Flashcards in Parasitic diseases Deck (106):
WHat are parasites?
Organisms that infect and cause disease in other animals
Protozoa, Helminths, and Arthropods
How are protozoa transmitted?
How is indirect transmission accomplished?
Most are mobile. How do they move?
Can be passed directly from host to host through
1. sexual contact,
2. by contaminated water, or
3. through arthropod vector
Results from ingestion of highly resistant spores that are shed in feces of infected host (can also be direct)
Most are mobile by means of
2. cilia, or
3. ameboid motion
What are the worm like parasites?
How does transmisison primarily occur? 2
Infections can involve many organs such as?
What are the three main groups?
Helminths - Wormlike parasites
Transmission occurs primarily through the
1. ingestion of fertilized eggs or the
2. penetration of infectious larval stages through the skin
Infections can involve many organs:
3. urinary and intestinal tract,
4. circulatory and
5. nervous systems, and
3 main groups
1. Flatworms (platyhelminths)
2. Thorny-headed worms (acanthocephalins)
3. Roundworms (nematodes)
Transmission from athropods can occur how? 2
What are the most common types? 5
Transmission from arthropod to human occurs either mechanically or biologically.
4. mosquitoes, and
How do parasites affect the host specifically 3
How would death occur in a parasite infected host if it did?
The stress placed on the host's resources can affect:
1. its growth,
2. ability to reproduce, and
Typically, a parasitic infection does not directly kill a host
This stress can sometimes lead to the host's premature death
Host begins to feel ill as a consequence of what from the parasite? 2
In majority of parasite infections what ocurrs?
Multiplies and increasingly interferes with the normal life functions of the host.
Host begins to feel ill as a symptom of the parasite's INVASION and ACTIVITIES.
In many cases, the host's immune system may be able to respond to the parasite and destroy it.
Hosts for parasites might be what?
Host species may be
1. animal (all types),
3. May live only in water, or
4. on vegetables
What are the types of protozoa? 4
What are the types of metazoa (helminths)?2
What are the types of flatworms (Platyhelminthes)? 2
What kind of organisms are protozoa?
This group of organisms has historically been the cause of more disease and death than any other category of disease-causing organisms.
Single cell (unicellular) organisms
African Sleeping Sickness
A term for the live adult protozoa
What are the non adult forms? 3
How are most of the diseases spread?
Cysts, spore, or “eggs” are non-adult forms
MOST OF THESE DISEASES ARE SPREAD BY THE FECAL-ORAL ROUTE
What protozoan causes giardiasis?
What does it infect?
Giardia lamblia, a flagellate, is a common pathogenic protozoan.
Infects duodenum and jejunum of humans.
How is it transmitted? 4
Humans are infected by ingestion of fecally
1. contaminated water or
2. food containing giardia cysts.
3. It is also spread by direct person-to-person contact, which has caused outbreaks in institutions such as day care centers.
4. (pets, rodents, livestock)
How long can giardiasis cysts survive?
When do symptoms occur after infection?
Describe their life cycle?
Cysts can survive in water for up to 3 months
takes up to 7-10 days for these cysts to open up and cause problems
Cysts and trophozoites (can go back and forth because they cant survove out of the body in adult form)
Parasites attached to the bowel wall may cause irritation and low-grade inflammation of the duodenal or jejunal mucosa
What diagnostic test do we do for Giardiasis and what will it show us?
Biopsy of small bowel will show:
1. crypt hypertrophy
2. villous atrophy or
epithelial cell damage
1. A large portion of infected patients are asymptomatic
The symptomatic forms are
2. Acute diarrhea
3. Chronic diarrhea
4. Malabsorption syndrome
Giardiadas Presenting symptoms can be what? 6
Patients with chronic infection show what? 3
What will the stools look like?
How long will symptoms last?
4. abdominal cramps & bloating,
6. N/V, and weight loss
1. major weight loss,
2. malabsorption, and
The stools may be
watery, semisolid, greasy, bulky, and foul-smelling at various times during the course of the infection
When does giardiasis typically encyst?
What will be found in the stool often in enourmous amounts?
As the parasites pass into the colon
Cysts are found in the stool—often in enormous numbers.
GIARDIASIS: WORK UP
1. STOOL Sample-fecal smear
2. Examination of the duodenal contents
What are we looking for un a stool sample/fecal smear for giardiasis? 2
What does the diagnosis depend on? 2
How many stool examinations should be done?
What lab test has shown to be a specific and sensitive rapid diagnostic tool?
To look for “ova and parasites”
Depends on finding the distinctive cysts in formed stools, or cysts or the protozoa in liquid stools.
A series of three or more stool examinations on alternate days is therefore recommended.
Stool enzyme-linked immunosorbent assay (ELISA)
Why may examination of the duodenal contents be necessary to establish the diagnosis?
as cyst production may be sporadic and not found in the stool by an ovum and parasite fecal smear examination.
Metronidazole (Flagyl) 250mg twice daily for 5 days will clear over 90% of Giardia lamblia infections.
Oral tinidazole and nitazoxinide are alternatives.
Could become lactose intolerant in infection
GIARDIASIS - PREVENTION?
Avoid contaminated water sources
Hikers or campers should boil water or use iodine or filtration with a large pore sized filter
Adequate disposal of diapers and frequent hand washing for daycare centers (does work in cyst form-hand sanitizers)
What is Cryptosporidiosis caused by?
What is the disease associated with?
One of the most common causes of waterborne illness in the United States
A coccidian protozoan parasite(Cryptosporidium hominis) which causes the disease Cryptosporidiosis
Contaminated water supply
Where are the Cryptosporidium hominis intracellular spheres found in great numbers?
What is the infectious agent of the bacteria?
The intracellular spheres are found in great numbers just under the outer membrane of the cells lining the stomach or intestine.
Oocysts, passed into feces in enormous numbers, are the infective agents.
Cryptosporidium: Site of infection?
(one most common)
Epithelial cells of the gastrointestinal tract
Has affected other tissues such as respiratory tract tissues and conjunctiva of the eye
What is the infectious dose of Cryptosporidium?
Cell death from Cryptosporidium is a direct result of what?
1. Cell death is a direct result of parasite invasion, multiplication, and extrusion
2. Cell damage could occur through T cell-mediated inflammation, producing microvilli death and Cryptosporidium excess growth
Cryptosporidium Symptoms 4
Severe disease symtpoms? 4
1. Some individuals can be asymptomatic
2. Stomach cramps and pain
3. watery diarrhea, dehydration, vomiting,
Severs symptoms –
1. profuse, watery diarrhea,
2. severe malabsorption,
3. electrolyte imbalance and
4. marked weight loss
Incubation period: 7-10 days (range 3-28)
How is a Cryptosporidium Diagnosis usually made?
What test specifically?
What tests have te best sensitivity and specificity? 2
Usually made by examining stool specimens, 3 stools may be required.
Microscopy with an acid fast stained stool smear is usually diagnostic
1. Enzyme immunoassay for greatest sensitivity and specificity or
2. molecular methods using PCR
Can be used for pediatric patients
500mg q12 hours
100mg q12 hours
200mg q12 hours
Cryptosporidium prevention 6
What is it resistant to?
1. Water purification and filtration
2. Routine testing
3. Use of 1 micron filter to remove cysts
4. Boil water
5. Drink bottled water when traveling abroad
6. Wash hands frequently
(Resistant to chlorine)
The sporocysts in cryptosporidium are resistant to most chemical disinfectants, but are susceptible to?
drying and the ultraviolet portion of sunlight
Intestinal Amebiasis is commonly caused by what?
What is this mostly a disease of?
Three stages are encountered:
The active amoeba
The inactive cyst
The intermediate precyst
Several strains of Intestinal Amebiasis ?8
The only two though to cause disease are what?
The only two though to cause disease are E. histolytica and Dientamoeba fragilis
Entamoeba histolytica AMEBIASIS-Pathogenesis
How is it transmitted?
After the cyst is inside the body how does it infect?
The cyst is ingested
1. The trophozoite emerges from the ingested cyst in the stomach and duodenum.
2. Each of which divides again to produce eight small trophozoites per infective cyst.
3. These pass to the cecum and produce a population of lumen-dwelling trophozoites.
Disease results when the trophozoites of Entamoeba histolytica invade what?
What helps the trophozoites do this?
What does it cause?
Mucosal invasion with the aid of proteolytic enzymes occurs through the bowel wall
Causes discrete ulcers with a pinhead-sized center and raised edges, from which mucus, necrotic cells, and amoebas pass
Subsequent spread of Entamoeba histolytica may coalesce colonies of amoebas causing what?
Trophozoites may penetrate the muscular coats and occasionally the serosa, leading to what?
undermining large areas of the mucosal surface.
1. Perforation into the peritoneal cavity.
2. Secondary bacterial invasion, and accumulation of neutrophilic leukocytes can occcur.
Entamoeba histolytica extraintestinal infection acts how?
infection is metastatic/amoebas spread through the blood
(Rarely occurs by direct extension from the bowel.)
What is the most common forms of Entamoeba histolytica extraintestinal infection?
What is this assumed to be due to?
By far the most common form is amoebic hepatitis or liver abscess (4% or more of clinical infections)
Assumed to be due to microemboli including trophozoites carried through the portal circulation.
Factors that determine invasion of Entamoeba histolytica amoebas include the following?
1. number of amoebas ingested
2. pathogenic capacity of the parasite strain
3. host factors such as gut motility and immune competence
AMEBIASIS—Clinical Findings. Symptoms vary greatly depending upon the site and intensity of lesions.
What are they?
1. Extreme abdominal tenderness
2. Fulminating dysentery and dehydration occur in serious disease
In less acute amebiasis disease, onset of symptoms is usually gradual. What are the symtpoms?
1. Episodic diarrhea,
2. abdominal cramps,
3. nausea and vomiting, and an
4. urgent desire to defecate
More frequently, there will be
5. weeks of cramps and general discomfort,
6. loss of appetite,
7. weight loss and malaise
Amebiasis- Diagnostic Laboratory Tests
1. Fluid feces for trophozoites
2. Formed feces for cysts
3. Serology is available
When do we want to look at stool species for Amebiasis and what will we find in them? 2
1. Fresh and warm for immediate examination for trophozoites.
2. After a saline purge for cysts and trophozoites.
EIA (Enzyme Immunoassay)
E. histolytica Amebiasis - Treatment:
Can we treat all Amebiasis the same?
Do we treat E. histolytica that is not symptomatic?
E. histolytica should be differentiated from morphologically similar species and treated appropriately
Given the small but substantial risk of invasive disease and the potential to transmit the infection to others, WHO recommends treating all cases of proven E. histolytica, regardless of symptoms
E. Histolytica Asymptomatic intestinal infection treatment? 2
Symptomatic E. Histolytica disease treatment? 3
What should we remember about the timing of the treatment?
1. Paromomycin 10 days of 30 mg/Kg divided into 3 doses and
2. diloxanide furoate 500 mg tid x 10 days
1. Paromomycin as above after
2. Metronidazole 750 mg, 3 times a day, for 5-10 days, treatment should be followed by administration of
3. diloxanide to eradicate any potential intestinal reservoirs
With early treatment the prognosis is good
Amebiasis - Prevention
1. Avoid contaminated food and water
2. Wash and cook vegetables
3. Hand washing
What is the vector that most commonly transmitts malaria?
Whats the most serious species?
The parasites multiplies within what kind of cells? 2
Mosquitoes of the genus Anopheles
Plasmodium falciparum most serious
Parasites multiply within liver cells and RBCs
Four species are responsible for human malaria:
Which is the most widely distributed?
Which is comparatively rare and found in temperate areas and subtropics?
Which is relatively uncommon, found in Asia, Europe and South America?
Which predominates throughout all tropical areas and is very often lethal?
Plasmodium vivax malaria attacks what?
When does it become symptomatic?
Plasmodium malariae attacks what?
How long can the infection persist for?
Plasmodium ovale can be dormant for how long?
Plasmodium falciparum invades what type of cells?
What does this cause?
Plasmodium knowlesi is newly identified and found where?
Plasmodium vivax –
1. attacks reticulocytes
2. may become symptomatic 6-12 months after leaving an area with malaria and can be dormant for years
Plasmodium malariae –
1. attacks mature red cells, after the acute infection, the infection becomes chronic and
2. can persist for years
Plasmodium ovale – can be dormant for years
Plasmodium falciparum –
1. Invades all red cells irrespective of age of red cells
2. cells agglutinate forming thrombi and emboli
Plasmodium knowlesi –
1. Found in Southeast Asia (70% of cases of malaria)
Onset with P. falciparum malaria?
Other types of malaria can cause onset when?
Onset 10-14 days up to 1 month with P. falciparum,
18-42 days occasionally 6 months to a year with other types
2. Night sweats
5. Muscle pain
6. Cough and chest pain
7. Splenomegaly in chronically infected patients
8. Hepatomegaly in chronically infected patients
Malaria infection during pregnancy can result because the mother became infected during her pregnancy, but it can also result from what?
it can also result from an infection acquired months or years before.
1. Vector control
2. Application of DEET
3. Mosquito nets
Examples of vector control for malaria?
1. Reduce stagnant water
2. Spraying with insecticide
Which ones are safe with pregnancy?2
1. Chloroquine *(most strains of Plasmodium show resistance)
2. Atovaquone & proguanil (Malarone)
Chloroquine and Mefloquine are safe with pregnancy
How do we diagnose malaria?
thin and think blood smear
First loading dose of chloroquine or atovaquone should be administered immediately after what?
What should be our DOC?
1. collecting the blood specimen, even without waiting for its report
In areas with high transmission of P. falciparum malaria, chloroquine alone as presumptive treatment may not be enough
2. Atovaquone should be the first choice
In an area with high transmission of malaria, it should be presumed that ALL cases of what symtpom are due to malaria?
Malaria prophylaxis treatment? 2
1. Chloroquine phosphate 500 mg weekly, continue 6 weeks after leaving area
2. + Fansidar ( 25 mg primethamine and 500 mg sulfadoxine) weekly in areas with chloroquine resistant P. falciparum
Primiquine phosphate 26.3 mg daily, start 1-2 days before travel and continue 7 days after leaving area
Toxoplasmosis is caused by what kind of bacteria?
What animal is the only one that can complete its reproductive life cycle?
Its a coccidian protozoan of worldwide distribution that infects a wide range of animals and birds but does not appear to cause disease in them.
Felines are the only animals that can complete its reproductive cycle
How is toxoplasmosis developed and transmitted to humans?
1. Oocysts develop in the cat GI tract,
2. pass into the gut lumen of the cat, and
3. pass out via the feces.
4. These cysts can then be ingested by other creatures, including humans (i.e. changing litter box of pet cat)
Pathology of toxoplasmosis cysts in humans?
1. The oocyst opens in the human's duodenum and releases the sporozoites
2. These pass through the gut wall, circulate in the body, and invade various cells, especially macrophages
3. They multiply, break out, and spread the infection to lymph nodes and other organs
4. They penetrate nerve cells, especially of the brain and eye,
5. where they multiply slowly to form tissue cysts, initiating the chronic stage of disease.
What cells does toxoplasmosis invade in early stages which allows it to spread to other parts of the body?
In late stages what cells do they infect that make them dangerous and form the chronic stage of the disease?
Toxoplasmosis - Symptoms?
What infection are the symtpoms similar to?
Symptoms similar to those of the flu or mononucleosis, occur in immunocompetent patients such as:
1. Body aches
2. Swollen lymph nodes
6. Occasionally, a sore throat
Immune competent patients – most will be asymptomatic
What pts will you mostly see sytmpoms in for toxoplasmosis?
What more serious effects will it cause?
Immune compromised patients - can cause:
3. blindness, and
4. severe neurological disorders.
Toxoplasmosis - Congenital Infection develops only when what happens?
Develops only when non-immune mothers are infected during pregnancy
Usually causes severe congenital defects
Toxoplasmosis- Congenital Infection leads to what? 5
Prenatal toxoplasmosis is a major cause of what and other congenital defects.
Symptoms may include?
3. intracerebral calcifications,
4. psychomotor disturbances, and
5. hydrocephaly or microcephaly.
1. Enlarged liver and spleen
2. Diarrhea or vomiting
4. Feeding problems
6. Low birth weight
7. Vision problems
8. Hearing loss
9. Skin rash at birth
Toxoplasmosis- Diagnostic Laboratory Tests?4
Whats the gold standard test?
Whats the test run in most labs?
3. Sabin-Feldman dye test
--However only a few labs will run the test
Standard test for most labs
Acute infections can be treated with a combination of
1. pyrimethamine and either
2. sulfadiazine or clindamycin
3. Leucovorin should be given to all patients receiving pyrimethamine
For use in pregnancy, spiramycin (Rovamycine) 1-2 grams BID is recommended, continued until delivery
1. Wear gloves when gardening or handling soil
2. Avoidance of human contact with cat feces is important in control, particularly for pregnant women with negative serologic tests
3. Since oocysts usually take 48 hours to become infective, daily changing of cat litter (and its safe disposal) can prevent transmission
4. Pregnant women should avoid all contact with cats, particularly kittens
5. Don't eat raw or undercooked meat
6. Cover children's sandboxes
THE HELMINTHS - WORMS:
What are the three types of concern?
What are exmples of nematodes? 3
What is an example of cestodes?
What is an example of a trematode?
1. Pin worms
2. Hook worms
3. Round Worms
Flukes (very rare in US)
Pinworm (Enterobius vermicularis):
How is it spread?
Where do the worms reside and where do they travel (2) to?
Seen in what age of children?
Spread: Fecal- Oral route; self contamination and internal reinfection
Worms resides in cecum, colon…
Crawl out of anus at night and rarely worms get in vaginal canal
1. ITCHY BUTT!
2. Squirming when sitting
Seen in school children age 5-10
Pinworm Life cycle and transmission:
After ingestion, eggs hatch and release larvae where?
Where do adult worms establish? 2
Gravid females migrate where and why?
What time of day does this usually occur?
How can it be transmitted? 2
After ingestion, eggs hatch and release larvae in small intestine
Adult worms establish in the cecum and appendix
Gravid females migrate to rectum onto perianal skin to deposit eggs (usually occurs at night)
Fecal oral transmission
Can get airborne (breath eggs in)
Pinworm (Enterobius vermicularis) diagnosis?
1. Stool for Ova & Parasites
2. Pinworm Preparation (Cellophane Tape Test)
Describe the Pinworm Preparation (Cellophane Tape Test)?
When are the best samples collected?
Wrap a 3” piece of clear Scotch tape around a glass slide (sticky side out). Touch the slide to the patient's perianal skin in four quadrants
Examine it under a microscope to find pinworm eggs.
The best sample is collected either in the early morning before bathing or several hours after going to bed
Pinworm (Enterobius vermicularis) treatment:
DOC and alternative?
Do we treat prophylactically?
Mebendazole (Vermox) >=2 years: 100 mg PO single dose; may repeat in 2-3 weeks
Albendazole >=2 years: 400mg PO single dose; may repeat in 2 weeks
Yes, postexposure. Treat the whole family
Pinworm (Enterobius vermicularis) hygiene measured?
Infxn not indicative of poor personal hygiene, common childhood infection
1. Hand washing
2. Discourage child from sucking thumb, biting nails, and scratching
3. Trim nails
4. Wash bedding and garments in hot water promptly and avoid shaking
Ascariasis - Round Worms:
Where does the adult release its larvae?
It then migrates where? 3
After 10 days in the lung they mature and go where?
Mature worms attach where?
Ingestion of contaminated food/water
Children playing in contaminated soil
When ingested ova hatch in small intestine and release larvae
Migrate in 1. blood or 2. lymphatics to 3. lungs within 4 days
After 10 days in the lung they mature, ascend the bronchial tree and get swallowed
Mature worms attach to the jejunum
Female worms produce 200,000 fertilized eggs/day
Round worms clincial presentation?
Ascariasis -Round Worms Laboratory Diagnosis?
Diagnosis is usually made microscopically by
detecting eggs in the stools.
The egg is oval with an irregular surface
Occasionally, the patient sees adult worms in the stools.
Ascariasis -Round Worms treatment?
1. Mebendazole 100 mg BID for 3 days or
2. Albendazole 200mg PO single dose
3. Pyrantel 11 mg/kg PO single dose for pregnancy
4. Ivermectin >15kg 150mc/kg single dose alternative agent
Ascariasis -Round Worms prevention?
Proper disposal of feces
Nematodes in the USA aka?
How were children getting hookworm?
Walking barefooted on soil predisposes to infection
Necator americanus hookworm are infected when what happens?
filariform larvae in moist soil penetrate the skin, usually of the feet or legs
How do Necator americanus infect the body? 4
Where do they deveop into adults?
They feed on blood from where?
1. Migrate into blood vessels and
2. are carried by the blood to the lungs,
3. migrate into the alveoli and up the bronchi and trachea, and
4. then are swallowed
They develop into adults in the small intestine, attaching to the wall with cutting plates (hooks)
They feed on blood from the capillaries of the intestinal villi
Hook Worm Infection: Pathogenesis & Clinical Findings
What is the major damage due to?
Blood is comsumed by the worm and oozes from the site in response to what?
What kind of anemia accompanies this kind of blood loss?
Skin penetration produces what?
Other symptoms? 4
The major damage is due to the loss of blood at the site of attachment in the small intestine
An anticoagulant made by the worm
Weakness and pallor accompany the microcytic anemia
a focal pruritic maculopapular eruption at site (“ground itch”)
1. Mild cough and
2. pharyngeal irritation
3. N/V, diarrhea, and
4. midepigastric pain
Hook Worm infection: Diagnosis? 3
1. Made microscopically by observing the eggs in the stools.
2. Occult blood in the stools is frequent.
3. Eosinophilia is typical.
Treatment of hook worm?
Both albendazole and mebendazole are effective.
1. Disposing of sewage properly and
2. wearing shoes are
effective means of prevention.
What causes causes trichinosis?
What are the biggest reserviors of Trichinella spiralis that cause human disease?
How is it transmitted to humans?
Any mammal can be infected, but pigs are the most important reservoirs of human disease in the US (except in Alaska, where bears constitute the reservoir)
Humans are infected by eating raw or undercooked meat containing larvae encysted in the muscle
Pathology of Trichinosis:
The larvae excyst and mature into adults where?
How does the infection spread and where do the larvae develop?
within the mucosa of the small intestine
Eggs hatch within the adult females, and larvae are released and distributed via the bloodstream to many organs; however, they develop only in striated muscle cells
What are the cells that Trichinosis grow and live in in the muscle cells?
How long does this allow them to stay alive for?
What allows them to be concealed from the immune system?
Within these "nurse cells," they encyst within a fibrous capsule and can remain viable for several years but eventually calcify
Allows to conceal from the immune system
Trichinosis: Pathogenesis & Clinical Findings
A few days after eating undercooked meat, usually pork, the patient experiences what?
What is the severity related to?
1–2 weeks later the pt will experience what? 4
What are important diagnostic criterion? 2
diarrhea (severity is related to the number of larvae ingested)
2. muscle pain,
3. periorbital edema, and
1. Subungual splinter hemorrhages or
2. conjunctival or retinal hemorrhages
are an important diagnostic criterion.
What signs are frequent in trichinosis because the larvae migrate to these tissue areas as well?
Death is rare but what is it due to if it does happen?
Signs of cardiac and central nervous system disease are frequent, because the larvae migrate to these tissues as well.
Death, which is rare, is usually due to congestive heart failure or respiratory arrest.
Trichinosis laboratoy diagnosis?
Results can be confirmed with?
1. Muscle biopsy reveals larvae within striated muscle.
3. indirect immunofluorescence, and
4. latex agglutination are reliable;
results can be confirmed with a Western blot.
Often self-limited and not required
Symptomatic- steroids plus albendazole or mebendazole
The disease can be prevented by
1. properly cooking pork or
2. freezing the meat and
3. by feeding pigs only cooked garbage.
Cestodes (Tapeworms) in USA are caused by what parasite?
There are two different kinds. What are they and where are they found?
T. solium (the pork tapeworm)
T. saginata (the beef tapeworm)
Morphology of Cestodes (Tapeworms)/Taenia?
Have head, neck, and segmented body
Each segment is called a proglottid
Tapeworm life cycle? 3
This infection occurs over what period of time and how long can it survive in the intestine?
1. Cattle or pigs ingest vegetation that is contaminated with eggs or proglottids
2. Humans become infected by eating infected undercooked meat
3. They attach to the small intestine and develop proglottids.
This occurs over about 2 months and can survive for years in the small intestine
Tapeworm Clinical Findings:
Most adult pts present how?
Where can we sometimes see the tapeworm?
1. Most patients with adult tapeworms are asymptomatic, but malaise and mild cramps can occur
2. In some, proglottids(segment or joint of tapeworm) appear in the stools and may even protrude from the anus.
Tapeworm laboratory diagnosis?
Identification of T. saginata consists of finding
1. gravid proglottids with 15–20 uterine branches in the stools.
2. Eggs are found in the stools less often than are the proglottids.