Cli Set 4
Cli Set 4
Cli Set 4
CASE SET #4
A Tickle in the Throat and Other Cases in Parasitology
This set of case studies is approved for 1.0 contact hour of P.A.C.E.® credit.
P.A.C.E.® credits are accepted for continuing education requirements for maintaining
certification by NCA & ASCP-BOR and for maintaining the licensure of laboratory
professionals in the states of CA, FL, LA, MT, NV, RI and TN.
©2009 American Society for Clinical Laboratory Science All rights reserved. 1
Clinical Laboratory Investigations
No part of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical, photocopying,
recording or otherwise, without prior written permission from the American Society for
Clinical Laboratory Science.
©2009 American Society for Clinical Laboratory Science All rights reserved. 2
CLINICAL LAB INVESTIGATIONS:
CASE STUDIES FOR THE LABORATORY PROFESSIONAL
CASE SET #4
A Tickle in the Throat and Other Parasitology Cases
Welcome to this ASCLS continuing education offering! To obtain P.A.C.E.® credit for this
learning activity, you must read the case and complete the 10 question multiple choice quiz
that accompanies these case studies.
Simply circle the single best answer for each question on the answer sheet. Upon
completion, mail or fax your answer sheet along with payment -- $15 for ASCLS members
and $25 for nonmembers -- to the address listed on the answer sheet. You must score a
70% or better to obtain P.A.C.E.® credit. Be sure to print your name and address legibly
on the answer sheet for receipt of your P.A.C.E.® certificate with 1.0 contact hour. Quizzes
may be taken more than once if needed by submitting another completed answer sheet with
payment.
Please return the P.A.C.E.® evaluation form with your completed quiz. Your evaluation of
this learning experience will help us to develop future learning activities.
©2009 American Society for Clinical Laboratory Science All rights reserved. 3
LEARNING OBJECTIVES
1. Briefly discuss the lifecycles of nematodes and cestodes causing human infection.
3. Given a description, identify the ova of nematodes and cestodes commonly associated
©2009 American Society for Clinical Laboratory Science All rights reserved. 4
A TICKLE IN THE THROAT AND OTHER CASES IN PARASITOLOGY
Written by:
Meridee Van Draska, MS, MT (ASCP), CLS (NCA)
Address for correspondence: Meridee Van Draska, Illinois State University, 5220 Health
Sciences, Normal, IL 61790-5220, 309-438-8269, mrust@ilstu.edu.
CASE PRESENTATION
Case #1
One afternoon an internist rushed into the microbiology department carrying a specimen
container. He asked if any of the technologists could help him with a strange situation. Earlier
that morning, an eighty-one-year-old, female patient dropped by his office requesting that she be
seen immediately. The women said she had been plagued by a tickling in her throat. She stated
that she coughed and coughed until she coughed-up the object she now held wrapped in a tissue.
The patient showed the nurse the tissue and the nurse was astounded when she saw it contained a
worm. The nurse quickly summoned the physician. The physician placed the worm in a
specimen cup and brought it to the hospital laboratory. The technologist opened the specimen
container and saw a cream colored worm, about 22 centimeters in length. It had a tapered head
The physician has several questions he wanted answered. They were: what kind of worm
was it? Could the patient really have “coughed-up” the worm? If she did, should the patient be
treated for a parasitic infection? Finally, was he or any of his staff at risk of contracting the
infection?
After examining the worm, the technologist told the physician that based on its size and
color the worm was Ascaris lumbricoides. She told him that Ascaris can indeed migrate through
the human body and sometimes exit through the mouth, which is likely what happened in this
©2009 American Society for Clinical Laboratory Science All rights reserved. 5
case. She suggested that if the doctor wanted further verification, he could have the patient
submit a stool specimen for ova and parasite examination. The technologist told the physician
that as long as he and his staff used gloves to handle the specimen and also practiced good hand
Case #2
A woman phoned the microbiology department requesting help with a problem. She said
she was potty-training her son when she saw worms in his stool. She had reported the worms to
the child’s pediatrician who ordered a cellophane tape preparation for pinworms. The cellophane
tape preparation was performed twice and found to be negative both times. Meanwhile, the
mother did some research on her own. She read a description of the adult pin worm and
concluded that what she saw in her son’s stool were not pinworms; these worms were bigger.
Since she was still seeing motile worms in her son’s stool, she phoned the laboratory to see if
The technologist had the woman describe what she was seeing in her son’s stool. The
mother said the worms were whitish, and not quite a half an inch in length. She said they
“wiggled around” when the stool was fresh and it was the movement that brought them to her
attention. The woman wanted to know, were these really worms she was seeing? If they were
Working with the patient’s physician, the technologist suggested submitting a fresh stool
specimen for ova and parasite exam. The mother submitted a specimen the next day and insisted
on showing one of the technologists the “worms” that were in the specimen. The technologist
saw the “worms.” They were as whitish and about the size and shape of a pumpkin seed. These
“worms” were too small to be Ascaris but too large in diameter to be pinworms or any of the
©2009 American Society for Clinical Laboratory Science All rights reserved. 6
other adult round worm species adults. The technologist suspected that they could be tape worm
proglottids. Some of the stool was concentrated using formalin-ethyl acetate. Microscopic exam
of the concentrate revealed the presence of Dipylidium caninum (dog tape worm) egg packets.
Case #3
An obstetric nurse phoned the laboratory in a panic. A woman had just delivered a baby.
During the course of her labor, she had passed some stool and the nurse and attending physician
observed “worms” wiggling around in the stool. The physician was concerned that the patient
had a tapeworm infection. He remembered from medical school, that some types of tape worms
could be transmitted from human to human. The nurse asked what they could do to find out
what kind of worms these were. She also asked if the baby or the staff members could become
infected because of contact with the worms. What should they do next?
The technologist who answered the phone instructed the nurse to use caution handling the
fecal materials. The technologist also asked the nurse to collect some of the worms in a plain
specimen container and some of the stool in a separate container and send both to the laboratory
for processing.
The technologists examined the “worms” macroscopically; they did fit the description of
Taenia proglottids. Because the proglottids were longer that they were wide, and the patient’s
religion prohibited her from eating pork, Taenia saginata was suspected. The technologist tried
to confirm the suspicion by injecting a proglottid with India ink, but was unsuccessful.
Remaining proglottids were preserved and sent to the state public health laboratory for
speciation. Some of the stool was concentrated, Taenia species ova were found. The state
©2009 American Society for Clinical Laboratory Science All rights reserved. 7
DISCUSSION
In the United States, intestinal helminth infections are not as prevalent as they are in other
countries, but with increased immigration, both legal and illegal, laboratories must be prepared to
assist physicians in the identification of these infections.1 Typically, physicians who suspect
their patient has a helminth infection will request a fecal ova and parasite examination. What is
unusual in the cases described above is the fact that instead of stool, the laboratory was initially
Infection caused by Ascaris lumbricoides is the most common helminth disease world-
wide. In the United States, cases of ascariasis are exceeded only by the number of cases of
pinworm infections. Regions where Ascaris is most likely to exist are those with warmer
climates and poor sanitation. In the United States, the majority of cases occur in and around the
Appalachian Mountains.2 Humans become infected when they ingest fertile eggs in food or
water contaminated with human feces. The eggs hatch into larvae in the small intestine. Here
they molt once, then travel through the lymphatics or portal vein to the right side of the heart.
Circulation carries them to the lungs where they reside in the alveoli. In the lungs they undergo
two additional molting cycles. Larvae then travel up the trachea to the throat where they are
swallowed. They return to the small intestine where they mature into adults.1 The adult females
will produce eggs. If a male worm is also present the eggs will be fertilized. Both fertile and
non-fertile ova may be shed in the feces. After a period of about two weeks in warm, moist soil
the eggs become capable of causing infection if ingested. These eggs can remain viable in the
soil for years.3 While adult worms are typically found in the intestine, they can migrate in the
human body, particularly when provoked by fever, certain drugs or anesthesia. The migrating
©2009 American Society for Clinical Laboratory Science All rights reserved. 8
Pinworm infections are common world-wide. Enterobius vermicularis ova are
swallowed by the host. The ova hatch in the small intestine. The larvae migrate through the
digestive tract. Adult worms live in the colon. Fertilized female worms migrate out of the anus
and lay their eggs on the perianal skin.3 In a warm, moist environment, the ova can live for
Trichuris trichiura infections are initiated by the host ingesting an embryonated egg. The
larvae hatch in the small intestine, where they live until mature. The mature worms migrate to
the colon. Here the female lays its eggs which are passed in the host’s feces.2
There are two species of hookworms, Necator americanus and Ancylostoma duodenale.
Human infections caused by hookworms occur when the worm’s filariform larvae penetrate the
skin. These larvae travel through the blood stream to the lungs. In the lungs they penetrate the
alveoli and migrate to the trachea and pharynx. The host then swallows the larvae. The larvae
develop into adult worms in the small intestine.3 The female worm lays eggs which are passed in
the feces. The eggs hatch in the soil becoming rhabditiform larvae. The larvae molt twice
developing into the filariform larvae which can infect another host. The life cycle of
Strongyloides stercoralis is similar to that of the hookworm species. The main difference is that
the ova of S. stercoralis usually hatch in the colon of the host and the rhabditiform larvae are
Dipylidium canium is commonly referred to as the dog tapeworm, the cat tapeworm or
the pumpkin seed tapeworm.2 When an animal is infected, the adult worm resides in the
intestine. Proglottids containing eggs migrate out of the anus. Fleas ingest the ova and act as the
intermediate host. The ova develop into cystcercoid larvae in the flea’s digestive tract. The
primary host, usually a dog or cat, then ingests the flea. Once in the host’s digestive tract, the
©2009 American Society for Clinical Laboratory Science All rights reserved. 9
larva escapes and develops into an adult worm.3 The adult worms can self-fertilize and the cycle
is repeated. Humans become accidental hosts when they ingest dog or cat fleas or they ingest
contaminated food.2 Human infections are rare and occur mainly in children.4
Taenia saginata and Taenia solium are called the beef tapeworm and the pork tape worm
respectively. They are species specific in that T. saginata is only found in cattle and T. solium
on found in pigs. In the United States, T. saginata is found more often than T. solium.3 The two
species share a similar lifecycle with humans acting as the primary host. Infection begins with
adult worms in the small intestine of the human. Eggs and gravid proglottids are passed in the
feces. A cow or a pig then ingests the egg.4 The egg hatches into an onchosphere, which
migrates through the blood to the muscle tissue. In the muscle the onchosphere becomes a
cysticercus larva. Humans ingest the larvae in uncooked or undercooked beef or pork. Once in
the human digestive tract the larvae attach to the intestinal wall and mature into the adult worm.3
One difference between T. saginata and T. solium is ability of the T. solium to cause a
human tissue infection called cysticerosis. In cysticerosis, the human ingests the eggs in
contaminated food or water. The eggs hatch into the onchosphere and migrate to the muscles.
Onchospheres can also travel to the brain which may lead to death.2
Humans contract Diphyllobotrium latum or the fish tapeworm by ingesting the pleurocoid
larva in raw or undercooked freshwater fish. This larva matures into the adult worm, which
attaches to the wall of the small intestine. Eggs are passed in the feces. Any eggs that get into
fresh water will hatch into a coracidium (ciliated larva). The coracdium is ingested by a copepod
and the copepod is in turn ingested by a freshwater fish. In the fish the procercoid larva migrates
to the muscle where it becomes a pleurocoid larva which can infect another human.4
©2009 American Society for Clinical Laboratory Science All rights reserved. 10
Humans are infected by Hymenolepis nana when they ingest the ova. The ova develops
into a larval stage and then into the adult form in the intestine. Adult worms produce eggs that
are passed in the feces. Ova can also remain in the host and hatch repeating the cycle. Unlike
Hymenolepis diminuta is sometimes called the rat tapeworm. Humans are accidental
hosts. Infected rats excrete the ova in their feces. The ova are ingested by fleas or grain beetles.
The ovum develops into a cysticercoids larva in the insect. Another rat or sometimes a human
ingests the insect the larva then develops into a mature worm and the cycle is repeated.
Diagnostic tests:
The cellophane tape test is the test most frequently used to detect either the ova or
sometimes the adults of E. vermicularis. Clear (not frosted) tape is wrapped around a tongue
depressor. The adhesive side of the tape is pressed firmly against the perianal area. In the lab,
the tape is placed adhesive side down on a clean microscope slide. The tape is examined under
Fecal ova and parasite examination is used to detect most other species of intestinal
roundworms and tapeworms. Ova and parasite examination includes both macroscopic and
microscope procedures. Although not common adult worms and gravid proglottids can be found
during the macroscopic examination of the stool specimen. During the microscopic examination,
specimens should be collected in a wide-mouthed waxed cardboard or plastic container. The lid
should fit securely to prevent spillage during transport. Specimens should be collected directly
©2009 American Society for Clinical Laboratory Science All rights reserved. 11
into the container. Specimens contaminated with urine or water from the toilet are
unacceptable.4
Ideally, the patient collects the specimen at the testing facility so it can be processed
immediately. But often, fecal specimens are collected by the patient at home and brought to the
laboratory. Because there may be a delay between the collection and processing, many
laboratories use preservatives to maintain the integrity of the specimen. Commonly used
preservatives are 5% formalin, 10% formalin, polyvinyl alcohol (PVA) and sodium-acetate
formalin (SAF).
All fecal specimens submitted for ova and parasite examination should be inspected
macroscopically before they are processed. The macroscopic exam includes evaluating the color
and consistency of the sample. The presence of blood and/or mucus should be noted. Finally,
the technologist should also look for the presence of adult worms and tapeworm proglottids.
Unfortunately, a complete macroscopic exam may not be possible if the specimen is collected
http://phil.cdc.gov/phil/. Accessed
December 9, 2008.
©2009 American Society for Clinical Laboratory Science All rights reserved. 12
A. lumbricoides adult worms are often found in stool specimens as well as in vomitus.
The adult worms are the largest intestinal round worm species that parasitize humans. Female
worms are creamy white, 22-35 cm in length and as thick as a pencil lead. The male is similar
The adult worms of Enterobius vermicularis may also sometimes be found in stool
preparation and finding the ova or adult worms on the sticky surface of the tape. Of the other
intestinal roundworms species, adult worms are rarely seen in stool specimens. They all are
significantly smaller than A. lumbricoides adults. The small size and color of these adult worms
add to the difficulty of finding them during the macroscopic exam of the stool specimen. See
Species Description
Ascaris lumbricoides Creamy-white with a pink tint, female 22-35 cm.; male up
to 30 cm.
Strongyloides stercoralis Colorless, females 2 mm.; males have not been described
The tapeworm consists of two distinct parts, the scolex which attaches to the host’s
intestine and the strobila. The strobila is made up of a series of segments called proglottids.
©2009 American Society for Clinical Laboratory Science All rights reserved. 13
Each mature proglottid contains both male and female reproductive organs. Individual
proglottids or short chains of proglottids may be shed in the feces.4 Proglottids can exhibit
proglottids of several cestode species that infect man. Except following treatment, the scolex is
December 9, 2008.
©2009 American Society for Clinical Laboratory Science All rights reserved. 14
Table: 2 Comparison of Gravid Proglottids of Cestodes Causing Human Infection
Species Description
Taenia saginata Proglottids are longer than they are wide (17-19 x 5-7
mm.); uterus has 15-30 lateral branches on each side
T. solium Proglottids are more square (12 x 5-7 mm.); uterus has 7-
13 lateral branches on each side
Diphyllobothrium latum Proglottids are wider than they are long (3 x 11 mm.); the
central uterus is arranged in a rosette pattern; the
proglottids are often passed in chains
Hymenolepis nana Rarely found in feces, proglottids twice as wide as they are
long (1 x 2 mm); sac-like uterus is filled with eggs
Hymenolepis diminuta Rarely found in feces; proglottids twice as wide as they are
long (1 x 3-4 mm); sac-like uterus is filled with eggs
Dipylidium caninum Proglottids longer than they are wide (12 x 3 mm);
proglottid is filled with eggs.
Specimens are examined microscopically for the presence of protozoa, cysts, ova and
larvae. When liquid specimens are submitted, a direct microscopic exam can be performed.
Otherwise, permanent slides and wet preparations of concentrated stool are made. Concentration
increases the likelihood of finding ova and cysts in the specimen. Permanent slides can be
prepared from PVA or SAF preserved samples. Permanent slides can be stained with Wheatley
With the exceptions of the hookworm species and Strongyloides stercoralis, the ova of
parasitic nematodes are distinctive enough to allow diagnosis based on their features. The ova of
A. lumbricoides are found in two forms, fertilized and non-fertilized. The fertilized ova are
©2009 American Society for Clinical Laboratory Science All rights reserved. 15
rounded, measuring 45 x 75 µm.5 They have thick, yellow-brown chitin shells, usually covered
with a mamillated albuminous coating. Inside a unicellular, undeveloped embryo can be seen.
The non-fertilized ova are larger and more oblong, measuring up to 90 µm in length.5 They have
http://phil.cdc.gov/phil/. Accessed
As previously noted, E. vermicularis ova are often identified using a cellophane tape
preparation. The ova are oval and a flattened on one side. They are 50-60 µm long and 20-30
µm in width. They have a thick, colorless shell. A developing embryo can be seen inside.
http://phil.cdc.gov/phil/. Accessed
©2009 American Society for Clinical Laboratory Science All rights reserved. 16
Trichuris trichiuris ova are barrel-shape with a unique, clear plug at either end. They are
50-55 µm long and 20-25 µm in width. The shell is smooth and yellow-brown in color. An
http://phil.cdc.gov/phil/. Accessed
They are oval with a thin colorless shell. The ova are 60-75 µm in length by 35-40 µm in width
(S. stercoralis is slightly smaller). An embryo of 2-, 4- or 8-cells can be seen inside.
Library, http://phil.cdc.gov/phil/.
©2009 American Society for Clinical Laboratory Science All rights reserved. 17
Table: 4 Comparison of Nematodes Ova Causing Human Intestinal Infection
Species Description
Depending on the species, microscopic observation of cestode ova can also be helpful in
identifying the species present. This was true in Case #2. Dipylidium caninum ova are unique
in that they are found in membrane enclosed packets. These packets may contain from 5-30
ova.2 Individual eggs are only occasionally seen because they tend to collapse in processing.
The ova have a similar appearance to Taenia species.3 They contain a six-hooked onchosphere
http://phil.cdc.gov/phil/. Accessed
©2009 American Society for Clinical Laboratory Science All rights reserved. 18
The ova of T. saginata and T. solium are identical in appearance. The ova are round, 30-
40 µm in diameter. The shell or embryosphere is thick, yellowish brown with radial striations.
The embryo has six hooklets arranged in pairs. Because the ova of these two species are so
much alike, speciation depends upon examining either the proglottids or the scolex of the worm.
http://phil.cdc.gov/phil/. Accessed
Hymenolepis nana and H. diminuta also have similar ova. H. diminuta is larger
measuring 60-80 µm. A colorless embryophore surrounds the embryo, which displays six
hooklets. H. nana ova are smaller, 40-45 µm in diameter. A key difference is that the
embryophore of the H. nana ova contain filaments that emerge from thickenings on opposite
http://phil.cdc.gov/phil/. Accessed
©2009 American Society for Clinical Laboratory Science All rights reserved. 19
This micrograph depicts an egg from a
Library, http://phil.cdc.gov/phil/.
The ovum of D. latum is the only tapeworm ovum seen in humans that is operculated.
The ova are oval; 40-50 µm by 55-75 µm. They are yellow-brown in color and the shell
©2009 American Society for Clinical Laboratory Science All rights reserved. 20
Table: 2 Comparison of Cestode Ova Causing Human Infection
Species Description
Dipylidium caninum Packets of 5-30 ova; individual ova are round; 35-40 µm
diameter; an embryophore surrounds the six-hooked
onchosphere
Hymenolepis nana Oval; 30-50 µm; filaments originating from poles on the
inner membrane fill the space between the inner and outer
membranes; onchosphere with six hooks
Hymenolepis diminuta Round or oval; 70-85 µm; space between the inner and
outer membrane is smooth or faintly granular;
onchosphere with six hooks
Diphyllobothrium latum Oval; 40-50 µm by 55-75 µm; operculum at one end and a
small knob at the other; smooth yellow-brown shell
CASE CONCLUSION
In all three cases, the patients were treated with drugs recommended for their individual
types of infection. Stool specimens were submitted following treatment and found to be negative
©2009 American Society for Clinical Laboratory Science All rights reserved. 21
REFERENCES
Company, 1997.
5. United States National Center for Infectious Disease. Division of Parasitic Disease.
December 9, 2008.
©2009 American Society for Clinical Laboratory Science All rights reserved. 22