This document discusses parasitic infections that can cause diarrhea. It focuses on the laboratory diagnosis of parasitic infections through microscopic examination of stool and other specimens. The most common protozoan parasites found in stool are described in detail, including Entamoeba histolytica, Giardia lamblia, Cryptosporidium species, and others. Diagnostic methods for specific parasites are also outlined.

1. Parasitology
Review
2019
MARGIE MORGAN,PHD, D(ABMM)

2. Diarrheal Disease due to Parasites
Travel history or poor sanitation put you at the highest risk for
parasitic infection
Poor immune status higher risk
Parasitic infections associated with sporadic symptoms
Dysentery not common (usually only amebiasis)
Most usual symptoms:
◦Abdominal pain, cramping, long term nausea, and malaise, mucous in stool,
and +/- fever, chronic in nature

3. Laboratory Diagnosis
Current diagnosis is predominately
based on microscopic exam
Specimen types:
◦Stool
◦Non-stool
◦Perianal specimen
◦Sigmoidoscopic specimen
◦Duodenal aspirates
◦Liver abscess
◦Sputum
◦Urine
◦Urogenital
◦Blood
◦Tissue
Alternative testing methods:
◦Serology for select pathogens
◦Fluorescent stains of stool for select
pathogens
◦Molecular assays of stool for select
pathogens

4. From the 2017 IDSA Practice
Guidelines: suggested
laboratory testing methods for
select pathogens
Parasite Test Method Specimen

5. Two-vial collection kit for stool
preservation for routine parasite
exam
10% formalin vial
Concentration of stool performed
with ethyl acetate washing to
eliminate fecal debris
Can use to perform: Wet mount,
Iodine mount, DFA staining and
NAAT
Detect: Helminth eggs, larvae,
microsporidia, and protozoan cysts
PVA with fixative
Polyvinyl alcohol (PVA)
Permanent smear
prepared from stool and
stained with Trichrome
stain
Detect: Protozoan
trophozoites and cysts

6. Most common PROTOZOAN
Parasites
Amebae
◦ Entamoeba coli
◦ Entamoeba histolytica
◦ Endolimax nana
◦ Iodamoeba butschlii
◦ Dientamoeba fragilis
Flagellates
◦ Giardia lamblia
◦ Chilomastix mesnili
Ciliates, Coccidia, Blastocystis
◦ Balantidium
◦ Cryptosporidium
◦ Cystoisospora (Isospora) belli
◦ Sarcocystis
◦ Cyclospora
◦ Microsporidium
◦ Blastocystis hominis
Blood-Borne Protozoa
◦ Babesia
◦ Leishmania
◦ Trypanosoma brucei
◦ T. cruzi
◦ Plasmodium
Other: Tissue and sterile body fluids
◦ Toxoplasma
◦ Naegleria fowleri
◦ Acanthamoeba
Stool-borne Protozoa

7. Protozoa Found in Stool: Amebae
Major pathogen

8. Protozoa: Intestinal amoeba of note
Entamoeba histolytica/dispar
Entamoeba hartmanni
Endolimax nana
Entamoeba coli
Iodamoeba butschlii

9. Entamoeba histolytica/dispar
E. histolytica (pathogen) and E. dispar (nonpathogen) species both occur in
the large intestine. Morphologically indistinguishable.
◦Use either antigen testing or molecular methods to distinguish the two
species
E. histolytica in the intestine
◦Cysts = infectious form found in the environment
◦Contaminated water and poor sanitation
◦Trophozoites = invasive form in the intestine
◦Colon biopsy shows “flask-shaped” ulcers with trophozoites
Extra-intestinal disease
◦Liver abscess – amebiasis with trophozoites in liver biopsy
◦Serology will be positive in most cases compared to <=50% of cases of
intestinal only infection

10. Entamoeba histolytica/dispar cyst
Cysts @10-12 um
In diameter
Up to 4 nuclei in
the cyst
Chromatoidal body
present in some cysts

11. Entamoeba histolytica/dispar
trophozoites
Trophozoite with ingested rbcs

12. Amebic abscess
Flask-shaped ulcer of intestinal amebiasis
Amebic liver abscess/ flask shaped ulcer
E. histolytica serology – high % positive
in extra-intestinal cases
trophozoite

13. Entamoeba coli
commensal in the intestine
Cyst @ 20 – 25µm
Up to 8 nuclei
Shed from host
Lives in environment
Trophozoite is the
invasive form that is
found in the
intestine
Single nucleus with a large
karyosome located
eccentrically with irregular
chromatin ring (differs from E.
histolyica).
The cytoplasm appears dirty
and vacuolated

14. Entamoeba coli – important to
differentiate from the pathogen E. histolytica
Trophozoites & Cysts
Cysts usually
15-25µm, with 5
or more nuclei
visible.

15. Endolimax nana
Trophozoites 8 – 10 µm, one
nucleus
Cysts – 6-8 µm in size, four
nuclei
Usually a commensal, seen in
stool specimens from HIV/AIDS
patients, some literature
suggesting it can cause
intermittent or chronic diarrhea

16. Iodamoeba butschlii
Cysts, 10 – 12 µm
Large starch inclusion
(glycogen mass) that is unique
to Iodamoeba
Usually not considered a pathogen
Iodine preparation – glycogen
inclusions stain with iodine

17. Flagellates
Giardia lamblia (duodenalis)
Dientamoeba fragilis
Trichomonas vaginalis

18. Protozoa Found in Stool: Flagellates
Pathogen

19. Giardia lamblia (G.
intestinalis,
and G. duodenalis)
Found in contaminated water & undercooked
foods
Mild diarrhea to severe malabsorption
Foul smelling , watery diarrhea
Day-care center outbreaks reported, traveler’s
diarrhea
Cysts/trophozoites may be seen in stool, but
can be difficult to detect; Fluorescent stains
and NAAT for more sensitive detection
Duodenal aspirations can be used if stool
specimens are negative
TROPHOZOITE
“falling leaf” motility
CYSTS

20. Giardia lamblia trophozoite
Waxing and waning
symptoms
Can be irregularly
shed in stool material
making antigen
and molecular methods
more sensitive for
detection
Russia & Mexico
-Hot beds of infection
Confined to intestine –
does not disseminate
Flagyl (Metronidazole)
is drug of choice

21. Giardia lamblia cysts
Clearing between the cell
wall and the cell membrane

22. Giardia lamblia
only invades intestinal tissue – shown are duodenal biopsies,
trophozoites near the surface epithelium

23. Chilomastix mesnili cyst
Nonpathogen
Morphology mimics Giardia
lamblia cyst – except for the clear
space at end of cyst
Internal structure looks like
“shepherd’s crook” or safety pin
C. mesnili trophozoite – seldom
seen in clinical specimens

24. Dientamoeba fragilis
Diarrhea, anal pruritus
Only a trophozoite stage 5 – 15 µm (No
cyst)
Usually two nuclei visible in the
trophozlite
Can occur in Co-infection with Enterobius
(pinworm)

25. Trichomonas vaginalis
Urogenital protozoan
STD in both men and women
Infection leads to Scant, watery
vaginal discharge in women
Infection in urethral orifice in men
Four flagella, short undulating
membrane

26. Protozoa Found in Stool:
Ciliates, Coccidia, Blastocystis

27. Ciliates
Balantidium coli
◦Contact with swine
◦Poor hygiene
◦Only ciliate that’s pathogenic to humans
◦Similar disease as amebiasis
◦Largest (50-200 um) trophozoite in parasitology
◦Surface covered with cilia; macronucleus
◦Cyst 40-60 um
◦Readily identified in fresh, wet mounts
◦Can cause flask shaped ulcer in intestine like that of
Entamoeba histolytica

28. Isospora(Cystoisospora)
belli
Contaminated food/water, oral-anal route of infection
Found most commonly in HIV/AID patients
Infects intestinal epithelium
Malabsorption syndrome mimicking giardiasis
Stains positive with modified acid fast staining
(+) Modified acid fast stain

29. Cryptosporidium spp
Contaminated water
◦Resistant to usual water-purification procedures
(chlorination, ozone)
Watery diarrhea -
◦More severe in HIV/AIDS – chronic/debilitating
infection
◦Daycare center outbreaks (fecal-oral transmission)
Not detected in routine O & P exams (left)
Modified acid-fast stains (PAF) aid in detection,
Oocysts measure 4-6 µm
Stool antigen, Direct Fluorescence antibody staining
and Molecular assays aid detection.

30. Cryptosporidiosis: Diagnosis
Not detected in routine O & P exams (left)
Requires modified acid-fast stains for detection, oocysts
measure 4-6 µm , Antigen, DFA and Molecular assays aid
detection.
PAF stain
positive
Direct Fluorescence Antibody stain –
Cryptosporidium spp

31. Cryptosporidia in the intestine –
located just below the plasma
membrane

32. Cyclospora
cayetanensis
Contaminated fruits and vegetables – particularly ones with plant hairs
Watery diarrhea; fatigue, anorexia, weight loss, flu like symptoms. More severe in
immune suppressed, can last for months
Infects upper small bowel
Treatment Oral Trimethoprim/sulfamethoxazole
Found in vacuoles in cytoplasm of jejunal epithelium, villous atrophy, crypt
hyperplasia
Modified acid
fast positive
Cysts 8-10
microns
UV autofluorescence
Also positive on Calcofluor
white stain

33. Microsporidia
Obligate intracellular fungal parasite (yeast like)
Enterocytozoon and Encephalitozoon species most
common genera
Infection by ingestion of spores
Chronic diarrhea in HIV/AIDS patients
Can also disseminate and be found in cases of
Myositis, hepatitis, peritonitis, keratitis,
gastrointestinal and biliary tract infection

34. Microsporidia
-Diagram of detailed internal spore
structures
Spores are 1 – 4um
Stain positive on Calcofluor white and
modified Trichrome stains – modified
by longer staining times that eventually
allow for stain to penetrate the spore

35. Blastocystis hominis
(algae)
Small #s: are considered commensal
Large #s: may be pathogenic
Found in Contaminated food and H20 
Primary a cause of Traveler’s diarrhea
Iodine wet mount
Nuclear blobs
Around the periphery Trichrome
stain

36. None;None;
self resolving.self resolving.
Maltese cross in rbcMaltese cross in rbcHemolytic anemia,Hemolytic anemia,
Jaundice, fever,Jaundice, fever,
hepatomegalyhepatomegaly
Ixodes tickIxodes tickBabesia microtiBabesia microti
Pentosam;Pentosam;
PentamidinePentamidine
isethionate.isethionate.
IntracellularIntracellular
(macrophages)(macrophages)
leishmanial bodiesleishmanial bodies
with kinetoplastwith kinetoplast
Visceral leishmaniasisVisceral leishmaniasis
(Kala-azar),(Kala-azar),
granulomatous skingranulomatous skin
lesionslesions
Iraq/Iran/AfghanistanIraq/Iran/Afghanistan
Phlebotomine sandflyPhlebotomine sandflyLeishmania donovaniLeishmania donovani
CNS:CNS:
melarsoperolmelarsoperol
Nifurtimox andNifurtimox and
Benzonidazole.Benzonidazole.
Hemoflagellate inHemoflagellate in
blood or tissue.blood or tissue.
C- or comma-shapedC- or comma-shaped
AmericanAmerican
trypanosomiasis;trypanosomiasis;
Chagas disease:Chagas disease:
megacolon, cardiacmegacolon, cardiac
failure.failure.
Reduvid (kissing) bugReduvid (kissing) bugT. cruziT. cruzi
Blood stage:Blood stage:
Suramin orSuramin or
petamidinepetamidine
isethionateisethionate
Hemoflagellate inHemoflagellate in
blood or lymph nodeblood or lymph node
AfricanAfrican
trypanosomiasis;trypanosomiasis;
Sleeping sicknessSleeping sickness
Encephalitis; cardiacEncephalitis; cardiac
failurefailure
Tsetse flyTsetse flyTrypanosoma bruceiTrypanosoma brucei
TreatmentTreatmentDiagnosisDiagnosisDisease/SymptomsDisease/SymptomsTransmissionTransmissionOrganismOrganism
BLOOD BORNE PROTOZOA

37. Trypanosoma cruzi  Chagas disease
(American trypanosomiasis)
Vector: Reduvid/Triatoma (kissing) bug
Trypomastigote is the form in the blood of an infected person; may be seen in
CSF in CNS infections
Motile circulating trypomastigotes are readily seen on slides of fresh
anticoagulated blood in acute infection but are rarely detectable by
microscopy in chronic T. cruzi infection.
A typical trypomastigote has:
◦ A large, subterminal or terminal kinetoplast,
◦ A centrally located nucleus,
◦ An undulating membrane, and
◦ A flagellum running along the undulating membrane, leaving the body at the
anterior end.
◦ 12 to 30 µm in length.
◦ Can appear C shaped
Amastigote stage parasite may be seen in histopathology specimens from
affected organs.
Trypomastigote
Amastigote

38. Trypanosoma brucei  Sleeping sickness
(African trypanosomiasis)
Vector: Tse Tse fly
The two T. brucei species that cause African trypanosomiasis are
indistinguishable morphologically
◦ T. brucei gambiense
◦ T. brucei rhodesiense
A typical trypomastigote has:
◦ A small kinetoplast located at the posterior end
◦ A centrally located nucleus
◦ An undulating membrane, and
◦ A flagellum running along the undulating membrane, leaving the
body at the anterior end
◦ 14 to 33 µm in length
Trypomastigote is the only stage found in specimens
kinetoplast
nucleus

39. Leishmania
Obligate intracellular parasite
Vector: female sand fly bite
Two forms of disease
◦Visceral leishmaniasis (kala azar)
◦L. donovani
◦Cutaneous leishmaniasis
◦L. tropica
◦L. braziliensis

40. Leishmania – Clinical
Disease
Cutaneous
◦Single or few chronic, ulcerating lesions; many species
◦Latin America, southern Europe, Middle east,
southern Asia, Africa
◦Mucocutaneous in Latin America
Visceral
◦primarily L. donovani complex (Asia), L.
infantum/chagasi (Africa and Latin America), others
◦Hepatosplenomegaly, anemia, cytopenias, systemic
symptoms
◦India, Bangladesh, Nepal, Sudan, and Brazil
◦Important opportunistic infection in HIV infection

41. Leishmania
Diagnosis
◦Biopsy of infected tissue (skin, bone marrow)
◦Multiple, tiny 2-5 um amastigotes within histiocytes
◦Distinct kinetoplast (bar-like structure adjacent to nucleus)
◦PCR methods
◦Urinary antigens (visceral)
DDx of multiple tiny intracellular organisms
◦Leishmania – kinetoplast
◦Histoplasma – budding
◦Toxoplasma – somewhat curved, mostly
extracellular

42. Babesia
Protozoan: B. microti, B. divergens
Zoonosis (deer, cattle, rodents; humans accidental host)
Transmission vector: Ixodes tick bite
Infects red blood cells
Found world-wide
B. microti along the Northeast US
◦ Nantucket Island, Martha’s vineyard, Shelter Island
Malaria-like syndrome
◦ Fever but without periodicity, night sweats, weight loss,
hemolytic anemia, hemoglobinuria, renal failure
Dx:
◦ Blood smear examination
◦ Ring form only (mimics P. falciparum)
◦ Tetrads (unlike P. falciparum)
Maltese cross
(tetrads)
Ixodes tick

43. MALARIA
Protozoan parasite
Transmitted by the anopheles mosquito
Endemic in tropical areas

44. Malaria Symptoms
Fever pattern
ParasiteParasite DiseaseDisease
Plasmodium falciparumPlasmodium falciparum MalignantMalignant tertiantertian
malariamalaria
P. vivaxP. vivax BenignBenign tertiantertian malariamalaria
P. ovaleP. ovale BenignBenign tertiantertian malariamalaria
P. malariaeP. malariae QuartanQuartan malariamalaria
Tertian = q 48 hours (every other day)
Quartan = q 72 hours

45. Malaria
Physical exam findings
◦Fever
◦Splenomegaly
◦P. falciparum - most pathogenic species** lethal malignant tertian fever
◦Jaundice
◦Hepatomegaly
◦Increase in respiratory rate
◦CNS involvement
◦Blackwater fever – hemolysis, renal failure
Diagnosis: peripheral blood smear, Antigen screen (EIA), and molecular
assays

46. Life Cycle of Plasmodium Species
Ring form  Trophozoite Schizont Merozoite
Ruptured Schizont
Gametocyte

47. Malarial Preparations
Thick smear
Drop of blood on slide (non-
anticoagulate blood is best)
Water rinse to eliminate rbc’s
Stain with Giemsa stain (not
Wright-Giemsa) proper pH
Need the proper pH to stain
the Schuffner’s granules
Concentrated to spot malaria
parasites
Thin smear
Feather edge smear
For optimal morphology, stain
with Giemsa (not Wright-
Giemsa) stain with proper pH
Speciation of malaria
Parasitemia (%)

48. P.vivax induces morphologic alterrations in the infected rbc
Schuffners dots/granules

49. P. vivax
Amoeboid
ring form
P.vivax – benign tertian malaria (fever every 48 hours), invades reticulocytes.
Duffy negative Red blood cell protects from Plasmodium vivax invasion-
African natives lack Duffy rbc antigen and this prevents them from serious P. vivax.
Untreated infections last several years remaining dormant in the liver.
Recurrent and chronic infection can lead to brain, kidney and liver damage

50. Schuffner’s
granules

51. P. ovale
Fimbriated
edge

52. “Rosette” schizont

53. P. malariae

54. P. falciparum
Multiple ring forms per cell can be seen
Accolade forms(ring forms on the edge of
cell)
No schizonts circulate in blood
Banana shaped gametocyte
High % parasitemia
Calculate % parasitemia
No. infected RBCs + total no. RBCs counted X 100 = % infected RBCs

55. Toxoplasma
gondii
T. gondii encystment in tissue T. gondii tachyzoites
Toxoplasmosis is considered to be a leading cause of death attributed to foodborne illness in the United
States. Caused by eating undercooked, contaminated meat (especially pork, lamb, and venison)
Accidental ingestion of oocysts after cleaning a cat's litter box when the cat has shed Toxoplasma in its
feces is also a cause
More than 30 million men, women, and children in the U.S. carry the Toxoplasma parasite, few have
symptoms the immune system keeps the parasite from causing illness.
Women newly infected with Toxoplasma during pregnancy (TORCH) and anyone with a compromised
immune system are most at risk for severe consequences.

56. Free-living Amoeba
Naegleria fowleri
Acanthamoeba
Balamuthia

57. Primary Amoebic meningoencephalitis (PAM) is
caused by Naegleria fowleri
Granulomatous amoebic encephalitis (GAE) is caused
by Acanthamoeba and Balamuthia
Clinical scenario: swimming or diving into fresh-water pools
and water goes up nose thru cribriform plate
N. fowleri
trophozoite

58. Contact-lens keratitis
Cause: Acanthamoeba
◦To culture Acanthamoeba, Corneal scrapings placed in a lawn of
E.coli
◦Visible tracks of ameba detected on agar plate
◦Wright stain of corneal scrapings is simpler/better way
Wright’s
stain
Amoeba in
wet mount

59. HELMINTHS
Nematodes (roundworms)
Trematodes (flukes)
Cestodes (tapeworms)

60. Nematodes (Roundworms)
Enterobius vermicularis
Ascaris lumbricoides
Trichuris trichuria
Necator americanus & Ancylostoma duodenale
Strongyloides stercoralis
Anisakis simplex
Microfilaria – Wucheria, Brugia, Loa loa, Mansonella, and
Onchocerca

62. Enterobius vermicularis
(pinworm)
Humans / only host
Most common helminth in US
Worms: Females 8-13mm, males 2-5 mm
◦Appear like strings in the stool
Dwell in the cecum
Migrate to perineum at night
◦Deposit eggs
◦Diagnosis- Scotch tape test or anal swab in AM
Oval with a flattened side: 50-60um by 20-30um

63. Ascaris lumbricoides
(roundworm)
1-1.2 billion people infected, Africa, the Americas, China and East Asia,
common in children
Developing countries with poor sanitation/ feces contaminated soil,
humans ingest eggs
Largest helminth to affect humans
◦Worms: Females 20-35cm long and straight, males 15-30cm with a curved
tale
◦Can cause intestinal obstruction
◦Loeffler’s syndrome – pulmonary infiltration and eosinophilia from
worm migration

64. Ascaris lumbricoides
Charcot Leyden crystals are hexagonal bipyramidal
structures localized in the primary granules of the
cytoplasm of eosinophils. Their presence is indirect
evidence of parasitic infestation particularly with
Ascariasis, Toxocara, Capilliriasis, or Fasciola.
Bolus of Ascaris
removed from
Bowel obstruction

66. Trichuris trichuria
(whipworm)
Soil transmitted/fecal contamination
Disease similar to amebiasis
PVA preserved samples inferior to formalin
Adult worm attaches to large intestine, rarely
recovered – diagnosis by detecting egg in stool
specimens
Thinnest part of worm is head
Egg is barrel shaped, golden brown, knobs on both
ends

67. Necator americanus and Ancylostoma
duodenale (Hookworms)
Soil transmitted – filiform larvae penetrate the skin
2nd
most common helminth infection
Necator or Ancylostoma – Hookworm egg
Both genera egg looks alike – egg
60 X 40 um

68. Strongyloides stercoralis
Soil transmitted
Larval form only –
◦Penetrate intact skin
Usually intestinal larval infestation
In immune suppressed - massive intestinal
infection with +/- migration to the respiratory tract
(eosinophilic pneumoniae) so called autoinfection
Strongyloides larvae

69. Anisakis simplex
Anisakiasis is a parasitic disease caused by anisakid nematode (worms) that can invade the
stomach wall or intestine of humans.
The transmission of this disease occurs when infective larvae are ingested from fish or squid
that humans eat raw or undercooked.
In some cases, this infection is treated by removal of the larvae via endoscopy or surgery. Can
in rare cases cause granuloma formation and obstruction.

70. Trichinella spiralis
-Tissue nematode
-Infection from the ingestion
of undercooked meat
-Usually an incidental finding
in muscle

71. Microfilariae
Sheathed
◦Wucheria bancrofti and Brugia malayi
◦Elephantiasis (lymphangitis/lymphedema)
◦Loa loa
◦Calabar swellings & migrating worms in the conjunctiva
Not sheathed
◦Onchocerca volvulus
◦Mansonella species
◦Allergic skin reactions, edema, Calabar swellings

73. Identification of microfilariae is based on the presence of a sheath covering the larvae, as well
as the distribution of nuclei in the tail region
A, W. bancrofti. B, B. malayi. C, L. loa. D, O. volvulus. E, Mansonella perstans. F, Mansonella
streptocerca. G, Mansonella ozzardi.

74. Filaria
Identification
a. W. bancrofti
◦ Sheathed, nuclei stop short of end
of tail
a. B. malayi
◦ Sheathed, two small nuclei in tail
a. O. volvulus
◦ Unsheathed, from skin, not blood
a. Loa loa
◦ Sheathed, nuclei to continue to
end of tail

75. Wucheria bancrofti

76. Brugia malayi

77. Loa loa

78. Mansonella perstans

79. Onchocerciasis Black Fly

80. Onchocerciasis
Unsheathed

81. Trematodes (Flatworms)
Intestinal and Liver flukes
◦Fasciolopsis buski
◦Fasciola hepatica
Liver flukes
◦Clonorchis sinensis (Chinese liver fluke)
Paragonimus westermani – oriental lung fluke
Schistosomes
◦S mansoni – intestinal bilharziasis
◦S haematobium - urinary
◦S japonicum – blood fluke, found in intestines

82. Intestinal and liver flukes

83. Fasciolopsis buski Fasciola hepatica
The two most common intestinal flukes

84. Fasciola hepatica
Distinct nose
Fascioliasis- Fasciola hepatica, "the common liver fluke" or "the sheep liver fluke.
Associated with sheep & cattle
Infected by eating raw watercress or other water plants contaminated with immature larvae.
The immature larval flukes migrate through the intestinal wall, the abdominal cavity, and the liver
tissue, into the bile ducts. The pathology is most pronounced in the bile ducts and liver.
Fasciola infection is both treatable and preventable
Eggs – ellipsoidal, operculated and large 140 X 80µm

85. Fasciolopsis buski, causes fasciolopsiasis, is the largest intestinal fluke of humans.
Prevented by cooking aquatic plants well before eating them.
Found in south and southeastern Asia.
Fasciolopsiasis is treatable.
Many people do not have symptoms from Fasciolopsis infection. However, abdominal pain
and diarrhea can occur 1 or 2 months after infection.
With heavy infections Fasciolopsis flukes can cause intestinal obstruction, abdominal pain,
nausea, vomiting, and fever.

86. Clonorchis sinensis
knobbin
Shoulders
operculates
Clonorchis is a liver fluke
that can infect the liver,
gallbladder and bile duct.
Found across parts of
Asia, it is also known as
the Chinese or oriental
liver fluke.

87. Egg is operculate, not
embryonated, thick shell,
asymmetrical and large
Paragonimus westermani
Paragonimus is a parasitic lung fluke.
Infections occur after a person eats raw or
undercooked infected crab or crayfish.
Paragonimus infection also can be very
serious if the fluke travels to the central
nervous system, where it can cause
symptoms of meningitis.

88. Schistosoma mansonii

89. Schistosomiasis, also known as bilharzia, more than 200 million people are infected
worldwide. Second only to malaria as the most devastating parasitic disease.
Live in certain types of freshwater snails. The infectious form of the parasite, known as
cercariae, emerge from the snail, and contaminate water. You become infected when your
skin comes in contact with contaminated freshwater. Most human infections are caused by
(1)Schistosoma mansoni, (2) S. haematobium, or (3) S. japonicum.
Examine Stool for S. mansoni or S. japonicum eggs and Urine for S. haematobium
eggs).
1 2 3

90. Schistosoma mansoni
Liver tissue
Schistosoma japonicum
Intestine tissue
Schistosoma
Haematobium –
bladder tissue

91. Cestodes (Tapeworms)
Examples
Diphyllobothrium latum
Taenia saginata
Taenia solium
Hymenolepis nana
Hymenolepis diminuta
Echinococcus granulosis
Head with armed or unarmed scolex
Proglottids – tapeworm elongates by
producing Proglottids

92. Diphyllobothrium
latum
Infected by ingesting poorly-cooked fresh-water fish
(salmon particularly problematic)
Scandinavian, Russia, Canada, N. USA, Alaska
Known as the Broad fish tapeworm
Scolex has a Longitudinal sucker
Eggs have non-shouldered operculum and knob
◦They are not embryonated
Infection causes VitaminB12 deficiency

93. Diphyllobothrium latum
Operculum
door
knob
Sucking plate
Broad proglottid

94. Taenia saginata
 Beef tapeworm
 4 suckers on scolex
 >12 uterine branches in
proglottids
Ingestion of cysticerci in
beef
Intestinal tapeworm
Ingestion of eggs ->
Non-human pathogen
No disease
Taenia Solium
Pig tapeworm
Ring of thorns/crown on
scolex
<12 uterine branches in
proglottids
Ingestion of cysticerci in
pork
Intestinal tapeworm
Ingestion of eggs ->
Cysticercosis

95. Taenia
species

96. Taenia eggs
Identical eggs for the two species

97. Taenia saginata
Proglottid > 12 uterine branches

98. Taenia solium
Proglottis – fewer uterine branches
(<=12 uterine branches)
Scolex - Ring of thorns

99. Cysticercosis
Caused by the ingestion of T. solium
Eggs / Not by eating infected pork

100. Hymenolepis nana (Dwarf Tapeworm)
Definitive host: Human and rodent
Worm is 2-4 cm – shortest of the tapeworms
Egg has inner & outer shell separated space
Water /food contaminated by rodent droppings

101. Hymenolepis
diminuta
Uncommon tapeworm
Big egg @ 80 microns
in diameter

102. Echinococcus – hydatid cyst disease
found in Africa, Europe, Asia, the Middle East, and Central
and South America.
Highest prevalence is found in populations that raise sheep.
Infection from ingestion of eggs found in animal feces.

103. Echinococcus – hydatid cyst
Short tapeworm
Sand like material
contained in the
Hydatid Cyst, due to
inverted folded
tapeworms
Hydatid cyst in liver

104. Relative size of Helminth
eggs
http://www2.bc.cc.ca.us/bio16/pal/Parasitology.htm

105. Additional Insects of
interest

106. Maggots
House fly larvae
Bot fly larvae
Bot fly bites human,
larvae develops in
subcutaneous area, matures
and then
extrudes from the skin
Native to central and south
America
Bot fly

107. Ticks of importance
Soft tick -
Expands with blood
engorgement
Hard Ticks

108. Black Widow spider
Hour glass
On tummy

109. Flea
Body louse
Crab louse
Hair nit – Body
louse egg on hair
shaft

110. Scabies
Tinyeggsunderskin
Mite