parasites
Protozoans
Eukaryotic
unicellular non-
photosynthetic organisms
Amoeba
Has pseudopods (false feet) for
locomotion
E.g.
Entamoeba histolytica
Flagellates
Helminths
Parasitic worms
Ascaris lumbricoides (giant
intestinal roundworm)
Trichuris trichuria
(whipworm)
Human hookworms
Ancylostoma
duodenale (Old world
hookworm)
Necator americanus
(New world
hookworm)
Strongyloides stercoralis
(Threadworm)
Enterobius vermicularis
(Pinworm
Seatworm).
Cestodes - tapeworms
Examples are:
Taenia solium (pork tapeworm)
Taenia saginata (beef
tapeworm)
Diphyllobothrium latum (Fish
broad tapeworm)
Trematodes - flukes
Examples are:
Monoecious flukes
Fasciola hepatica
(Sheep liver fluke)
• Paragonimus
westermani (Lung
Fluke)
Dioecious flukes
Blood flukes such as
Schistosoma
japonicum
Schistosoma
mansoni
and
Schistosoma
haematobium
Development of Parasitology
Early Written Records
• Bible
-
1250 to 1200 BC: Described “fiery serpents” which is
most likely Dracunculus medinensis (Guinea worm)|
• Ebers Papyrus
-
first written records of intestinal worms confirmed by
the discovery of calcified helminth eggs in mummies
dating from 1200 BC
Detailed account of aat (nature of infection with
Dracunculus medinensis and techniques for removing
the worm) swelling in the limbs among some ancient
Egyptians
- detailed description of aaa (possibly Hookworm
infection) among ancient Egyptians
• Hippocrates
- Described worms from fishes
domesticated animals
and humans
• Roman physicians Celsus and Galen
Were familiar with Ascaris lumbricoides
Enterobius
vermicularis and tapeworms belonging to genus
Taenia
• Paulus Aegineta
-
Clearly described Ascaris
Enterobius
tapeworms; Also gave good clinical descriptions of
their respective infections
• Avicenna
Has whip-like structures called
the flagella for locomotion
E.g.. Giardia lamblia
Ciliates
Has hair-like cilia for locomotion
5 . alansion cilian
for locomotio not have organs
Arabic physician who recognized the guinea worm
Dracunculus medinensis
- • Carolus Linnaeus
Father of Taxonomy
- Described & named six helminth worms
• Ascaris lumbricoides
• Ascaris vermicularis (now Enterobius
vermicularis) |
• Gordius medinensis (now Dracunculus
medinens/s)
• Fasciola hepatica
Taenia solium
Taenia lata (now Diphyllobothrium latum)
Discovery of Common Parasites
Discovery of Parasitic Protozoa
• Anton van Leeuwenhoek (1681): Discovered Giardia
lamblia
the first parasitic protozoan in humans
• Friedrich Losch/ Fedor Lesh (1873): Discovery of
Entamoeba histolytica
the causative agent of
amoebiasis
• Everett Dutton (1902): Identified Trypanosoma brucei
gambiense which causes chronic sleeping sickness
• J.W.W Stephens & Harold Fantham (1910): Identified
Trypanosoma brucei rhodesiense that causes acute
sleeping sickness
• Alphonse (Charles) Laveran (1880): Discovered that
malaria is caused by protozoans known as the
Plasmodium species
• Ronald Ross (1897): Discovered that mosquitoes can
transmit malaria to birds
Establish mosquitoes (Female Anopheles) as
vectors
Contributed significantly to the study of the life cycle of
Plasmodium spp.
Discovery of Ascaris lumbricoides
• Edward Tyson: Gave the first detailed anatomy of A.
lumbricoides
• Francesco Redi: Gave another detailed description of
A. lumbricoides
• The publications by Tyson and Redi marked the
beginnings of the subdiscipline of helminthology
which reached a peak in the 19th century
• Casimir Joseph Davaine (1862): Demonstrated that
ingestion of eggs of A. lumbricoides as correct mode
of transmission
• Giovanni Battista Grassi (1862): Validated Davaine’s
work; Infected himself with eggs of A. lumbricoides &
subsequently found eggs in his feces
• Shimesu Koino (1922)
Discovered the life cycle of A. lumbricoides
including the migration of larval stages around the
body
-
Infected a volunteer and himself; Subsequently
found large numbers of larvae in his sputum
Discovery of Hookworm & Strongyloides stercoralis
19th century: Scientists used the term ‘Egyptian
chlorosis’ to describe the greenish pallor associated
with Hookworm infection
• Angelo Dubini (1838): Found hookworms in a human
patient
• Wilhelm Griesinger (1854): Established the association
between Hookworm infection and the (then) unknown
disease characterized by anemia
greenish yellow
pallor
and laziness
•
Edoardo Perroncito (1879): Established the real
connection between pallor and Hookworm infection
while investigating the diseases of miners in the St.
Gothard tunnel
• Arthur Looss (End of 19th century): “Hookworm &
Strongyloides stercoralis larvae enter the body by boring
through the skin”
Accidentally infected himself with the hookworm
larvae
Deliberately placed S. stercoralis on his skin; Found
larvae in his feces 64 days later
Discovery of Trichinella spiralis
•
James Paget (1835): Discovered T. spiralis in humans
• Rudolf Virchow (1859) and Friedrich Zenker (1860):
Discovery of the adult worms of T. spiralis
• Friedrich Zenker (1860): Recognized clinical
significance of infection; Concluded that infections
come from eating raw and improperly cooked pork
Discovery of Tapeworm
• Edward Tyson (Late 17th century)
-
Scientific observations on the tapeworms of
humans
dogs
- Recognize the “head” (scolex) of a tapeworm
• Johann Goeze (1784)
Discovered Taenia saginata
- First to state that intermediate hosts are involved in
the life cycles of Taenia
- Observed that the scolices of the tapeworm in
humans resembled cysts in the muscle of pigs
• Friedrich Heinrich Kuchenmeister
-
Middle of the 19th century: Recognized the
difference between Taenia solium (pork tapeworm)
and Taenia saginata (beef tapeworm)
1850s: In a much-criticized experiment
fed pig meat
containing Taenia solium to criminals in execution
and recovered adult tapeworms after the execution
• Edoardo Perroncito (1877)
Confirmed that eating “measly” beef causes
tapeworm infections
1
Routine Techniques in the Parasitology Section
Routine Fecalysis
A. Macroscopic Examination
Normal Characteristics for Fecal Analysis
Color: Light to Dark Brown
Consistency: Soft to well-formed
Other characteristics not usually noted or reported in a
laboratory report
Quantity: 100 -250 grams/ day
Odor: Foul to Offensive
pH: 7.0-8.0
Color
Black
tarry
Observation of Stool Color
Description/Causes
Called as melena
Bright Red
Upper Gl bleeding
(esophagus
stomach
duodenum
Ingestion of Fe
Bi
charcoal
Called as hematochezia
Pale/Chalky
Green
Yellow
Lower Gl bleeding (colon
rectum)
Medications (Rifampin)
food (beets)
Blockage of bile duct or
use of barium sulfate
Oral antibiotics and
increased intake of green
vegetables or food
coloring
Ingesting milk diet
corn
meal
rhubarb
Observation of Stool Consistency
Watery
Soft
Semi-Formed
Formed
B.
Microscopic Examination
Necessary to identify helminth eggs and larvae
as well as protozoans
Routine microscopic examination: Direct Fecal
Smear
Mounts
Saline Wet
• Protosoal boph. Mottity
lodine Wet
Procedure
a.
One or two drops of
normal saline solution
(NSS) is aspirated and
transferred onto a glass
slide.
b.
A clean wooden
applicator stick is then
used to acquire a
representative portion of
the fecal sample.
C.
The wooden stick (now
containing the sample
is then applied over the
NSS to prepare a fecal
emulsion. A cover slip is
placed on top followed
by microscopic
examination
**Note: For watery stool
samples
the sample itself is
directly
used and is not mixed with
NSS
Similarly prepared as
saline wet mount
only
that a solution of
iodine (Lugol’s iodine)
is used instead
Best in highlighting
details of protozoan
cysts
thus
correct identification
loome war
«Cy morphologital detail:
- Fecal Occult (Hidden) Blood Testing (FOBT)
Most frequently performed fecal chemical
examination
- Used to detect “occult” or “hidden” blood that may
be present in fecal samples.
- Necessary because any bleeding more than 2.5
mL/150 g of stool is PATHOLOGICALLY
SIGNIFICANT and there may be no visible signs of
bleeding with this amount of blood
A mass screening procedure for the early detection
of colorectal cancer
Recommended by the American Cancer Society
especially for those >50 years old
