Parasitology Update 2018

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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 st...

Laboratory Diagnosis
Currently diagnosis is mostly based on
microscopic exam
Specimen types:
◦Stool
◦Non-stool
◦ Perianal ...

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 e...

Most Common Parasitic
Pathogens
Protozoa
◦Intestinal & urogenital
◦ E histolytica, Blastocystis hominis, Giardia lamblia, ...

PROTOZOA
Amebae (found in stool)
◦ Entamoeba coli
◦ Entamoeba histolytica
◦ Endolimax nana
◦ Iodamoeba butschlii
◦ Dientam...

Protozoa Found in Stool: Amebae
Major pathogen

Protozoa: Intestinal
amoeba
of note
Entamoeba histolytica/dispar
Entamoeba hartmanni
Endolimax nana
Entamoeba coli
Iodamoe...

Entamoeba
histolytica/dispar
E. histolytica (pathogen) and E. dispar (nonpathogen) species both
occur in the large intesti...

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

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...

Entamoeba coli
considered a commensal in the intestine
Cyst @ 20 – 25µm
Up to 8 nuclei
Shed from host
Lives in environment...

Entamoeba coli – important to
differentiate from the pathogen E. histolytica
Trophozoites & Cysts
Cysts usually
15-25µm, w...

Endolimax nana
Trohphozoites 8 – 10 µm, one
nucleus
Cysts – 6-8 µm in size, four nuclei
Usually a commensal, seen in stool...

Iodamoeba butschlii
Cysts, 10 – 12 µm
Large starch inclusion
(glycogen mass) that is unique
to Iodamoeba
Usually not consi...

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 , wate...

Giardia lamblia trophozoite
Waxing and waning
symptoms
Can be irregularly
shed in stool material
making antigen
and molecu...

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
In...

Dientamoeba fragilis
Diarrhea, anal pruritus
Only a trophozoite stage 5 – 15 µm (No cyst)
Usually two nuclei visible in th...

Trichomonas vaginalis
Urogenital protozoan
Infection leads to
Scant, watery vaginal
discharge
Four flagella, short
undulat...

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 ...

Isospora(Cystoisospora)
belli
Contaminated food/water, oral-anal route of
infection
Found most commonly in HIV/AID patient...

Cryptosporidium spp
Contaminated water
◦Resistant to usual water-purification procedures
(chlorination, ozone)
Watery diar...

Cryptosporidiosis: Diagnosis
Not detected in routine O & P exams (left)
Requires modified acid-fast stains for detection, ...

Cryptosporidia in the
intestine - located
just below the plasma
membrane
Direct Fluorescence Antibody stain –
Cryptosporid...

Cyclospora cayetanensis
Contaminated fruits and vegetables – particularly ones with plant
hairs
Watery diarrhea; fatigue, ...

Microsporidia
Obligate intracellular fungal parasite (yeast like)
Enterocytozoon and Encephalitozoon species most
common g...

Microsporidia
-Diagram of detailed internal spore
structures
Spores are 1 – 4um
Stain positive on Calcofluor white and
mod...

Blastocystis hominis (algae)
Small #s: are considered commensal
Large #s: may be pathogenic
Found in Contaminated food and...

None;None;
self resolving.self resolving.
Maltese cross in rbcMaltese cross in rbcHemolytic anemia,Hemolytic anemia,
Jaund...

Trypanosoma cruzi  Chagas
disease
(American trypanosomiasis)
Vector: Reduvid/Triatoma (kissing) bug
Trypomastigote is the...

Trypanosoma brucei 
Sleeping sickness (African
trypanosomiasis)
Vector: Tse Tse fly
The two T. brucei species that cause ...

Leishmania
Obligate intracellular parasite
Vector: female sand fly bite
Two forms of disease
◦Visceral leishmaniasis (kala...

Leishmania – Clinical
Disease
Cutaneous
◦Single or few chronic, ulcerating lesions;
many species
◦Latin America, southern ...

Leishmania
Diagnosis
◦Biopsy of infected tissue (skin, bone marrow)
◦Multiple, tiny 2-5 um amastigotes within histiocytes
...

Babesia
Protozoan: B. microti, B. divergens
Zoonosis (deer, cattle, rodents; humans accidental host)
Transmission vector: ...

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

Malaria Symptoms
Fever pattern
ParasiteParasite DiseaseDisease
PlasmodiumPlasmodium
falciparumfalciparum
MalignantMalignan...

Malaria
Physical exam findings
◦Fever
◦Splenomegaly
◦P. falciparum - most pathogenic species** lethal malignant
tertian fe...

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...

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...

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 circula...

Toxoplasma
gondii
T. gondii encystment in brain T. gondii tachyzoites
Toxoplasmosis is considered to be a leading cause of...

Free-living Amoeba
Naegleria fowleri
Acanthamoeba
Balamuthia

Primary Amoebic meningoencephalitis (PAM) is
caused by Naegleria fowleri
Granulomatous amoebic encephalitis (GAE) is
cause...

Contact-lens keratitis
Cause: Acanthamoeba
◦To culture Acanthamoeba, Corneal scrapings placed in
a lawn of E.coli
◦Visible...

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

Nematodes (Roundworms)
Enterobius
Ascaris
Trichuris
Necator and Ancylostoma (Hookworm)
Microfilaria – Wucheria, Brugia, Lo...

Enterobius vermicularis
(pinworm)
Humans considered only host
Most common helminth in US
Worms: Females 8-13mm, males 2-5 ...

Ascaris lumbricoides
(roundworm)
1-1.2 billion people infected, Africa, the Americas,
China and East Asia, common in child...

Ascaris lumbricoides
Charcot Leyden crystals are hexagonal bipyramidal
structures localized in the primary granules of the...

Trichuris Trichiura
(whipworm)
Soil transmitted/fecal contamination
Disease similar to amebiasis
PVA preserved samples inf...

Necator americanus and
Ancylostoma duodenale
(Hookworms)
Soil transmitted – filiform larvae penetrate the skin
2nd
most co...

Strongyloides
stercoralis
Soil transmitted
Larval form only –
◦Penetrate intact skin
Usually intestinal larval infestation...

Anisakiasis
Anisakiasis is a parasitic disease caused by anisakid nematode (worms)
that can invade the stomach wall or int...

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

Microfilariae
Sheathed
◦Wucheria bancrofti and Brugia malayi
◦Elephantiasis (lymphangitis/lymphedema)
◦Loa loa
◦Calabar sw...

Identification of microfilariae is based on the presence of a sheath covering the larvae, as well
as the distribution of n...

Filaria
Identification
a. W. bancrofti
◦ Sheathed, nuclei stop short
of end of tail
a. B. malayi
◦ Sheathed, two small nuc...

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 sinensi...

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 fl...

Fasciolopsis buski, causes fasciolopsiasis, is the largest
intestinal fluke of humans.
Prevented by cooking aquatic plants...

Clonorchis sinensis
knobbin
Shoulders
operculates
Clonorchis is a
liver fluke that can
infect the liver,
gallbladder and
b...

Egg is operculate, not
embryonated, thick shell,
asymmetrical and large
Paragonimus westermani
Paragonimus is a parasitic ...

Schistosoma mansonii

Schistosomiasis, also known as bilharzia, more than 200 million
people are infected worldwide. Second only to malaria as t...

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
E...

Diphyllobothrium
latum
Infected by ingesting poorly-cooked fresh-water
fish (salmon particularly problematic)
Scandinavian...

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
be...

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 i...

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...

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

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
extrud...

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

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