Parasitology
Review
2018
MARGIE MORGAN, PHD, D(ABMM)

Clinical presentation
Travel history or poor sanitation put you at the
highest risk for parasitic infection
Poor immune status higher risk
Infections associated with sporadic symptoms
Dysentery not common (amebiasis)
Most usual symptoms:
◦Abdominal pain, cramping, long term nausea, and
malaise, mucous in stool, and +/- fever, chronic in nature

Laboratory Diagnosis
Currently diagnosis is mostly 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 for
select pathogens
◦Molecular assays for
select pathogens

From the 2017 IDSA Practice Guidelines
Suggested Laboratory Testing Methods
Parasite Test Method
Specimen

Two-vial collection kit for Stool
preservation for parasite exam
10% formalin vial
Concentration of stool
performed with ethyl acetate
to eliminate fecal debris
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 and
stained with Trichrome stain
Detect: Protozoan trophozoites
and cysts

Most Common Parasitic
Pathogens
Protozoa
◦Intestinal & urogenital
◦ E histolytica, Blastocystis hominis, Giardia lamblia, Dientamoeba fragilis,
Balantidium coli, Cryptosporidium sp., Cyclospora sp, Cyclospora,
Cytoisospora(Isospora) belli, and Microsporidia
◦Blood & tissue
◦ Plasmodium, Babesia, Trypanosomes
◦ Toxoplasma gondii, Leishmania
◦ Naegleria, Acanthamoeba, Balamuthia
Helminths
◦Nematodes
◦ Ascaris, Trichuris, hookworm, pinworm, and Strongyloides
◦Cestodes
◦ Taenia, Hymenolepis, Diphyllobothrium
◦Trematodes
◦ Fasciola, Fasciolopsis, Schistosoma, Paragonimus, Clonorchis

PROTOZOA
Amebae (found in stool)
◦ Entamoeba coli
◦ Entamoeba histolytica
◦ Endolimax nana
◦ Iodamoeba butschlii
◦ Dientamoeba fragilis
Flagellates (found in stool)
◦ 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
◦ Toxoplasma
◦ Naegleria fowleri
◦ Acanthamoeba

Protozoa Found in Stool: Amebae
Major pathogen

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

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

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

Entamoeba histolytica/dispar trophozoites
Trophozoite with ingested rbcs

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

Entamoeba coli
considered a 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

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

Endolimax nana
Trohphozoites 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

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

Flagellates
Giardia lamblia (duodenalis)
Dientamoeba fragilis
Trichomonas vaginalis

Protozoa Found in Stool: Flagellates
Pathogen

Giardia lamblia
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

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

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

Giardia lamblia
only invades intestinal tissue – duodenal
biopsies, trophozoites near the surface
epithelium

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

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)

Trichomonas vaginalis
Urogenital protozoan
Infection leads to
Scant, watery vaginal
discharge
Four flagella, short
undulating membrane

Protozoa Found in Stool:
Ciliates, Coccidia, Blastocystis

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

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

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.

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

Cryptosporidia in the
intestine - located
just below the plasma
membrane
Direct Fluorescence Antibody stain –
Cryptosporidium spp

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

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

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

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

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

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

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

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

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

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

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

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

Malaria Symptoms
Fever pattern
ParasiteParasite DiseaseDisease
PlasmodiumPlasmodium
falciparumfalciparum
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

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

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

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 (%)

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

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

Schuffner’s
granules

P. ovale
Fimbriated
edge

“Rosette” schizont

P. malariae

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

Toxoplasma
gondii
T. gondii encystment in brain 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.

Free-living Amoeba
Naegleria fowleri
Acanthamoeba
Balamuthia

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

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

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

Nematodes (Roundworms)
Enterobius
Ascaris
Trichuris
Necator and Ancylostoma (Hookworm)
Microfilaria – Wucheria, Brugia, Loa loa,
Mansonella, and Onchocerca

Enterobius vermicularis
(pinworm)
Humans considered 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

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

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

Trichuris Trichiura
(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

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

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

Anisakiasis
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.

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

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

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.

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

Wucheria bancrofti

Brugia malayi

Loa loa

Mansonella perstans

Onchocerciasis Black Fly

Onchocerciasis
Unsheathed

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

Intestinal and liver flukes

Fasciolopsis buski Fasciola hepatica
The two most common intestinal flukes

Fasciola hepatica
Distinct nose
Fascioliasis- caused by 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 parasite larvae.
The immature larval flukes migrate through the intestinal wall,
the abdominal cavity, and the liver tissue, into the bile ducts.
The pathology typically is most pronounced in the bile ducts and
liver.
Fasciola infection is both treatable and preventable
Eggs – ellipsoidal, operculated and large 140 X 80µm

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.

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.

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.

Schistosoma mansonii

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

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

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

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

Diphyllobothrium latum
Operculum
door
knob
Sucking plate
Broad proglottid

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
Taenia Species – two species
Outstanding characteristics

Taenia
species

Taenia eggs
Identical eggs for the two species

Taenia saginata
Proglottid > 12 uterine branches

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

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

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

Hymenolepis
diminuta
Uncommon tapeworm
Big egg @ 80 microns
in diameter

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.

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

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

Additional Insects of
interest

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

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

Black Widow spider
Hour glass
On tummy

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

Scabies
Tinyeggsunderskin
Mite